Regulation of Stroke Volume The stroke volume is regulated by three variables: the end-diastolic volume (EDV), which is the volume of blood in the ventricles at the end of diastole; the total peripheral resistance, which is the frictional resistance, or impedance to blood flow, in the arteries; and the contractility, or strength, of ventricular contraction. The end-diastolic volume is the amount of blood in the ven- tricles immediately before they begin to contract. This is a work- load imposed on the ventricles prior to contraction, and thus is sometimes called a preload. The stroke volume is directly proportional to the preload; an increase in EDV results in an increase in stroke volume. (This relationship is known as the Frank-Starling law of the heart, discussed shortly.) The stroke volume is also directly proportional to contractility; when the ventricles contract more forcefully,...
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