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要旨:
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.
