Cardiac atrophy after bed-rest deconditioning: A nonneural mechanism for orthostatic intolerance

Benjamin D. Levine, Julie H. Zuckerman, James Anthony Pawelczyk

Research output: Contribution to journalArticle

246 Citations (Scopus)

Abstract

Background: The cardiovascular adaptation to bed rest leads to orthostatic intolerance, characterized by an excessive fall in stroke volume (SV) in the upright position. We hypothesized that this large fall in SV is due to a change in cardiac mechanics. Methods and Results: We measured pulmonary capillary wedge pressure (PCWP), SV, left ventricular end-diastolic volume (LVEDV), and left ventricular mass (by echocardiography) at rest, during lower-body negative pressure, and after saline infusion before and after 2 weeks of bed rest with -6°head-down tilt (n=12 subjects aged 24±5 years). Pressure (P)-volume (V) curves were modeled exponentially by P=ae(kV)+b and logarithmically by P=-Sln[(V(m)-V)/(V(m)-V0], where V0 indicates volume at P=0, and the constants k and S were used as indices of normalized chamber stiffness. Dynamic stiffness (dP/dV) was calculated at baseline LVEDV. The slope of the line relating SV to PCWP during lower-body negative pressure characterized the steepness of the Starling curve. We also measured plasma volume (with Evans blue dye) and maximal orthostatic tolerance. Bed rest led to a reduction in plasma volume (17%), baseline PCWP (18%), SV (12%), LVEDV (16%), V0 (33%), and orthostatic tolerance (24%) (all P<.05). The slope of the SV/PCWP curve increased from 4.6±0.4 to 8.8±0.9 mL/mm Hg (P<.01) owing to a parallel leftward shift in the P-V curve. Normalized chamber stiffness was unchanged, but dP/dV was reduced by 50% at baseline LVEDV, and cardiac mass tended to be reduced by 5% (P<.10). Conclusions: Two weeks of head-down-tilt bed rest leads to a smaller, less distensible left ventricle but a shift to a more compliant portion of the P- V curve. This results in a steeper Starling relationship, which contributes to orthostatic intolerance by causing an excessive reduction in SV during orthostasis.

Original languageEnglish (US)
Pages (from-to)517-525
Number of pages9
JournalCirculation
Volume96
Issue number2
DOIs
StatePublished - Jul 15 1997

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Orthostatic Intolerance
Bed Rest
Stroke Volume
Atrophy
Pulmonary Wedge Pressure
Lower Body Negative Pressure
Starlings
Plasma Volume
Head-Down Tilt
Evans Blue
Dizziness
Mechanics
Heart Ventricles
Echocardiography

All Science Journal Classification (ASJC) codes

  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

Cite this

@article{e95f89dd32b04fc1a3c9ef86b4104ef8,
title = "Cardiac atrophy after bed-rest deconditioning: A nonneural mechanism for orthostatic intolerance",
abstract = "Background: The cardiovascular adaptation to bed rest leads to orthostatic intolerance, characterized by an excessive fall in stroke volume (SV) in the upright position. We hypothesized that this large fall in SV is due to a change in cardiac mechanics. Methods and Results: We measured pulmonary capillary wedge pressure (PCWP), SV, left ventricular end-diastolic volume (LVEDV), and left ventricular mass (by echocardiography) at rest, during lower-body negative pressure, and after saline infusion before and after 2 weeks of bed rest with -6°head-down tilt (n=12 subjects aged 24±5 years). Pressure (P)-volume (V) curves were modeled exponentially by P=ae(kV)+b and logarithmically by P=-Sln[(V(m)-V)/(V(m)-V0], where V0 indicates volume at P=0, and the constants k and S were used as indices of normalized chamber stiffness. Dynamic stiffness (dP/dV) was calculated at baseline LVEDV. The slope of the line relating SV to PCWP during lower-body negative pressure characterized the steepness of the Starling curve. We also measured plasma volume (with Evans blue dye) and maximal orthostatic tolerance. Bed rest led to a reduction in plasma volume (17{\%}), baseline PCWP (18{\%}), SV (12{\%}), LVEDV (16{\%}), V0 (33{\%}), and orthostatic tolerance (24{\%}) (all P<.05). The slope of the SV/PCWP curve increased from 4.6±0.4 to 8.8±0.9 mL/mm Hg (P<.01) owing to a parallel leftward shift in the P-V curve. Normalized chamber stiffness was unchanged, but dP/dV was reduced by 50{\%} at baseline LVEDV, and cardiac mass tended to be reduced by 5{\%} (P<.10). Conclusions: Two weeks of head-down-tilt bed rest leads to a smaller, less distensible left ventricle but a shift to a more compliant portion of the P- V curve. This results in a steeper Starling relationship, which contributes to orthostatic intolerance by causing an excessive reduction in SV during orthostasis.",
author = "Levine, {Benjamin D.} and Zuckerman, {Julie H.} and Pawelczyk, {James Anthony}",
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Cardiac atrophy after bed-rest deconditioning : A nonneural mechanism for orthostatic intolerance. / Levine, Benjamin D.; Zuckerman, Julie H.; Pawelczyk, James Anthony.

