Conditions of Cervical Vestibular Evoked Myogenic Potentials Test to Minimize Interaural Variation / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Cervical vestibular evoked myogenic potentials (cVEMP) test has been widely used to assess the function of the saccule and inferior vestibular nerve. Electrode location and stimulating sound are important factors which might affect the test results. Today those parameters are usually selected to maximize the waveform response. In this study, we tried to find the optimal condition to minimize the range of normal value of cVEMP. SUBJECTS AND METHOD: Thirteen normal subjects (26 ears) were included. We placed electrodes at five different locations over the sternocleidomastoid muscle (SCM) and used four different stimulation sounds. Variances of parameters, including interpeak amplitude, interaural difference (IAD) and normal value were analyzed and compared. RESULTS: When using the classical condition (mid point of SCM and 500 Hz) without rectification, IAD ratio was 20.8+/-14.2% and the range of normal value was 39%. When we used 2000 Hz tone burst sound at the classical electrodes site, IAD ratio and normal value were minimized, resulting in 18.7+/-14.3% and 31% respectively. After the rectification, when using the classical condition, IAD ratio was 26.4+/-22.3% and the range of normal value was 49%. The minimum IAD ratio was measured as 17.4+/-13.7% when we used click sound at SCM at the level of mandibular angle. And the minimum normal value of 32% was measured when we used 1000 Hz tone burst sound at SCM at the level of mandibular angle. CONCLUSION: Although the condition was not optimal for maximizing the interpeak amplitude, we could alternatively use the condition to minimize the normal value.

Changes of the Video Head Impulse Test Gains by the Directions of Head Rotation at Different Target Distances and Rotation Speeds / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The conventional instrument for video head impulse test (vHIT) records the movement of the right eye only. The aim of this study was to evaluate the changes in the gain of vHIT results qdue to different directions of head rotation directons at different target distances and rotation speeds. SUBJECTS AND METHOD: Horizontal head impulse was recorded by vHIT in 20 normal subjects. vestibulo-ocular reflex (VOR) gains to the right and left directions were compared at different test conditions. Two different impulses with low (50-150 deg/sec) and high (200-300 deg/sec) peak-head-velocities were tested and the subjects were also instructed to fixate a laser dot on a screen at different distances of 60, 100, and 200 cm. Eye movements were recorded on the right eye. RESULTS: Regardless of the target distances and peak-head-velocities, the VOR gains to the rightward head rotation were significantly greater than those to the leftward head rotation. In more than 85% of normal subjects, vHIT gain to the rightward head rotation was greater than that to the leftward head rotation. Mean gain asymmetries were 2.16-3.33% and the mean interaural vHIT gain differences were 0.04-0.07. CONCLUSION: Regardless of the target distances and peak-head-velocities, the VOR gains to the rightward head rotation were significantly greater than those to the leftward head rotation. Directional asymmetry of VOR gain should be considered when interpreting vHIT results in patients with vestibular disorders.