Page 6, Cardiac Performance, Dr. D. Penney

Stroke Volume Control (continued..)

There are a number of intrinsic factors which control stroke volume, some important, others trivial. The Frank-Starling mechanism (Law of the Heart), named for Otto Frank and Ernest Starling, involves a change in cardiac performance as a function of preload.

Preload - Increased tension on muscle fibers before contraction begins; usually due to increased luminal volume/pressure; imposed during diastole.

Its basis is the length-tension curve of muscle. For heart, only the ascending limb is involved. It is sometimes referred to as Heterometric Autoregulation. A Frank-Starling curve, or ventricular function curve is produced (Figure 2.02). Performance is altered by moving up and down this curve.

This change DOES NOT increase / decrease inotropicity (contractility) of the muscle.

The heart operates on the ascending limb of the L/T curve, unlike skeletal muscle which operates at or near Lmax.