Document Detail

Time course analysis of baroreflex sensitivity during postural stress.
MedLine Citation:
PMID:  16861691     Owner:  NLM     Status:  MEDLINE    
Postural stress requires immediate autonomic nervous action to maintain blood pressure. We determined time-domain cardiac baroreflex sensitivity (BRS) and time delay (tau) between systolic blood pressure and interbeat interval variations during stepwise changes in the angle of vertical body axis (alpha). The assumption was that with increasing postural stress, BRS becomes attenuated, accompanied by a shift in tau toward higher values. In 10 healthy young volunteers, alpha included 20 degrees head-down tilt (-20 degrees), supine (0 degree), 30 and 70 degrees head-up tilt (30 degrees, 70 degrees), and free standing (90 degrees). Noninvasive blood pressures were analyzed over 6-min periods before and after each change in alpha. The BRS was determined by frequency-domain analysis and with xBRS, a cross-correlation time-domain method. On average, between 28 (-20 degrees) to 45 (90 degrees) xBRS estimates per minute became available. Following a change in alpha, xBRS reached a different mean level in the first minute in 78% of the cases and in 93% after 6 min. With increasing alpha, BRS decreased: BRS = -10.1.sin(alpha) + 18.7 (r(2) = 0.99) with tight correlation between xBRS and cross-spectral gain (r(2) approximately 0.97). Delay tau shifted toward higher values. In conclusion, in healthy subjects the sensitivity of the cardiac baroreflex obtained from time domain decreases linearly with sin(alpha), and the start of baroreflex adaptation to a physiological perturbation like postural stress occurs rapidly. The decreases of BRS and reduction of short tau may be the result of reduced vagal activity with increasing alpha.
Berend E Westerhof; Janneke Gisolf; John M Karemaker; Karel H Wesseling; Niels H Secher; Johannes J van Lieshout
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2006-07-21
Journal Detail:
Title:  American journal of physiology. Heart and circulatory physiology     Volume:  291     ISSN:  0363-6135     ISO Abbreviation:  Am. J. Physiol. Heart Circ. Physiol.     Publication Date:  2006 Dec 
Date Detail:
Created Date:  2006-11-08     Completed Date:  2007-01-16     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  100901228     Medline TA:  Am J Physiol Heart Circ Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  H2864-74     Citation Subset:  IM    
BMEYE, Academic Medical Centre, University of Amsterdam, NL-1105 AZ Amsterdam, The Netherlands.
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MeSH Terms
Adaptation, Physiological
Baroreflex / physiology*
Blood Pressure / physiology
Dizziness / physiopathology*
Head-Down Tilt / physiology
Posture / physiology*
Stress, Physiological
Time Factors
Vagus Nerve / physiology

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

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