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Cardiac Output: Prcssurc-Volumc Loop

CARDIOVASCULAR PHYSIOLOGY

Pressure (mm Hg>

f Preload    f Afterload

łf venoui return)    (f arteria/ pressure)

t Cardiac output

Ficurf 4.10 Prfssurf-Volumf Loop_

Cardiac output is the volume of blood pumped by the heart

each minutę. In the steady siatę the output rrom both the right and

left ventrides is the same. The pressure-volume loop for

the left ventricle is depicted here. The cardiac output is calculated

as:

Cardiac output = Heart ratę X Stroke volume

IBM

where:

Stroke volume = End-diastolłc volume - End-systolic volume

Increases in venous return (increased preload) increase the stroke volume and thus cardiac output. Increases in arterial pressure (increased afterload) decrease stroke volume and thus cardiac oul-put (lower panel).

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