Document Detail

Head rotation during upright tilt increases cardiovagal baroreflex sensitivity.
MedLine Citation:
PMID:  17539439     Owner:  NLM     Status:  MEDLINE    
INTRODUCTION: Vestibular activation of semicircular canals has been linked to increased activity of parasympathetic neurons and has been proposed as a contributing factor to orthostatic intolerance. However, the functional consequences of head yaw rotation during orthostasis on human autonomic function have not been documented. The purpose of this study was to determine the effects of voluntary head rotation on autonomic function during upright tilt. METHODS: ECG, beat-by-beat finger arterial pressure, respiratory rate, PetCO2, and cerebral blood flow velocity were recorded in 10 healthy subjects. Subjects were studied supine and during two separate 5-min periods of upright tilt to 70 degrees with and without continuous head yaw rotation (180 degrees at 0.25 Hz). Breathing frequency was controlled strictly at 0.25 Hz during each trial and data were analyzed in both time and frequency domains. Cross-spectral techniques (transfer functions) were used to assess cardiovagal baroreflex sensitivity and dynamic cerebral autoregulation. RESULTS: Head rotation during upright tilt increased transfer function magnitude between systolic pressure and R-R interval at the low frequency (0.04-0.15 Hz) from 8.1 +/- 2.3 to 10.4 +/- 1.6 ms x mmHg(-1) (p = 0.04), but did not affect estimates of vagal-cardiac efferent activity or cerebral blood flow velocity, hemodynamic oscillations, or dynamic cerebral autoregulation. CONCLUSIONS: Increased cardiovagal baroreflex sensitivity in conjunction with preserved cerebral autoregulation suggests that head rotation during upright tilt is unlikely to trigger orthostatic instability in normal, healthy humans.
William H Cooke
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Aviation, space, and environmental medicine     Volume:  78     ISSN:  0095-6562     ISO Abbreviation:  Aviat Space Environ Med     Publication Date:  2007 May 
Date Detail:
Created Date:  2007-06-01     Completed Date:  2007-07-19     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  7501714     Medline TA:  Aviat Space Environ Med     Country:  United States    
Other Details:
Languages:  eng     Pagination:  463-9     Citation Subset:  IM; S    
Laboratory for Applied Autonomic Neurophysiology, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA.
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MeSH Terms
Baroreflex / physiology*
Blood Flow Velocity
Blood Pressure
Cerebrovascular Circulation / physiology*
Head / physiology*
Hypotension, Orthostatic / etiology*
Neck / innervation,  physiology
Posture / physiology*
Prospective Studies
Semicircular Canals / physiology*
Tilt-Table Test
Torsion Abnormality*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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