Jendrassik maneuver facilitates cVEMP amplitude: some preliminary observations

The cervical vestibular evoked myogenic potential (cVEMP) is an acoustically driven electrophysiological measure of saccular and inferior nerve function that requires tonic sternocleidomastoid muscle (SCM) activity in order to be elicited. The cVEMP is gaining increased interest in the clinical and research communities based on the anatomical specificity it adds to vestibular test batteries, because it is noninvasive, and since it can be performed with instrumentation commonly found in audiology clinics worldwide.

Because maintaining a constant level of tonic background electromyography (EMG) over the entire course of the recording epoch is a requirement for response elicitation, active participation for some individuals including the elderly and those with cervical problems can be difficult. As a way to facilitate the response for some clinical populations, this study addressed whether cVEMPs could be modulated by remote or local changes in EMG related neural activity by applying various maneuvers during the course of the recording epoch.

Keeping acoustic stimulation and recording parameters constant, three separate experimental conditions, Jendrassik maneuver, jaw (teeth) clenching, and forced-eye closure, were used to determine whether cVEMP amplitudes could be enhanced from the control condition.

Nine adults (2 males; 7 females) ranging in age from 24 to 42 yr with normal pure-tone hearing sensitivity and a negative history of otological disease, neurological disease, and head trauma.

Cervical vestibular evoked myogenic potentials were recorded from the SCM using surface electrodes in response to suprathreshold 500 Hz Blackman windowed tone bursts under a control and three experimental conditions. Three separate one-way repeated measures analyses of variance (ANOVAs) were used to evaluate the effects of these maneuvers on P1/N1 peak-to-peak amplitudes and P1 and N1 peak latencies.

A significant main effect of experimental condition was shown to increase P1/N1 peak-to-peak cVEMP amplitude. Post hoc analysis found that Jendrassik maneuver versus control was the only the condition that produced significantly increased response amplitudes in comparison to all other post hoc contrasts. P1 and N1 peak latencies were unchanged across the various experimental conditions.

In adults with normal hearing sensitivity and a negative history of otological disease, neurological disease, and head trauma, Jendrassik maneuver increased cVEMP amplitude by over 39% in comparison to the control condition. Such a simple modulation effect warrants further investigation for application in clinical studies.