Clinical Implication of High VOR Gain in Slow Harmonic Acceleration / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The purpose of this study was to verify if high vestibulo-ocular reflex (VOR) gain in slow harmonic acceleration (SHA) test can be considered as a hallmark of a distinct disease entity. We hypothesized that patients with high VOR gain in the SHA test can be classified as a distinct disease group and looked for evidence that can support this hypothesis. SUBJECTS AND METHOD: For this study, 306 patients who had undergone a rotation chair test were enrolled. We checked other VOR measurements (caloric test and step velocity) and clinical manifestation of the patients with high gain in SHA (HG group). The data were compared to those of the migraine associated vertigo (MAV), benign recurrent vertigo (BRV) and psychogenic dizziness (PsyD). RESULTS: An abnormally long time constant and a large response to the caloric test were found more frequently in the patient group with high gain in SHA. The incidence of high gain in SHA was significantly higher in MAV, BRV and PsyD. The clinical manifestation of HG group was not distinguishable from the effects of BRV and PsyD. But MAV was different from HG group. CONCLUSION: We failed to find any evidence that the patients with high gain in the SHA could be classified as a distinct disease group. It seems that high gain is not merely a non-specific or incidental finding but a reproducible finding that reflects an aspect of the subject's vestibular function. Also, the high gain in SHA is more suggestive of BRV or PsyD than MAV.

Effects of Flight Training on Vestibuloocular Reflex in Student-pilots

The aim of this study was to investigate the effect of flight training on vestibuloocular reflex (VOR) induced by rotational chair test in student-pilots. The study group was divided into followings; control, prepilot (student-pilots before flight training), and student-pilot (after training). Gain, phase and symmetry of eye movement induced by sinusoidal harmonic acceleration with frequencies of 0.01, 0.02, 0.04, 0.08, 0.16, 0.32 Hz. Gain and phase did not show any significant differences between control and student-pilots before flight training in all frequencies. But there were significant gain differences between control and student-pilots after flight training in 0.01, 0.04, 0.08 frequencies. And phase showed significant differences between before and after flight training in student-pilots in 0.01, 0.04 Hz. These results suggest that the flight training would be attributable to modulate the vestibular function in the student-pilots.

Comparative Study of the Sinusoidadal Harmonic Acceleration Test andthe Caloric Test in Peripheral Vestibular Disorders / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The shinusoidal harmonic acceleration (SHA) test is known to be useful for differentiating peripheral and central disorders and monitoring the progress of vestibular diseases. However, it is not fully known how SHA test results correlate with the degree of caloric response, which have been widely used and accepted as a standard test in evaluating vestibular functions. This study was designed to investigate the relationship between SHA test and caloric test in an attempt to further elucidate the clinical significance of SHA test. MATERIALS AND METHODS: Fifty-four patients who were diagnosed with peripheral vestibular disorder at Asan Medical Center participated in this study. All patients underwent caloric tests and SHA tests. The results of both tests were compared. RESULTS: The present study reveals that the results of the SHA test in peripheral vestibular disorder are correlated with those of the caloric test, that is, patients with unilateral canal paresis in the caloric test also tend to show phase leads at lower frequency and low response gain in the SHA test. CONCLUSION: This study could be used as a basis for further studies and for the clinical use of the SHA test.

Plasticity of Vestibulo-ocular Reflex in Slow Harmonic Acceleration Test / 대한이비인후과학회지

The results of rotation chair test were known to variable by many parameters such as eye opening and alertness, etc. The situational change in rotation chair test must be considered to interpretation of its result. But in Korea, there were no reports or articles about parameters which influence the result of rotation chair test. So, we assumed that eye opening and alertness were main parameters and took rotation chair test in neurotologically normal subjects. For evaluation of the effect of eye-open or eye-closure and alertness on the rotational vestibular stimulation, we have taken sinusoidal harmonic acceleration test in 30 otoneurologically normal subjects. The maximal slow phase eye velocity, gain and asymmetry were obtained and compared with each other in four different conditions with properly fixed conditions such as in darkness and 0.05Hz frequency. At least five minutes interval was given between the tests and recalibrations were done before each tests. The results of this test were as follows. 1) Vestibular-ocular reflex(VOR) changes according to eye open or closure. In cases of examinees which were given alerting tasks, larger gain was obtained with eyes opened than with eyes closed, and that was statistically significant(p0.05). 2) VOR changes according to alertness. In cases of examinees which opened their eyes, larger gain was obtained with alerting tasks than without alerting tasks, and that was statistically significant(p<0.05). In cases of examinees which closed their eyes, larger gain was obtained with alerting tasks than without alerting tasks, and that was statistically significant(p<0.05). 3) There was no significant changes of asymmetry according to the conditions. Therefore, from above results, we recommend the condition in which examinees open their eyes and be given alerting tasks as one of the optimal condition in sinusoidal harmonic acceleration test.

Vestibulo-Ocular Reflex according to the Change of Angular Acceleration in Sinusoidal Harmonic Acceleration Test / 대한이비인후과학회지

We investigated the vestibulo-ocular reflex which is followed by the change of angular acceleration in sinusoidal harmonic acceleration test. 20 normal volunteers with no evidence of previous otoneurologic disease were tested. The maximal slow phase eye velocity, gain and asymmetry were obtained in five different amplitudes of rotation, 30degrees, 60degrees, 90degrees, 120degrees and 150degrees with properly fixed conditions such as darkness and the frequency of rotation fixed at 0.05Hz. During each test, we asked the examinees to be alert and keep the eyes open. At least 5 minute interval was given between the tests and recalibrations were done before each test. The results of this test were as follows. 1) The maximal slow phase eye velocities were gradually increased according to the increment of the amplitudes of rotation with the statistical significances(p0.05). Therefore, from the above results, sinusoidal harmonic acceleration test with the frequency fixed at 0.05Hz, gain is higher when the amplitude of rotation is smaller and the pattern of the nystagmus is more evident when the amplitude of rotation is bigger. But The authors conclude that in order to get the results which are statistically significant, the amplitude of rotation should be lower than 90degrees.