Electrotherapy Part-2

Methods of Heating the Tissues

Physiological effects of heat

Heating the tissues by the methods included in this section results in a

rise in temperature, the main reactions to which are:

    1. Increased metabolic activity.

    2.Inereased blood low

    3. Stimulation of neural receptors in the skin or tissues.

These changes in the tissues may be produced by local, general or remote effects. Their extent will depend on various factors, for example:

     1. The size of the area heated.

     2. The depths of absorption of specific radiation (see Fig. 3.30, p.I32).

     3.The duration of heating.

     4.The intensity of irradiation.

     5.The method of application.

The summary that follows is only a superficial guide to the physiological effects of heating. It is recommended that further information should be sought from current physiology textbooks.

Increased metabolism

This is in accordance with van’t Hoffs statement that any chemical change capable of being accelerated by heat is accelerated by a rise in temperature. Consequently heating of tissues accelerates the chemical Changes, i.e. metabolism. The increase in metabolism is greatest in the region where most heat is produced, which is in the superficial tissues. As a result of the increased metabolism there is an increased demand Tor oxygen and foodstuffs, and an increased output of waste products,

including metabolites.

Increased blood supply

As a result of the increased metabolism, the output of waste products from the cells is increased. These include metabolites, which act on walls of the capillaries and arterioles causing dilatation of these vestal In addition, the heat has a direct effect on the blood vessels, causing vasodilatation, particularly in the superficial tissues where the heating is greatest. Stimulation of superficial nerve endings can also cause reflex dilatation of the arterioles. As a result of the vasodilatation there

is an increased flow of blood through the area, so that the necessary Oxygen and nutritive materials are supplied and waste products are removed. The superficial vasodilatation causes erythema of the skin which, unlike that produced by ultraviolet irradiation, appears as soon as the part becomes warm and begins to fade soon after the exposure of heat ceases. With infra-red radiation the erythema may be mottled in appearance, and following repeated exposure to infra -red rays there may be an increase in pigmentation; this may be observed in the legs of

individuals who habitually sit close to the fire.

Effects of heating on nerves

Heat appears to produce definite sedative effects. The effect of heat on nerve conduction has still to be thoroughly investigated but a physiological explanation has been offered by Sidney Licht (1965): there is evidence that any sensory excitation reaching the brain simultaneously with a pain excitation results in the pain impulse being more or less attenuated.

Indirect effects of heating

Muscle tissue Rise in temperature induces muscle relaxation and increases the efficiency of muscle action, as the increased blood supply ensures the optimum conditions for muscle contraction.

        General rise in temperature As blood passes through the tissues in which the rise of temperature has occurred, it becomes heated and carries the heat to other parts of the body, so that if heating is extensive and prolonged a general rise in body temperature occurs. The vasomotor centre is affected, also the heat-regulating centre in the hypothalamus, and a generalized dilatation of the superficial blood

vessels results.

Fall in blood pressure If there is generalized vasodilatation the peripheral resistance is reduced, and this causes a fall in blood pressure. Heat reduces the viscosity of the blood, and this also tends to reduce the blood pressure.

Increased activity of sweat glands There is reflex stimulation of the sweat glands in the area exposed to the heat, resulting from the effect of the heat on the sensory nerve endings. As the heated blood circulates throughout the body it affects the centre concerned with regulation of temperature, and there is increased activity of the sweat glands throughout the body. When generalized sweating occurs there is

increased elimination of waste products.

Short-wave diathermy

A short-wave diathermic current has a frequency of between 1o’ and Io8 Hz and sets up wireless waves with a wave-length of between 30 and 3 m. The use of any current within this range is classed as short- wave diathermy, but that commonly used for medical work has a frequency of 27 120 000 Hz (27.I2 MHZ) and sets up wireless waves with a wave-length of 1I m. This current is generated in a machine circuit, which is in turn coupled to a patient (resonator) circuit which is used to treat the patient.

Provided a suitable method of application is chosen, short-wave diathermy provides as deep a form of heat as any available to the physiotherapist.

The machine circuit

It is not possible to construct any mechanical device which causes

sufficiently rapid movement to produce a high-frequency current, so this type of current is obtained by discharging a condenser through an inductance of  low ohmic resistance. The basic oscillator circuit consists of a condenser and an inductance (see Fig. I.44, P. 35), and currents of different frequencies are obtained by selecting suitable condensers and inductances. If a current of very high frequency is required, the capacitance and inductance are small, while to produce a current of lower frequency a larger condenser and/or inductance are used.

In order to produce the high -frequency current, the condenser must be made to charge and discharge repeatedly, and to achieve this the Oscillator is incorporated in a valve circuit.

The patient circuit

The circuit is coupled to the machine circuit by inductors, i.e. a matching high-frequency current is produced in the resonator circuit by electromagnetic induction. For this to happen the oscillator and resonator circuits must be in resonance with each other, which requires that the product of inductance and capacitance must be the Same for both circuits. When short-wave diathermy is applied by the condenser’ field method, the electrłes and patient’s tissues form a capacitor, (pp. 32-34), the capacitance of which depends on the size of the electrodes and on the distance and material between them, and so is different for each application. When the cable electrode is used it forms an inductance the value of which varies according to its arrangement. Consequently either the capacitance or the inductance of the patient’s circuit is varied at each treatment, and a variable condenser is incorporated in the patient circuit to compensate for this. When the

electrodes have been arranged in position, the capacitance of the variable condenser is adjusted (the process of tuning) until the product of the inductance and capacitance of the resonator circuit is equal to that in the oscillator circuit. When the oscillator and resonator circuits are in tune with each other, there is maximum power transfer to the patient circuit. Indications that this is occurring are:

1. An indicator light on the equipment either comes on or changes colour.

2. An ammeter wired into the resonator circuit shows a maximum reading, which is diminished by turning the knob controlling the variable condenser either way.

3.A tube containing a small amount of neon gas placed within the electric field between the electrodes or the ends of the cable will glow at maximum intensity when the circuits are in resonance.

Some machines have an automatic tuning (resonator) control. This automatically searches for and selects the adjustment of the variable capacitor to ensure maximum power transfer to the patient circuit.

Physiological effects of diathermy current

A high-frequency current does not stimulate motor or sensory nerves.

When studying the muscle-stimulating currents in Chapter2 it was observed that (except for impulses of long duration) the shorter the duration of the impulse the less was the effect on the nerves, 0.0I ms being the shortest duration of impulse generally used. A high-frequency current has a frequency of more than approximately 500 kHz. This provides one million impulses per second, so each has a duration of o.00I ms, which is beyond the range used for nerve stimulation. Thus when such a current tis passed through the body there is no discomfort alternating, therefore there is no danger of chemical burns. and no muscle contractions are produced. The current is evenly Consequently it is possible to pass through the tissues Currents of a much greater intensity than can be used with low-frequency currents. The intensity of the current can be great enough to produce a direct heating effect on the tissues, similar to the heating effect of the current on any other conduct Or, and the term diathermy’ means through heating’.

Methods of application

1he transfer of electrical energy to the patient occurs via an electrostatic or an electromagnetic field. There are therefore two methods of application: the ‘condenser’/capacitor field and the inductothermy (cable) method.

Capacitor field method

Electrodes are placed on each side of the part to be treated, separated from the skin by insulating material. The electrodes act as the plates of a capacitor, while the patient’s tissues together with the insulating material which separates them from the electrodes form the dielectric. When the current is applied, rapidly alternating charges are set up on the electrodes and give rise to a rapidly alternating electric field between them. The electric field influences the materials which lie within it.

Effects of the electric field

A conductor is a material in which electrons can easily be displaced from their atoms, and when such a material lies within a varying electric field there is a rapid oscillation of electrons and a high- frequency current is set up.

An electrolyte is a substance which contains ions, and when a varying electric field passes through an electrolyte the ions tend to move first in one direction then in the other. As the frequency of the short-wave diathermic current is very high, the result is vibration rather than actual movement of the ions. Electrolytes also contain dipoles, which are molecules consisting of two oppositely charged ions. The particle as a whole is electrically neutral, but one end bears a negative and the other a positive charge. As the electric field changes in direction the dipoles swing round so that each end lies as far as possible from the electrode bearing the same charge (Fig. 3.1). Thus in the electrolytes there is rotation of dipoles as well as vibration of ions.

An insulator is a substance in which the electrons are so firmly held by the central nuclei that they are not easily displaced from their atoms, and in such a substance the varying electric field causes molecular distortion. As the charges on the electrodes alternate, the electron orbits swing first to one side then to the other, and the molecules are distorted (see Fig. I.41, p. 32).

In the body, the tissue fluids are electrolytes, and when tissues

containing an appreciable quantity of fluid lie in the electric field, Vibration of ions and rotation of dipoles take place within them. Other tissues, such as fat, are virtually insulators and the effect of the electric field on these tissues is to produce molecular distortion. All these Processes constitute electric currents and produce heat in accordance

Fig 3.I Rotation of dipoles in an electrolyte:

            a. Condenser not charged.

            b. Condenser charged.

with Joule’s law. Heat production is the primary effect of short-Wave diathermy on the tissues, but it differs from that of other heat treatments in the distribution of the heat produced. This depends primarily on the distribution of the electric field.

Differential heating of the tissues

The characteristics of electric lines of force and their distribution form the basis of the following principles.

The electric field tends to spread between the electrodes and so its density is usually greatest close to the electrodes. The superficial tissues lie closer to the electrodes than do the deep ones, so the density of the field, and consequently the heating, is commonly greater in the superficial than in the deep tissues. The lines of force pass more easily through materials of high than of low dielectric constant, and as the tissues of the body have a mean dielectric constant of about 8o they have a considerable effect on the distribution of the electric field. The lines of force can travel easily through the tissues, so they tend to spread considerably as they pass through the body (Fig. 3.2) and this increases the tendency for the heating to be greater in the superficial than in the deep tissues. An exception occurs when the cross-sectional area of the part is less than that of the electrodes, as the lines of force travel through the tissues rather than through the surrounding air. 1f,

for example, one electrode is placed on the sole of the foot and the other above the flexed knee, the field density, and so the heating, is greatest in the ankle (Fig. 3.3).

The dielectric constants of the various tissues differ considerably those of low impedance (such as blood and muscle) having much higher dielectric constants than the tissues with a high impedance (such as fat and white fibrous tissue). The relative arrangement of the tissues in the pathway of the electric field affects the distribution of the

Fig. 3.2   Spread of lines of force in the tissues

Fig. 3.3 Concentration of lines of-force in the ankle.

lines of force, and so the heating. If the different tissues lie parallel to

the electric field the density of the field, and consequently the heat

production, is greatest in the tissues of low impedance. This occurs When the field is passed longitudinally through a limb, when the blood, having the lowest impedance, is heated most. If, on the other hand, the tissues lie transversely across the electric field, the density of the lines of force is the same throughout and tissues with the highest impedance are heated most. This corresponds to the heating of resistances which are wired in series with each other, when most heat is produced in the highest resistance. The subcutaneous tissue contains fat, which has a high impedance and lies in series with the other tissues, so it is probable that an appreciable amount of heat is generated in this region. Usually the arrangement of the tissues is such that they do not offer either a true series or a true parallel pathway but a mixture of the two. The lines of force must pass through the skin, superficial fascia and muscle, but then have alternative pathways through the underlying tissues. As the deep tissues generally lie in parallel with the field, the

heating is greatest in those of low impedance and it is difficult to obtain a direct heating effect on deeply placed structures of high impedance.

             There is also some rise in temperature in tissues which are not heated directly by the current. Tissues in contact with those in which the heat is produced are heated by conduction of heat, so when the muscles surrounding a deeply placed joint are heated some heat is transmitted to the joint. As the blood circulates through the area in which the heat is produced, its temperature rises and heat is carried to adjacent tissues through which it passes.

Heat loss The blood passing through the part being treated carries heat away from this area. This occurs particularly in vascular areas, and as the temperature of the part rises the blood vessels dilate and the effect is increased. For this reason all forms of heat should be applied gradually, to allow for vasodilatation to take place and a steady rate of heat loss to be established. If any factor impedes the flow of blood through the area the heat is not carried away, and over-heating is liable to occur. Heat is

also Just by conduction to surrounding tissues and to some extent by radiation and the evaporation of sweat from the surface.

           When short-wave diathermy is applied by the condenser field method, heat production is determined by the distribution of the electric field and tends to be greatest in the superficial tissues and those of low impedance. However, the tendency for the heating to be confined to these areas can be minimised by suitable arrangement of the electrodes. In order to obtain deep heating it is necessary to avoid over-heating the skin, as the resulting sensation of warmth limits t

current tolerated. In most cases the aim is to achieve as even a field possible throughout the deep and the superficial tissues.

Size of electrodes

As a general rule the electrodes should be rather larger than t structure that is being treated. The electric field tends to spread particularly at the edges, resulting in a lower density of field (and so less heating) in the deep than in the superficial tissues. If the electro are large, the outer part of the field where the spread is greatest is deliberately not utilized; the structure to be heated lies in the more

even central part of the field (Fig. 3.4), For treatment of the trunk the

Fig. 3.4 Joint lying in central, uniform part of the electric field.

Fig. 3.5 Correct size of electrodes: the lines of force converge towards

the limb.

electrodes should be as large as possible, while for a limb they should be rather larger than the diameter of the limb.

            The tissues of the body have a higher dielectric constant than air. Consequently, if the part of a limb between the electrodes is smaller in diameter than the electrodes, the lines of force bend in towards the limb as shown in Fig. 3.5. If the diameter of the electrodes is smaller than that of the limb, the lines of force spread in the tissues, causing more heating of the superficial than of the deep structures (Fig. 3.6). If the diameter of the electrodes is far larger than that of the limb, some of the lines of force by-pass it completely and so part of the electrical

Fig. 3.6 Electrodes too small, resulting in superficial structures being heated more than deep structures.

Fig. 3.7 Electrodes too large: part of the electrical energy is wasted.

energy is wasted, though a satisfactory heating effect may be obtained (Fig. 3.7).

