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Am J Physiol Regul Integr Comp Physiol 273: R615-R622, 1997;
0363-6119/97 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 2 615-R622, Copyright © 1997 by American Physiological Society

ARTICLES

Effects of vestibular and oculomotor stimulation on responsiveness of the carotid-cardiac baroreflex

V. A. Convertino, F. H. Previc, D. A. Ludwig and E. J. Engelken
Physiology Research Branch, Brooks Air Force Base, Texas 78235, USA.

Twelve healthy men underwent measurement of their carotid-cardiac baroreflex response during varying conditions of vestibulo-oculomotor stimulation to test the hypothesis that vestibular and/or oculomotor stimulation associated with head movements in the yaw plane inhibit baroreflex control of heart rate. We assessed the carotid-cardiac baroreflex response by plotting R-R intervals (in milliseconds) at each of eight neck pressure steps with their respective carotid distending pressures (in millimeters mercury). Baroreflex sensitivity was measured under four experimental conditions: 1) sinusoidal whole body yaw rotation of the subject in the dark without visual fixation (combined vestibular-oculomotor stimulation); 2) yaw oscillation of the subject while tracking a small head-fixed light moving with the subject (vestibular stimulation without eye movements); 3) subject stationary while fixating on a small light oscillating in yaw at the same frequency, peak acceleration, and velocity as the chair (eye movements without vestibular stimulation); and 4) subject stationary in the dark (no eye or head motion). Head motion alone reduced baseline baroreflex responsiveness by 30% from 3.8 +/- 0.5 to 2.6 +/- 0.5 ms/mmHg. Eye motion alone also reduced the baroreflex response by 13% (0.5 ms/mmHg) to 3.3 +/- 0.5 ms/mmHg. During head motion, the effect of eye motion was negligible (2.7 +/- 0.4 ms/mmHg). These results suggest that vestibular stimulation associated with head movements in yaw inhibits vagally mediated baroreflex control of heart rate, whereas oculomotor stimulation is less of a factor and only in the absence of vestibular stimulation.


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