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Zusammenfassung:
BACKGROUND : In previous studies with a total of 10 astronauts, we demonstrated that symptoms of the Space Adaptation Syndrome (SAS) can be induced by long duration centrifugation on earth. After a 60 min. exposure to hypergravity (+3Gx) in a human centrifuge, about 50% of the astronauts, but also of non- astronaut subjects, experienced SA S-like symptoms at 1G again: nausea, dizziness and/or visual illusions, mainly provoked by head movements. This correspondence suggests that vestibular adaptation is required for any kind of gravity transition within the gravitational continuum, and that any G-reduction may elicit symptoms of SAS. This would have clear implications for G-transitions occurring during space flight (use of artificial G, planet's gravity). To ga in more insight in the nature of the stimulus causing the SAS-like symptoms, a ground based centrifuge study was recently performed, focusing on the effects of G-level and duration of exposure. METHODS : Twelve healthy male subjects each und erwent four different centrifuge r uns varying in dose: 45 min. at 2 and 3G, and 90 min at 2 and 3G. A standardized head movement test was used to measure the after- effect of each centrifuge condition on head angular position and velocity. Subjects made a maximum of 40 head movements in yaw and pitch as part of a base-line and four post run tests. The level of discomfort caused by the head movements (nau sea) was rated on an 11-pont scale. Kennedy's Simulator Sickness Questionnaire was used to assess the overall symptom severity after each centrifuge run. RESULTS : Preliminary results show large differences between the effect of the four centrifuge conditions on movement characteristics. Generally, head movement velocity was inversely related to symptom severity: susceptible subjects performed the head movements more slowly after the hypergravity exposure than in the pretest. Pitch movements were rated provocative whereas yaw movements were not. Although symptom severity differed between subjects, all subjects reported that the effects of both 3G runs exceeded those of the 2G runs. Furthermore, symptoms were more severe after the 90 min exposure at 3G than after the 45 min exposure. This was supported by the total symptom scores. CONCLUSIONS : With this study we have thus been able to quantify the effect of a gravity-reduction following long duration centrifugation on SAS development, depending on the G-level difference and exposure duration.
