Nerve conduction velocity. Relationship of skin, subcutaneous and intramuscular temperatures

The purpose of this study was to investigate the correlation between skin temperature and nerve conduction velocity (NCV) and to determine the relationship of skin temperature to subcutaneous and intramuscular temperatures. Twenty-five normal subjects were tested for tibial motor, and sural sensory NCVs and tibial H-reflex latency. NCVs, skin, subcutaneous and intramuscular temperatures were measured first at ambient temperature (mean, 25C), and then at calf skin temperatures of approximately 30, 28, and 26C, after cooling of the lower extremities. Results showed a linear correlation of skin temperature with subcutaneous and intramuscular temperatures (all p<0.025). Change of tibial motor and sural sensory NCVs correlated significantly with the corresponding change in skin subcutaneous and intramuscular temperatures (all p<0.001). Tibial motor NCV changed 1.1 m/sec/1C change of skin temperature (p<0.001): and sural sensory NCV was altered 1.7 m/sec/1C change of skin temperature (p < 0.001). H-reflex latency did not significantly correlate with temperature changes measured at the gastrocnemius muscle belly (p>0.050). It appears that skin temperature is a reliable means of determining temperature influence on NCVs. It is suggested that skin temperature be measured 15 cm above medial malleolus and that NCV of peripheral nerves in the lower extremities be corrected to a standard skin temperature of 32C in order to reduce error in NCV reporting. The following equations are suggested for NCV correction. (1) Tibial NCV (corrected)=1.1 (32-skin temp C) + (NCVm/sec): (2) Sural NCV (corrected)=1.7 (32-skin temp C) + (NCVm/sec): (3) Sural latency corrected = 1/0.012 (32-skin temp C) + (1/latency msec).