A process by which electric currents can be passed into the deeper parts of the body so as to produce internal warmth and relieve pain; or, by using powerful currents, to destroy tumours and diseased parts bloodlessly. The form of electricity used consists of high-frequency oscillations, the frequency of oscillation ranging from 10 million to 25,000 million oscillations per second. The current passes between two electrodes placed on the skin.
The so-called ultra-short-wave diathermy (or short-wave diathermy, as it is usually referred to) has replaced the original long-wave diathermy, as it is produced consistently at a stable wave-length (11 metres) and is easier to apply. In recent years microwave diathermy has been developed, which has a still higher oscillating current (25,000 million cycles per second, compared with 500 million for short-wave diathermy).
When the current passes, a distinct sensation of increasing warmth is experienced and the temperature of the body gradually rises; the heart’s action becomes quicker; there is sweating with increased excretion of waste products. The general blood pressure is also distinctly lowered. The method is used in painful rheumatic conditions, both of muscles and joints.
By concentrating the current in a small electrode, the heating eﬀects immediately below this are very much increased. The diathermy knife utilises this technique to coagulate bleeding vessels and cauterise abnormal tissue during surgery.