Automated head motion system improves reliability and lessens operator dependence for head impulse testing of vestibular reflexes

Abstract

Deficiency of the eye-stabilizing vestibulo-ocular reflex (VOR) is a defining feature in multiple diseases of the vestibular labyrinth, which comprises the inner ear's sensors of head rotation, translation and orientation. Diagnosis of these disorders is facilitated by observation and measurement of eye movements during and after head motion. The video head impulse test has recently garnered interest as a clinical diagnostic assessment of vestibular dysfunction. In typical practice, it involves use of video-oculography goggles to measure eye movements while a clinician examiner grasps the subject's head and manually rotates it left or right at sufficient acceleration to cover ~20 deg over ~150 mS, reaching a peak velocity of >120 deg/S midway through the movement. Manual delivery of head impulses incurs significant trial-by-trial, inter-session and inter-operator variability, which lessens the test's reliability, efficiency, safety and standardization across testing facilities. We describe application of a novel, compact and portable automated head impulse test (aHIT™) device that delivers highly repeatable head motion stimuli about axes parallel to those of the vestibular labyrinth's six semicircular canals, with programmable Gaussian and sinusoidal motion profiles at amplitudes, velocities and accelerations sufficient to test VOR function over the spectral range for which the VOR dominates other vision-stabilizing reflexes. We tested the aHIT™ on human subjects and demonstrated its high reproducibility compared to manually delivered head impulses. This device has the potential to be a valuable clinical and research tool for diagnostic evaluation and investigation of the vestibular system.

Keywords: aHIT; automated head impulse test; head impulse test; vestibular system; vestibulo-ocular reflex.

Fig. 1

Orientation of semi-circular canals (in gray) with respect to the human head, as viewed from above. Dotted lines represent the LARP and RALP axes.

Fig. 2

aHIT™ device, consisting of a servo motor, which is connected to a curved track guided by bearings; the curved track is attached to a mouth piece

Fig. 3

Head angular velocity on aHIT device delivering sinusoids in the horizontal (top), LARP (middle) and RALP (bottom) planes, at frequency of 0.5Hz with peak velocity 35 °/s, frequency of 1Hz with peak velocity of 70°/s, and frequency of 2Hz with peak velocity of 140°/s. Green traces are motions in the LARP axis, blue traces are motions in the RALP axis, and red traces are velocities in the z axis, or horizontal plane.

Fig. 4

4a: Ten head impulses by clinician in each plot, 4b: Ten head impulses with aHIT device in each plot; in the horizontal (top), LARP (middle) and RALP (bottom) planes.