Sodium-potassium pump assessment by submaximal electrical nerve stimulation

Abstract

OBJECTIVE: Sodium-potassium pump dysfunction in peripheral nerve is usually assessed by determining axonal hyperpolarization following maximal voluntary contraction (MVC) or maximal electrical nerve stimulation. As MVC may be unreliable and maximal electrical stimulation too painful, we assessed if hyperpolarization can also be induced by submaximal electrical nerve stimulation. METHODS: In 8 healthy volunteers different submaximal electrical stimulus trains were given to the median nerve at the wrist, followed by 5 min assessment of thresholds for compound muscle action potentials of 20%, 40% or 60% of maximal. RESULTS: Threshold increase after submaximal electrical nerve stimulation was most prominent after an 8 Hz train of at least 5 min duration evoking submaximal CMAPs of 60%. It induced minimal discomfort and was not painful. Threshold increase after MVC was not significantly higher than this stimulus train. CONCLUSIONS: Submaximal electrical stimulation evokes activity dependent hyperpolarization in healthy test subjects without causing significant discomfort. SIGNIFICANCE: Sodium-potassium pump function may be assessed using submaximal electrical stimulation.