Figure 1.

A, data from Guyton et al. (1959) are plotted showing the steady state relation between flow (F= cardiac output = venous return) and right atrial pressure (P_RA) measured when flow was altered by limiting the inflow to an artificial pump with a collapsible tube. B, the data from A are replotted with flow plotted on the abscissa correctly indicating that cardiac output is the independent variable. The intercept on the ordinate is the right atrial pressure (equal to the mean systemic pressure) when flow (cardiac output) is zero. C, the calculated arterial pressure according to Guyton's model, with constant systemic vascular resistance, when flow is varied over the range defined in A and B. See Beard & Feigl (2011) for details. Figure reproduced, with permission, from the American Journal of Physiology Heart – Heart and Circulatory Physiology.