Ocular vestibular evoked myogenic potentials in response to three test positions and two frequencies

Abstract

Objectives/hypothesis: To determine how eye closure, test positions, and stimulus frequencies influence ocular vestibular evoked myogenic potentials.

Study design: This study used a within-subjects repeated measures design.

Methods: Twenty asymptomatic subjects were each tested on ocular vestibular evoked myogenic potentials in three head/eye conditions at 500 Hz and 1,000 Hz using air-conducted sound: 1) sitting upright, head erect, eyes open, looking up; 2) lying supine, neck flexed 30°, eyes open, looking up; and 3) lying supine, neck flexed 30°, eyes closed, relaxed. The four dependent variables measured were n10, p16, amplitude, and threshold.

Results: Supine/eyes open was comparable to sitting/eyes open and better than supine/eyes closed. Eyes closed resulted in lower amplitude, higher threshold, and prolonged latency. Significantly fewer subjects provided responses with eyes closed than with eyes open. No significant differences were found between both eyes open conditions. Both n10 and p16 were lower at 1,000 Hz than at 500 Hz. Amplitude and threshold were higher at 1,000 Hz than at 500 Hz.

Conclusions: Supine/eyes open is a reliable alternative to sitting/eyes open in patients who cannot maintain a seated position. Testing at 1,000 Hz provides a larger response with a faster onset that fatigues faster than at 500 Hz. The increased variability and decreased response in the eyes closed position suggest that the eyes closed position is not reliable.

Level of evidence: 3b.

Keywords: Diagnostic testing; labyrinth; stimulus frequency; vestibular evoked myogenic potential.

Figure 1

Plots showing n10 in each test position and frequency: Sitting eyes open (sit EO), Supine eyes open (Sup EO), Supine eyes closed (Sup EC). Center horizontal bars are medians, rectangle ends are interquartile ranges, error bars are 10^th and 90^th deciles, and circles are outliers. The latency of oVEMP onset is increased in supine EC compared to both EO conditions and the n10 values are more variable in supine EC than in both EO conditions. Latency is decreased at 1000 Hz when compared to 500 Hz.

Figure 2

Box and whisker plot showing p16 in each test position and frequency: Sitting eyes open (sit EO), Supine eyes open (Sup EO), Supine eyes closed (Sup EC). Center horizontal bars are medians, rectangle ends are interquartile ranges, error bars are 10^th and 90^th deciles, and circles are outliers. Latency is increased in supine EC compared to both EO conditions. The p16 values are more variable in supine EC than in the EO conditions. Latency is decreased at 1000 Hz compared to 500 Hz.

Figure 3

Box and whisker plot showing amplitude in each test position and frequency: Sitting eyes open (sit EO), Supine eyes open (Sup EO), Supine eyes closed (Sup EC). Center horizontal bars are medians, rectangle ends are interquartile ranges, error bars are 10^th and 90^th deciles, and circles are outliers. Amplitude is decreased in supine EC compared to both EO conditions. Amplitude is significantly increased at 1000 Hz compared to 500 Hz.

Figure 4

Box and whisker plot showing threshold in each test position and frequency: Sitting eyes open (sit EO), Supine eyes open (Sup EO), Supine eyes closed (Sup EC). Center horizontal bars are medians, rectangle ends are interquartile ranges, error bars are 10^th and 90^th deciles, and circles are outliers. Threshold is higher in supine EC than in both EO conditions. Threshold is higher at 1000 Hz compared to 500 kHz indicating that the response fatigues faster at 1000 Hz than 500 Hz.