Regulation of muscle sympathetic nerve activity after bed rest deconditioning

James A. Pawelczyk, Julie H. Zuckerman, C. Gunnar Blomqvist, Benjamin D. Levine

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

Cardiovascular deconditioning reduces orthostatic tolerance. To determine whether changes in autonomic function might produce this effect, we developed stimulus-response curves relating limb vascular resistance, muscle sympathetic nerve activity (MSNA), and pulmonary capillary wedge pressure (PCWP) with seven subjects before and after 18 days of -6° head-down bed rest. Both lower body negative pressure (LBNP; -15 and -30 mmHg) and rapid saline infusion (15 and 30 ml/kg body wt) were used to produce a wide variation in PCWP. Orthostatic tolerance was assessed with graded LBNP to presyncope. Bed rest reduced LBNP tolerance, from 23.9 ± 2.1 to 21.2 ± 1.5 min, respectively (means ± SE, P = 0.02). The MSNA-PCWP relationship was unchanged after bed rest, though at any stage of the LBNP protocol PCWP was lower, and MSNA was greater. Thus bed rest deconditioning produced hypovolemia, causing a shift in operating point on the stimulus-response curve. The relationship between limb vascular resistance and MSNA was not significantly altered after bed rest. We conclude that bed rest deconditioning does not alter reflex control of MSNA, but may produce orthostatic intolerance through a combination of hypovolemia and cardiac atrophy.

Original languageEnglish (US)
Pages (from-to)H2230-H2239
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume280
Issue number5 49-5
DOIs
StatePublished - May 2001

All Science Journal Classification (ASJC) codes

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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