Ultrasound's effect on the conduction latency of the superficial radial nerve in man.

Research has clearly demonstrated that ultrasound has an effect on nervous tissue and its ability to propagate an action potential, but controversy exists concerning what physiological changes occur and whether these changes are due to the thermal or mechanical properties of ultrasound. The purpose of this study was to clarify the effect caused by mechanical and heating factors on sensory nerve conduction by comparing the effects of equivalent temperature changes by a strictly thermal source and by ultrasound. Ten healthy adults were exposed to ultrasound and infrared on separate treatment sessions to create a 1.2 degrees C increase in subcutaneous tissue temperature. Nerve conduction latencies were recorded for each 0.3 degrees C increase during both the ultrasound and infrared treatments. Results were analyzed using a two-way analysis of variance and a matched-group Student's t test. The combined mechanical and heating effects of ultrasound caused a decrease in latency of the lateral cutaneous branch of the radial nerve, similar to that of the heating effects of infrared. The results indicated that ultrasound's mechanical effects did not play a significant role in affecting the nerve conduction latency.