Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model.

Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model. Research Abstract Details 

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Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model. Abstract Text:

Justin Broskey,M Keith Sharp,

A significant fraction of astronauts experience postflight orthostatic intolerance (POI) during 10-min stand tests conducted on landing day. The average time that nonfinishers can stand is about 7 min. This phenomenon, including the delay in occurrence of presyncope, was studied with a five-compartment model of the cardiovascular system incorporating compartments for the heart/lungs, systemic arteries and cephalic, central, and caudal veins. The model included 28 independent parameters, including factors characterizing cardiac performance, vascular resistance, intrathoracic pressure, nonlinear venous compliance and circulating blood volume, and 13 dependent parameters, including cardiac output and cardiac and vascular compartment pressures and volumes. First, a sensitivity analysis of hemodynamic indicators of presyncope to independent parameters was performed. Results demonstrated that both cardiac output and arterial pressure were most sensitive to volume-related parameters, particularly total blood volume, and less sensitive to peripheral resistance. Next, a simulated postflight stand test confirmed that fluid loss due to capillary filtration, particularly from the caudal region where transmural pressure is high during standing, is a plausible mechanism of POI that also explains the delayed onset of symptoms in most astronauts. An accumulated drop in arterial pressure sufficient to compromise cerebral perfusion and, therefore, cause syncope was reached in about 7 min with a fluid loss of 280 mL. Finally, additional simulations showed that a 75% increase in peripheral resistance, similar to finishers of stand tests, was insufficient to overcome the loss of circulating fluid associated with capillary filtration, and extended the time that the modeled astronaut could stand by only about 1 min. It is therefore concluded that capillary filtration may play a key role in producing POI and that development of countermeasures should perhaps focus on reducing postflight capillary permeability or on stimulating volume-compensating mechanisms.

Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model. Publishing Authors By Initials

J Broskey,MK Sharp,

For similar natural sciences: physics: gravitation: gravity, altered: hypogravity: weightlessness research abstracts see: natural sciences: physics: gravitation: gravity, altered: hypogravity: weightlessness research

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Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model. Journal Published:

PUBLICATION TYPE: Journal Article

Journal: Annals of biomedical engineering

VOLUME: 35

Page Numbers: 1800-11

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ISSN: 0090-6964

DAY: 26

MONTH: 06

YEAR: 2007

Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model. Information

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LANGUAGE: eng

NlmUniqueID: 361512

Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model. Keywords Mesh Terms:

KEYWORDS: Weightlessness

MESH TERMS: adverse effects

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Grant and Affiliation Information for Evaluation of mechanisms of postflight orthostatic intolerance with a simple cardiovascular system model.

AFFILIATION: Biofluid Mechanics Laboratory, Department of Mechanical Engineering, University of Louisville, 200 Sackett Hall, Louisville, KY 40292, USA.

Country: United States

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MEDLINETA: Ann Biomed Eng

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