Figure 2
From: Clinical review: Positive end-expiratory pressure and cardiac output
Effects of positive end-expiratory pressure (PEEP) on venous return and cardiac output. (a) Theoretical effects of PEEP on venous return (VR) and cardiac output (CO). PEEP causes an increase in intrathoracic pressure (ITP) and a right shift in the cardiac function curve. If there were no change in the VR curve, then CO and VR would decrease (from point A to point B). However, if there is a compensatory increase in mean systemic pressure (from Pms1 to Pms2), then the system will exist in equilibrium at point C, at which VR and CO would be maintained compared to zero end-expiratory pressure (ZEEP) conditions. Pms can increase either by an increase in stressed volume or sympathoadrenal stimulation. (b) Another possible scheme for the changes in VR with PEEP. If there is an increase in the pressure at which flow limitation occurs, then the ability of an increase in Pms to buffer PEEP-induced decreases in VR is markedly less. FL1, flow limiting point at ZEEP; FL2, flow limiting point at PEEP. Modified from [8], with permission.