Published Online
on October 25, 2004

A more recent version of this article appeared on November 2, 2004

This Article Full Text (PDF) Data Supplement All Versions of this Article: 110/18/2931    most recent 01.CIR.0000146384.91715.B5v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fu, Q. Articles by Levine, B. D. Search for Related Content PubMed PubMed Citation Articles by Fu, Q. Articles by Levine, B. D. Related Collections Autonomic, reflex, and neurohumoral control of circulation

Submitted on December 31, 2003
Revised on May 25, 2004
Accepted on June 29, 2004

Vasoconstrictor Reserve and Sympathetic Neural Control of Orthostasis

Qi Fu MD, PhD, Sarah Witkowski MS, and Benjamin D. Levine MD^*

From the Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and the University of Texas Southwestern Medical Center at Dallas, Dallas, Tex.

^* To whom correspondence should be addressed. E-mail: BenjaminLevine{at}texashealth.org.

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° 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° 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.

Key words: vasoconstriction • nervous system, sympathetic • blood pressure

This article has been cited by other articles:

				B. Verheyden, H. Ector, A. E. Aubert, and T. Reybrouck Tilt training increases the vasoconstrictor reserve in patients with neurally mediated syncope evoked by head-up tilt testing Eur. Heart J., June 2, 2008; 29(12): 1523 - 1530. [Abstract] [Full Text] [PDF]

				C. A. Rickards, K. L. Ryan, W. H. Cooke, K. G. Lurie, and V. A. Convertino Inspiratory resistance delays the reporting of symptoms with central hypovolemia: association with cerebral blood flow Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R243 - R250. [Abstract] [Full Text] [PDF]

				Q. Fu, R. P. Shook, K. Okazaki, J. L. Hastings, S. Shibata, C. L. Conner, M. D. Palmer, and B. D. Levine Vasomotor sympathetic neural control is maintained during sustained upright posture in humans J. Physiol., December 1, 2006; 577(2): 679 - 687. [Abstract] [Full Text] [PDF]

				Q. Fu, S. Witkowski, K. Okazaki, and B. D. Levine Effects of gender and hypovolemia on sympathetic neural responses to orthostatic stress Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2005; 289(1): R109 - R116. [Abstract] [Full Text] [PDF]