Fig. 4

Effects on venous return and its determinants of typical clinical situations. A Hypovolaemic shock. Hypovolaemia decreases the stressed volume and therefore the mean systemic filling pressure (Pmsf). Then, the gradient between Pmsf and right atrial pressure (RAP) decreases, while the resistance to venous return (RVr) is not modified. As a consequence, the equilibrium point is shifted to the bottom left, and cardiac output (CO) and venous return decrease. B Cardiogenic shock. The slope of the Frank–Starling curve decreases. The equilibrium point is shifted to the bottom right, following the new, flattened, Frank–Starling curve. Right atrial pressure (RAP) increases, whereas mean systemic filling pressure (Pmsf) and resistance to venous return (RVr) are not modified. The (Pmsf–RAP) gradient decreases, reducing venous return and cardiac output (CO). C Septic shock. Vasodilation increases the venous capacitance, which decreases mean systemic filling pressure (Pmsf). Consequently, the gradient between Pmsf and right atrial pressure (RAP) decreases. Resistance to venous return (RVr) may also decrease. As a consequence, venous return and cardiac output (CO) decrease. A “hyperdynamic state”, with increased cardiac contractility, may steepen the Frank–Starling curve, while septic myocardial dysfunction may flatten it. Dashed lines and the index “1” indicate the normal state. Solid lines and the index “2” correspond to the pathological state