ABSTRACT
Preload refers to the initial muscle fiber length or stretch on the cardiac muscle before ventricular contraction. Increases in preload are associated with increases in both the extent and velocity of muscle fiber shortening, which combine to produce an increase in stroke volume. In the normal heart, preload corresponds to enddiastolic blood volume (EDV) in the ventricles, just before ventricular systole, and is directly related to venous return to the heart during diastole. As pressure is directly related to blood volume, diastolic pressure is a surrogate measure of diastolic volume. There is a direct relationship between preload and the force of myocardial contraction and stroke volume. Preload may be described by both right and left ventricular end-diastolic ventricular filling pressures and is clinically assessed by measurements of both right and left atrial pressure or pulmonary capillary wedge pressure (PCWP). The terms generally referring to left ventricular preload include: left ventricular end-diastolic blood volume (LVEDV), left ventricular end-diastolic pressure (LVEDP), left atrial pressure (LAP), pulmonary capillary wedge pressure/pulmonary artery wedge pressure (PAWP), or pulmonary artery occlusion pressure (PAOP).
