Abstract - The influence of voluntary tonic EMG level on the vestibular-evoked myogenic potential

James H. Quillen Department of Veterans Affairs (VA) Medical Center, Mountain Home, TN; Departments of Surgery and Communicative Disorders, East Tennessee State University, Johnson City, TN; Department of Physical Therapy, East Tennessee State University, Johnson City, TN

Abstract — Vestibular-evoked myogenic potentials (VEMPs) are proposed as a reliable test to supplement the current vestibular test battery by providing diagnostic information about saccular and/or inferior vestibular nerve function. VEMPs are short-latency electromyograms (EMGs) evoked by high-level acoustic stimuli and recorded from surface electrodes over the tonically contracted sternocleidomastoid muscle. VEMP amplitude is influenced by the EMG level, which must be controlled. This study examined the ability of subjects to achieve the EMG target levels over a range of target levels typically used during VEMP recordings. In addition, the influence of target EMG level on the latency and amplitude of the click- and tone-evoked VEMP was examined. The VEMP amplitude increased as a function of EMG target level, and the latency remained constant. EMG target levels ranging from 30 µV to 50 µV are suggested for clinical application of the VEMP.

Key words: electromyography, motor-evoked potentials, saccule, sternocleidomastoid muscle, vestibular function tests, vestibular nerve.