A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress

J. Truijen, M. Bundgaard-Nielsen, J.J. van Lieshout

Research output: Contribution to journalArticle*Academicpeer-review

Abstract

The Frank-Starling mechanism describes the relationship between stroke volume and preload to the heart, or the volume of blood that is available to the heart-the central blood volume. Understanding the role of the central blood volume for cardiovascular control has been complicated by the fact that a given central blood volume may be associated with markedly different central vascular pressures. The central blood volume varies with posture and, consequently, stroke volume and cardiac output (Q) over dot are affected, but with the increased central blood volume during head-down tilt, stroke volume and (Q) over dot do not increase further indicating that in the supine resting position the heart operates on the plateau of the Frank-Starling curve which, therefore, may be taken as a functional definition of normovolaemia. Since the capacity of the vascular system surpasses the blood volume, orthostatic and environmental stress including bed rest/microgravity, exercise and training, thermal loading, illness, and trauma/haemorrhage is likely to restrict venous return and (Q) over dot. Consequently the cardiovascular responses are determined primarily by their effect on the central blood volume. Thus during environmental stress, flow redistribution becomes dependent on sympathetic activation affecting not only skin and splanchnic blood flow, but also flow to skeletal muscles and the brain. This review addresses the hypothesis that deviations from normovolaemia significantly influence these cardiovascular responses
Original languageUndefined/Unknown
Pages (from-to)141-157
JournalEuropean journal of applied physiology
Volume109
Issue number2
DOIs
Publication statusPublished - 2010

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