Microwave diathermy By Abdullah Radwan
Microwave diathermy • They are radar waves i.e. a form of electromagnetic radiation. • Like other electromagnetic waves, microwaves travel at the speed of light. They can be propagated through a vacuum. • Its wavelength is between infra-red and short-wave diathermy radiations. • It is produced by a special apparatus consisting of: • The magnetron tube which produces the high frequency oscillations, and • The applicator (the antenna).
The wavelength of microwave is 12.2 cm. • The power is expressed in watts/cm2. • The total output of available microwaves is up to 100 watts.
Physiological effects • The microwave heating effects are responsible for the vast majority of the therapeutic effects. • Non-thermal reaction could also be demonstrated.
Thermal effects lead to: • Analgesia, sedation, and soothing effect on the irritated nerve endings. • Increased blood flow and elevation of tissue temperature. • Increased metabolism. • Increased phagocytosis. • Increased cardiac output. • Increased clearance of metabolites. • Increased supply of nutrients, antibodies, and leucocytes.
Non-thermal effects • Most of the biologic reactions are mostly due to thermal effects. • The significance of these effects in therapeutic purposes is still not well understood.
Propagation and absorption of microwaves in tissues • Tissues with high water content, such as muscles, subcutaneous fat, and fluid media such as eyes and sweat glands absorb more microwave energy than is the bones. • Microwave diathermy with a frequency of 2456 megacycles adequately heat the subcutaneous fat and the depth of penetration is poor in muscle tissues. • Microwave diathermy with a frequency of 900 megacycles→ best heating of musculature will result.
Propagation and absorption of microwaves in tissues • Undesirable hot spots at the muscle-bone inter-surfaces my result with 2456 megacycles due to energy reflection which is less to occur with 900 megacycles or below. • The data now suggest that the optimal frequency would be at 900 megacycles or below to minimize the heating effect of subcutaneous tissues and heating the underlying tissues more adequately (better depth of penetration) and to prevent hot spots (bone reflection).
Dosage • Like short wave diathermy, until the present time there is no way to assess the absolute level of temperatures obtained in the tissues. • It is necessary to depend on the feeling of warmth on the part of the patient as in short wave diathermy.
Technique and duration of application • Vigorous heating can be obtained when the applicator is closer to the skin. • One inch is satisfactory if vigorous heating is required. • Joint heating can be achieved by multiple field method of application and the joint should be exposed from all sides. • The mild heat can be achieved either by increasing the distance between the applicator and skin of the patient or by decreasing the output of the machine. • Duration: 20- 30 min • Patient should be undressed and no clothing should cover the treated area. • Eyes should be protected from vigorous heating by use of a shield. • Metals should be kept away from the microwave field.
Indications • Joint diseases either degenerative or inflammatory. • Calcific bursitis, tendinitis and periarthritis of the shoulder. • Prolapsed intervertebral disc. • Traumatic conditions as sprains and strains. • Superficial inflammatory conditions as furuncles. • Low doses microwaves only in eye conditions as iridocyclitis, keratitis.
Contraindications General contraindications to heat therapy should be applied. +++ • Direct eyes application especially in high dosage. • Over bony prominences. (hot spots) • Over the reproductive organs ???
Hazards of microwave diathermy • Burn of bones due to energy reflection at bone surfaces. • Selective burns may occur in hollow organs, viscera and stomach and may be considered as hot spots. • Tissues over the thoracic cage may be selectively burned. • Anterior cardiac surface may be selectively heated. • Selective absorption may occur in metallic implants present in tissues.