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Interaction of semicircular canal stimulation with carotid baroreceptor reflex control of heart rateThe carotid-cardiac baroreflex contributes to the prediction of orthostatic tolerance; experimental attenuation of the reflex response leads to orthostatic hypotension in humans and animals. Anecdotal observations indicate that rotational head movements about the vertical axis of the body can also induce orthostatic bradycardia and hypotension through increased parasympathetic activity. We therefore measured the chronotropic response to carotid baroreceptor stimulation in 12 men during varying conditions of vestibulo-oculomotor stimulation to test the hypothesis that stimulation of the semicircular canals associated with head movements in the yaw plane inhibits cardioacceleration through a vagally mediated baroreflex. Carotid-cardiac baroreflex response was assessed by plotting R-R intervals (ms) at each of 8 neck pressure steps with their respective carotid distending pressures (mmHg). Calculated baroreflex gain (maximal slope of the stimulus-response relationship) was measured under 4 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 and with eye movement reduced baseline baroreflex responsiveness to the same stimulus by 30%. Inhibition of cardioacceleration during rotational head movements may have significant impact on functional performance in aerospace environments, particularly in high-performance aircraft pilots during high angular acceleration in aerial combat maneuvers or in astronauts upon return from spaceflight who already have attenuated baroreflex functions.
Document ID
20040172824
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Convertino, V. A.
(Physiology Research Branch Brooks Air Force Base, TX 78235-5117, United States)
Date Acquired
August 22, 2013
Publication Date
January 1, 1998
Publication Information
Publication: Journal of vestibular research : equilibrium & orientation
Volume: 8
Issue: 1
ISSN: 0957-4271
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
Review, Tutorial
NASA Discipline Cardiopulmonary
Review
Non-NASA Center

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