Regulation+of+Stroke+Volume

= = =Regulation of Stroke Volume=

Ventricular stroke volume (SV) is the difference between the ventricular end-diastolic volume (EDV) and the end-systolic volume (ESV). In a typical heart, the EDV is about 120 ml of blood and the ESV about 50 ml of blood. The difference in these two volumes, 70 ml, represents the SV. Therefore, any factor that alters either the EDV or the ESV will change SV.


 * SV = EDV - ESV**

There are three primary mechanisms that regulate EDV and ESV, and therefore SV. 1) SV is regulated is by the [|__Frank-Starling mechanism__]. Briefly, an increase in venous return to the heart increases ventricular EDV ([|preload]) and the force of ventricular contraction, which enables the heart to eject the additional blood that was returned to it. Conversely, a decrease in venous return leads to a decrease in SV by this mechanism. 2) Changes in [|__afterload__] affect the ability of the ventricle to eject blood and thereby alter ESV and SV. For example, an increase in afterload (e.g., increased aortic pressure) decreases SV by increasing ESV. Conversely, a decrease in afterload augments SV. 3) Changes in [|__inotropy__] (contractility) alters the rate of ventricular pressure development thereby affecting ESV and SV. For example, an increase in inotropy (e.g., sympathetic activation of the heart) decreases ESV and increases SV. Conversely, a decrease in inotropy (e.g., [|__heart failure__]) reduces SV by increasing ESV. It is important to note that the effects of changes in EDV and ESV on SV are not independent. For example, an increase in ESV usually results in a compensatory increase in EDV. Furthermore, if SV is increased by increasing EDV, this can lead to a small increase in ESV because of the influence of increased afterload on ESV caused by an increase in aortic pressure. Therefore, while the primary effect of a change in preload, afterload or inotropy may be on either EDV or ESV, secondary changes can occur that can partially compensate for the initial change in SV. For a more detailed description of these interactions, see the web pages describing [|preload], [|afterload], or [|inotropy].