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Related Experiment Videos

Cardiorespiratory response to lower body negative pressure

C M Chang1, Y Cassuto, D R Pendergast

  • 1Hermann Rahn Laboratory for Environmental Physiology, Department of Physiology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo 14214.

Aviation, Space, and Environmental Medicine
|July 1, 1994
PubMed
Summary
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Lower body negative pressure (LBNP) significantly reduces cardiovascular function, including cardiac output and stroke volume, at -15 mm Hg. Higher LBNP levels beyond -35 mm Hg exceed physiological limits, causing further reductions and blood pressure drops.

Area of Science:

  • Cardiovascular Physiology
  • Human Physiology

Background:

  • Lower body negative pressure (LBNP) is a model used to simulate hypovolemia and study cardiovascular responses.
  • Understanding the limits of cardiovascular compensation during simulated hypovolemia is crucial for physiological research.

Purpose of the Study:

  • To investigate the cardiovascular effects of graded lower body negative pressure (LBNP) in humans.
  • To determine the threshold at which LBNP elicits significant cardiovascular changes and exceeds physiological compensation.

Main Methods:

  • Ten human subjects were exposed to various levels of supine LBNP (-8 to -45 mm Hg) in a randomized order.
  • Measurements included leg blood flow, cardiac output (Q), stroke volume (SV), heart rate, and blood pressure.
  • Cardiovascular parameters were assessed during 20-minute LBNP applications with 15-minute recovery periods.
Keywords:
NASA Discipline CardiopulmonaryNon-NASA Center

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Main Results:

  • Significant reductions in leg blood flow, cardiac output (Q), stroke volume (SV), and estimated lung blood volume were observed at -15 mm Hg LBNP.
  • Increasing LBNP to -35 mm Hg did not cause further significant changes in these parameters.
  • At -45 mm Hg LBNP, Q and SV decreased further, heart rate increased, and mean arterial pressure was maintained by increased vascular resistance up to -35 mm Hg, but dropped progressively at higher levels.

Conclusions:

  • LBNP up to -35 mm Hg can be compensated by physiological mechanisms, primarily increased vascular resistance.
  • Levels of LBNP at -45 mm Hg exceed the body's compensatory capacity, leading to a progressive decline in blood pressure.
  • These findings highlight the physiological limits of cardiovascular adaptation to simulated hypovolemia.