diathermy
Meaning of diathermy: One word covering two unrelated things: the electrical cutting tool of an operating room and the deep warming used in physiotherapy.
Definition of diathermy
Diathermy means heating tissue below the surface with a high-frequency electric current, radio waves, microwaves or ultrasound. In surgery it names the instrument that passes current through tissue to cut it and seal bleeding vessels, heating a tiny volume to boiling point. In physical therapy it names equipment that gently warms deeper muscle and joints without destroying anything.
How does the surgical kind work?
Current alternating hundreds of thousands of times a second passes through tissue. Nerve and muscle cannot respond that fast, so the current produces no shock and no contraction, and all it does is deposit heat. Heat concentrates wherever the current is squeezed into a small area, which is the fine tip of the instrument, so a tiny volume boils while the tissue a short distance away is untouched. A continuous waveform vaporizes cells and cuts; an interrupted one heats more slowly, shrinking and sealing vessels instead. Strictly this is electrosurgery, and true cautery means a tip heated beforehand with no current entering the body at all, a distinction routinely blurred in speech.
How is the physiotherapy version different?
In purpose and in dose. Shortwave, microwave and ultrasound equipment raises the temperature of muscle and joint tissue a few degrees over a wide region to increase blood flow and ease stiffness. Nothing is destroyed and no incision is involved. This is the sense the word carries in physical therapy departments. Deliberately heating tissue far enough to damage it is a separate treatment, called hyperthermia when it is aimed at a tumor, and the source of the confusion is that similar equipment can deliver both.
What are the hazards?
| Form | Purpose | Effect on tissue |
|---|---|---|
| Surgical diathermy | Cutting and sealing during an operation | Destroys a small volume at the tip |
| Shortwave and microwave | Easing stiffness and pain | Warms without damage |
| Ultrasound | The same, over a smaller area | Warms without damage |
| Heat aimed at a tumor | Damaging cells within a defined region | Kills cells |
In the monopolar arrangement the current runs from the tip, through the body, to a large pad on the thigh, and a pad in poor contact concentrates the return and burns the skin under it. The bipolar arrangement confines current between the two tips of a forceps and avoids that path. Sparks can ignite alcohol-based skin preparation or oxygen near an airway, implanted pacemakers and defibrillators can be disturbed by the current, and the smoke produced carries particles that are extracted rather than breathed. The term electrodiathermy refers to the surgical form.
Also known as
Used in a sentence
Bleeding from the wound edge was controlled with diathermy.
Good to know
The word covers two different things: surgical diathermy destroys tissue at the instrument tip, while shortwave, microwave and ultrasound diathermy in physical therapy warm tissue without damaging it.
Word origin
Where “diathermy” comes from
From the Greek dia, meaning through, and therme, meaning heat, so literally a heating through the tissue.