        Both electrodes should be of the same size. If they are of different sizes they form a capacitor with different sized plates, so that different quantities of electricity are required to charge them to the same potential. This puts an uneven load on the machine and may give rise to difficulties in tuning. Apart from this, the charge may concentrate on that part of the larger electrode which lies opposite to the smaller one, as shown in Fig. 3.8, so that no advantage is gained from using

electrodes of different sizes. The main reason for doing so would be to obtain different degrees, of heating under the two electrodes, and this can be achieved more satisfactorily by adjusting the spacing.

Electrode spacing

The spacing between the electrodes and the patient’s tissues should be as wide as the output of the machine allows, and the material between

Fig. 3.8 Electrodes of different sizes.

the electrodes and the skin should be of low dielectric constant, air being the most satisfactory.

         The lines of force spread as they pass between the plates of a charged condenser, particularly if the distance between the plates is small and the material between them of high dielectric constant (see Fig. 1.43a, p. 34). When the distance between the electrodes is large the spreading-out of the electric field is minimal, while the use of spacing material of a low dielectric constant also limits the spread of the field. The field does, however, spread to some extent and so the density of the lines of force is greatest close to the electrodes. When the electrode- spacing is narrow the superficial tissues lie in the concentrated part of the field close to the electrodes (the regions marked A in Fig. 3.9) and are heated to a greater degree than the deep tissues, where the density of the lines of force is less (B in Fig. 3.9). When the electrode-spacing is wide no tissues lie in the concentrated part of the field close to the electrodes and there is less difference between the field density in the deep and that in the superficial tissues. Thus wide spacing helps to reduce the tendency for the superficial tissues to be heated to a greater extent than the deep ones, particularly if the spacing material is of low dielectric constant. It does, however, put considerable demands on the output of the machine.

          Wide spacing, particularly with material of low dielectric constant (i.e. high impedance), has the additional advantage that it reduces the tendency for the lines of force to concentrate in the tissues of low impedance. The different tissues offer different impedances, but where the total impedance of the pathway is great, these slight variations have little effect on the whole, so the distribution of the field

is relatively even.

Fig 39 Electrodes close to body surfaces, resulting in excessive heating of superficial structures (in the dense part of the field) compared with deeper structures.

Fig. 3.10 Electrodes at unequal distance from body surfaces: heating is more intense under the one closer to the body surface.

          If one electrode is placed nearer to the skin than the other there is a greater heating effect under the closer electrode than under the further one. This is illustrated in Fig. 3.10. The lines of force under the further electrode have a greater distance in which to spread before reaching  the skin than those under the nearer one. They therefore cover a greater area of skin and their density is less than under the nearer electrode. When treating a structure which lies nearer to one surface of

the body than to the other, e.g. the hip joint, the directing electrode on the further surface is placed at a greater distance from the skin than the active. This reduces the possibility of the patient experiencing excessive heating under the directing electrode, which might limit the total current tolerated.

Position of electrodes

The position of the electrodes should be chosen with the aim of directing the electric field through the structure to be treated. If the structure is of high impedance the electrodes should be arranged, as far as is possible, so that the different tissues lie in series with each other i.e. at right-angles to the electric field. To heat a structure of low impedance it is most satisfactory if the tissues are parallel to the field. When treating the ankle joint electrodes are commonly placed on the medial and lateral aspects, so that the tissues lie in series with each

other and some heating of the joint should be obtained. If a longitudinal application is used (see Fig. 3-3) a sensation of warmth is experienced in the ankle region, but as the tissues lie in parallel to the field the heating is in fact mainly confined to the blood vessels and muscles. Such heating is therefore satisfactory for treatment of the soft structures.

               The electrodes should be placed parallel to the skin, otherwise the

field concentrates on the area of tissue lying closest to the electrode. The insulating material between the electrodes and the skin should have a low dielectric constant, i.e. it should offer considerable impedance to the lines of force, the majority of which will then take the shortest pathway through it. Placing the electrodes parallel to the skin may result in their not lying parallel to each other, but provided that

the extra length of pathway between the more widely separate parts of the electrodes is through the body tissues, this has little effect on the field distribution (Fig. 3.I1). The tissues have a high dielectric constant, so the lines of force can travel through them easily, and the longer pathway offers little more impedance than the shorter one. Fig. 3.11 represents the lateral aspect of the shoulder, which is narrower above than below. If the electrodes lie parallel to the skin they are at a

slight angle to each other, but an even field is obtained. In Fig. 3.1la the pathway CD is longer than AB, but the extra length is through the body tissues and the two pathways have about the same impedance. If, however, the electrodes are placed parallel to each other (Fig. 3.I1b), the field tends to concentrate between their lower parts: the pathways AB and CD are in this case of the same length, but much more of AB than of CD is through the air. Consequently AB has the greater

impedance and the field tends to concentrate between C and D.

Fig. 3.11 Positioning electrodes relative to the surface of the body, e.g. the shoulder.

      a. Correct: electrodes parallel to the skin produce an even electric field.

      b. Incorrect: parallel electrodes produce a field of uneven intensity.

Fig. 3.12 Electrodes allowed to come too close to each other: the separation at A is less than the total spacing (s, + s) and many lines of force by-pass the tissues altogether.

Care must be taken that the distance between the electrodes is greater than the total spacing. In Fig. 3.12 the distance between the electrodes at A is less than the total spacing (S, + s,) and many of the lines of force pass directly from one electrode to the other, not through the tissues.

       Electrodes should, where possible, be placed over an even surface of the body. Should the surface be irregular, the field tends to concentrate on the more prominent parts. Where an irregular surface cannot be avoided, the concentration can be reduced by using wide spacing. In Fig. 3.13a the distance between the electrodes and the skin at A is less than half that at B, and so the field concentrates at A. In Fig 3.13b there is much less difference in the distance between the skin and electrode at A and at B, and the field is much more even.

Fig. 3.13 Electrode spacing:

1. Too narrow, producing a concentration of field where the tissues are close  

to the electrodes.

        b. Greater spacing makes for a more even field.

Fig. 3.14 Coplanar arrangement of electrodes:

          a. Correct spacing.

          b. Incorrect spacing, resulting in the electric field forming directly between  

             the electrodes.

Contraplanar positioning of electrodes This method is usually the most satisfactory, especially for the treatment of deeply placed structures. The electrodes are placed over opposite aspects of the trunk or limb so that the electric field is directed through the deep tissues. If the structure is nearer to one surface of the body than to the other the directing electrode (on the more distant surface) is placed further away from the skin than the active. The position of the electrodes can, if necessary, be modified so that they do not lie exactly opposite each other: provided that they are both parallel to the skin and do not approach too close to each other, a satisfactory field can be obtained.

Coplanar positioning of electrodes Electrodes can be placed side by side on the same aspect of the part, provided that there is adequate distance between them, as the pathway through the tissues offers less impedance to the lines of force than that through the air between the electrodes. The distribution of the resulting field is as shown in Fig. 3.14a. It is important that the distance between the electrodes is more

than the total width of spacing otherwise the electric field will not pass through the tissues at all (Fig. 3.I4b). The heating is more superficial U an with the contraplanar method, but this may be satisfactory for certain areas: superficial structures which are too exteusive for a

Fig. 3.15 Cross-fire treatment of a sinus. The areas (x) of the sinus wall that escape   

         treatment in the first exposure (a) because the low dielectric constant of the  

         air in the sinus distorts the electric field, are treated in the second exposure  

         (b) after the field is rotated through 9o

contraplanar application may be treated in this way. The spine, for example, can be heated with electrodes over the dorsal and lumbar regions.

        The method is particularly suitable for the treatment of superficial structures where some factor contraindicates the placing of an electrode immediately over the lesion. For example, when a boil is treated, the prominence tends to cause concentration of the field on the apex of the boil, and as pus has a high dielectric constant its presence also tends to cause concentration of the field. Alternatively there may be loss of cutaneous sensation, which makes it unsafe to place an electrode immediately over the area: for such a case the coplanar method would be the most suitable. It is also of value for treating superficial lesions when heating of the deep structures is undesirable, e.g. a stitch abscess following an abdominal operation.

         Cross-fire treatment Half the treatment is given with the electrodes in one position, then the arrangement is changed so that the electric field lies at right angles to that obtained during the first part of the treatrment. As an example; for the knee joint, half the treatment would be given with the electrodes over the medial and lateral aspects, the other half with them over the anterior and posterior aspects.

        The cross-fire method is used to treat the walls of cavities containing

air, e.g. the frontal, maxillary and ethmoid sinuses (Fig. 3.16). lines of force pass through the tissues between the electrodes but avoid the cavity, as the air within it has a low dielectric constant. Thus walls of the cavity which face the electrodes are not treated (XX in Fig 3.15). If the position of the electrodes is then changed I so that the field

Fig. 3.16 Cross-fire treatment of the sinuses. The spacing on the affected

               side (approx. 2 cm) should be less than that on the unaffected side  

               (approx. 3 cm).

              a. The location of the sinuses.

              b. Treatment of the frontal sinuses with one 8 cm electrode placed on the   

                  lateral part of the forehead and another on the other side of the face  

                  high on the cheek (1). For the second half of the treatment the elecrodes     

                  are moved to position 2

• Treatment of the maxillary sinuses with one 8 cm electrode placed on

   the lateral part of the cheek and another on the opposite side of the face     

    below the car (1). For the second half of the treatment the elecrodes are    

     moved to position 2,

• Treatment of all the sinuses (including the ethmoidal) with electrodes,  

one on the lateral part of the forehead, the other on the opposite side of the face, below the angle of the jaw.

lies at right angles to the previous one, these walls are heated. If this

treatment to the face is used, patients with contact lenses should be

asked to remove them because the heating effect may cause melting of

the lens!

         The cross -fire method may also be used for the treatment of deeply

Placed structures, particularly if they lie in extensive vascular areas,

Fig. 3.17 Cross-fire treatment of a deeply placed structure X avoids excessive heating of the skin.

Fig. 3.18 A monopolar electrode producing a radial electric field.

e.g. the pelvic organs. The dielectric constant of the vascular tissues is

very high and the cross-sectional area of the part is larger than the electrodes, so the field spreads in the deep tissues, which consequently receive less heating than the superficial ones. By passing the field through the area in two directions, the deep tissues (X in Fig. 3.17) receive twice as long an exposure as the skin.

Monopolar technique The active electrode is placed over the site of the lesion and the indifferent electrode is applied to some distant part of the body, or may not be used at all. A separate electric field is set up under each electrode, the lines of force radiating from the electrode (Fig. 3.18). Thus the density of the field becomes less as the distance from the electrode increases, and the heating is superficial.

Cable method

When short wave diathermy is applied by use of a cable the effect of the electric field may be used or that of the magnetic he (inductothermy), or use may be made of both effects at the same time. The electrode consists of a thick, insulated cable which completes the patient’s circuit of the machine. The cable is arranged in

Fig. 3.19 Electric and magnetic fields around the cable electrode. E indicates the   

               electric field, M the magnetic.

relationship to the patient’s tissues, but separated from them by a layer of insulating material. As the high-frequency current oscillates in the cable, a varying electrostatic field is set up between its ends and a varying magnetic field around its central part. These fields are shown diagrammatically in Fig. 3.19 and affect the tissues that lie within them.

The electrostatic field

The tissues which lie between the ends of the cable are in the strong electrostatic field, and the effects on these tissues are similar to those produced when the current is applied by the capacitor field method. The distribution of the field follows the same principles, so while the heating tends to be greatest in the superficial tissues and those of  low impedance, it should be possible to obtain some heating of the more deeply placed structures of high impedance provided that a suitable technique is used.

The magnetic field

The magnetic field varies as the current oscillates, and so EMFs are produced (by electromagnetic induction) in any conductor which is Cut by the magnetic lines of force. If the conductor is a solid piece of conducting material the EMFs give rise to eddy currents (see p. 19- 22). Such currents are produced in the tissues which lie close to the centre of the cable. The eddy currents produce heat, and as they are set

up only in conductors the effect is confined to the tissues of  low impedance, so that heating of the subcutaneous fat is avoided. However, the currents are produced primarily near the surface of the conductor (where the magnetic field is strongest), so it is he Superficial tissues that are affected most. Some heat is of course transferred to adjacent tissues by conduction and by the circulation of the heated blood, bur the effects are primarily on the superficial tissues of low impedance.

Relative effects of the two fields

has been shown experimentally that if the cable is coiled round material of high impedance the effect of the electric field predominates,

Fig. 3.20 Whole cable applied to the lower limb.

Fig 3.21  Ends of cable applied to the knee.

while the currents produced by electromagnetic induction are strongest when the material around which the cable is coiled is of low impedance. Thus when treating an area of high impedance, particularly if deep heating is required, the electric field between the ends of the cable is utilized in preference to the magnetic field at its

centre. When treating an area of low impedance, particularly it superficial heating is required, the eddy currents set up by the magnetic field at the centre of the cable are utilized in preference to the electric field. Alternatively, both effects can be utilized at the same time: if the whole cable is arranged in relationship to the patient’s tissues, an electric field is set up between its ends and eddy currents

near its centre.

          For treatment of the limbs the cable is usuallv coiled round the part If the area is extensive, .g. the whole of a limb (Fig. 3.20) or two limbs, all the cable is used and both electrostatic and magnetic fields are utilized. When treating a smaller area the whole of the cable may not be required: either the ends or the centre may be used, according to the depth of heating required and the impedance of the tissues. If the area is of high impedance the electrostatic field between the ends of cable is most effective: e.g. for the knee joint, two turns may be made

with each end of the cable, these lying above and below the joint ( 3.21). When treating two joints, e.g. both shoulders, a few turns be made with one end of the cable round one joint and a similar arrangement of the other end round the other joint. 1f the area to be treated is of low impedance, e.g. the muscles of the calf or thigh (Fig

Fig 3.22 Middle section of cable applied to the thigh.

Fig. 3.23 Cable arranged in a flat helix.

Fig. 3.24 Grid arrangement of cable.

3.22), the eddy currents produce satisfactory heating so the centre of

the cable is used.

