Effects of acute alcohol intoxication on human sensory orientation and postural control

Sammanfattning: Alcohol affects balance and is related to falls and injuries. Even though alcohol effects on balance and eye movement have been studied before we know less about the dose and time dependent effects and how each supportive sense to balance contributes during acute alcohol intoxication. The purpose was to investigate parallel effects of acute alcohol intoxication on balance (postural control), balance efficiency (adaptation) and its supporting senses. We included 25 healthy subjects on three different test occasions during acute alcohol intoxication of 0.06% and 0.1% blood alcohol concentration (BAC) and sober, ensured using a real time breath analyzer. Balance was evaluated with a balance force plate and a 3D-system for individual body segment detection. Spatial orientation and eye movements were measured. Foot sensation was measured when sober and the subjective feeling of intoxication was continuously followed. Instability was considerably higher at 0.1% BAC compared to 0.06% BAC and was more obvious in the medio-lateral (side to side) direction compared to the anterior-posterior (front and back). When standing balance is perturbed by vibration of the calf muscles, body movement increases. Repetition of these perturbations drives balance learning (adaptation) in sober subjects and the result is a reduction of body movement. When intoxicated however, normal adaptation is reduced or abolished. Whilst visual feedback is important for maintaining stability, it didn’t fully compensate for being intoxicated and contradictorily decreased medio-lateral stability. This could partly be explained by the impaired eye movements by intoxication. Additionally, being intoxicated increased visual dependence, i.e., the use of visual senses for positioning ourselves within the environment. Together, it illustrates that being intoxicated causes an over-reliance on visual senses which aren’t always helpful. When visual senses are absent, intoxicated subjects will rely upon foot mechanoreceptive sensation for standing balance, and change their balancing strategy by pivoting more prominently forwards and backwards around the knee level. One’s own perception of drunkenness matches slow eye movements as well as upper body movement. In summary, alcohol intoxication at levels common in society, has a widespread disturbing effect on the components of the human balance system, from each sensory system to the Central Nervous System’s integrative and cognitive processing, and also effects adaptive ability, the summation of which produces a complex attack on postural and oculomotor behaviors.