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.