In: Circulation, Vol. 96, No. 2, 15.07.1997, p. 517-525.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Cardiac atrophy after bed-rest deconditioning

T2 - A nonneural mechanism for orthostatic intolerance

AU - Levine, Benjamin D.

AU - Zuckerman, Julie H.

AU - Pawelczyk, James Anthony

PY - 1997/7/15

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N2 - Background: The cardiovascular adaptation to bed rest leads to orthostatic intolerance, characterized by an excessive fall in stroke volume (SV) in the upright position. We hypothesized that this large fall in SV is due to a change in cardiac mechanics. Methods and Results: We measured pulmonary capillary wedge pressure (PCWP), SV, left ventricular end-diastolic volume (LVEDV), and left ventricular mass (by echocardiography) at rest, during lower-body negative pressure, and after saline infusion before and after 2 weeks of bed rest with -6°head-down tilt (n=12 subjects aged 24±5 years). Pressure (P)-volume (V) curves were modeled exponentially by P=ae(kV)+b and logarithmically by P=-Sln[(V(m)-V)/(V(m)-V0], where V0 indicates volume at P=0, and the constants k and S were used as indices of normalized chamber stiffness. Dynamic stiffness (dP/dV) was calculated at baseline LVEDV. The slope of the line relating SV to PCWP during lower-body negative pressure characterized the steepness of the Starling curve. We also measured plasma volume (with Evans blue dye) and maximal orthostatic tolerance. Bed rest led to a reduction in plasma volume (17%), baseline PCWP (18%), SV (12%), LVEDV (16%), V0 (33%), and orthostatic tolerance (24%) (all P<.05). The slope of the SV/PCWP curve increased from 4.6±0.4 to 8.8±0.9 mL/mm Hg (P<.01) owing to a parallel leftward shift in the P-V curve. Normalized chamber stiffness was unchanged, but dP/dV was reduced by 50% at baseline LVEDV, and cardiac mass tended to be reduced by 5% (P<.10). Conclusions: Two weeks of head-down-tilt bed rest leads to a smaller, less distensible left ventricle but a shift to a more compliant portion of the P- V curve. This results in a steeper Starling relationship, which contributes to orthostatic intolerance by causing an excessive reduction in SV during orthostasis.

AB - Background: The cardiovascular adaptation to bed rest leads to orthostatic intolerance, characterized by an excessive fall in stroke volume (SV) in the upright position. We hypothesized that this large fall in SV is due to a change in cardiac mechanics. Methods and Results: We measured pulmonary capillary wedge pressure (PCWP), SV, left ventricular end-diastolic volume (LVEDV), and left ventricular mass (by echocardiography) at rest, during lower-body negative pressure, and after saline infusion before and after 2 weeks of bed rest with -6°head-down tilt (n=12 subjects aged 24±5 years). Pressure (P)-volume (V) curves were modeled exponentially by P=ae(kV)+b and logarithmically by P=-Sln[(V(m)-V)/(V(m)-V0], where V0 indicates volume at P=0, and the constants k and S were used as indices of normalized chamber stiffness. Dynamic stiffness (dP/dV) was calculated at baseline LVEDV. The slope of the line relating SV to PCWP during lower-body negative pressure characterized the steepness of the Starling curve. We also measured plasma volume (with Evans blue dye) and maximal orthostatic tolerance. Bed rest led to a reduction in plasma volume (17%), baseline PCWP (18%), SV (12%), LVEDV (16%), V0 (33%), and orthostatic tolerance (24%) (all P<.05). The slope of the SV/PCWP curve increased from 4.6±0.4 to 8.8±0.9 mL/mm Hg (P<.01) owing to a parallel leftward shift in the P-V curve. Normalized chamber stiffness was unchanged, but dP/dV was reduced by 50% at baseline LVEDV, and cardiac mass tended to be reduced by 5% (P<.10). Conclusions: Two weeks of head-down-tilt bed rest leads to a smaller, less distensible left ventricle but a shift to a more compliant portion of the P- V curve. This results in a steeper Starling relationship, which contributes to orthostatic intolerance by causing an excessive reduction in SV during orthostasis.

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