Which cardiovascular change occurs when a healthy individual transitions from standing to a supine position?

When a healthy individual transitions from standing to a supine position, one of the primary cardiovascular changes observed is an increase in stroke volume. In the standing position, gravity causes blood to pool in the lower extremities, which can lead to reduced venous return to the heart. When the position changes to supine, there is a more even distribution of blood throughout the cardiovascular system due to the elimination of gravity's effect on venous return. As a result, the volume of blood returning to the heart increases, leading to an increase in left ventricular filling and ultimately an increase in stroke volume.

This increase in stroke volume is also facilitated by the Frank-Starling mechanism, where the heart's output is enhanced due to the increased volume of blood filling the ventricles during diastole. This mechanism helps to maintain cardiac output and stabilize blood pressure as the body adjusts to the new position. Thus, the transition to a supine position is associated with improved hemodynamic stability and increased efficiency in blood flow and volume utilization by the heart.