Acute Alcohol Intake Impairs the Velocity Storage Mechanism and Affects Both High-Frequency Vestibular-Ocular Reflex and Postural Control

Abstract

Background: Acute alcohol intake is known to cause gait instability, dizziness, and lack of psychomotor coordination. Previous studies demonstrated the positive effects of alcohol on the oculomotor system and the low-frequency vestibulo-ocular reflex (VOR). However, the low-frequency VORs is a rather un-physiologic stimulation, and the reported explanations regarding the relations between the alcohol-induced VOR changes and posture control are inconsistent.

Objective: The present study evaluates how acute alcohol intake affects more physiologic mid- to high-frequency VORs, postural control, and elucidates the connection between the VOR and posture control after alcohol intake.

Methods: A total of 31 healthy volunteers participated. Each participant received calculated amounts of alcohol drinks according to their body weight and genders with the targeted blood alcohol content (BAC) level of 0.05% using the Widmark formula. A vestibular test battery composed of posturography, video head impulse test, rotatory chair test (slow harmonic acceleration (SHA) and step velocity), and subjective visual vertical/horizontal tests (SVV/SVH) were conducted twice in alcohol-free condition (no alcohol intake within 24 h) and acute alcohol condition.

Results: Acute alcohol intake decreased stability scores in all NS/EO (normal stability-eyes open), NS/EC (normal stability- eyes closed), PS/EO (perturbed stability-eyes open), and PS/EC (perturbed stability-eyes closed) conditions. High-frequency VOR gains decreased, but mid-frequency VOR gains were not significantly affected by alcohol intake. In addition, time constants were reduced significantly after alcohol ingestion in both clockwise and counter-clockwise rotation. Phase lead in SHA test and SVV/SVH was not affected by alcohol intake.

Conclusion: Acute alcohol intake affected postural stability, high-acceleration head impulses, and the velocity storage mechanism.

Keywords: alcohol; postural balance; velocity storage mechanism; vestibulo-ocular reflex (VOR).

Figure 1

Effect of alcohol on mid-frequency VOR and time constant. (A) In the SHA test, VOR gains were not different in healthy condition and in acute alcohol condition in most frequencies. However, in 0.32 Hz sinusoidal rotation, VOR gain increased from 0.52 ± 0.02 to 0.60 ± 0.02 after acute alcohol intake (p = 0.008). (B) The number of participants with phase lead increased after alcohol consumption, but the change was not statistically significant (p = 0.209). (C) In step velocity test, time constants reduced significantly after alcohol intake in both clockwise (from 16.43 ± 6.80 s to 12.70 ± 3.06 s; p = 0.008) and counter-clockwise rotation (from 14.73 ± 4.31 s to 12.37 ± 2.95 s; p = 0.003). * Significance at p < 0.05 after false discovery rate adjusted.