Comparison of the Nerve Conduction Parameters in Proximally and Distally Located Muscles Innervated by the Bundles of Median and Ulnar Nerves

OBJECTIVE: The aim of this study was to investigate and compare the conduction parameters of nerve bundles of median and ulnar nerves that innervate proximal and distal muscles. SUBJECTS AND METHODS: Thirty male and 30 female healthy volunteers between 18 and 70 years of age were enrolled in the study. The conduction parameters were recorded from the proximally located flexor carpi ulnaris, pronator teres and the flexor carpi radialis muscles to the distally located abductor digiti minimi and abductor pollicis brevis muscles for the ulnar and median nerves. Each nerve was stimulated at the region above the elbow and at the axillary region separately. The Student t test was used for statistical analysis, and Levene's test was used to assess whether or not the group variances exhibited a uniform distribution. RESULTS: The conduction velocities were faster (78.27 ± 6.55 vs. 67.83 ± 6.76 m/s, and 74.57 ± 5.66 and 74.23 ± 5.88 vs. 66.38 ± 6.85 m/s) and the durations of compound muscle action potential (CMAP) response were longer (15.65 ± 2.43 vs. 13.55 ± 1.78 ms, and 16.38 ± 2.39 and 16.04 ± 2.34 vs. 13.40 ± 1.79 ms) in proximally located muscles than in distally located muscles that are innervated either by ulnar or median nerves (p < 0.001). However, the CMAP amplitudes were smaller (2.52 ± 1.16 vs. 5.81 ± 3.13 mV, and 2.90 ± 1.20 and 3.59 ± 1.66 vs. 6.88 ± 2.77 mV) in proximal muscles than in distal muscles (p < 0.001). There was no significant difference (p > 0.05) between males and females regarding conduction velocities and CMAP amplitudes recorded from proximal and distal muscles. CONCLUSION: Proximal muscles innervated by median or ulnar nerves had lower CMAP amplitude values, longer CMAP durations and higher conduction velocities than distal muscles. These findings could reveal a temporal dispersion and phase cancellation due to desynchronized conduction during nerve stimulation.