Frank-Starling Curve

The Frank-Starling mechanism describes a relationship where increasing ventricular filling increases cardiac output. Increased preload increases sarcomere stretch inside cardiac myocytes which generate more force during contraction and thereby allows the heart to eject more blood. However, there is a limit to which this relationship can be maintained. In failing ventricles, overstretch can limit or decrease cardiac output. In these cases, reducing myocyte stretch to a more optimal length can improve overall cardiac function. Graphically, the Frank-Starling mechanism can be illustrated by cardiac function curves. Cardiac output can change by moving between different points on a single curve or changing to different curves. Physiologic changes altering preload can cause movement along the same cardiac curve, while changes in inotropy can cause shifts to different curves. On the steep, positively sloped portion of a cardiac function curve (sometimes called the preload dependent segment), cardiac output increases as ventricular stretch increases. If preload continues to increase, the point of overstretch is reached and eventually passed. Cardiac output plateaus and then begins to fall. The plateaued segment is sometimes called the preload independent portion.