             To treat a flat surface such as the back, the cable can be arranged in a

flat helix (Fig. 3.23), two helices made from its ends (see Fig. 3.26), or a grid arrangement may be used (Fig. 3.24). With the grid the magnetic field is complex and probably does not penetrate very deeply into the tissues, so heating is mainly by the electric field, but with the other two methods the tissues are heated by eddy currents. These flow at right angles to the magnetic lines of force and the heating produced by a single helix is therefore in the form of a hollow ring in the tissues lying under the coil (Fig. 3.25). In Fig. 3.2sa the coil is viewed from the side;

the broken lines show the magnetic lines of force and the line with arrows the eddy currents. In Fig. 3.25b the coil is viewed from above and the shading shows the area in which heat is produced. When the double helix is used, the magnetic lines of force link the two coils, as Shown in Fig. 3.26. Eddy currents are prodųced in the tissues lying between the two helices, so heating occurs in thịs area, being greatest in the superficial tissues where the magnetic field is strongest. Care

Fig. 3.25    Heating due to eddy currents in the tissues produced by a cable

in the form of a single helix.

         a. The magnetic field which creates the eddy currents, show by dotted lines.

         b. The area (shaded) in which heat is produced, seen from above.

Fig. 3.26     Heating with a double helix, with the two coils flat on the bod

surface.

          a. The magnetic field which creates the eddy currents is shown

              dotted.

1. The area (shaded) in which most heat is produced.

must be taken that there is a reasonable distance between the helices, otherwise intense heating may occur, causing a burn. The  two coils may be placed on a flat surface as in Fig. 3.26, or they may be arranged on opposite aspects of the body in a similar manner to condenser electrodes.

       The cable may be used in conjunction with one condenser electrode. This method is useful for the treatment of the hip joint when flexion deformity renders an antero-posterior application of condenser electrodes unsuitable. The cable is coiled round the thigh. One end is attached to the machine and the other is insulated, often with a crutch rubber. A condenser electrode is placed level with the sacrum,

Fig 3.27 Treatment of the hip joint using a cable (with one end insulated) and on malleable electrode to direct the electric field through the region of the hip.

side of the affected hip, and directs the electric field through the region of the hip (Fig. 3.27).

            The cable method is useful for the treatment of an extensive area which could not be included between condenser electrodes, or when the area is irregular, as with hands affected by rheumatoid arthritis, or when it is desirable to avoid heating the subcutaneous fat. The disadvantage of the cable is the impossibility of using air spacing, as the skin is liable to become warm so limiting the effect that can be obtained on the deep tissues.

Monode electrode

The monode works on the same principle as the cable. It consists of a flat helix of thick wire mounted in a rigid support. A condenser in parallel with the coil makes it possible to use a shorter length of wire than that required for the cable. Heating is produced by eddy currents in a region shaped like a hollow ring (like that produced by the single helix) but the rigid support enables the electrode to be used with air

spacing.

Techniques of short-wave diathermy

Testing of the machine

The machine should be tested before use. When condenser electrodes are to be used these are arranged opposite to each other with a gap in- between. The operator places her hand between the electrodes, Switches on and tunes the machine, then increases the current until a comfortable warmth is felt.

           When the cable is to be used, it may be arranged in a single loop and

tested with a neon tube, which lights up when the two circuits are in resonance, or the operator may place her hand between the ends of the

 cable (in the electrostatic field) and turn up the current in the machine until warmth is felt.

Preparation of the patient

The couch, chair or table that is used for supporting the patient should not contain metal, as this is liable to distort the electric field and to be heated by currents which may be induced in it. A deck chair is satisfactory as electrodes can be placed behind the canvas.

         Clothing should be removed from the area of treatment, for a number of reasons. It may be slightly damp from perspiration, and its presence would interfere with the circulation of air, which aids the evaporation of any sweat which may form during the treatment. Tight clothing could interfere with the flow of blood through the area, causing over-heating, or, if the patient is resting on an electrode, it could cause uneven pressure. If the clothing is not removed, the

necessary inspection of the skin before and after treatment is not possible, and the skin-electrode distance and position of the electrodes cannot be judged accurately. The presence of clothing makes it difficult for the patient to appreciate the sensation of warmth. Moreover, metal objects in the clothing may easily pass undetected. Metal and moisture both have a high dielectric constant, and a localized area of either causes concentration of an electric field, with consequent over-heating. Metal objects, and anything that is damp, should be removed from the vicinity of the area to be treated, i.e. at least 30 cm away from the electrodes.

         Wounds and sinuses must be cleansed and covered with a dry dressing before commencing treatment. The area to be treated must be dry. if the area is damp, the moisture on the surface of the skin is heated quickly and gives rise to a sensation of warmth which limits the intensity of current that can be applied.

                The patient must be comfortable and the part to be treated must be fully supported, as movement may alter the skin-electrode distance.

         The ammeter is no guide to the amount of heating of the tissues) merely of value for tuning the circuits. Consequently the dose estimated by the amount of heat felt by the patient. It is therefore very important for the patient to understand the degree of warmth that should feel, that undue heat should be reported, and that there danger of burns if the heat becomes excessive.

            Skin sensation must be tested before the first treatment. The tes may be carried out with test tubes, one full of warm water and the other of cold water. Should the sensation be defective in any part of the a it is unwise to apply heat treatment. The patient may be unable to assess the degree of heating produced, and also the vasomotor response in an insensitive area is less than that in a normal one, so that l heat is not carried away so quickly and over-heating is liable to occur.

Fig. 3.28   Electric fields produced by (a) flat and (b) convex electrodes. The field    

                  produced by the convex electrode is more even.

Hearing aids must be removed and left well away from the machine, as induced currents may cause serious damage to them.

Types of electrode

There are various types of capacitor electrodes, but each consists of a metal plate surrounded by some form of insulating material.

One type has a cover within which the position of the metal plate can be adjusted. These electrodes are commonly circular, but special shapes are made for some irregular areas, such as the axilla. Electrodes of this type are arranged in position on supporting arms and it is advisable to leave a small gap between the cover and the skin to allow for the circulation of air.

            Another type of electrode consists of a rigid metal plate coated with a

thin layer of insulating material, either rubber or plastic. These plates are frequently convex at the edges, which provides a more even electric field than a flat disc. This is because an electric charge concentrates at the edges of a conductor and sets up a more intense electric field in this area than elsewhere: with the convex electrodes the edges are further from the skin than is the centre, so the peripheral part of the field has

room to spread before reaching the skin (Fig. 3.28). These electrodes

are arranged in position on supporting arms and are separated from the Skin by an air gap. They may have an adjustable device projecting from the centre to ensure correct spacing.

       A third type of electrode consists of a malleable metal plate covered With a thin layer of rubber. This can be moulded to the part, but should not be bent sharply or the metal plate may crack. Electrodes of this type are separated from the skin by perforated felt and their position is maintained by body weight. Undue pressure, which would interfere With the blood flow, must be avoided. The felt is perforated so that it Contains a proportion of air, which is the most satisfactory spacing material, but the impossibility of entirely air spacing is one of the

disadvantages of this type of electrode. The cable electrode consists of a thick wire covered with rubber. It is separațed from the skin by at least four layers of dry turkish towelling,

Forming a thickness of at least I cm (preferably more). The towelling is necessary to absorb any perspiration which may be produced by the eat and result in a scald. The turns of the cable should be at least 2.5 part and may be secured with spacers made of insulating material.

Position and size of electrodes

This has been considered in the sections on the condenser field and cable methods of treatment. When arranging the electrodes it is important to remember that an electric field can be set up around the edges and back of the electrode as well as from the front. If these parts approach too close to the patient’s tissues a field is set up in this area and may cause uncomfortable heating. For example when treating one knee-joint the back of the electrode placed on the medial aspect of the joint may lie too close to the other knee, which is consequently heated.

Connecting leads

In all cases the leads or cable must be of the correct length for the particular electrodes and machine that are used. The leads should lie parallel to each other, at least as far apart as the terminals of the machine, and not approach close to any conductor. Currents may be induced in any conductor which lies near to the leads, with consequent loss of energy from the leads and possible damage to the conductor from over-heating. Similarly the leads must be separated from the

patient’s skin by a distance at least as great as the electrode spacing, otherwise they induce currents in the tissues and cause heating in this area.

Application of current

When the patient, electrodes, and leads are in position, the current is turned on and the circuits tuned. The current is then turned up slowly to allow time for vasodilatation to occur and for the patient appreciate the degree of heating. The operator should remain within call of the patient throughout the treatment, and turn the current immediately if the heating becomes excessive.

            At the end of the treatment the controls are returned to Zero current is switched off and the electrodes are removed. The skin be faintly pink, but there should be no strong reaction. Notes should be made of the size and spacing of the electrodes, the meter reading, the duration of the treatment and any reaction that is observed

Dosage

In most cases the intensity of the application should be sufficient to cause a comfortable warmth and the duration of the treatment should be 20-30 minutes (except for the treatment of chronic inflammatory lesions, when a duration of at least 30 minutes is desirable). The treatment may be carried out daily, or on alternate days.

                 For the treatment of acute inflammation, or recent injury, the

application should be less intense than that suggested above, but may be carried out more frequently, e.g. twice daily. The current used may be that which produces a mild sensation of warmth, or it may be increased until mild warmth is felt then reduced to the point at which the sensation is no longer perceptible. The duration of the treatment is limited to 5-10 minutes; the dose is increased progressively but

cautiously according to the effects observed. When the inflammation is

within a confined space, such as the air sinuses of the face, it is particularly important that excess treatment should be avoided, as rise in tension in such an area seriously aggravates the symptoms.

Therapeutic uses of short-wave diathermy

Effects on inflammation

The dilatation of arterioles and capillaries results in an increased flow of blood to the area, making available an increased supply of oxygen and nutritive materials, and also bringing in more antibodies and white blood cells. The dilatation of capillaries increases the exudation of fluid into the tissues and this is followed by increased absorption which, together with the increased flow of blood through the area, assists in the removal of waste products. These effects help to bring about the resolution of inflammation. Additional effects are obtained when the inflammation is associated with bacterial infection: these are considered below.

             In the acute stages of inflammation, caution should be exercised in

applying the treatment to areas in which there is already marked vasodilatation and exudation of fluid, as an increase in these processes may aggravate the symptoms. In the sub-acute stages, stronger doses may be applied with considerable benefit. When the inflammation is chronic, a thermal dose of fairly long duration must be used to be effective.

Short-wave diathermy is particularly valuable for lesions of deeply placed structure such as the hip joint, which cannot easily be affected by other forms of electrotherapy and radiation. It is of value, in conjunction with other forms of physiotherapy, in various inflammatory conditions (e.g. rheumatoid arthritis, capsulitis and tendinitis) and for the inflammatory changes which frequently occur

in the ligaments surrounding osteo-arthritic joints.

Effects in bacterial infections

Inflammation is the normal response of the tissues to the presence of bacteria, the principal features being vasodilatation, exudation of fluid into the tissues, and an increase in the concentration of white blood cells and antibodies in the area. Heating the tissues augments these Changes and so reinforces the body’s normal mechanism for dealing With the infecting organisms, therefore short-wave diathermy may be of value in the treatrment of bacterial infections such as

Carbuncles and abscesses. Treatment in the early stages may occasionally bring about resolution of the inflammation without pus formation occurring; failing this, the development of the inflammatory response is accelerated. Until there is free drainage, the treatment should be given cautiously, as in all cases of acute inflammation. When the abscess is draining freely, stronger doses may be applied, the increased blood supply assisting the healing processes once the

infection has been overcome.

          In some cases short -wave diathermy appears to aggravate the condition, but increased discharge for a few days is an indication of acceleration of the changes occurring in the tissue, and not a contra-indication to treatment. However, should the increased discharge persist it may be an indication that the body’s defence mechanism is already taxed to its uttermost, so that it is impossible to reinforce its

action. This is most liable to occur in cases of long-standing infection, and under these circumstances no benefit is derived from the application of short -wave diathermy.

          Bacteria can be destroyed directly by heat, but it would be impossible to raise the body tissues to the necessary temperature without causing damage to the tissues themselves.

Traumatic conditions

The beneficial effects of short-wave diathermy on traumatic lesions are similar to those produced in inflammation. The exudation of fluid (followed by increased absorption) and the increased flow of blood through the area assist in the removal of waste products, while the improved blood supply makes available more nutritive materials, so assisting the healing processes.

            Recent injuries should be treated with the same caution as acute inflamma-tion, as excessive heating is liable to increase the exudation of fluid from the damaged vessels. Stiff joints and other after -effects of injury require stronger doses, the treatment being a preliminary to the exercise which is usually the essential part of the treatment.

Reducing healing time

To promote the healing of, for instance, a wound, an increased blood supply to the tissues may be of assistance, provided that the vascular responses to heat are normal.

Relief of pain

It is found that a mild degree of heating is effective in relieving pain presumably as a result of a sedative effect on the sensory nerves. It has been suggested that pain may be due to the accumulation in the tissue of the waste products of metabolism and that the increased flow of blood through the area assists in removing these substances. Su superficial heating probably relieves pain by counter-irritation, but

is unlikely that the heating of the skin produced by short-wave diathermy is great enough to have this effect. When pain is due to inflammatory processes, resolution of the inflammation is accompanied by relief of pain: short-wave diathermy assists in bringing about the resolution of inflammation, and so indirectly in relieving the pain. However, strong heating in these cases may cause an increase of pain, especially in acute inflammation, if the increased blood flow and exudation of fluid cause an increase of tension in the tissues.

           Thus when short-wave diathermy is used in .the treatment of inflammatory and post-traumatic lesions, it brings about relief of pain in addition to its other effects. This is particularly valuable when the treatment forms a preliminary to active exercise, which can then be performed more efficiently.

Effects on muscle tissue

The heating of the tissues induces muscular relaxation, so short-wave diathermy may be used for the relief of muscle spasm associated with inflammation and trauma, usually as a preliminary to movements. Increased efficiency of muscle action should also aid the satisfactory performance of active exercises.

        Short-wave diathermy has been used in an attempt to reduce muscle spasm due to upper motor-neurone lesions, but other methods of inducing relaxation are more satisfactory for these cases.

Summary of uses

1. Disorders of the musculo-skeletal system, e.g. degenerative joint disease:

Chronic rheumatoid arthritis and osteo-arthrosis

Sprains

Strains

Haematoma

Muscle and tendon tears

Capsule lesions

2. Inflammatory conditions (chronic or acute)

Boils

Carbuncles

Sinusitis

Pelvic conditions

Infected surgical incision

Dangers of short-wave diathermy

Burns

Heat burns can be caused by short-wave diathermy, therefore the word “burn’ must be used to warn the patient of this possible danger. In

Fig. 3.29   The effect of metal embedded in the tissue on an applied electric field.

