Diathermy

Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical therapy and in surgical procedures. The earliest observations on the reactions of high-frequency electromagnetic currents upon the human organism were made by Jacques Arsene d'Arsonval. The field was pioneered in 1907 by German physician Karl Franz Nagelschmidt, who coined the term diathermy from the Greek words dia and θέρμη therma, literally meaning 'heating through' (adj., diather´mal, diather´mic). Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical therapy and in surgical procedures. The earliest observations on the reactions of high-frequency electromagnetic currents upon the human organism were made by Jacques Arsene d'Arsonval. The field was pioneered in 1907 by German physician Karl Franz Nagelschmidt, who coined the term diathermy from the Greek words dia and θέρμη therma, literally meaning 'heating through' (adj., diather´mal, diather´mic). Diathermy is commonly used for muscle relaxation, and to induce deep heating in tissue for therapeutic purposes in medicine. It is used in physical therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body. Diathermy is produced by three techniques: ultrasound (ultrasonic diathermy), short-wave radio frequencies in the range 1–100 MHz (shortwave diathermy) or microwaves typically in the 915 MHz or 2.45 GHz bands (microwave diathermy), the methods differing mainly in their penetration capability. It exerts physical effects and elicits a spectrum of physiological responses. The same techniques are also used to create higher tissue temperatures to destroy neoplasms (cancer and tumors), warts, and infected tissues; this is called hyperthermia treatment. In surgery diathermy is used to cauterize blood vessels to prevent excessive bleeding. The technique is particularly valuable in neurosurgery and surgery of the eye. The idea that high-frequency electromagnetic currents could have therapeutic effects was explored independently around the same time (1890-91) by French physician and biophysicist Jacques Arsene d'Arsonval and Serbian American engineer Nikola Tesla. d'Arsonval had been studying medical applications for electricity in the 1880s and performed the first systematic studies in 1890 of the effect of alternating current on the body, and discovered that frequencies above 10 kHz did not cause the physiological reaction of electric shock, but warming. He also developed the three methods that have been used to apply high-frequency current to the body: contact electrodes, capacitive plates, and inductive coils. Nikola Tesla first noted around 1891 the ability of high-frequency currents to produce heat in the body and suggested its use in medicine. By 1900 application of high-frequency current to the body was used experimentally to treat a wide variety of medical conditions in the new medical field of electrotherapy. In 1899 Austrian chemist von Zaynek determined the rate of heat production in tissue as a function of frequency and current density, and first proposed using high-frequency currents for deep heating therapy. In 1908 German physician Karl Franz Nagelschmidt coined the term diathermy, and performed the first extensive experiments on patients. Nagelschmidt is considered the founder of the field. He wrote the first textbook on diathermy in 1913, which revolutionized the field. Until the 1920s noisy spark-discharge Tesla coil and Oudin coil machines were used. These were limited to frequencies of 0.1 - 2 MHz, called 'longwave' diathermy. The current was applied directly to the body with contact electrodes, which could cause skin burns. In the 1920s the development of vacuum tube machines allowed frequencies to be increased to 10 - 300 MHz, called 'shortwave' diathermy. The energy was applied to the body with inductive coils of wire or capacitive plates insulated from the body, which reduced the risk of burns. By the 1940s microwaves were being used experimentally. The three forms of diathermy employed by physical therapists are ultrasound, short wave and microwave. The application of moderate heat by diathermy increases blood flow and speeds up metabolism and the rate of ion diffusion across cellular membranes. The fibrous tissues in tendons, joint capsules, and scars are more easily stretched when subjected to heat, thus facilitating the relief of stiffness of joints and promoting relaxation of the muscles and decrease of muscle spasms.