Introduction: Recent investigations involving medical devices have brought increased attention to medical diathermy equipment. This ITG has been written to give those who are unfamiliar with high frequency electrical therapy equipment a fundamental knowledge of diathermy theory.
Diathermy is the controlled production of "deep heating" beneath the skin in the subcutaneous tissues, deep muscles and joints for therapeutic purposes. There are basically two types of diathermy devices on the market today: radio or high frequency and microwave. Ultrasonic or ultrasound therapy is also a form of diathermy, and is sometimes combined with electrical stimulation. Radio frequency (r.f.) diathermy is assigned an operating frequency of 27.12MH Z (short wave) by the Federal Communications Commission. Older radio frequency units were assigned an operating frequency of 13.56MH Z. Microwave diathermy is assigned 915MH Z and 2450MH Z as operating frequencies (these are also Microwave oven frequencies).
The present informal position of the Food and Drug Administration is that a diathermy device should be capable of producing heat in tissue from a minimum of 104 F to a maximum of 114 F at a depth of two inches in not more than 20 minutes. When diathermy equipment is utilized, the power output is maintained below the pain threshhold of the patient.
There are basically two methods of applying high or radio frequency diathermy - Dielectric and Inductive.
1.Dielectric - When dielectric coupled diathermy is used, a rapidly alternating voltage differential is created between two electrodes producing a rapidly alternating electric field between the electrodes. The electrodes are placed either one on each side or both on the same side of the part of the body to be treated so that the electric field penetrates the tissues of the concerned area of the body. Because of the electrical charges within the tissue molecules, the tissue molecules will try to align themselves with the rapidly changing electric field. This rapid movement, or alternation, of the molecules, causing friction or collisions with other molecules, produces heat in the tissues. The electric field strength is determined by the degree of difference in potential between the electrodes set by the unit power control. Since frequency is not varied, the average power output determines the intensity of heating. The electrodes are usually small metal plates mounted in cushion like enclosures, but may be made of a flexible material such as wire mesh so that they may be contoured to fit a particular portion of the body.
2.Inductive - In Inductive coupled r.f. diathermy, high frequency current is generated through a coil to produce a rapidly reversing magnetic field. The coil is normally wound inside an applicator attached to the diathermy unit by an adjustable arm. The applicator is made in various forms for ease of application to the concerned area and is positioned directly over or next to the area to be treated. The rapidly reversing magnetic field induces circulating currents and electric fields into the body tissues, producing heat in the tissues. Induction coupling is generally employed at the lower r.f. diathermy region. Intensity of heating is again determined by average power output.
Post time: Jan-11-2022