This study investigated the effect controlling the phase of respiration on the development of nausea provoked by periodic motion at 0.2 Hz which is maximal for provocation of motion sickness.
Subjects were exposed to 60° peak–peak, pitch backwards from upright motion while viewing a video of the environment with 180° phase delay. Motion duration was a maximum of 30 min and frequency was set to match individuals' spontaneous respiration. Conditions were: A, spontaneous breathing; B, inspiration cued to begin when head-down; C, inspiration cued to begin when upright; D, inspiration cued with a ±18° desynchronizing phase drift with respect to the tilt cycle. Nausea was rated and ventilation was recorded.
Magnitudes of nausea ratings were ordered D < C < B < A (p = 0.008) and speed at which nausea developed were ordered A < B < C < D (p = 0.001).
The lower sickness ratings and prolonged times to develop nausea in B, C, D confirm that controlled breathing gives some protection against motion sickness. The differences between B, C and D in the development of nausea support the hypothesis of Von Gierke and Parker [von Gierke HE, Parker DE. Differences in otolith and abdominal viscera graviceptor dynamics: implications for motion sickness and perceived body position. Aviat Space Environ Med. 65:747–51, 1994.] that motion sickness can be provoked by a conflicting mismatch between visceral and otolithic signals of orientation to the vertical. The mismatch is greatest in the more provocative condition B because the viscera are mechanically unloaded due to exhalation when the body attains uprightness whereas mismatch is lessened by the mechanical reinforcement afforded by inspiration in (C) and by inconstant relationships between visceral and otolithic signals in (D), both of which afford better protection against sickness.