Cardiovascular responses elicited by linear acceleration in humans.

Although activation of otolith receptors is known to elicit cardiovascular responses in animals, it is unclear whether vestibular stimulation can evoke changes in blood pressure and heart rate (which are independent of motion sickness) in humans. In the present study, ten normal subjects and three patients with profound bilateral reduction in vestibular function, who were seated upright with the torso aligned with the gravitation vector, were subjected to fore, aft, or lateral linear acceleration (approximately 0.2 g, attaining approximately 2 m/s in 900 ms, and decelerating for 3 s at 0.07 g). The head was fixed in the upright position, pitched maximally downward (chin on chest) or maximally backward (approximately 40-50 degrees) during the accelerations. In normal subjects, all directions of linear acceleration produced an average increase in systolic blood pressure of approximately 7-9 mm Hg and a rapid decrease in the interval between R-waves of the electrocardiogram of 14-27 ms; these responses persisted for only a few seconds. In contrast, the cardiovascular responses in patients with vestibular dysfunction were much smaller (e.g., the maximal pressor response to forward linear acceleration was <4 mm Hg). Head position during accelerations had little effect on the cardiovascular responses that were elicited in the population of normal subjects. However, although the population response was similar across directions of acceleration and head positions, many individuals exhibited larger cardiovascular changes during some stimulus conditions than during others. These data suggest that vestibular stimulation during linear accelerations can produce cardiovascular responses in humans and support the hypothesis that the vestibular system contributes to maintaining stable blood pressure during movement and changes in posture.