Effect of stimulus intensity on the rising phase of the nerve action potential in healthy subjects and in patients with peripheral nerve lesions.

Abstract

Rise times at the ulnar nerve action potential at threshold and supramaximal stimulation were studied in 25 patients with nerve lesions and 50 controls. Potentials were recorded from the ulnar nerve at the elbow after electrical stimulation at the wrist. In patients with peripheral nerve lesions rise times were markedly prolonged and the rise length of the action potential was found to be characteristically prolonged. As strength of stimulation decreases, rise times become longer, reaching the greatest value at near threshold stimulation. In peripheral nerve paralysis this effect becomes much more prominent than in healthy individuals. Results suggest a marked sensitivity of the slope of rise to reduction of stimulus intensity primarily in cases of peripheral neuropathy. Changes in rate of rise would be helpful in detecting early evidence of a nerve lesion.