Effects of the head impulses that are repeated with different time intervals on video head impulse test (VHIT) measurements

Video head impulse test (vHIT) is a new method for the assessment of vestibular system. The test technique may vary between different vHIT devices and technicians. Time interval that should be left between repetitive head impulses is not clear. Besides, the effect of that time interval on measurement results is not known. The aim of this study is to investigate the effects of the time interval between repetitive head impulses on vHIT measurements. The results of this study will also allow the detection of normative data of our clinic that can be used as reference values in the assessment of patients. The study was conducted with twenty-one healthy volunteers with no ear complaints, at Baskent University Department of Otorhinolaryngology. vHIT was applied to the volunteers and the tests were repeated with leaving 2 sec, 5 sec and 10 sec between repetitive head impulses. Instantaneous vestibuloocular reflex (VOR) gains at 40 msec, 60 msec and 80 msec for lateral semi-circular channels and average gain and gain asymmetry values were determined for all semi-circular channels. The data from measurements were compared and the effects of repetitive head impulses with 2 sec, 5 sec and 10 sec time gaps on VOR gains were assessed. Time period between head impulses were shown to have no statistically significant effect on instantaneous (at 40 msec, 60 msec and 80 msec) and average gains and gain asymmetry values for the lateral semi-circular channels (p>0.05). 80 msec instantaneous gain and average gain values can be used for the assessment of VOR responses of lateral semi-circular channels. There were differences among the average gain values between 2 sec, 5 sec and 10 sec measurements of the right anterior (p=0.001) and left posterior (p=0.034) semi-circular channels. Other results that belong to the vertical channels showed no statistically significant significance between 2 sec, 5 sec and 10 sec measurements (p>0.05). vHIT is a non-invasive test that can relatively be quickly applied in adults. Time intervals more than 2 sec between repetitive head impulses have no significant effect on the lateral semi-circular channel measurements. Vertical channel measurements may be affected from the time interval between repetitive head impulses. However, measurements are subject to errors that are related to the test technique.