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.