1. A strip of metal parallel to the electric field concentrates the electric 

lines of force considerably, with consequent danger of overheating.

• A strip of metal lying perpendicular to the electric field has little 

disturbing effect on the field.

severe cases there is coagulation and therefore destruction of the tissues, and the burn appears as a white patch surrounded by a reddened area of inflammation. In milder cases tissue is not destroyed but a bright red patch is seen and blistering is liable to occur. The damage should be visible on removing the electrodes; it is only in exceptional circumstances that the deep tissues are raised to a higher temperature than the superificial ones. Burns may arise from various causes: concentration of the electric field, use of excess current, hypersensitivity of the skin, impaired blood flow, or leads touching the skin.

       1. Concentration of the electric field This causes overheating of the

tissues in the affected area. It may be due to the presence of a small area of material of high dielectric constant within the field, such as metal or a localized patch of moisture, to inadequate electrode spacing over a prominent area of tissue, or to an electrode being badly placed so that one part of it lies nearer to the tissues than the rest.

           In some cases metal may be embedded in the tissues, e.g. a plated fracture, and the danger of causing burns then varies with the position in which the metal lies. It is the concentration of the electric field, not overheating of the metal, that is dangerous. If a narrow strip of metal lies parallel to the lines of force it provides a pathway of low impedance for a considerable distance and is liable to cause serious concentration of the field (Fig. 3.29a). If, however, it lies across the field (Fig. 3.290 the easier pathway is provided only for a short distance, and being wide

is much less likely to cause concentration of the lines of force. It is possible to calculate the degree of concentration that will occur, and the consequent danger, but if there is any doubt the matter should be discussed with the clinician in charge of the case.

            2. Excess current The patient’s sensation is the only indication of the

intensity of the application, and excess current may be applied if he does not understand the sensations that he should experience, or if cutaneous sensation is defective, or if he should fall asleep during treatment. If the intensity of the current is increased quickly at the beginning of the treatment a dangerous level may be reached, and failure to reduce the current immediately if the heat becomes intense

may result in a burn. The patient should be told that he should feel a mild, confortable warmth and no more, otherwise a burn could result.

         3. Hypersensitive skin If the skin has been rendered hypersensitive, e.g.by X-ray therapy or the recent use of liniment, a dose which would normally be safe may cause damage.

        4. Impaired blood flow The blood circulating through the tissues normally dissipates the heat and prevents excessive rise of temperature. Should the blood flow be impaired, e.g. by pressure on a bony point, a burn is liable to occur.

         5. Leads touching the skin If a lead approaches close to the patient’s tissues, heat is produced in the area and may be sufficient to cause a burn.

If a burn does occur, it must be reported immediately to the head of the physiotherapy department, who in view of the possibility of subsequent legal proceedings will deal with the situation according to the particular hospital’s regulations. The burn must be kept clean and dry, usually being protected with a dry sterile dressing.

Scalds

A scald is caused by moist heat, and may occur if the area being treated

is damp, e.g. from perspiration, or if damp towels are used for treatrment with the cable. If the moisture is not localized it does not cause concentration of the field, but it may become over-heated, scalding the skin.

Overdose

his causes an increase in symptoms, especially pain, and is most liable to occur when there is acute inflammation within a confined pace, It can occur under other circumstances and any increase in pain 1olowing treatment is an indication to reduce the intensity of subsequent applications.

Precipitation of gangrene

Heat accelerates chemical changes, including metabolic processes : the tissues, so increasing the demand for Oxygen. Normally this is supplied by the increased blood flow, but should there be Some impedance of the flow of arterial blood to the tissues the demand for oxygen is not met and gangrene is liable to develop. Consequently heat should never be applied directly to an area with an impaired arterial blood supply.

Electric shock

A shock can occur if contact is made with the apparatus circuit with the current switched on, but the construction of modern apparatus is usually such that this is not possible. Under certain circumstances an electric shock could result from contact with the casing of the apparatus (see pp. 93-96).

Sparking

Sparking is liable to occur if one of the electrodes is touched while the current is applied. The patient must be warned not to touch the electrodes.

Faintness

Faintness is produced by hypoxia of the brain following a fall in blood- pressure. It is particularly liable to occur if, after an extensive treatment, the patient rises suddenly from the reclining to the erect position.

Giddiness

Any electrical current applied to the head may cause giddiness from its effects on the contents of the semicircular canals. All diathermic treatments to the head should be given with the patient fully supported and, if possible, with the head in a horizontal or an erect position.

Damage to equipment

The action of cardiac pace-makers, hearing aids and other electronic devices may be affected by disturbances set up by the short-wave diathermic current. Patients with such devices should not be treated with short-wave diathermy or allowed to come in close proximity to the apparatus. Altered action has been reported at up to two me from a short-wave diathermic machine (see Health and Safety

regulations).

        Leads may be damaged by over-heating if they are allowed to make contact with a conductor, and should there be a break in the continuity of the wire, or a crack in an electrode, sparking may occur, resulting overheating. The fault may not be apparent if the insulation covering the metal is undamaged. Particular care should be taken with: malleable electrodes, which are liable to crack within their rubber covering.

         Treatments should not be carried out with the patient resting on an interior sprung mattress, as sparking between the springs may be sufficient to ignite the mattress.

Contra-indications to short-wave diathermy

Haemorrhage The heating of tissues by a diathermic current causes dilatation of blood-vessels, so it should not be employed directly after an injury or in any case where haemorrhage has recently occurred. It should not be applied to the abdomen or pelvis during menstruation, nor should it be used for conditions in which haemorrhage might Occur, such as gastric or intestinal diseases associated with ulceration or haemophilia.

            Venous thrombosis or phlebitis These conditions contra-indicate the

application of short-wave diathermy to the area drained by the affected vessel, as the increased flow of blood may dislodge the clot or aggravate the inflammation.

Arterial disease Diathermy should not be applied to parts which have a defective arterial blood supply. The inability of the circulation to disperse the heat could result in an increasę of temperature to a level which could produce a tissue burn. Moreover, the unsatisfied tissue demand for nutrients could precipitate gangrene.

Pregnancy Diathermy*should not be applied to the abdomen or

pelvis during pregnancy.

Metal in the tissues See p. I26.

Disturbed skin sensation It is safer to avoid the application of diathermy to areas where there is loss of skin sensation.

Tumours Short-wave diathermy should not be applied in the region of malignant growths. The increase in metabolism resulting from the increase in temperature could accelerate the rate of growth.

X-ray therapy X-rays devitalize the tissues and render them more susceptible to damage. Short-wave diathermy should therefore not be applied to areas recently exposed to therapeutic doses of X-rays.

Patients at particular risk It is unsafe to apply short-wave diathermy to patients who are unable to understand the degree of heating required and the necessity of reporting excessive heating. For this reason small children and mental defectives are not suitable for treatment. Similarly it is not safe :to treat unconscious patients or those who are liable to lose consciousness, such as epileptics.

Infra-red radiation

Infra-red rays are electromagnetic waves with wavelengths of 750 nm- 400 000 nm (see pp. 22-23). Any hot body emits infra-red rays; the sun, gas fires, coal fires, electric fires, hot water pipes, etc. Various types of infra-red generator are employed in physiotherapy departments, all designed to comply with DHSS regulations. There are two main groups, the non-luminous and the luminous generators. Non-luminous generators provide infra-red rays only, while luminous

generators emit visible and a few ultra-violet rays as well as infra -red. Treatment with a luminous generator is often referred to as ‘radiant heat’, the term ‘infra-red’ generally being applied to the radiation from non-luminous sources. In fact these terms are misleading, as it is the infra-red rays that are utilized with both types of generator, and both emit heat-producing rays.

Non-luminous generators

A simple type of element for producing infra-red rays consists of a coil of wire wound on a cylinder of some insulating material, such as fireclay or porcelain, rather like the element of a radiant electric fire. An electric current is passed through the wire and produces heat. Infra-red rays are emitted from the hot wire and from the fireclay former; which is heated by conduction. Some visible rays are produced as well as the infra-red, and when the element is hot a red glow is visible, so this type of element is not perfectly ‘non-luminous’. More usually, the coil of wire is embedded in the fireclay or placed behind a plate fireclay. The emission of rays is then entirely from  the fireclay, which is commonly painted black, and very few visible rays are produced. Both types of element are connected into the circuit by a screw device and placed at the focal point of a parabolic or gently curved

spherical reflector. The reflector is mounted on a stand and its position can be adjusted as required.

            A third type of non-luminous generator consists of a steel rube approximately 8 mm in diameter, within which is a spiral of wire embedded in some electrical insulator which is a good conductor. heat. Current is passed through the central wire and produces which is conducted by the insulator to the steel tube which emits red rays. The tube is bent into two or three large turns and mounted in in a suitable reflector.

All non- -luminous elements require some time to heat up before the emission of rays reaches maximum intensity. Elements of the first type, which emit rays directly from the wires, require about five minutes, but the others need longer, ten or fifteen minutes according the construction. Lamps must therefore be switched on an appropriate time before they are required.

             The construction of all lamps should be such that the reflectors and

other parts do not become unduly hot during use, and it is essential that there is a wire guard to prevent inadvertent contact with the clement.

           Non-luminous elements produce infra-red rays with wavelengths from 15 000 nm down to 750 nm, or less if some visible rays are emitted. The maximum emission is in the region of 4000 nm.

Luminous generators

The rays emitted from the luminous generators are produced by one or more incandescent lamps. An incandescent lamp consists of a wire filament enclosed in a glass bulb, which may be evacuated or may contain an inert gas at a low pressure. The filament is a coil of fine wire and is usually made of tungsten, as this material tolerates repeated heating and cooling. The exclusion of air prevents oxidation of the filament, which would cause an opaque deposit to form on the inside of the bulb. The passage of an electric current through the filament

produces heat; infra-red, visible and a few ultra-violet rays are emitted. The spectrum is from 350 to 4000 nm, the greatest proportion of rays having wave -lengths in the region of 1o00 nm. Often the front of the bulb is red to filter out the shorter visible and the ultra-violet rays.

Depth of penetration of rays

The depth of penetration of electromagnetic radiation depends on its wavelength and the nature of the material. The human skin will allow the passage of infra-red, visible and ultra-violet rays, and their approximate depth of penetration into the skin is shown in Fig. 3.30.

Techniques of infra-red treatment

Choice of apparatus

In many cases luminous and non-luminous generators are equally Suitable, but in some instances one proves more satisfactory than the Other. When there is acute inflammation or recent injury, the sedative effect of the rays obtained from. the non-luminous generator may prove more effective for relieving pain than the counter-irritant effect of those from the luminous source. For lesions of a more chronic type

Fig. 3.3o Cross -section of the skin, showing the extent of penetration of

                radiation of different frequencies.

the counter-irritant effect of the shorter rays may prove to be of value, and under these circumstances a luminous generator is chosen.

             Select the generator most suitable for the area to be treated. If only

one surface of the body requires irradiation a lamp with a single element mounted in a reflector is satisfactory, but if several aspects require treatment a tunnel bath is more effective. The temperature reached in a tunnel bath is higher than that produced by other lamps and this may be an advantage, particularly for the treatment of chronic lesions.

        Before use the lamp is checked to ensure that it is working correctly. Non-luminous generators must be switched on an adequate time before use.

Preparation of the patient

Clothing is removed from the affected part and at the first attendance skin sensation to heat and cold is tested. Should the sensation be defective it is unwise to apply the treatment; apart from the patient’s inability to appreciate possible over-hearing, the vasomotor response in the affected area is likely to be less than in a normal one, so that heat is not carried away so rapidly. The patient is warned that he should experience comfortable warmth, and that he should report immediately if the heating becomes excessive, as undue heat may cause a burn; also that he should not touch the lamp or move nearer to it. The patient should be comfortable and fully supported so that he does not move unduly during treatment.

Arrangement of  lamp and patient

The lamp is positioned so that it is opposite to the centre of the area to be treated and the rays strike the skin at right angles, thus ensuring maximum absorption. The distance of the lamp from the patient should be measured. It is usually 75 or 5o cm, according to the output of the generator.

          Care must be taken that the patient’s face is not exposed to infra-red rays. If it is not possible to avoid irradiating the face, the eyes must be shielded.

Application of infra-red treatment

At the commencement of the exposure, the intensity of radiation should be low, but after 5-10 minutes, when vasodilatation has taken place and the increased blood-flow has become established, the Strength of the radiation may be increased. This can be achieved by moving the lamp nearer to the patient or by adjusting the variable resistance.

        The physiotherapist should be at hand throughout the treatment Session and should reduce the intensity of the radiation if the heat becomes excessive. If the irradiation is extensive, it is desirable that Sweating should occur to counteract any undue rise in body temperature. Sweating is encouraged if the patient is provided with water to drink during the treatment.

At the end of the exposure the skin should be red, but not excessively 30. Following extensive irradiation the patient should not rise suddenly from the recumbent position, or go out into the cold immediately.

Duration and frequency of treatment

For acute inflammation or recent injuries and for the treatment of wounds an exposure of 1o to 15 minutes is adequate but may be applied several times during the day. Longer exposures may be used for chronic conditions.

Therapeutic uses of infra-red

Relief of pain

Infra-red radiation is frequently an effective means of relieving pain When the heating is mild, the relief of pain is probably due to the sedative effect on the superficial sensory nerve endings. Stronger heating irritates the superficial sensory nerve endings, and so relieves pain by counter-irritation. It has been suggested that pain may be due to the accumulation in the tissues of waste products of metabolism, and an increased flow of blood through the part removes these substances and so relieves the pain. In some cases the relief of pain is probably

associated with muscle relaxation (see below).

           Pain due to acute inflammation or, recent injury is relieved most effectively by mild heating. Too intense a treatment may cause an increase in the exudation of fluid into the tissues, and so actually increase the pain. When pain is due to lesions of a more chronic type, stronger heating is required. The irradiation should cause a

comfortable warmth and the treatment last for at least thirty minutes.

