MICROWAVE DIATHERMY
At the end of this unit the student will be able to
Explain the characteristics and therapeutic effects of microwave
diathermy.
Describe and demonstrate the application techniques of
microwave diathermy.
List the indications and contraindications microwave diathermy.
Explain the precautions and potential harmful effects of
microwave diathermy.
Explain the dosage of microwave diathermy.
- The waves of 1 m (frequency 300 MHz) to 1 mm (300 GHz) in the electromagnetic spectrum.
- - Radiation with a wavelength of 12.25 m and a frequency of 2450 MHz (commonly used) – UK and Australia
. - Radiation with a wavelength of 69 cm and a frequency of 433.92 MHz.Also 327 mm (915 MHz)– North America.
- Production of Microwaves
- Production of high frequency currents
- Special type of valve called a magnetron is used.
- Warm-up required.
- HF – coaxial cable.
- Coaxial cable- a small aerial – Emitter or director or applicator.
- Application
1
- Circular or rectangular emitter with air spacing.
- Circular emitter- rays circular in cross-section and is more dense at the periphery than in the centre.
- - Rectangular emitter-beam is oval in cross-section and is of greatest density centrally.
. - Rays diverge
. - Spacing – commonly between 10 and 20 cm / 2-6 cm
. - Small emitters- for use in contact with the tissue and for the treatment of cavities
. - Concave surface emitters
- Physiological effects
- Absorbed, transmitted, refracted or reflected
. - Absorption of the waves results in the production of heat in the tissues by means of dipole rotation and molecular distortion
. - The effects deeper than infra-red irradiation, but less than shortwave diathermy
. - Microwaves are strongly absorbed by water- so tissues with good blood supply such as muscle, moist skin, blood vessels, internal organs and eyes gets appreciable heating than tissue with low fluid
content like fat
. - Physiological effects of heating is applicable
. - Non-thermal effects
image
graph
5.Therapeutic effects
- A local rise in temperature (like SWD)
. - Traumatic and inflammatory lesions - increase in blood supply and relief of pain and muscle spasm are beneficial
. - Bacterial infections – increase in blood supply brings more white blood cells and antibodies and reinforces the body’s normal defence mechanism
. - Effective for in the superficial tissue and those of high fluid content
. - Reduced joint pain and increased walking time – RA
- Increased extensibility of collagenous tissue and reduced joint stiffness.
6.Danger of Microwave Diathermy
1.Burns -
patient sensation is the primary guide to the
intensity. Remove the metal objects.
- Poor technique
- Inability of tissues to dissipate heat
- Inability of patient to detect heat (decreased thermal sensation)
- Treatment over areas with surface or implanted metal.
- Treatment of moist open wounds, or over wet dressings - water concentrates microwaves.
- Treatment near the eyes, including sinuses and
temporomandibular joint
2.Exacerbation of symptoms following treatment of:
- Inflammatory conditions
- Infective disorders
- Areas of increased fluid tension such as bursitis, oedema, synovial effusion.
- Haemorrhagic condition – menstruation is unlikely to be affected.
- Severe cardiac disease
- Cardiac failure due to electric shock or interference with cardiac pacemakers
. - Spread of existing pathologies including tumours, active tuberculosis and acute infections
. - Early pregnancy (first 3 months) – heat may be teratogenic
. - Eyes – PT and patient wear protective goggles made of a wire mesh
. - Circulatory defects – ischaemic areas should not be treated. Haemorrhage, thrombosis, phlebitis and other vascular lesions should not receive MWD.
- Contraindications
- Malignant growth
- Tuberculosis infection
- Areas recently exposed to therapeutic doses of X-rays
- Hypersensitive skin
- Testicles
- Damage to equipment – reflection by metal plate can damage the Microwave machine.
- Cardiac pacemakers
- Hearing aids
- PT should not remain in the direct line of the beam or within 2 m of the director.
- Recflection -50 to 75% from the patient and nearly 100% from the metal of the apparatus.
- Technique of application
Preparation of apparatus:
- The selected emitter is connect to the machine by the appropriate cable and the power switched on.
- There will be some delay in the output.
- Test the machine - PT hand or arm to feel the warmth by increasing the output. Then controls to zero and keep it in standby mode.
Preparation of the patient
- Same as SWD.
- Avoid excessive movement.
- Full support and comfortable position.
- Patient and PT wear a pair of wire mesh goggle to protect his eyes.
- Application of the emitter
- The emitter surface should be parallel to the skin and at the appropriate distance. (the inverse square law of distance)
- Surface marking of the structure to be treated.
- Irregular surfaces and areas which perspire freely should, if possible, avoided.
- Irradiation
- The patient is reminded of the sensation to be expected and of the need to report accurately on that experienced
. - Output is increased slowly until a sensation of warmth is experiences or the selected output is reached whichever comes first
. - Appropriate time
. - Then output reduced and switched off
. - Slight erythema may be observed and there should be no marked skin reaction.
- Dosage
- The dose can be calculated from the power output from the machine, (upto 200 watts)
. - In all cases the sensation experienced by the patient must be the primary guide
. - Duration – 10 to 30 minutes
. - Progressive increase in exposure must depend on the patient’s reaction
. - Daily or on alternate days.