Normal Variations of Video Head Impulse Test in Adult Populations at Peak Head Velocity of Below 150 Degrees/Second

The preferred peak head velocities for video head impulse test (vHIT) are over 150 degrees/second (°/s) but in some patients, reaching these velocities isn't possible. This study aims to evaluate the variations of the vHIT at lower peak head velocities in healthy adult populations. Subjects were 100 healthy adults (20 to 80 years old) with no history of dizziness, vertigo, imbalance, or otologic, neurologic, orthoscopic, or ocular disorders. Each semicircular canal (SC) was evaluated by twenty impulses at peak head velocities of below 150°/s. The impulses were unpredictable in aspects of time, direction, and velocity. The VOR gain for left and right horizontal, left anterior, right posterior, left posterior, and right anterior SCs were 0.94 ± 0.108, 1.01 ± 0.110, 0.84 ± 0.091, 0.74 ± 0.070, 0.81 ± 0.088, and 0.85 ± 0.130, respectively. The Age didn't affect the VOR gain or presence of covert and overt catch-up saccades (CSs). The right ear had higher VOR gain except for posterior SC. The 43.15% and 45.54% trials had covert and overt CSs. There was no significant difference between the vHIT gains in different peak head velocities. However, the number of covert and overt CSs was increased in lower peak head velocities. At lower peak head velocities, the VOR gains are close to 1.0 with more covert and overt CSs in anterior and posterior than horizontal SCs. Considering the presence of many CSs especially in the anterior and posterior SCs, the CSs should be interpreted with caution. It may be better to rely more on VOR gains in the interpretation of velocities below 150°/s.