The effects of repeated optokinetic stimulation on human autonomic function.

Numerous animal studies have suggested that the vestibular system modulates respiratory and cardiovascular function. However, relatively few studies have examined vestibular-autonomic interaction in humans. In this study we investigated the effects of repeated horizontal (clockwise or anticlockwise) optokinetic stimulation on systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse and latency to circularvection (CV) in humans, and compared the effects with those of repeated exposure to a stationary visual stimulus. Although all subjects experienced CV, neither mean SBP, DBP or pulse differed significantly between the clockwise/anticlockwise optokinetic stimulation and no optokinetic stimulation conditions. However, SBP and DBP changed significantly over the 20 trials in each test session, even when there was no optokinetic stimulation (P < 0.001 in each case). These results suggest that while horizontal optokinetic stimulation does not significantly affect SBP, DBP or pulse in humans, changes in these variables can be induced by trial repetition itself, even when no optokinetic stimulation occurs.