Ocular vestibular evoked myogenic potentials: The effect of head and body tilt in the roll plane

• Head and body tilt below the horizontal plane results in a significant decrease in the amplitudes of oVEMPs evoked by both air-conducted (AC) and bone-conducted (BC) stimulation.
• The asymmetry ratio of the BC oVEMP was unaffected by head tilt in the roll plane, implying that BC stimuli and static tilt each activate different populations of afferents.
• oVEMPs are optimally recorded in the upright position.

ObjectiveTo explore effects of whole-head/body tilt in the roll plane on ocular-vestibular evoked myogenic potentials (oVEMP).MethodsTwenty healthy subjects were randomly tilted in an Eply Omniax rotator across a series of eight angles from 0° to 360° (at 45° separations) in the roll plane. At each position, oVEMPs to air-conducted (AC) and bone-conducted (BC) stimulation were recorded from unrectified infra-orbital surface electromyography during upward gaze. oVEMP amplitudes, latencies and amplitude asymmetry were compared across each angle of orientation.ResultsHead orientation had a significant effect on oVEMP reflex amplitudes for both AC and BC stimulation (p < 0.001). For both stimuli there was a trend for lower amplitudes with increasing angular departure from the upright position. Mean amplitudes decreased by 42.6–56.8% (AC) and 23.2–25.5% (BC) when tilted 180°. Roll-plane tilt had a significant effect on amplitude asymmetry ratios recorded in response to AC stimuli (p < 0.001), indicating a trend for lower amplitudes from the dependent (down) ear. Amplitude asymmetry ratios for BC stimuli were unaffected by head and body orientation.ConclusionsThe results confirm an effect of head and body orientation on oVEMP reflexes recorded in response to air- and bone-conducted stimuli.SignificanceThe upright position yields an optimal oVEMP response.