Muscle relaxation

Muscles relax most readily when the tissues are warm, and the relief of pain also facilitates relaxation. Infra-red irradiation is thus of value in helping to achieve muscular relaxation and for the relief of muscle spasm associated with injury or inflammation.

        Because it relieves pain and induces muscle relaxation, infra-red irradiation is frequently used as a preliminary to other forms of physiotherapy. After irradiation movements can frequently be made through a greater range than before, and the relief of pain makes it possible to perform exercises more efficiently.

Increased blood supply

This effect is most marked in the superficial tissues, and may be used in the treatment of superficial wounds and infections. A good blood supply is essential for healing to take place, and if there is infection the increased number of white blood cells and the increased exudation of fluid are of assistance in destroying the bacteria.

            Infra-red treatment is frequently used for arthritic joints and other

inflammatory lesions, and for the after -effects of injuries. In these cases the relief of pain and muscle spasm is undoubtedly of value, but the effect of irradiation on the flow of blood through the site of the lesion is uncertain. When superficial structures are affected, e.g. Small joints of the hands and feet, there may be some heating and consequent vasodilatation. This will increase the supply of oxygen and foodstuffs available to the tissues, accelerate the removal of waste products and

help to bring about the resolution of inflammation. On the other hand, irradiation of the skin over deeply placed structures is more likely to cause vasoconstriction in the deep tissues, but this may be of value in relieving congestion.

Dangers of infra-red irradiation

Burns

Infra-red radiation can cause superficial heat burns. A red patch is Seen on the skin, which subsequently blisters, either during or after the treatment. The burn is most often caused by too great an intensity of radiation. This can occur if the patient does not under Stand the nature of the treatment , fails to report over-heating, moves nearer to the lamp or falls asleep during the treatment. It may also occur if the skin sensation is defective so that the patient is unable to appreciate the

degree of heating, or if the physiotherapist is not at hand to reduce the heat if necessary. Failure to allow adequate time for a non-luminous generator to warm up before placing it in position may result in over- heating when the temperature of the element rises.

           The recent use of liniment renders the skin hypersensitive and so increases the danger of burns. Impaired blood flow through the part, which may be due to pressure or to some circulatory defect, increases the risk of over-heating, as heat is not carried away from the area as rapidly as usual.

         Burns can also occur as a result of touching the lamp when it is hot, or from scattered hot glass if an incandescent bulb breaks. It is possible for blankets or pillows to catch fire, especially pillows placed carelessly in a tunnel bath.

        Should a burn occur the procedure is the same as for a short-wave

diathermy burn (p. 127).

Electric shock

Electric shock can occur as a result of touching some exposed part of the circuit, but the chief danger arises if the live wire comes in contact With the apparatus casing. This is considered on page 93. In view of the extensive metal framework of many infra-red generators it is essential that appropriate precautions are taken.

Gangrene

The danger of inducing gangrene by applying infra -red rays to an area with defective arterial blood supply is the same as for short-wave diathermy (p. 127).

Headachc

Headache may follow infrared irradiation, especially if sweating does not occur or if the treatment is given during hot weather. The patient Should take plenty of fluid to encourage sweating and it is wise to discontinue extensive infra-red treatments when the weather is very hot. Irradiation of the back of the head may cause headache: this area should be protected.

Faintness

Extensive irradiation is accompanied by a fall in blood pressure which may result in faintness due to hypoxia of the brain. This is particularly liable to occur if the patient rises suddenly from the recumbent position after an extensive treatment.

Injury to the eyes

It has been suggested that exposure to infra-red rays may predispose to cataracts, and it is wise to protect the eyes from irradiation.

Contra-indications to infra-red treatment

Infra-red radiation should not be applied to areas with a defective arterial blood supply nor where there is danger of haemorrhage. It is also unwise to apply the treatment to areas where the skin sensation is defective or on which liniment has recently been used.

Microwave diathermy

Microwave diathermy is irradiation of the tissues with radiation in the shorter wireless part of the electromagnetic spectrum (Hertzian rays), i.e. with a wavelength between infra -red and short-wave diathermic radiation. There is some variation in definition, but waves of 1 -100 cm may conveniently be classified as microwaves (decimetre’ waves). Radiation with a wavelength of 12.25 cm and a frequency of 2450 MHz is frequently used, and some use is made of radiation with a wavelength of 69 cm and a frequency of 433.92 MHz.

Production of microwaves

Wireless waves are produced by high-frequency currents and have the same frequency as the currents which produce them. The principles of production of the currents are similar to those for other high” frequency currents, but in order to obtain the necessary very high frequency a special type of valve called a magnetron is used. As with other valves, the magnetron requires time to warm up so output is not obtained immediately the apparatus is switched on. A stand-by switch should be provided for use between treatments: this enables the output

circuit to be disconnected without cutting off the current to the valves so that repeated heating and cooling of the valves is avoided.

Fig. 3.31 Two differently-shaped microwave emitters, shown in plan and

               elevation, and the distribution of the radiation they produce.

Current must be carried from the high-frequency circuit by a coaxial cable. A coaxial cable consists of a central wire with an outer metal sheath separated from the wire by insulating material. The wire and the sheath run parallel to each other throughout and form the output and return wires of the circuit. The cable must be of the correct length for the particular frequency.

            The coaxial cable carries the current to a small aerial from which the

microwaves are emitted. The aerial is mounted in a reflector, which is packed with some material which transmits the waves, so forming a solid unit. The whole device is used to direct the waves onto the tissues and may be termed the ’emitter’, ‘director’ or ‘applicator’. The patient does not form part of the circuit, which is constructed in such a way that no tuning is necessary for individual treatments.

            As with short-wave diathermy, microwaves can interfere with radio

communications, so the generator must be constructed so as to minimize interference, and only specified frequencies may be used for medical work. The frequencies of 2450 MHz and 433.92 MHz (wavelengths 12.25 and 69 cm respectively) are among those permitted.

Application of microwaves

Various types of emitter are available. Those most commonly used are placed at a distance from the body and the waves pass through the intervening air to reach the tissues. Emitters of this type may be circular or rectangular in shape. The circular ones give a beam of rays which is circular in cross-section and is more dense at the periphery than in the centre (Fig. 3.31). The rectangular emitter provides a beam which is oval in cross section and is of greatest density centrally

         In both cases the rays given off from the emitter diverge , so that their density becomes less as the distance from the emitter increases Reduction in the intensity of the beam is also caused by absorption of the rays. The distance from the skin at which these emitters are used depends on the particular emitter, the output of the generator and the structure to be treated. Commonly it is between 10 and 20 cm. Larger areas require a greater distance and a greater distance requires a greater output from the emitter.

         Small emitters are made for use in contact with the tissues and for the treatment of cavities, but they do not appear to be as effective as distant emitters. Recently an emitter with a concave surface which fits round the body has been used with the 69 cm waves. It is claimed that this gives a deeper effect than the other methods.

Physiological effects of microwaves

Absorption of the waves results in the production of heat in the tissues, but microwave diathermy differs from other heat treatments in the penetration of the heat. Microwaves penetrate more deeply than do infra-red rays, but do not pass right through the tissues in any appreciable density like the electric field used in short-wave diathermy. Thus the effects are deeper than those of infra-red irradiation, but less suitable for the treatment of deeply placed structures than short -wave diathermy. The effective depth of penetration of microwaves appears to be about 3 cm. With equipment generally available it is possible to irradiate only one aspect of the body at a time.

           Microwaves are strongly absorbed by water, so there is appreciable heating of tissues which have a good blood supply, such as muscle, but less heat is produced in those with a low fluid content, such as fat Thus the heating of the subcutaneous fat, which is a disadvantage of  short -wave diathermy applied by the condenser field method, is avoided.

          The physiological effects of the local rise in temperature produced by microwave diathermy have been described on pp. 97-99.

Therapeutic effects of microwaves As the physiological effects of microwave diathermy are similar to those of short-wave diathermy, it can be used in the treatment of the same types of condition:

traumatic and inflammatory lesions, in which the increase in blood supply and relief of pain and muscle spasm a value, and bacterial infections, where the increase in blood supply brings more white blood cells and antibodies to the area and so reinforces the body’s normal defence mechanism.

              Microwave diathermy is most likely to be effective for lesions in the

superficial tissues and those of high fluid content. It is therefore suitable for the treatment of traumatic and rheumatic conditions affecting the soft tissues and small superficial joints. As it is generally possible to irradiate only one apsect of the body at a time, it is more satisfactory for localized than for widespread conditions. The ease of application may make microwave diathermy preferably to short -wave

diathermy in those conditions where both are applicable.

Dangers of microwave diathermy

Burns

Microwave diathermy can produce heat burns. The patient’s sensation is the primary guide to the intensity of treatment to apply, so it is unwise to use the method if skin sensation is defective. Some authorities claim that the heating of the underlying tissues is greater than that of the skin, but damage should not occur if the dose is limited to that suggested (see p. 141).

         Water is heated rapidly by the waves, so the skin must be dry. Wet

dressings and adhesive tapes should be avoided, as should areas which perspire freely. Concentration of the waves may cause over-heating over bony prominences or where the emitter is unevenly spaced from the tissues. As with short -wave diathermy, metal objects should be removed from the field.

Eyes

In animals, opacities of the lens have developed following exposure of the eye to microwaves. The treatment of eye conditions by microwaves is unwise, and irradiation of the eyes in the course of other treatments must be avoided. As a precaution it is now common practice for both the physiotherapist and patient to wear protective goggles made of a very fine wire mesh.

Circulatory defects

Ischaemic areas should not be treated, because of the increased demand for oxygen which results from the rise in temperature. Patients at particular risk of haemorrhage, thrombosis, phlebitis and other vascular lesions should not receive microwave treatment.

Other contra-indications

Microwaves should not be applied to regions where there are malignant growths or tubercular infections, nor to areas which have recently been exposed to therapeutic doses of X-rays. It is wise to avoid areas where the skin has been rendered i hypersensitive by the use of liniments and it is said to be advisable to avoid irradiation of the testicles.

Damage to equipment

Damage to the magnetron can result from leaving the apparatus on with the emitter facing a metal plate, which reflects the waves. The effect of microwaves on electronic devices such as cardiac pacemakers and hearing aids is not known, but it should be assumed that the situation is the same as with short-wave diathermy, and that such devices may be damaged by microwaves.

Technique of application

Preparation of apparatus

The selected emitter is connected to the machine by the appropriate cable and the power switched on. There will be some delay before output is obtained, but then the physiotherapist tests the apparatus by placing her hand or arm in front of the emitter and increasing the output until a sensation of warmth is experienced. The controls are then returned to zero and the switch turned to the stand-by position (if

no stand-by switch is provided the current is turned off).

Preparation of the patient

This is the same as the preparation for the application of short –wave diathermy (see p. 12o). The patient must be warned to avoid movement once the emitter has been arranged in position, and full support in a comfortable position is necessary to ensure this. The patient is fitted with pair of wire mesh goggles to protect his eyes.

Application of the emitter

The emitter is arranged so that its surface is parallel to the skin and at the appropriate distance, due consideration being given to the surface marking of the structure to be treated. Irregular surfaces and areas which perspire freely should, if possible, be avoided.

Irradiation

The patient is reminded of the sensation to be expected and of the need

to report accurately on that experienced. The output is increased slowly until a sensation of warmth is experienced or the selected output is reached, whichever comes first. Irradiation continues for an appropriate time, the physiotherapist visiting the patient frequently to ensure that nothing untoward has occurred. The output is then reduced and switched off. Slight erythema may be observed. but there should be no marked skin reaction.

Dosage

The dose can be calculated from the power output from the machine, which may be up to 200 watts, but in all cases the sensation experienced by the patient must be the primary guide. This should never be more than a comfortable warmth, and as a general rule weaker doses should be used for acute than for chronic conditions.  The duration of irradiation ranges from 10 to 30 minutes, shorter exposures being used on small areas and for acute conditions. It is advisable to commence cautiously and in all cases progressive increases in exposure must depend on the patient’s reaction. Treatment may be given daily or on alternate days.

Electric heating pads

Electric pads are produced commercially in various sizes. Their construction is such that the temperature produced by a heating element may be regulated by a series of resistors to the required level. Heating of the tissues is by conduction so that the effect is merely superficial, but this method is both easy and comfortable for the patient. The precautions to be taken before treatment with electric heating pads are those common to all forms of heat treatment.

Paraffin wax

Wax baths are available in many variations of size and shape. The melted wax needs to be maintained at a temperature of 40°-44°C for treatment purposes, so thermostatic control is essential. The temperature of the wax must be checked before treatment is given. This method of heating the tissue has the advantage that it is the most convenient way of applying conducted heat to the extremities. As

the wax solidifies from its molten state it releases its energy of latent heat (see p. s) and this heat energy is conducted into the tissues.

Method

The part to be treated must be clean and free from cuts, rashes or infection. Position the patient according to the part to be treated and the type of wax bath selected, and instruct the patient to dip the part in and out of the bath until a thick coat of wax sets on the skin. This usually takes four immersions.

             Wax gives off heat slowly due to its low thermal conductivity, but after removal from the bath the part cools quickly. In order to retain the heat, wrap the part in a layer of plastic sheet or greaseproof paper and a towel.

Treatment is usually given for about 20 minutes. After this time remove the towel and the wax glove, taking care not to drop any wax on the floor. Inspect and dry the part.

        The discarded wax is finally remelted, strained and placed back in

the bath at the end of the day.

Effects and indications

Following application of wax there is a marked increase in the temperature of the skin, and to a lesser degree that of the other superficial tissues. The temperature obviously drops rapidly after the 20 minutes of treatment is over.

Circulatory effects

There is stimulation of superficial capillaries and arterioles, causing local hyperaemia and reflex vasodilatation. The vasodilatation may be due to the action of a vasodilator (bradykinin neurogenic a polypeptide) formed as the result of sweat gland activity (Fox & Hilton 1958, Samson Wright 1971).

Effects on sensory nerves

Mild heating appears to have a sedative effect on the sensory nerve endings. As wax can be moulded round the contours of the hands and feet, it is of value in treating rheumatoid arthritis or ‘degenerative joint disease, reducing pain and muscle spasm.

