Collecting Normative Data for Video Head Impulse Testing, Horizontal and Vertical Measures

A new test of vestibular function, video head impulse testing (vHIT), evaluates function of the anterior and posterior vertical semicircular canals as well as the horizontal canals. Our goal was to collect normative data for vHIT in both horizontal and vertical planes. Horizontal data was compared to bithermal calorics. Data was collected from 19 participants with normal auditory function and no complaints regarding dizziness or balance. All occulomotor results were normal. Bithermal water caloric irrigations revealed an average unilateral weakness and directional preponderance of < 10%. For vHIT, average velocity gains (comparison of head velocity to compensatory eye velocity) were calculated for right lateral and left lateral maneuvers using instantaneous velocity measurements at 40, 60, and 80 ms and using the velocity regression measurement from 1-100 ms. Average instantaneous velocity gain at 60 ms was 1.175 for right lateral and 1.159 for left lateral. Average velocity regression gain (1-100 ms) was 1.147 for right lateral and 1.172 for left lateral, with an average gain asymmetry of 2.6%. The RALP average velocity gain, based on the velocity regression measurement from 1-100 ms, was 1.514 for right anterior and 1.665 for left posterior, with an average gain asymmetry of 7.26%. The LARP average velocity gain, based on the velocity regression measurement from 1-100 ms, was 0.923 for left anterior and 0.876 for right posterior, with an average gain asymmetry of 7.11%. Unlike with laterals, consistent vertical responses were more difficult to obtain. Contributing factors are camera slippage, inexperience, technique, and the constrained eye movement in the vertical plane.