14.short Wave Diathermy (swd) 50y48

Short Wave Diathermy (SWD)

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Introduction • Use of high freq electromagnetic waves of the freq b/w 107 and 108 Hz. and

wavelength b/w 30 to 3m to generate heat in the body tissues. • The therapeutically used freq and wavelengths are 27.12MHz and 11m.

Principle • This type of current can only be produced by discharging a condenser through an inductance of low ohmic resistance. • If a current of very high freq is required , the capacitance and inductance should be small and if a current of low freq is required the capacitance and inductance should be large. • This the mechanism of high freq current.

Construction The machine circuit • consist on two transformers, whose primary coils are connected to source. • one is step down. whose sec coil supplies current to filament of triode valve. • other is step up. which is connected to anode circuit. it carries the current produce by valve. here it consist of triode valve and oscillator circuit. • oscillator circuit consist of condenser and oscillator coil. • current of different freq can be obtained by selecting suitable condensers and inductances. • to produce high freq current, the capacitance and inductance should be small.

The patient circuit • patient circuit is coupled to machine by inductor coil. • high freq current is produced in resonator circuit by electromagnetic induction.' • for this to happen , the oscillator and resonator circuits must be in resonance with each other

Working • The AC from main es through primary coils of the transformers and EMF is induced in sec coils. • An EMF of 20 to 25 volt is step-up in sec coil of step-down transformer and produces current through filament of the valve. • The filament is heated and thermionic emission takes place and current flows through valve.

Methods of application • Condenser field method • Cable method When short wave diathermy is applied by the condenser field method, the electrodes and the patient’s tissues form a capacitor. The capacitance of such a capacitor depends upon 1. Size of electrodes 2. Distance b/w electrodes 3. Tissue b/w electrodes.

Capacitor field method • The electrodes are placed on each side of the part being treated. • The electrodes are separated by the skin by means of an insulating material. • The electrodes act as the plates of the capacitor, while the patient’s tissues together with the insulating material which separates them from the electrodes for the dielectric. • When the current is applied, rapidly alternating charges are step-up on the electrodes and gives rise to a rapidly alternating electric field b/w them. • The electric field also influences the materials which lies within it.

Types of electrodes Pad electrodes Plate electrodes Disk electrodes

Spacing of electrodes

If distance is small, and material b/w them is of high dielectric constant, lines of forces spread. Size of electrodes If distance is large, the spreading out If the two electrodes are of different size, of the electric field is minimal. they will behave as a capacitor of different plates. If space is narrow, superficial tissue If the electrodes are little larger than lies in concentrated part of field close area treated, outer part where spread is to electrode. greatest is deliberately no utilized. If the diameter of the electrodes is smaller If two electrodes are placed at two than that of the limbs of forces spread in unequal distance from body, one the tissues, causing more heating of electrode is placed nearer to body superficial than deep structures than other, then there will be greatest If diameter of electrodes is far larger than that of diameter of limb, some of heating effect under closer electrode lines of force by it completely and than under the further one. thus results in wastage of energy.

Positioning of electrodes Coplanar

Monopolar

• Used over large area of body e.g. spine • Also called as parallel method • Suitable for superficial structures.

• One electrode is used on the treatment area and other placed at a distance site or not used at all. • Electrode used produces a radial electric field.

Contra planar

Crossfire technique

• Used for those structures where through • In this tech one electrode placed in one direction (medial or lateral) and and through heating is required. E.g. other in other direction (anterior or Hip, shoulder t. posterior). • Suitable for deeper structures and • Used in treatment of knee t , tissues. sinuses and for pelvic organs.

Cable method • In this method, a thick insulated cable is used for treatment purpose. • Electric field or magnetic field or both are achieved by the use of cable method. • When the high freq current oscillates in the cable, a varying electrostatic field is set up b/w its ends and a varying magnetic field around its center. • The cable is coiled around the patient’s body and is separated from the patient's body by a layer of insulating material.

Advantages of cable method • For the treatment of extensive area • When the area is irregular • When it is desirable to avoid heating of the subcutaneous fat.

Disadvantages of cable method

• The impossibility of using air spacing.

Dosage • The treatment dosage should have an intensity that causes sufficient warmth (thermal dosage) of the tissues and the duration of the treatment should be 20 to 30 min. • The treatment may be given daily or on an alternate day.

Physiological effects • Effects • Effects • Effects • Effects • Effects

on metabolism of the body. due to inc blood supply. of heat on the nervous tissues. of heat on the muscular tissues. of heat on the sweat glands.

Therapeutic effects • Effect on inflammation • Effects in bacterial infection • Relief of pain • Effects of muscle tissue • Traumatic conditions • Reducing healing time.

Dangers • Burns • Scalds • Electric shock • Overdose • Precipitation of gangrene. • Faintness • Giddiness • Dangers to hearing aids or cardiac pacemaker. • Dangers to other equipments.

Contraindications • Open wounds or hemorrhage • Metal in the tissue • Disturbed skin sensation • Venous thrombosis or thrombophlebitis • Arterial disease • Menstruation • Pregnancy • Tumors • Deep x-ray cobalt therapy • Unconscious patient • Epileptic patients • Uncooperative patient.

Pulsed short wave diathermy • It is referred to as pulsed electromagnetic energy which is created by simply interrupting the output of continuous short wave diathermy at regular intervals. • It was invented in 1930s • The freq of pulsed short wave diathermy is same as that of continuous short wave diathermy. • Pulse freq is b/w 25 and 600pps, pulse width is b/w 20 and 40ms. • By adding rest period to the treatment, the average power is considerably reduced. • The heat developed in the tissues is dispersed by the circulation and treatment is thus referred to as nonthermal treatment. • Pulsed short wave diathermy inc the cellular activity, inc the reabsorption of hematoma, reduces inflammation, reduce swelling and inc the repair process. • The treatment duration varies from 15 to 60 min and indications and contraindications are almost similar to that of short wave diathermy.

Microwave diathermy

Introduction • Use of microwaves for various therapeutic purposes is term as microwave diathermy. • It has much higher freq and shorter wavelength than short wave diathermy. • The freq and wavelength ranges from 300MHz to 300GHz and 1cm to 1m . • The microwave diathermy can directly penetrate into the tissues to some extent and can be strongly absorbed by water and high vascular tissues.

Production of microwave • The microwave diathermy apparatus is connected to main AC which provides it a current of 50Hz and a voltage of 220volts. • It is not possible to produce microwaves by mechanical means and hence a special type of thermionic valve is used which is called a magnetron. • The function of a magnetron is to produce high freq current required for the production of microwaves. • Magnetron is special type of thermionic valve characterized by centrally placed cathode and a surrounding circular metal anode. • Coaxial cable carries these high freq currents from the magnetron and es it to the antenna of the emitter. • Antenna is mounted in front of a metal reflector. • Reflector is a metal plate which directs the microwaves in only one direction.

Physiological and therapeutic effects • Same as SWD

Dangers and contraindications Same

Long wave diathermy

• use of high freq electromagnetic waves of the freq 1MHz and wavelength 300m. • Long wave diathermy has less freq (1MHz) than short wave diathermy (27.12MHz) so there is minimal loss of energy. • The power output req for long wave diathermy is 25-75 watts only, whereas short wave diathermy generates 250 to 1000watts of power. • Unlike short wave diathermy, long wave diathermy does not produce any interference with other equipment. • It is said that long wave diathermy can be used even with patients having metal implants. • Also the portability and affordability of equipment is good in long wave diathermyas compared to short wave diathermy.

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