Electrophysiologic responses of human sural nerve to temperature

The purpose of this study was to assess the conduction, specifically the latency and amplitude of the sensory nerve action potential (SNAP), of the sural nerve as a function of intraneural temperature of the leg. The electrophysiologic responses of the sural nerve were determined at different temperatures in 22 healthy adults. Distal sensory latency and amplitude of the sural SNAP was determined at 1 degree C intervals over a limb temperature range of 23 degrees to 40 degrees C. Limb temperature was monitored with a thermistor probe placed subcutaneously near the sural nerve. Ice bath soaks were used for cooling and infrared radiation for warming the limbs. An analysis of covariance was performed for the SNAP latencies and amplitudes to determine the effect of gender and leg (right or left) at each temperature level. No effect of gender or leg on neural conduction was detected in individual subjects. A regression analysis was then used on pooled data to determine the effect of temperature on sural SNAP latency and amplitude. An inverse linear change in the latency of sural SNAP was observed over the temperature ranges used. Mean latency increased 0.1 msec per 1 degree C increase in subcutaneous temperature. A direct relationship between amplitude of the SNAP and temperature was determined. Mean amplitude increased 0.3 muV per 1 degree C increase in subcutaneous temperature. The results of this study support previous reports, which state that SNAP latency is indirectly related to the intraneural temperature. Clinical electromyographers must monitor the temperature of the lower leg and foot whenever sensorineural conduction of the lower limbs is performed.