Evaluation of evoked-muscle potentials from stimulation of ulnar nerves of the dog.

Evoked muscle potentials were evaluated in 19 anesthetized dogs after stimulation of the ulnar nerve. Subsequently, unilateral dorsal rhizotomy was performed on 6 dogs, and ulnar nerve stimulation was repeated. The evoked muscle potentials were begun at 1 V and increased. Threshold, optimum, and maximum stimuli for the M wave, and the reflex-evoked response (H reflex) were recorded. Threshold voltages for the M wave and the H reflex were 4.4 V and 4.0 V, respectively. The latencies for these stimuli also were recorded for the H reflex from proximal and distal sites. The optimal latency for the proximal and the distal sites were 15.4 +/- 2.5 ms and 18.3 +/- 2.6 ms, respectively (mean +/- SD). The motor nerve conduction velocity was 68 +/- 11 m/s. In addition, a mixed orthodromic sensory-antidromic motor conduction velocity was 75.2 +/- 13.3 m/s. Ratios between thoracic limb length and H reflex latency were 27.5 +/- 3.9 from the proximal site and 23 +/- 2.7 from the distal site. A waveform with a latency less than that of the H reflex, but greater than that of the M wave was observed inconsistently. An additional group of low amplitude waves was observed with a latency greater than the H reflex latency. The H reflex latency/limb length ratio may be clinically useful in evaluation of proximal neuropathies in the dog.