What effect does systemic vasodilation have on stroke volume?

Systemic vasodilation affects stroke volume primarily by altering the resistance that the heart must work against during contraction. When systemic vasodilation occurs, the blood vessels relax and widen, resulting in a decrease in systemic vascular resistance. This reduction in resistance allows the heart to pump blood more easily, which can lead to an increase in stroke volume.

Moreover, vasodilation can enhance venous return to the heart by decreasing the pressure in the veins, thereby increasing the amount of blood filling the heart during diastole (the filling phase). An increased preload (the initial stretching of the cardiac muscle prior to contraction) due to enhanced venous return further supports an increase in stroke volume, following the Frank-Starling mechanism that states the more the heart fills, the more it ejects.

In contrast, systemic vasodilation typically does not lead to a decrease in stroke volume, influence it neutrally, or create an outcome that depends largely on other factors, as these scenarios do not hold true when the primary effect of vasodilation—decreased resistance—is considered along with improved venous return. Therefore, the correct assertion is that systemic vasodilation increases stroke volume through decreased afterload and enhanced preload.