The effect of stimulus intensity on latency of nerve action potential in healthy subjects and in patients with peripheral nerve lesions

Abstract

Sensory latency at threshold and at supramaximal stimulation of the ulnar nerve was studied in 12 normal subjects and in 9 patients with nerve lesions. The nerve was stimulated at the wrist and recorded above the elbow. Latencies of the nerve action potentials at threshold stimulation were prolonged in comparison with those at supramaximal stimulation (P = 0.05 in control subjects; P < 0.05 in patients with peripheral nerve lesions). Intercorrelations between the latency duration and stimulating intensity were statistically highly significant. The correlation coefficient was r = -0.64 : P< 0.001 in control subjects and r = -0.70 : P< 0.001 in patients with peripheral nerve lesions. With increasing stimulus intensity there was a gradual decrease of latency duration along the regression line (equation of regression line was y = 5.60 - 0.0086 x for control group of healthy people and y = 10.414 - 0.0279 x for group of patients). The course of the regression line in control subjects is significantly different from that of patients with nerve lesions (P< 0.05). Our findings involving the duration of sensory latency with threshold and supramaximal stimulation can be utilized to detect the early stage in nerve damage.