Compound nerve action potentials from the median and ulnar nerves.

The compound nerve action potentials from mixed motor/sensory (MNAP) and sensory (SNAP) nerve stimulation in the median and ulnar nerves were recorded in both arms of 20 able-bodied subjects. Intranerve and internerve peak-to-peak amplitudes were compared. An SNAP/MNAP amplitude ratio greater than 0.25 exceeded the mean by 2SD. The fastest, intermediate, and slowest conduction velocities were calculated from chosen points on the biphasic waveform. An intermediate MNAP conduction velocity for the median and ulnar nerves of less than 49.5m/sec exceeded more than 2SD below the mean. Likewise, an intermediate SNAP conduction velocity of less than 45.5m/sec exceeded 2SD below the mean. Median MNAP latency across the carpal tunnel was 1.0 +/- 0.3 and ulnar MNAP conduction velocity across the elbow was 59.7 +/- 3.8m/sec. This technique may supplement traditional electrodiagnostic studies in evaluating upper extremity neuropathies.