Reducing motion sickness during simulated astronaut post-spaceflight water landings using anticipatory cues or postural control.

Abstract

Astronauts returning to Earth after adapting to microgravity are susceptible to Entry Motion Sickness while they are readapting to 1G. We assessed the efficacy of two countermeasures in reducing the incidence and severity of motion sickness symptoms using a series of ground-based analogs meant to simulate the scenario of a post-spaceflight water landing: one hour of habituation to 2Gx centrifugation followed by up to an hour of passive wave-like motion at 1 G. The first countermeasure provided rich visual cues of current self-motion overlaid with anticipatory cues of self-motion one second in the future, presented in virtual reality with the subject's head and torso restrained. The second countermeasure encouraged active postural control by instructing subjects to keep their unrestrained head aligned with Earth-vertical during wave-like motion. Both groups were compared to a control group that did not receive any Earth-fixed visual cues and had the head and torso restrained. As a secondary metric, we also considered how these countermeasures impacted vestibular-mediated standing balance performance. While the multi-symptom Motion Sickness Questionnaire scores did not significantly differ between the three groups, the development of gastrointestinal symptoms was diminished for the anticipatory visual cues group compared to the control ( $p=0.03$ ) and active posture ( $p=0.02$ ) groups. Additionally, the anticipatory cues group was significantly more likely to tolerate the full period of wave-like motion (90% of subjects with cues vs. 33% without, $p=0.017$ ). Finally, across all three groups, subjects had significantly increased sway ( $p=0.0002$ ) following wave-like motion, which returned to a baseline equivalency after an hour of recovery. Enabling the brain to form a better expectation of sensory stimulation, anticipatory cues reduce the incidence of nausea, which may be beneficial for motion sickness in astronauts, as well as here on Earth.