Effect of pulse repetition rate on the perception of thermal sensation with pulsed shortwave diathermy

Pulsed shortwave diathermy (PSWD) is a form of therapy commonly used to enhance tissue repair and reduce pain. It is normally considered to be an athermal form of treatment; however, there is some evidence to suggest that thermal effects can arise with adequate dosage. The purpose of this study was to determine the pulse repetition rate (PRR) required to generate a 'possible' and 'definite' thermal sensation when PSWD was applied to the thigh.

Thirty healthy subjects were randomly assigned to placebo or treatment groups. The treatment group was exposed to PSWD at a constant setting of pulse duration (400 microseconds) and pulse power (190 W) while the PRR was increased from 26 Hz to 400 Hz in 10 increments. Each dose was applied for a period of two minutes. At the end of each application, subjects were asked if they felt a (1) 'possible' or (2) 'definite' thermal sensation. Skin temperature was measured immediately after each application. Placebo subjects were exposed to PSWD at its lowest settings throughout the experiment (pulse power = 5 W; pulse duration = 65 microseconds and PRR = 26 Hz).

The results showed a significant correlation (p < 0.048) between PRR at 'definite' thermal sensation and skin temperature post-treatment and PRR at 'possible' thermal sensation (p < 0.001). Mean skin temperature increased significantly as PRR was increased, from 28.69 (+/- 0.75) degrees C pre-treatment to 31.14 (+/- 1.04) degrees C post-treatment, a mean difference of 2.34 degrees C.

These results suggest that PSWD at adequate dosages can generate thermal effects, and that there is a relationship between these thermal effects and the PRR used. These results may have significant implications for the safe use of PSWD in the clinical arena.