The relationship between cerebral T2 hyperintensity and fixation suppression of vestibulo-ocular reflex in elderly patients with dysequilibrium symptoms

A New Suppression Index Calculation Using the Visually Enhanced Vestibulo-Ocular Reflex and Vestibulo-Ocular Reflex Suppression Paradigms in the Video Head Impulse Test

The aim of this study is to calculate the gains of the quantified visually enhanced vestibulo-ocular reflex (qVVOR) and the quantified vestibulo-ocular reflex suppression (qVORS), using a specific system to generate a visual suppression index (SI) in healthy subjects obtained through the gains of qVVOR and qVORS, and to determine the normal values of the index, as well as the influence of age and sex variables on the SI.

METHODS

This prospective observational clinical study includes 83 healthy subjects who underwent the head impulse and suppression tests (HIMP and SHIMP, respectively), qVVOR, and qVORS tests, all of the vHIT. The sinusoidal tests (qVVOR and qVORS) were conducted at an intended frequency of 0.75 Hz. The gains of these tests were calculated using a system specifically designed for this purpose. A formula for the SI was established using a ratio of the gains from these tests. Two SI values are presented: unilateral, distinct for each direction of head movement, and bilateral, representing the suppression of both sides simultaneously.

RESULTS

Mean gains for the qVVORs were 0.981 ± 0.070 and 0.978 ± 0.077 for the rightwards and leftwards qVVORs, respectively. The gains for the suppressed tests were 0.334 ± 0.112 and 0.353 ± 0.110 for the rightwards and leftwards qVORSs, respectively. A difference of 0.05 Hz was observed between the expected (0.75 Hz) and the obtained frequency of head movement, which is statistically significant (p < 0.001). The SI was 0.342 ± 0.118 for the right side (right SI) and 0.363 ± 0.117 for the left side (left SI). The bilateral SI had a mean value of 0.295 ± 0.104. No significant differences in the SI were noted according to the subject's age. The SI for women was lower than in the case of males.

CONCLUSIONS

The VVOR/VORS quantification algorithm allows for the reliable calculation of the numerical gain of qVVOR and qVORS with mathematical soundness and consistency of results. Our data support the use of a single or specific measure for direction of head movement; although significant differences exist, these differences are not clinically relevant.

Visual suppression of vestibulo-ocular reflex in patients treated with carotid artery revascularization: A potential biomarker for cerebral perfusion

BACKGROUND

Carotid endarterectomy (CEA) and carotid artery stenting (CAS) are common treatments for ischemic stroke prevention in patients with carotid artery stenosis. However, the beneficial effects of CEA/CAS for cerebral hypoperfusion due to carotid artery stenosis have yet to be fully established. As dizziness is a common symptom in patients with carotid artery stenosis, we aimed to evaluate the effects of CEA/CAS on cerebral function in patients with carotid artery stenosis, using equilibrium function tests.

METHODS

This prospective observational cohort study included 50 patients who had carotid artery stenosis and were scheduled to undergo CEA or CAS. Before CEA/CAS, we quantitatively evaluated the vestibulo-ocular reflex (VOR) and vestibular evoked myogenic potential (VEMP), as indicators of brainstem/inner ear functions related to balance, and visual suppression of VOR, as an indicator of cerebral control over the brainstem reflex related to balance. These were then compared with supratentorial cerebral blood flow (CBF). Changes in VOR, VEMP, visual suppression of VOR, CBF, and dizziness after CEA/CAS were also evaluated.

RESULTS

The visual suppression rates of VOR correlated with supratentorial CBFs before CEA/CAS (correlation coefficient = 0.47, p = 0.003). The visual suppression rates of VOR (p < 0.001) and supratentorial CBFs (p = 0.003) were improved by CEA/CAS, while VOR and VEMP did not change. Symptoms of dizziness improved after CEA/CAS.

CONCLUSIONS

Our results suggest that visual suppression of the VOR may be a novel and practical marker for the beneficial effects of CEA/CAS on supratentorial cerebral function.