Regulation of Stroke Volume

The stroke volume, which is the volume of blood ejected by a ventricle with each heartbeat, is regulated by three factors: preload, contractility, and afterload.

Preload is the degree of stretch in the cardiac muscles just before ventricular contraction. It is directly proportional to the end-diastolic volume.

According to the Frank-Starling law, greater preload means greater force of ventricular contraction and a higher stroke volume.

Certain factors, such as an increased ventricular filling during diastole, put more strain on the ventricular myocardium, increasing the preload and the stroke volume.

Contractility is the strength of contraction of ventricles at any given preload. Higher contractility pushes more blood out, reduces the end-systolic volume, and boosts the stroke volume.

Positive inotropic agents, like epinephrine, elevate contractility by enhancing calcium ion inflow into the muscle cells. Negative agents, like acetylcholine, reduce contractility by increasing potassium ion efflux from cardiac tissues.

Afterload refers to the threshold pressure needed for ventricular ejection. Higher afterload reduces ventricular pumping capacity. It increases the ESV and reduces stroke volume.

Conditions such as hypertension and atherosclerosis can elevate afterload.