Effect on the skin

The skin is moist and pliable following wax application, which can therefore help to soften adhesions and scars in the skin prior to mobilizing and stretching procedures.

Contra-indications

Open wounds

Allergic rash

Skin conditions

Defective arterial blood supply (including deep vein thrombosis and

varicose veins)

Impaired skin sensation.

                           Ultrasonic Therapy

Sound is by definition the periodic mechanical disturbance of an elastic medium such as air. Sound requires a medium for its transmission and cannot cross a vacuum in the way electromagnetic waves can. An Oscillating source, such as a tuning fork, is required to produce sound waves (Fig. 4.1). The frequency of the sound wave is the same as the rate of oscillation of the source. Sound waves are travelling pressure waves in the medium which cause an alternate compression and

rarefaction (moving apart) of the particles in the medium. It is therefore only the form of the wave which moves forward; the actual particles merely vibrate back and forth, each about a mean point.

            The wavelength is the distance between the two closest points on a

wave that are performing the same motion at any instant in time.

          The frequency is the number of times a particle undergoes a complete cycle in one second.

 The velocity of a wave is the speed at which the wave moves through the medium, and varies depending upon the physical nature of the medium. Air is a relatively poor transmitter of sound whereas water is very good. The velocities of sound in some media are:

Air                  344 m/s

Water             1410 m/s

Muscle            I540 m/s

Ultrasound

The upper limit of hearing is just over 20 kHz (20 o00 cycles per second). Ultrasound is well above this, therapeutic frequencies being in the region of 1 MHz or 3 MHz.

The production of ultrasound

For a 1 MHz machine a vibrating source with a frequency of one million cycles per second is needed. This is achieved using either a quartz or a barium titanate crystal. These crystals deform when subjected to a varying potential difference a piezo-electric effect.

Fig. 41 The vibration of a tuning fork, which oscillates between shapes

            A and B. Each shaded area contains the same number of particles, but they           

            are either compressed (by the spread of the fork in position B) or rarefied  

            (by the closing-in of the fork in position A).

Fig. 4.2  The components of  ultrasonic apparatus

The basic components of the ultrasonic apparatus are shown in Fig. 4.2. There is a source of high-frequency current, which is conveyed by a coaxial cable to a transducer circuit or treatment head. Inside the transducer circuit, the high-frequency current is applied to the crystal via a linking electrode, the crystal being fused to the metal front plate of the treatment head. Any change in the shape of the crystal causes a movement of the metal front plate which in turn produces an

ultrasonic wave.

           Strict frequency control of the high-frequency current (1 MHz or 3 MHz) ensures a steady and regular rate of deformation. Fig. 4-3 shows the effect of a change of potential applied to the crystal and the effect this has on adjacent cells.

Reflection of ultrasound

Sound obeys the laws of reflection (see p. 24) and if an ultrasonic beam travelling through one medium encounters another medium which will not transmit it (i.e. let it pass into the new medium),

Fig. 43. The effect of a varying applied potential on the shape of a quartz

             crystal and the effect the resulting ultrasound has on adjacent cells.

Fig 44.  Refraction of ultrasonic waves in passing from one medium into another in   

            which the speed of sound is greater.

reflection takes place. Air will not transmit ultrasonic waves, so in ultrasonic treatment great care is taken to avoid leaving air between the treatment head and the patient, to minimize reflection.

Transmission of ultrasound

If the ultrasonic beam encounters an interface between two media and is transmitted, it may be refracted, i.e. deflected from its original path, as light is (see p. 25). When travelling from a medium in which its velocity is low into one in which its velocity is high, it is refracted away from the normal (Fig. 4.4).

The significance of refraction is that in Fig. 4.4 if T were the target, refraction would cause the ultrasonic beam to miss it. As refraction does not occur when the incident waves travel along the normal, treatment should be given with the majority of waves travelling along the normal (i.e. perpendicular to the interface between the media) whenever possible.

Fıg. 45. The near and far fields of an ultrasound transducer. The near field is   

               stronger but more variable than the far field.

Attenuation of ultrasound

The space -averaged intensity of ultrasound produced from a transducer is measured in watts/cm. As the ultrasonic beam passes through a medium its intensity is reduced (attenuated) by two mechanisms: absorption (the energy of the ultrasonic beam is converted to heat by the tissues) and scatter (the normally parallel beam becomes more dispersed the further it passes into a medium).

These two factors reduce the intensity of the ultrasonic beam by a constant fraction per cm, so that at a certain depth below the surface the intensity of the ultrasonic beam has been reduced by half. This depth (d) is called the half-value thickness. After travelling the same distance again through the tissues, i.e. a total distance of 2d, the beam will have a quarter of its surface intensity. The half-value thickness for soft tissues varies for I MHz and 3 MHz machines and has been shown to be 4 cm and 2.5 cm respectively (ter Haar, 1978).

          Half-value distance may be of significance when using ultrasound to treat deeply placed structures, as it must be remembered that the intensity reaching these deep structures will be much less than the intensity being applied to the surface.

Ultrasonic fields

A further consideration relating to depth of penetration and intensity of the ultrasonic beam is the division of the beam into a near and a far field (Fig. 4.5). The extent of the near field depends upon the radius (r) of the transducer and the wavelength (w) of the ultrasound in the medium. The depth of the near field can be calculated using the formula r/2. As wavelength and frequency are inversely related, the depth of the near field varies with the frequency of the ultrasound, a

can be seen in Table I.

Table 1. Depth of near field for 1 MHz and 3 MHz ultrasonic transducers of    

              different sizes

Transducer radius(mm)            Frequency (MHz)           Extent of near field (cm) 15                                                         1                                                  15 15                                                         3                                                  45 10                                                         1                                                  6.5 20                                                         1                                                  26.5

The extent of the near field is of significance in that it is more intense than the far field and may have a more profound effect in the treatment of certain conditions. However, the near field has a much greater variation in intensity than the far field. Consequently the frequency of the ultrasound and radius of the transducer may need to be considered when treating tissues at a depth greater than 6.5 cm (the shortest near field in Table 1).

Coupling  media

Ultrasonic waves are not transmitted by air, thus some couplant which does transmit them must be interposed between the treatment head (transducer) and the patient’s skin (Fig. 4.6).

         Unfortunately no couplant affords perfect transmission and only a

percentage of the original intensity is transmitted to the patient, as Table 2 shows: even the most efficient couplant reduces the applied dose by a quarter.

Fig. 4.6       A coupling medium may be used to exclude air from the space

                    between the treatment head and the skin.

Table 2.       Efficiency of transmission of ultrasound by various coupling

                    media (after Reid & Cummings 1977)

Couplant                                                                  %  transmission Aquasonic gel                                                                   72.6 Glycerol                                                                            67 Distilled water                                                                  59                                         Liquid paraffin                                                                 19 Petroleum jelly                                                                  o Air                                                                                     o

Fig. 47  The reflection of an ultrasonic wave from bone may produce localized  

              concentration of heating effect leading to periosteal pain.

Air (zero transmission) will in fact reflect the ultrasonic beam back into the treatment head and this could set up a standing wave which might damage the crystal. Consequently the treatment head is never left switched on when not in contact with a transmitting medium.

Pulsed ultrasound

Most ultrasonic generators allow the selection of either a continuous or a pulsed ultrasound output. A pulsed output usually consists of 2 ms of ultrasound followed by an 8 ms silence, but this ratio can be varied on some apparatus.

Effects of ultrasonic waves on tissues

Thermal effects

As the ultrasonic waves are absorbed they are converted to thermal energy (heat). The amount of heat produced depends upon factors Such as the number of times per second the transducer passes over a part and on the space-averaged intensity (watts/cm²) used.

         Reflection of ultrasound may occur at tissue interfaces, producing a

concentrated heating effect at that point. This is particularly likely at the interface between periosteum and bone (Fig. 4.7). As reflection from bone occurs there is double the intensity of ultrasound in the periosteum region, which may cause localized over -heating and can manifest itself as periosteal pain (Fig. 4.7). In practical terms this means that it is best to avoid passing the ultrasonic head over

subcutaneous bony points if possible.

         Pulsed ultrasound has little thermal effect, as any heat produced by the 2 ms of ultrasound is carried away by the circulation in the 8 ms Test. 1ulsed ultrasound may thus be indicated in the treatment of acute conditions where a thermal effect is not required.

Mechanical effects

A mechanical effect is caused by the pressure changes applied to the

tissues by the sound waves.

        Cavitation is a condition in which a bubble of gas is produced in the tissues as a result of insonation. Stable cavitation is not dangerous to the tissues, as the bubbles remain intact and oscillate harmlessly in the ultrasonic field. Transient cavitation is dangerous to the tissues, as the bubble grows and collapses rapidly in the ultrasonic beam and this is thought to cause very great increases in temperature.

          In practice the danger of tissue damage due to cavitation is minimized by the following measures:

        1. Using space-averaged intensities below 4 watts/cm².

        2. Using a pulsed source of ultrasound.

        3. Moving the treatment head during insonation.

The micromassage effect of ultrasound occurs at a cellular level where the cells are alternately compressed and then pulled further apart. This is analogous to massage and is claimed to have an effect on inter-cellular fluids and thus to reduce oedema. Ultrasound has been found to be effective at reducing both recent traumatic oedema and chronic indurated oedema.

        Dyson (1973) has shown that a standing wave produced in the tissues can produce inhibition of blood flow and cause the blood cells to congregate at intervals of half a wavelength. However, pulsing the ultrasonic beams or moving the treatment head should prevent this occurring.

Chemical and biological effects

Acoustic streaming is an effect produced by the ultrasonic beam. It is a

unidirectional flow of tissue components, which occurs particularly at the cell membrane (Dyson 1978). Streaming has been shown to Produce changes in the rate of protein synthesis and could thus have a role in the stimulation of repair. Significant improvement in the rate of tissue repair has been shown to occur as a result of insonation of damaged tissues (Dyson 1970).

            Ultrasound also reduces pain. Although this could be attributed to

thermal effect with a continuous beam, pain relief is also achieved With a low thermal pulsed beam. The mechanism of pain relief may be is stimulation of mechanoreceptors in the tissues which then have the effect on cells in the spinal cord of reducing the appreciation of pain a peripheral level (the ‘pain-gate’ theory).

Uses of ultrasound

Recent injuries and inflammation

Ultrasound is often of use after soft-tissue injuries, as the mechanical effect helps to remove traumatic exudate and reduces the danger adhesion formation. Analgesia produced by the ultrasound allows cautious early use of the part and makes the condition more tolerable Accelerated protein synthesis stimulates the rate of repair of damaged tissues.

          Inflammatory conditions treated with appropriate doses of ultrasound respond in the same way.

Scar tissue

Claims have been made that scar tissue is made more pliable by the

application of ultrasound, which allows for more effective stretching of

contracted scars. If the scar is bound down on underlying structures

ultrasound may help in gaining its release.

Chronic indurated oedema

The mechanical effect of ultrasound has an effect on chronic oedema and helps in its treatment. It also breaks down adhesions formed between adjacent structures.

Dangers

Burns

If a continuous beam is used and is allowed to remain stationary excess heat can accumulate in the tissues and eventually lead to a burn. (The mechanism of excess heating in the periosteum was described on p. 148.) However, the danger of burns is effectively elịminated by keeping the treatment head moving, using pulsed beams and avoiding. bony prominences if possible.

Cavitation

See p. I49.

Overdose

Excessive treatment may cause an exacerbation of symptoms.

Damage to equipment

If the treatment head is held in the air while switched on, reflection of the beam back into the treatment head may set up a standing wave which could damage the crystal. Consequently the head is never turned on unless it is in contact with a transmitting medium.

Contra-indications

 Vascular conditions

Conditions such as thrombophlebitis, where insonation may cause emboli to be broken off, are not treated with ultrasound.

Acute sepsis

An area which presents acute sepsis is not treated with ultrasound

because of the danger of spreading the infection.

Radiotherapy

Radiotherapy has an adverse effect on the tissues, therefore ultrasound

is not applied to a radiated area for at least six months after irradiation.

Tumours

Tumours are not insonated because they may be stimulated into

growth or throw off metastases.

Pregnancy

A pregnant uterus is not treated as the insonation might produce fetal

damage. (Ultrasonic scanning as a diagnostic aid in pregnancy is different from that used for therapeutic purposes.)

Cardiac disease

Patients who have had cardiac disease are treated with low intensities in order to avoid sudden pain, and areas such as the cervical ganglion and the vagus nerve are avoided because of the risk of cardiac stimulation. Patients fitted with cardiac pacemakers are not usually treated with ultrasound in the area of the chest, as the ultrasonic generator may have an effect on the pacemaker’s rate of stimulation.

Testing the apparatus

testing should always be carried out prior to treatment. The simplest Way of finding out whether ultrasound is in fact being produced is to use a water bath and to reflect an ultrasonic beam up to the surface where it should produce ripples (Fig. 4.8) The apparatus is turned on and off with the treatment head below the water.

Fig. 48 Testing the output of an ultrasonic treatment head by the

underwater production of surface ripples.

Techniques of application

Direct contact

If the surface to be treated is fairly regular then a coupling medium is applied to the skin in order to eliminate air between the skin and the treatment head and transmit the ultrasonic beam from the treatment head to the tissues. The treatment head is moved in small concentric circles over the skin in order to avoid concentration at any one point, keeping the whole of the front plate in contact with the skin if possible. The machine is turned on and off while in contact with the patient.

Water bath

A water bath filled with de-gassed water is used if possible. Ordinary tap water presents the problem that gas bubbles dissociate out from the water, accumulate on the patient’s skin and the treatment head, and reflect the ultrasonic beam. If tap water has to be used then the gas bubbles must be wiped from these surfaces frequently.

             The technique of application is that the treatment head is held I cm from the skin and moved in small concentric circles, keeping the front plate parallel to the skin surface to reduce reflection to a minimum

Water bag

On irregular bony surfaces a rubber bag filled with de-gassed water can be used. A coupling medium has to be placed both between the rubber bag and the skin and between the rubber bag and the treatment head to eliminate any air. This somewhat slippery bag then has the treatment head moved over it in the same way as if it were the patient’s skin.

