Artificial gravity : neurovestibular adaptation to incremental exposure to centrifugation

Abstract

(cont.) not build up adaptation, all subjects in the experimental group who completed the protocol showed signs of adaptation to the stimulus. Only one subject did not complete the five sessions, setting the drop-out rate at about 14%. If this conclusion holds true with more subjects, then a better protocol of adaptation has been unveiled.

In order to counteract the debilitating effects of the space environment on the human body, short-radius intermittent centrifugation is investigated as a possible means to expose astronauts to artificial gravity. Whereas AG is efficient in providing stimuli for muscles, bones and cardiovascular system, short-radius centrifugation elicits discomfort and illusory sensations of motion if particular head movements are made while spinning. Past research has shown that human beings can adapt to these sensations and undergo various stimuli without the disturbing effects of motion sickness, sensations of tumbling and inappropriate eye movements. However, current protocols for adaptation basically consist in repeated exposure to the discomfort. This solution is not satisfactory because the drop-out rate oscillates between 30 and 50%. Since it is not acceptable to spend days of training on astronauts who, in the end, because of this training, could become unsuitable for flight, it is of primary importance to find a training protocol that achieves adaptation without going through permanent discomfort. Incremental exposure to centrifugation is expected to be a compromised protocol to bring trainees to adaptive level without exposing them to maximum discomfort. Seven subjects were exposed to centrifugation during a five-day protocol, over which the speed of rotation was progressively increased. As in previous protocols of adaptation, subjects performed provocative head movements at all speeds. A control experiment had ten subjects exposed to centrifugation without making head turns, in order to verify to what extent the experimental conditions of measurement impact the subjects' behavior and reactions. While subjects in the control experiment did