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A. The cardiac function curve relates right atrial pressure (Pra) or end-diastolic pressure (EDP; abscissa) to cardiac output (ordinate). As EDP increases,
cardiac output increases; however, at high EDPs, further increases cause less increase in cardiac output. B. The relation between EDP (Pra, abscissa)
and venous return (ordinate) is illustrated. When EDP equals mean systemic pressure (Pms), there is no pressure gradient (Pms-Pra) driving the blood
flow back to the heart, so venous return is zero. As EDP (Pra) decreases, the gradient from the veins to the heart to drive blood flow back to the heart
increases, so venous return increases. At very low EDPs (Pra 0 mm Hg), central veins collapse and act as Starling resistors, so further decreases in EDP
do not increase venous return. C. The cardiac function curve and the venous return curve are drawn on the same axes (continuous lines). The intersection
Source: Chapter 22. Ventricular Dysfunction in Critical Illness, Principles of Critical Care, 3e
of the cardiac function curve and the venous return curve defines the operating point of the circulation, here at an EDP (Pra) of approximately 5 mm Hg
Citation:
JB, Schmidt GA,
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Principles of
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April 30, 2017
and a cardiac
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output (∼3 L/min) at a higher EDP (Pra = 10 mm Hg).