To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
Reproduction of Starling's law.
In this first example in order to reproduce the Starling’s law of the heart a simple open network of the cardiovascular system was used. The simple network is composed by a fixed preload (left atrial reservoir) that (in the software simulator) can be changed manually (see the Frank-Starling Law section).
Events of the ventricular pressure-volume loop. During the early phase of ventricular systole (pase 1 - filling), pressure in the ventricle exceeds that in the atrium and the mitral valve closes (end of phase 1 - End-diastolic volume EDV). The ventricles continue to contract and generate pressure (isovolumic contraction - phase 2) until the pressure in the ventricle is greater than that in the aorta, and the aortic valve opens (end of pase 2). The ventricles continue to contract and now eject volume (phase 3). As the ventricles begin to relax, pressure in the ventricles drops below that in the aorta, and the aortic valve closes (end of phase 3). The ventricles continue to relax (isovolumic relaxation - phase 4) until pressure in the ventricles drops below the pressure in the atrium, and the mitral valve opens (end of phase 4 - End-systolic volume ESV). The ventricles then fill until the cycle begins again.
When atrial pressure Pa (preload) decreases (increases) the pressure-volume loop shifs in the left (right) side, the slope (Emax) of End Systolic Pressure Volume Relationship (ESPVR) does not changes and End Systemic Arterial Elastance (Esae) shifts in the left (right) side, but does not changes its slope. When preload decreases (increases) ESV (end systolic volume) and EDV (end distolic volume) descrease (increase).
When peripheral resistance Ra (afterload) decreases (increases) ESV (end systolic volume) decreases (increases), but EDV (end distolic volume) does not change, the slope of End Systolic Pressure Volume Relationship (ESPVR) does not changes and End Systemic Arterial Elastance (Esae) reduces (raises) its slope.
When the slope of ESPVR (Emax) decreases (increases) the value of ESV (end systolic volume) raises (reduces), but EDV (end distolic volume) does not change. End Systemic Arterial Elastance (Esae) does not change its slope.
The ESPVR incorporates afterload so that indices of ventricular contractility derived from the ESPVR are independent of afterload. Emax is an excellent measure of intrinsic ventricular contractility, which is less load sensitive than other indices of ventricular contractility and is insensitive to heart rate within the normal physiologic range.