Respiratory impact on motion sickness induced by linear motion.

Motion sickness incidence (MSI) for vertical sinusoidal motion reaches a maximum at 0.167 Hz. Normal breathing frequency is close to this frequency. There is some evidence for synchronization of breathing with this stimulus frequency. If this enforced breathing takes place over a larger frequency range (0.05-0.8 Hz) and whether this contributes to the high MSI at 0.167 Hz was investigated. Sinusoidal motion (amplitude 0.3 g, frequencies 0.05, 0.1, 0.2, 0.4, and 0.8 Hz) was applied. Nausea with the MISC-scores and respiratory parameters, such as tidal volume, respiratory frequency, end-tidal CO(2) (PetCO(2)), and respiratory minute volume, were measured. Control conditions included rest and the hyperventilation provocation test. The nausea scores were highest at 0.2 Hz. With increasing frequencies the respiratory minute volume increased and the PetCO(2) values decreased. The hyperventilation provocation test did not cause nausea. The main conclusion is that the high MSI at 0.167 Hz is not due to enforced breathing, since enforced breathing still increases with higher stimulus frequencies.