Document Detail


Vasoconstrictor reserve and sympathetic neural control of orthostasis.
MedLine Citation:
PMID:  15505093     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
BACKGROUND: We tested the hypothesis that individual variability in orthostatic tolerance is dependent on the degree of neural and vasomotor reserve available for vasoconstriction. METHODS AND RESULTS: Muscle sympathetic nerve activity (MSNA) and hemodynamics were measured in 12 healthy young volunteers during 60 degrees head-up tilt (HUT), followed by a cold pressor test (CPT) in HUT. Orthostatic tolerance was determined by progressive lower-body negative pressure (LBNP) to presyncope. The same protocols were performed randomly in normovolemic and hypovolemic conditions. We found that mean arterial pressure increased and stroke volume decreased, whereas heart rate (HR), MSNA, and total peripheral resistance (TPR) increased during HUT (all P<0.01). Application of the CPT in HUT did not increase HR or decrease stroke volume further but elevated mean arterial pressure (P<0.01) and increased MSNA and TPR in some subjects. There was a positive correlation between the time to presyncope from -50 mm Hg LBNP (equivalent to 60 degrees HUT alone) and the changes in MSNA produced by the CPT under both conditions (r=0.442, P=0.039). Those who had greater increases in MSNA had greater increases in TPR during the CPT and longer time to presyncope (both P<0.05). One subject had dramatic increases in MSNA but small increases in TPR during the CPT, which indicates a disassociation between sympathetic activity and the increase in peripheral vascular resistance. CONCLUSIONS: These results support our hypothesis and suggest that vasoconstrictor capability is a contributor to orthostatic tolerance in humans. Vasoconstrictor reserve therefore may be one mechanism underlying individual variability in orthostatic intolerance.
Authors:
Qi Fu; Sarah Witkowski; Benjamin D Levine
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2004-10-25
Journal Detail:
Title:  Circulation     Volume:  110     ISSN:  1524-4539     ISO Abbreviation:  Circulation     Publication Date:  2004 Nov 
Date Detail:
Created Date:  2004-11-02     Completed Date:  2005-09-30     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0147763     Medline TA:  Circulation     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2931-7     Citation Subset:  AIM; IM    
Affiliation:
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and the University of Texas Southwestern Medical Center at Dallas, Dallas, Tex 75231, USA.
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MeSH Terms
Descriptor/Qualifier:
Adult
Blood Pressure / physiology
Cardiac Output / physiology
Cold Temperature / diagnostic use
Female
Genetic Variation
Heart Rate / physiology
Hemodynamics / physiology*
Humans
Hypotension, Orthostatic / physiopathology
Hypovolemia / physiopathology
Lower Body Negative Pressure
Male
Posture / physiology*
Stroke Volume / physiology
Supine Position / physiology
Sympathetic Nervous System / physiology*
Tilt-Table Test
Vascular Resistance / physiology
Vasoconstriction / physiology*
Vasomotor System / physiology*

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


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