[Vestibular function of middle-aged persons exposed to 30-day head-down tilt hypokinesia]

Vestibular responses of 15 men (aged 42-50) to 30-day head-down tilt (-8 degrees) were investigated. The test subjects showed atherosclerotic symptoms and neuro-circulatory dystonia of the hypertensive type. They were exposed to the Fitzgerald-Hallpike caloric test, indirect otolithometry (eye counter-rolling reflex according to the method of successively presented images), and motion sickness according to Bryanov. In the pretest period vestibular changes were seen at the level of labyrinths and central formations (change in the nystagmic pattern, dissociation of the components of the caloric reaction, vestibular asymmetry, negative counter-rolling). During head-down tilt cupular reflexes remained essentially unaltered, except for the asymmetry and enhancement of the sensory and autonomic components of the caloric reaction. The otolith function was modified in all the test subjects. After exposure tolerance to motion sickness was not deteriorated. The time-course variations of the vestibular reactions of the tilted subjects were similar to those seen in young and healthy test subjects. The results of this simulated study suggest that vestibular reactions of crewmembers of the above age group in real space flight should be close to those of the young and healthy crewmembers.