Figure 2
A simple Frank-Starling model of the cardiovascular system. A simple two compartment model of the circulation, with control of the cardiac output via the Frank-Starling mechanism. When the heart is not pumping, the pressures on the venous (Pv) and arterial (Pa) sides of the circulation are equal (the mean circulatory pressure (MCP = Pv = Pa) is approximately 7 mmHg). The unstressed volumes of the venous (Vv0) and arterial sides (Va0) are governed by the relative compliance of the venous and arterial pools (CPLv and CPLa, respectively). If the pumping action of the heart is initiated, a fraction of the blood (dV) moves from the venous to the arterial side thereby increasing arterial pressure and decreasing venous pressure. The pressure gradient causes blood to flow from the arterial side to the venous side (at a rate given by the venous return, COR). This depends on the pressure gradient (Pa-Pv) and the systemic vascular resistance (SVR).