Effects of vestibular and oculomotor stimulation on responsiveness of the carotid-cardiac baroreflex.
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.
Convertino
V A
VA
Physiology Research Branch, Brooks Air Force Base, Texas 78235, USA.
Previc
F H
FH
Ludwig
D A
DA
Engelken
E J
EJ
D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D002339:Carotid Arteries / Q000294:innervation*; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009801:Oculomotor Muscles / Q000502:physiology*; D010812:Physical Stimulation; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000502:physiology*