Resting Sympathetic Baroreflex Sensitivity in Subjects with Low and High Tolerance to Central Hypovolemia Induced by Lower Body Negative Pressure

Abstract

Central hypovolemia elicited by orthostasis or hemorrhage triggers sympathetically-mediated baroreflex responses to maintain organ perfusion; these reflexes are less sensitive in patients with orthostatic intolerance, and during conditions of severe blood loss, may result in cardiovascular collapse (decompensatory or circulatory shock). The ability to tolerate central hypovolemia is variable and physiological factors contributing to tolerance are emerging. We tested the hypothesis that resting muscle sympathetic nerve activity (MSNA) and sympathetic baroreflex sensitivity (BRS) are attenuated in male and female subjects who have low tolerance (LT) to central hypovolemia induced by lower body negative pressure (LBNP). MSNA and diastolic arterial pressure (DAP) were recorded in 47 human subjects who subsequently underwent LBNP to tolerance (onset of presyncopal symptoms). LT subjects experienced presyncopal symptoms prior to completing LBNP of 60mm Hg, and subjects with high tolerance (HT) experienced presyncopal symptoms after completing LBNP of 60mm Hg. Contrary to our hypothesis, resting MSNA burst incidence was not different between LT and HT subjects, and was not related to time to presyncope. BRS was assessed as the slope of the relationship between spontaneous fluctuations in DAP and MSNA during 5 min of supine rest. MSNA burst incidence/DAP correlations were greater than or equal to 0.5 in 37 subjects (LT: n = 9; HT: n = 28), and BRS was not different between LT and HT ( 1.8 0.3 vs. 2.2 0.2 bursts (100 beats) 1 mm Hg 1, p = 0.29). We conclude that tolerance to central hypovolemia is not related to either resting MSNA or sympathetic BRS.

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Document Details

Document Type
Technical Report
Publication Date
Jun 01, 2014
Accession Number
ADA614382

Entities

People

  • Carmen Hinojosa-Laborde
  • Caroline A Rickards
  • Kathy L. Ryan
  • Victor A Convertino

Organizations

  • United States Army Institute of Surgical Research

Tags

Communities of Interest

  • Biomedical

DTIC Thesaurus Topics

  • Blood Flow
  • Blood Volume
  • Cardiovascular Physiological Phenomena
  • Cardiovascular System
  • Data Analysis
  • Health Services
  • Heart Rate
  • Hemorrhage
  • Hemorrhagic Shock
  • Hypovolemia
  • Linear Regression Analysis
  • Medical Personnel
  • Nerves
  • Nervous System
  • Regression Analysis
  • Sensitivity
  • United States

Fields of Study

  • Medicine
  • Psychology

Readers

  • Cardiovascular Physiology