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Microwave Diathermy Properties of Microwave Diathermy Microwave diathermy (MWD), is a form of electromagnetic radiations (part of electromagnetic spectrum), lying between shortwave and infrared waves. The microwaves diathermy gives superficial heating where energy is first absorbed at the surface of the body (skin) and a part of it penetrate and absorbed in deep tissues. Properties of Microwave Diathermy The general frequency of microwave is between 300 to 30000MHz with wave length of 10mm to 1 meter. The therapeutic microwave generators used frequency of 2450MHz with wave length of 122.5mm. Physiotherapeutic microwaves at 327mm (915 MHz) and 690mm (433.9MHz) may be also available to give minimal heating of subcutaneous tissues and produce more heating of underlying tissues. Production of Microwave Radiation The generator used to produce microwaves has three main components: A multi-cavity magnetron valve. A coaxial cable to transmit the high frequency energy to an antenna. A director for transmitting the energy (through air) to the patient. Production of Microwave Radiation The magnetron (a diod valve) produces a high frequency alternating current which is carried by coaxial cable to the transducer (director). The coaxial cable transmit the energy to the director where a radiating system comprising an antenna within a reflector is used to direct the microwave to the patient. Directors Used in Microwave Applications There are different shapes of directors used in microwave applications: Large circular field director: the effective diameter is 200mm. The heating pattern is more intense around the outer portion than the centre. The power output range is up to 250 watts. Directors Used in Microwave Applications Small circular field director: the effective diameter is 100 mm. the heating pattern is more intense around the outer portion than in the center. The power output is up to 25 watts Directors Used in Microwave Applications Longitudinal director: the effective treatment area is 500mm by 100mm. the heating pattern tends to be more concentrated in the center of this area. The power output is up to 250 watts Biophysical and Biochemical Effects of MWD Penetration: the depth of penetration depends on the frequency of the wave and the medium. The effective penetration of 2450MHz is approximately 30mm. Absorption: non-polar molecules will distort toward the alternating charge in the field. -Dipolar molecules will rotate back and for the ions will vibrate in the field direction heat energy. Biophysical and Biochemical Effects of MWD Reflection: the proportion of waves reaching the deeper tissues is also dependent upon the amount of energy which is reflected at the air- skin, skin-fat, and the fat-muscle. At frequencies below 1000MHz most of the distribution of the energy depends critically on the thickness of the skin and the subcutaneous fat. Heat conduction: heat applied to the skin (in a restricted area) results in an increased blood flow of the skin accompanied by vasodilatation. Mild heat produces reflex reduction of increased muscle tone. Therapeutic Effects of Microwave Diathermy Relief of pain: by microwave diathermy is useful in the treatment of traumatic and rheumatic conditions affecting superficial muscles, ligaments and small superficial joints. Reduce muscle spasm: may be reduced directly by microwave diathermy or may be reduced by relieving of pain. Inflammation: increase in the blood supply will increase venous return from the inflamed area and aids the reabsorption of edema exudates. Therapeutic Effects of Microwave Diathermy Delayed healing: to promote healing of open skin by increase cutaneous circulation. Infection: MWD can control the chronic infection by increasing the circulation. Fibrosis: heat increase the extensibility of fibrous tissues such as tendons, joint capsules and scars. Dosage of MWD Duration of treatment 20 minutes is the optimum. :Intensity: the patient should feel mild and comfortable warmth. Frequency: daily or on alternating day. Indications of MWD Musculoskeletal disorders: Sprain- strain – muscle and tendon tear – degenerative joint disease- joint stiffness in superficial joints- capsular lesions. Superficial inflammatory or infective conditions : Tenosynovitis – bursitis – synovitis – infected surgical incisions – carabuncles – abscess. Contra-indications Over malignant tissues. Over ischemic tissues. Moderate and excessive edema. Over wet dressings and adhesive tapes. Metal implants. Pacemaker. Over growing bone. Male gonads: repeated irradiation can cause sterility. Hemorrhage. Tuberclous joints. Impaired thermal sensation. Unreliable patients. Contra-indications The eyes: cause cataract. Recent radiotherapy. Hypersensitivity to heat. Acute infection or inflammation. Obesity: with 2450MHz microwave, there is danger of producing an excessive heat in the subcutaneous fat layer. Analgesic therapy: the thermal sensation diminished. Venous thrombosis or phlebitis. Pregnancy: heat applied to pelvis or hip in pregnancy may cause hemorrhage or miscarriage. Menstruation. Acute dermatological conditions. Severe cardiac conditions. Blood pressure abnormalities.
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