Gastrointestinal motility in space motion sickness.

Gastrointestinal (Gl) symptoms in space motion sickness (SMS) are significantly different from those in ordinary motion sickness (MS). Vomiting is sudden, often unexpected, infrequent, never prolonged and usually without nausea. Inflight bowel sounds are absent in those with SMS but present after recovery and in those not affected. Recording and tabulation of sounds was the only technique that could be used as a measure of motility during spaceflight operations. There were 17 subjects, 6 unaffected by SMS, who made ambulatory recordings pre- and inflight. With one exception, all those affected had sharply reduced sounds while those unaffected had increases or moderate reductions. The mechanism of vomiting in SMS appears to be secondary to this ileus in contrast to vomiting in ordinary MS, where the emesis center is thought to be directly triggered by the vestibular system. This ileus appears to be the only consistent and reliable indicator for SMS to date.