RESUMO
Effect of thermal stimulation on the flexion reflex as a pain index was examined in healthy human subjects who gave informed consent (n=9, male, mean age 26 ± 8 years old). The evoked electromyogram (EMG) of biceps femoral muscle elicited by transcutaneous electrical stimulation of the sural nerve (5 trains of pulses at 100 Hz delivered at intervals of 13 sec) was successively recorded. The subjective pain sensation elicited by nerve stimulation was simultaneously recorded by the visual analogue scale (VAS) method. Significant correlation coefficients between the amplitudes of evoked EMGs and the stimulus intensity (r=0.791, P< 0.01), and the VAS value (r=0.724, P < 0.01) were observed. Conditioning hot water immersion of the hand (47 °C, 156s) tended to reduce the amplitudes of evoked EMGs, although change was not significant (P=0.678, Kruskal-Wallis test). However, C-statistics, a simple time series analysis method, demonstrated significant trends in several trials. These results suggest that the flexion reflex used in the present study is useful for pain research in human subjects and C-statistics are also useful for analyzing the effect on each individual.