Adaptation to motion sickness from torso rotation affects symptoms from supine head nodding.

INTRODUCTION: Space motion sickness affects more than 50% of astronauts. Adaptation to one kind of nauseogenic motion can affect the response to another. We hypothesized that repeated exposure to torso rotation (TR) would diminish motion sickness (MS) due to supine head nodding (HN), a ground-based analogue for space sickness. METHODS: During TR, standing subjects swept their gaze back and forth between two targets located 135 degrees to either side of straight ahead. For HN, the subject lay supine on a platform with his/her head and neck hanging over the edge. The head was pitched back and forth between the horizontal position and rotated back as far as possible. MS was quantified in 5 male and 20 female subjects using numerical estimates of discomfort and a more detailed questionnaire. Susceptibility to TR and HN was determined on three occasions for each stimulus. At least 1 mo separated any two tests. Subjects were exposed to TR once a day for 7 consecutive days 1 mo after the final control session. Within 24 h of the seventh session, and 1 mo later, susceptibility to HN was evaluated again. RESULTS: There was a significant decrease in MS susceptibility during repeated exposure to TR (time to stop 17.7 min on Day 1, 31.8 min on Day 7). In contrast, there was a significant increase in MS susceptibility to HN after repeated exposure to TR (mean time to stop 11.7 min before TR, 9.5 min after). Susceptibility to HN was back to normal (time to stop 11.4 min) 1 mo later. DISCUSSION: Subjects can adapt to TR by repeated exposure. At the same time, susceptibility to HN increases. Strategies for pre-adaptation to space motion sickness need to be chosen carefully as they could actually be counterproductive.

Motion sickness provoked by torso rotation predicts that caused by head nodding.

INTRODUCTION: Some degree of space motion sickness is experienced by at least 50% of astronauts early in flight. It is unpleasant and could be hazardous during an extravehicular activity or urgent re-entry in the first few days after launch. To date, there is no reliable ground-based test to predict who will be affected. METHODS: Head nodding (HN) in a supine position was used as a model of motion sickness caused by an unusual gravito-inertial environment. Torso rotation (TR) was used as a means of predicting susceptibility to development of symptoms caused by HN. Motion sickness was quantified in 26 subjects (5 men, 21 women, age range 18-52) using numerical estimates of discomfort and a more detailed questionnaire. Susceptibility to TR and HN was determined on three occasions for each stimulus, with test sessions at least 1 mo apart. RESULTS: Subjects reached their stopping point at a mean duration of 13.72 min +/- 1.06 CI) for TR and 11.31 min (+/- 0.38 CI) for HN. When susceptibility to HN was plotted as a function of susceptibility to TR and a linear regression line was added, the correlation coefficient was 0.744. DISCUSSION: Susceptibility to TR predicts susceptibility to HN. The method may be useful as a screening test for potential astronauts.