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Investigation of Vestibular adaptation to changing gravity levels on earth


Nooij,  SAE
Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Nooij, S., Bos, J., & Ockels, W. (2004). Investigation of Vestibular adaptation to changing gravity levels on earth. Talk presented at XXIII. International Congress of the Bárány Society. Paris, France.

Background: During the first days in space 50-80 of the astronauts suffer from the Space Adaptation Syndrome (SAS). The symptoms of SAS, like nausea and dizziness, are especially provoked by head movements. Although it is generally agreed that the vestibular system is involved in causing SAS, no distinct clue has been found to its aetiology, the individual's susceptibility, and its predictability. Susceptibility to SAS does not correlate with susceptibility to motion sickness on earth. However, astronauts have mentioned close similarities between the symptoms of SAS and the symptoms they experienced after a 3G centrifuge run on earth (Sickness Induced by Centrifugation, SIC). This suggests that a gravity transition from 3 to 1G provokes the same effects as a transition from 1 to 0G, implicating a general vestibular adaptation mechanism to changing G-levels. Objectives: This study aims to further the insight in the process of vestibular adaptation to G-transitions. Two important parameters are the perception of body motion and attitude during the adaptation process. A second objective is to investigate the correlation between susceptibility to SAS and SIC. Methods: During several space missions the correlation between susceptibility to SIC and SAS has been investigated [1]. Since head movements are shown to be provocative, this provocativeness was taken as an indicator for SIC and SAS susceptibility. Susceptibility to SIC was assessed after a 1 h centrifuge run at 3Gx, susceptibility to SAS during the mission. Within the framework of the 2004 Delta Mission, vestibular adaptation was addressed for 2 astronauts in four vestibular function tests carried out about a 1h 3Gx centrifuge run (-1h, +0h, +2h, +4h). The tests included motion perception and sickness ratings, stabilometry in a tilting room, subjective vertical measurements in a tilting chair, and eye movement registrations (Listing's plane). Results: At present, a total of 9 astronauts were tested both in the centrifuge and in space. We found a positive correlation between susceptibility to SIC and SAS: 3 astronauts were both susceptible to SIC and to SAS, 6 were not (i.e. no cross-findings have been observed yet). The vestibular function tests showed that postural stability was decreased after the centrifuge run in one SIC-susceptible subject and unaffected in the other non-susceptible subject. So far we have not observed a clear effect of the centrifuge run on tilt perception. Conclusion: The positive correlation between susceptibility to SIC and to SAS is in agreement with the hypothesis that SIC and SAS share the same underlying mechanism. This makes long duration centrifugation a valuable tool for investigating vestibular adaptation to G-transitions on earth. The gained knowledge can be implemented in a general model of vestibular adaptation. The vestibular tests showed that several vestibular driven processes are affected by the gravity transition. However, further testing is needed to identify key adaptation parameters.