Preload (cardiac)

Description

Preload is described as the stretching of a single cardiac myocyte immediately prior to contraction and is, therefore, related to the sarcomere length. (Sarcomeres are composed of long, fibrous proteins that slide past each other when the muscles contract and relax). Since sarcomere length cannot be determined in the intact heart, other indices of preload such as ventricular end-diastolic volume or pressure is used. Preload increases when venous return is increased. This is because the end-diastolic pressure and volume of the ventricle are increased, which stretches the sarcomeres.

Related formulas

Variables

PRPreload (mmHg)
LVEDPLeft ventricular end-diastolic pressure (mmHg)
LVEDRLeft ventricular end-diastolic radius (at midpoint of ventricle) (mm)
hThe thickness of the ventricle (mm)