Dosage

Dosage is probably the most controversial area when discussing ultrasound. The arguments about whether pulsed or continuous modes should be used and the intensities of ultrasound required to produce beneficial effects have been long and are as yet unresolved. The experience of the physiotherapist is probably very important in this area, so only general principles and guidelines will be given here.

        When treating a patient with ultrasound it is worth remembering that the intensity of ultrasound leaving the treatment head is not the intensity being applied to the deep tissues. Intensity there has been reduced by:

       1. Absorption in the coupling medium.

       2. Attenuation of the beam by absorption and scatter.

       3. Refraction of the beam at tissue interfaces which may deflect the beam           

          away from the offending tissue.

All of these factors need to be considered when selecting an appropriate dose for treatment purposes. A major consideration is whether the condition to be treated is acute or chronic.

Dosage in acute conditions

As with any acute condition, treatment is applied cautiously to prevent

exacerbation of symptoms. In the initial stages a low dose (0.25 or o.5 warts/em²) is used for 2-3 minutes. Using a pulsed beam will reduce the heating effect which could provoke symptoms. Progression of dosage is unnecessary if the condition improves; the same dose can be repeated. A failure to improve might require a slight increase in the intensity of ultrasound to o.8 watts/cm or an increase in the time of insonation to 4 or 5 minutes.

            Aggravation of symptoms is not always a bad sign as it may indicate that repair processes are taking place. A reduction in dosage, in both intensity and time, may be indicated, or treatment with ultrasound may be deferred until the symptoms subside to their original level.

Dosage in chronic conditions

Chronic conditions can be treated with either a pulsed or a continuous beam. With a continuous beam, the maximum intensity of ultrasound which should be used is that which produces a mildly perceptible warmth. This usually occurs around 2 watts/cm.

         Initially a low dose is given (usually o.8 watts/cm* for 4 minutes) to see that there are no adverse effects. If a dose produces beneficial effects it is repeated next time. If no improvement results, the dose can be gradually increased by increasing the intensity (watts/cm’) or the period of insonation until the treatment is found to be effective. A suitable progression of increased doses to try might be:

           o.8 watts/cm² for 4 minutes

          to 1 watt/cm² for 4 minutes

          to 1 watt/cm² for 6 minutes

          to 1.5 warts/cm² for 6 minutes

          to 1.5 watts/cmn² for 8 minutes

          to 2 watts/cm² for 8 minutes.

A dose of 2 watts/cm² for 8 minutes is usually considered to be the maximum permitted. If no improvement has resulted using this six- treatment progression then it is doubtful whether ultrasound will be of great benefit.

                               Ultra-violet radiation

Ultra-violet radiation is electromagnetic energy which is invisible to the human eye, with wavelengths between 10 nm and 400 nm. Ultra- violet lies between visible light and X-rays in the electromagnetic spectrum (p. 22) and for descriptive purposes the therapeutic part of the ultra-violet spectrum may be divided into:

           UVA (315-400 nm)

           UVB (280 315 nm)

           UVC (below 28o nm)

The sun emits ultra-violet radiation which can often have an effect on the skin, e.g. sunburn, but for therapeutic purposes some form of generator is used.

Ultra-violet generators

These usually take the form of lamps which employ either a high- or a

low-pressure rube across which a current is passed.

High-pressure mercury-vapour burner

This is often U-shaped so that it acts more or less as a point source. The burner is made of quartz: this material allows the passage of ultraviolet, can withstand very high temperatures and has a fairly low coefficient of expansion. Enclosed in the tube is argon gas at a low pressure, as a low pressure considerably reduces its electrical resistance. A small quantity of mercury is also enclosed in the tube and

an electrode is sealed into either end. Surrounding the ends are two metal caps across which a high potential difference is applied in order to ionize the argon.

           Argon is normally extremely stable and inert as it has a full outer shell of electrons, so in order to pass a current through the tube the argon atoms must be ionized. An electron is stripped from the outer shell of the atom producing a negative particle (the electron) and a

Fıg 5.1  High-pressure mercury vapour tube.

positive ion (the remaining part of the argon atom which now has an excess of positive protons).

         A considerable amount of energy is required to ionize the argon and this is obtained by applying a very high potential difference (400 volts) across the tube, via the metal caps at either end, for a fraction of a second. In practice this is accomplished by pressing the ‘Start’ button on the lamp, which introduces an auto-transformer into the circuit in order to step-up the mains voltage to 40o volts. Once the argon has been ionized, normal mains voltage between the electrodes causes the positive and negative particles to move through the burner, so constituting an electric current. The electrons move to the positive terminal and then around the circuit, the positive ions move to the negative terminal and collect an electron. Overall, exactly the same number of electrons leave the burner at the positive terminal as enter at the negative. As the two-way movement of charged particles takes place, collisions between moving ions and neutral argon atoms cause

further ionization so that there is continuous generation of ionized particles to sustain the current flow across the tube. This current flow can be seen as a glow discharge, and as with any electrical current considerable heat is produced (Joule’s law). Eventually sufficient heat is produced to vaporize the liquid mercury inside the tube, and tis mercury vapour itself becomes ionized.

Ultra-violet radiation is produced partly as energy released by the re-combination of electrons and positive mercury ions, and partly by photons released when excited electrons return from a higher –energy quantum shell to their normal shell within the mercury atoms (see page 4). At the same time however, visible and infra-red electromagnetic waves are produced, and ultra-violet forms only a

portion of the total output.

            The whole process of argon ionization, mercury vaporization and

ionization takes some time, and a period of 5 minutes elapses between starting the burner and ultra-violet emission reaching its peak.

              Once the lamp has been turned off, the ions of argon re-combine, as

do the ions of mercury, so that within the tube everything returns to its original neutral state. However, considerable heat has been generated and this raises the electrical resistance across the tube, so that some time has to elapse, allowing the tube to cool down, before it is possible to strike the arc again.

Tridymite formation

The heat produced inside the burner unfortunately causes some of the quartz to change to another form of silica called tridymite. Tridymite is opaque to ultra-violet rays and therefore the total output of the lamp gradually falls as the proportion of tridymite increases. As a very crude method of compensation a variable resistance is included in the burner circuit, and as the quartz changes to tridymite the resistance is reduced, thus increasing the intensity of current across the tube (Ohm’s law). Thus the production of ultra-violet is increased but as

less is transmitted by the quartz, output is kept constant. To allow the stabilizing resistance to be reduced at appropriate times (approximately every 100 hours), the ‘burning time’ is recorded either in a book or on a meter incorporated in the machine. After 1000 hours of burning, so much tridymite has formed that the whole burner rube needs to be replaced.

Cooling

A considerable portion of the output of the high-pressure burner is infra-red, which when absorbed by the human body is converted to heat. Consequently, if the lamp is air-cooled the closest it can safely be placed to a patient is 5o cm, otherwise a burn may result. The burner is usually housed in a parabolic reflector (see PP. 24-25), the position of which can be adjusted on a stand.

The Kromayer lamp

The Kromayer Lamp is a water-cooled mercury vapour lamp, which eliminates the danger of an infra-red burn. It has the advantage that it

Fig. 5.2  Section through the Kromayer lamp: W water; A arc tube; J

              space between inner metal case and burner.

can be used in contact with the tissues, or, with a suitable applicator, to irradiate inside a sinus or body cavity (see Fig. s.8, p. 170).

Construction The Kromayer lamp consists of a high-pressure mercury vapour burner, the working of which is the same as for the air- cooled lamp already described. However, it is completely enclosed in a jacket of circulating distilled water, the purpose of which is to absorb the infra-red. A pump and cooling fan are incorporated into the body of the Kromayer lamp in order to cool the water. After use, the water circulation should be continued for five minutes after the burner is

switched off in order to cool the lamp:

            At the front of the Kromayer head the water circulates between two quartz windows which allow the ultra-violet to emerge. If a sinus is to be treated an applicator of quartz is fixed to this window via a special attachment (see Fig. 5.8, p. 170). These applicators convey the ultra- violet rays to their tip by total internal reflection (see p. 25), but as they are often long they inevitably absorb some ultra-violet and therefore a considerably longer dose must be given.

Spectrum of high-pressure mercury vapour burner

Mercury vapour lamps produce ultra-violet, visible and infra-red electromagnetic waves. Only a small proportion of the output is UVC (wavelength <28o nm), the majority of ultra-violet being UVA (315- 400 nm) and UVB (280-315 nm). The depth of penetration of these three groups of ultra-violet rays is shown on Fig. 3.30 (p. 132).

Fig. 5.3 Theraktin tunnel arrangement of fluorescent tubes.

Fluorescent tubes for ultra-violet

production

One of the major problems with the mercury lamp is that it produces a certain proportion of short ultra-violet rays. Modern  treatment regimes often require the use of long-wave ultra-violet without the short-wave and so various types of fluorescent rube have been produced. The spectrum of each tube depends upon the type of phosphor coating. Each tube is about 120 cm long and made of a type

of glass which allows long-wave ultra-violet to pass. The inside of the tube is coated with a special phosphor.

               A low-pressure arc is set up inside the tube between its ends by a process of ionization similar to that described for the mercury vapour tube. Short ultra-violet is produced, but it is absorbed by the phosphor and re-emitted at a longer wavelength. Depending upon which particular phosphor is used, the output of the tube may be part UVB and part UVA (28o-400 nm) or totally UVA (36o-400 nm), as in PUVA apparatus.

Theraktin tunnel

The Theraktin tunnel is a semi-cylindrical frame in which are mounted four fluorescent rubes as shown in Fig. 5-3. Each tube is mounted in its own reflector in such a way that an even irradiation of the patient is produced, allowing treatment of the whole body simultaneously. Normally fluorescent tubes with a spectrum of 280- 400 nm are used.

PUVA apparatus

Irradiation with UVA only may be performed with special fluorescent tubes, which may be mounted in a vertical battery on a wall, or on four sides of a box totally surrounding the patient. This form of ultra-violet is usually given two hours after the patient has taken a photoactive drug such as psoralen: hence the term PUVA (Psoralen Ultra-Violet A).

Physiological effects of ultra-violet

The skin acts as a protective layer, in that it absorbs most ultra –violet light and prevents its penetration down to vulnerable cells. If ultra- violet waves are absorbed by the skin, the energy they release is sufficient to cause damage to cells and intra-cellular structures. The extent of this damage, and the consequent reaction, depends upon wavelength of ultra-violet and the amount of ultra-violet absorbed. UVC and UVB are absorbed in the epidermis, but UVA may penetrate

as far as the capillary loops in the dermis (see Fig. 3.30, p. I32).

Cancer

Carcinogenesis is a danger if long exposure to UVB or UVC occurs, as these rays may have an effect on DNA and thus on cell replication. The evidence supporting the hypothesis that skin cancer is produced by ultra-violet radiation is considerable, so prolonged exposure of the patient’s skin to the shorter ultra-violet waves should be avoided and courses of treatment should not exceed four weeks.

Erythema

Damage to cells causes the release of histamine-like substances from the epidermis and the superficial dermis. A gradual diffusion of this chemical takes place until sufficient has accumulated around the blood vessels in the skin to make them dilate. This accounts for the latency of the erythema. The greater the quantity of histamine-like chemical produced, the sooner and fiercer is the reaction.

          The erythema reaction has been used to classify doses of ultra-violet given to patients. There are four visible degrees of erythema, shown in

Table 3. In practice today a suberythemal dose of half EI is often given.

Pigmentation

Pigmentation develops within two days of irradiation. Ultra-violet stimulates melanocytes in the skin to produce melanin, which is then passed to numerous adjacent cells. The melanin forms an ‘umbrella’ over the nucleus of the cell to protect it from ultra-violet radiation: pigmentation substantially reduces the penetration of UVB.

Table 3. Standard doses of ultra-violet (Er-B4) classified by erythema reaction  

Dose Latent period          Appearance           Pigmentation            Desquamation           (hours) E1      Up to 12               Slightly pink                 Nil                               Nil E2      4-6                        Red                              Slight                       Powdery E3      1-4                       Fiery, red & painful            Marked                          In sheets E4      As E3 but with the formation of blisters

Thickening of the epidermis

A sudden over-activity of the basal layer of the epidermis causes a marked thickening, particularly of the stratum corneum (the outermost layer) which may become as much as three times its normal thickness. This substantially reduces UV penetration and so in order for subsequent treatments to have the same effect the dose must be increased (provided that peeling has not occurred). For example, an

EI dose must be increased by 25%, an E2 by so% and an E3 by 75%- It is unlikely than an E4 dose would be given to an area covered with skin: it is a dose normally given to open wounds or ulcers where this increase in dosage is unnecessary.

Peeling

The increased thickness of the epidermis is eventually lost as desquamation (peeling). When this happens the resistance of the skin to UV is substantially  lowered.

Production of vitamin D

In the presence of UV, 7-dehydrocholesterol in the sebum is converted to vitamin D in the skin. Vitamin D is necessary for the absorption of calcium and so has a role to play in the normal formation of bones and teeth.

Solar elastosis and ageing

The normal ageing process of the skin is accelerated if there is continued exposure to UV. There is thinning of the epidermis, loss of epidermal ridges, loss of melanocytes, dryness as a result of poor function of sebaceous and sweat glands, and wrinkling from lack of dermal ‘connective tissue. These effects are often seen in members of the fair-skinned races who live in a very sunny climate such as

Australia or South Africa.

Antibiotic effect

Short ultra -violet rays can destroy bacteria ‘and other small organisms

and so can be used to sterilize a surface.

Photosensitization

There is sometimes an enhanced response of the skin to ultra-violet irradiation. The agent responsible is usually a chemical present in the skin which absorbs the ultra-violet and transfers the energy to adjacent tissue-molecules in a photochemical reaction. Photosensitizers may be ingested or applied directly to the skin. Photosensitivity may be deliberately produced in a patient’s skin by the local application of substance such as coal-tar, or by the ingestion of substances such e

psoralen. However, many drugs and foods may increase an individual’s reaction to UVR. In practical terms, this means that patients must inform the physiotherapist when starting or stopping courses of drugs.

Indications for ultra-violet irradiation

Ultra-violet is used in the treatment of skin conditions and for both infected and non-infected lesions of the skin.

