According to Starling's Law, what influences the stroke volume?

Starling's Law, also known as the Frank-Starling mechanism, states that the stroke volume of the heart is influenced primarily by the preload, which is the degree of stretch of the cardiac muscle fibers at the end of diastole. Preload is dependent on the volume of blood returning to the heart and the filling pressure. When the preload increases, the heart muscle fibers are stretched more, leading to a more forceful contraction and, therefore, a higher stroke volume. This relationship allows the heart to adjust its output in response to varying volumes of venous return.

On the other hand, factors such as protein concentration in plasma, heart rate, and oxygen content in the blood do not directly dictate stroke volume as defined by Starling's Law. While they can impact overall cardiac performance or oxygen delivery, they do not determine the stroke volume in the same manner as preload does. Understanding this relationship helps in assessing and managing conditions related to heart function and fluid dynamics effectively.