Acne

Acne is a skin condition which presents pustules, papules and comedomes blocking the hair follicles and sebaceous glands on the face, back and chest. An E2 dose of ultra-violet radiation may be given with the following aims:

1. An erythema will bring more blood to the skin and so improve the condition of the skin.
2. Desquamation will remove comedomes and allow free drainage of sebum, thus reducing the number of lesions.
3. The UVR will have a sterilizing effect on the skin.

Although ultra-violet radiation has been used in the treatment of acne for some time, a number of reservations have been expressed about use. The intensity of dose needed (E2+) is often painful an Cosmetically unsightly to the patient. Treatment is only palliative and the condition usually returns within a few weeks of UVR. Unfortunately it may even appear to be worse a few weeks after UVR,

as all the lesions in the skin reach their peak at the same time, w whereas in the normal course of acne some will be resolving as others develop. Irregular rates of desquamation may restrict the frequency of treatment and possibly produce a mottled erythema.

Psoriasis

Psoriasis is a skin condition which presents localized plaques in which the rate of cell turnover from the basal layer through to the superficial layer is too rapid. The aim of ultra-violet irradiation is to decrease the rate of DNA synthesis in the cells of the skin and thus slow down their proliferation. Treatment can be given using the Leeds regimen or PUVA.

Leeds regimen

In the Leeds regimen the sensitivity of the patient’s skin to UVR is increased by the local application of coal-tar, added to a bath prior to treatment. Dithranol cream is applied to the lesions after the treatment. The patient’s reaction to UVR is tested in the sensitized condition.

          A sub-erythemal dose (half Er) is given to the patient, using a Theraktin tunnel or an air-cooled lamp at I00 cm. The dose is repeated daily, increasing by 12-1/2% each time.

PUVA

Patients on a PUVA regimen take a sensitizing drug derived from psoralen, two hours before exposure to UVA rays. The presence of the drug in the skin increases photosensitivity by absorbing the ultra- violet and transferring the energy to adjacent cells.

               Dosage on a PUVA regimen is measured using J cm-2 (joules per square centimetre) which means that the output of the generator needs to be measured regularly using special apparatus. Dosage depends upon the patient’s skin-type and progressive increases are made in terms of energy-density applied rather than in the length of time. For example, patients who burn after exposure to the sun have their minimum dose (one which produces slight erythema within 72 hours

of irradiation) increased by o.5 J. cm-2 at each treatment. The sensitizing psoralen drug means that these patients must avoid sunlight and wear dark glasses during daylight to protect their eyes.

Skin wounds

Infected wounds

Ultra-violet may be used in the treatment of infected skin wounds such as ulcers, pressure sores or surgical incisions. The aim of the ultra- violet is to destroy bacteria, remove the slough (infected dead material) and promote repair. UVB is normally used to achieve this, being applied locally to the lesion using a Kromayer lamp and an E3 or E4 dose. Progressive increase of dose is unnecessary as there is no skin over the wound.

Non-infected wounds

Once infection has cleared, or if it was never present, the aim of UVR is to stimulate the growth of granulation tissue and thus speed up repair. Short UVB rays damage granulation tissue whereas longer UVA stimulate its growth. Consequently, some form of filter is used which will allow UVA to be emitted but not UVB. This filter may be either Blue Uviol glass or cellophane.

Intact skin

Intact skin may be treated with UV if it is in a pressure area that is likely to break down. An EI dose is given in order to increase the circulation through the area and improve skin conditions. This may also be done for more resistant conditions such as chilblains.

Counter-irritation

Historically, ultra -violet was used to produce a strong counter- irritation effect over the site of a deep-seated pain (e.g. lumbar spine). An E3 or E4 dose was given and the area was then covered with a dry dressing. Theoretically the superficial pain produced by the erythema should mask the deeper pain. Provided that some other treatment was instituted in this period of relief, e.g. exercise, some long-term benefit was thought to be possible. This use of ultra-violet has now been largely superceded by other forms of treatment.

Contra-indications to ultra-violet

irradiation

Hypersensitivity to sunlight Some patients react adversely to sunlight and so are not treated with UV.

DXT Deep X-ray therapy produces local hypersensitivity to UV and patients are not treated with UV for three months following deep X-ray treatment.

Erythema’ If the patient’s skin still presents an erythema from either UV or infra-red, the reaction to UV is dramatically increased. Consequently UV is contra-indicated until the erythema has subsided.

Skin conditions Certain skin conditions such as eczema, lupus erythematosis and herpes simplex may be exacerbated by UV.

Dangers of ultra-violet irradiation

If ultra-violet rays are allowed to fall on the eye, conjunctivitis may occur, To prevent this the physiotherapist always wears protective goggles when the lamp is on. The patient is also provided with goggles or his eyes are screened using cotton wool.

Overdose This should not occur if an accurate technique is used. However, a number of factors may result in the patient receiving a stronger dose than that given at a previous treatment. These include:

I. Using a different lamp with a stronger output.

2. Moving the lamp closer to the patient (or vice-versa), thus giving a more intense    

    dose.

3. A change in the patient’s drug regimen.

4. Poor timing technique.

Unfortunately the effects of overdose do not appear for some time and there is little that can be done once the erythema appears. If, however, an accidental overdose is immediately suspected, infra -red may be given to the area in an attempt to increase local circulation and thereby disperse the histamine-like substance that produces the erythema.

Techniques of application

Test dose

To assess the individual patient’s reaction to ultra-violet irradiation a test dose is administered. The technique is very similar whether a Theraktin tunnel, an air-cooled or a Kromayer lamp is used. Only the distances and timings vary.

Air-cooled lamp

A suitable area of skin is selected for the test dose, e.g. flexor aspect of the forearm, and this is washed to remove grease. Three differently shaped holes are cut in a material resistant to the passage of UV, e.g. paper or lint, as in Fig. 5.4. The middle hole should be approximately 2 cm by 2 cm, with the hole on one side larger and the other smaller.

             Every lamp should have its average EI time and distance clearly marked as a result of averaged reaction tests on a number of people. It is wise to test using the erythema reaction required at the distance that will be used. Given the average Er of the lamp, the duration of the E2,

Fig  5.4   Holes used for a test dose of ultra-violet radiation.

E3 and E4 doses can be calculated as follows:

         E2 time= EI time x  2.1/2

         E3 time=EI time x 5

         E4 time= EI time x 10

For example: if acne requires treatment with an E2 dose at so cm and the known EI for the lamp is I minute at I00 cm, the duration of exposure required can be calculated as follows:

          By the inverse square law, half the distance requires a quarter the time for the same effect (see p. 27), thus E (60 seconds at IO0 cm) is I5 seconds at 5o cm.

       To find the duration of an E2 dose at 5o cm, the EI time is multiplied

by 2.1/2, giving 37.1/2 seconds.

The cut-out test paper or lint is applied to the patient’s forearm and the rest of the body screened. The middle hole receives the calculated E2 dose (provided the patient has an average reaction to sunlight). The small hole (c) receives an exposure slightly longer than that for E2, the larger hole (a) an exposure slightly shorter.

           This procedure is carefully recorded on the patient’s card and the patient is given a drawing of the three holes and asked to record on it when the erythema appears, how severe it is and how long it lasts. The patient’s reaction will then determine further dosages.

Theraktin tunnel

The test procedure is very similar to that described above, but larger holes (4 cm %4 cm) are usually used, and are placed on the abdomen, the rest of the body being screened.

Kromayer lamp

Testing the dosage can be done with the Kromayer lamp in contact with the skin, so very small holes are used, e.g. o,25 cm x 0.25 cm, since

Fig 5.5  Preparation of the face for treatment with ultra-violet radiation.

exposure times need only be very short. It is often useful if the Kromayer lamp has standard BI dosage times recorded on it for Contact and IO cm.

Local treatment using the air-cooled lamp

For descriptive purposes only, treatment of the face will be discussed: many of the principles apply to local treatment for any part of the body.

1. The patient’s reaction to UV should already have been calculated by using a test dose.
2. The patient’s face is washed to remove creams and allow maximum   

penetration of UV.

• An explanation is given to the patient about what is going to happen. He is  

then seated in a chair with his head fully supported on pillows piled up behind him on a table.

• The patient applies a thin film of petroleum jelly (an effective screening     

agent) to his eyelids, lips and ear lobes, as these areas are covered in very thin skin.

• The patient’s hair is tied back as far as possible using clips or a bandage,  

ensuring that no forehead skin is covered. This gives maximum surface exposure and prevents the burning of previously unexposed areas when the next dose is given.

• An acceptable neckline is agreed with the patient, who may leave a garment  

in the department to be worn during treatment. Alternatively, dressing towels may be used up to an easily identified point around the neck. It is important, as subsequent doses are increased, to ensure that no new skin is exposed.

• A thin strip of cotton wool is placed over the junction of the eyelids and  

can be held in place with a strand of cotton tied around the head. This cotton wool stops UV penetrating the eye and so causing conjunctivitis.

Fig. 5.6  Ultra-violet treatment of the face: two oblique exposures may be made during a single treatment (a) or the two sides may be exposed during one treatment, with an additional frontal exposure at the next treatment (b).

• The shape of the face is assessed and the number of exposures decided upon

 For the following points of the procedure the more common treatment of two   

 oblique exposures will be described (Fig. 5.6):

• The rest of the patient’s body is screened with a blanket and the head is covered with a dressing towel for protection.
• The lamp, which should already have been on for 5 minutes, is placed in a position close to the patient and centre on the Zygomatic arch of one side. The distance from the burner (50ćm) is accurately measured and its position adjusted so that the majority of rays strike the skin at go° for maximum absorption (see pp. 26-27).
• The patient is warned to sit still, the screening for the whole head is carefully removed and the appropriate exposure given. At the end of this time the towel is quickly replaced over the head and the same procedure carried out for the other side. There is no need to screen half of the face as the UV will be travelling at an inappropriate angle to affect the far side.
• Check that no-one else wants to use the lamp before switching it off. Remove the screening and petroleum jelly from the patient and warn him of the expected reaction. Arrange the next appointment time, explaining to the patient that he may not be treated if he still has an erythema or is peeling.
• Subsequent exposures will depend on the patient’s reaction in terms of erythema and peeling.

Techniques of general irradiation

General irradiation may be performed using an air-cooled lamp, a Theraktin tunnel or a PUVA box.

General irradiation with an air-cooled lamp This lamp is probably not the best source of UV for a general dose, as it emits the shorter UVB rays. However, it is sometimes the only source available.

Fig. 5.7  Positioning of an air –cooled mercury vapour lamp.

The patient is positioned in the oblique side-lying position using pillows and wearing only goggles (modesty may demand the provision of very small briefs). This position allows for easy alignment of the lamp (Fig. 5.7).

            The whole front or the whole back may be exposed, the lamp being

accurately positioned over the screened patient’s mid-point with the entire surface exposed at the same time.

        Alternatively a ‘fractional’ method may be used. The line joining the anterior superior iliac spines or the posterior superior iliac spines is taken as the mid-point of the body, dividing it into an upper and lower half. Each half is treated separately for the appropriate time, leaving the other half screened. This fractional method requires a total of four exposures, each at a distance of I0o cm from the burner.

          The dosage given for a total body exposure is usually a suberythemal

dose, which is taken as half the patient’s Er dose as ascertained from the test done.

General irradiation with a Theraktin tunnel This is probably the easiest way to give a general dose of UV, and it emits only a small proportion of UVB rays. The patient is tested to establish his EI dose under the Theraktin and then given half of this dose.

          Once again the patient wears only protective goggles, and lies supine on a plinth. The tunnel is lowered to the appropriate distance from the plinth (usually pre-set with ropes and chains) and the patient is irradiated for the correct time. When one aspect of the patient’s body has been treated he is instructed to roll over for the other surface to be exposed.

           Dosage is progressively increased, by 12% from one treatment to the next or, often just by one minute per session.

Fig. 5.8  A quartz rod applicator may be used with the Kromayer head for

the treatment of a shelving sore or a sinus.

General irradiation with a PUVA box The box may consist of a cabinet, on the walls of which are mounted fluorescent tubes which emit mainly UVA and visible rays.

        The patient’s skin type is of great importance when calculating the amount of UV energy (in J cm) that he will receive. Psoralen drugs are taken 2 hours prior to exposure and the UVA produced reacts with this drug in the skin. The patient is initially given a minimal phototoxicity dose’ which has been previously determined by test. dosing: it is a dose which just produces a mild erythema within 72 hours of exposure. UV -sensitive patients are progressed by o.5 J cm-2 per session, the less sensitive by I J cm. Treatments are usually given on alternate days for a month, after which a maintenance dose can be given on a monthly basis.

N.B. Regular checks of the output of the apparatus need to be made using a photometer.

Focal treatment

Focal treatment is usually applied to an ulcer or infected would using a Kromayer lamp. However the role of UV in the treatment of these conditions is becoming less important with the advent of more efficient de-sloughing agents and local antibiotics. If UV is to be used on, for example, a bed-sore, then the following procedure might be adopted:

1. All sterile precautions are taken and the bed-sore is thoroughly cleaned,   

using a standard procedure, prior to treatment.

      2. The bed-sore is screened right up to its edge using UV-resistant material, e.g.  

           a sterile towel with a hole cut in it. Normal precautions are taken to protect  

           the patient’s and physiotherapist’s eyes and the normal skin.

• The front face of the Kromayer lamp is cleaned with an appropriate solution and when it has had its full s minute warming-up period the lamp is ready for use.
• The front of the lamp is held as close as possible to the bed-sore without actually putting it in contact (to reduce the risk of infecting the whole treatment head). At least an E4 dose is given. Treatment could in fact be given at a set distance of, say, 4 cm, but this is difficult to hold if treatment time is long.
•  Following treatment the sore is re-dressed if necessary and the lamp is cleaned again.
• Progression of dosage is unnecessary as there is no skin present, but once the sore is clean and granulating, the shorter UV rays may be filtered out using a Blue Uviol filter or cellophane.
• A shelving ulcer or sinus may require the use of a quartz rod applicator (Fig. 5.8) which transmits the UV to the appropriate point by total internal reflection (see Fig. I.29, p. 25). The longer the quartz rod the more UV it absorbs, and the dose has to be increased accordingly.