End-systolic and end-diastolic ventricular interaction.

Right ventricular volume affects left ventricular volume via direct interaction across the interventricular septum and series interaction because the right and left hearts are connected in series through the lungs. Because it is difficult to sort out complex physiological mechanisms in the intact circulation, the relative importance of these two effects is unknown. We used statistical analyses of transient changes in left and right ventricular pressures and dimensions following pulmonary artery and venae caval constrictions to separate and quantitate the direct (immediate) from the series (delayed) interaction effects on left ventricular size at end systole and end diastole. With the pericardium closed, direct interaction was one-half as important as series interaction at end diastole and was one-third as important at end systole. With the pericardium removed, direct interaction was one-fifth as important as series interaction at end diastole and one-sixth as important at end systole. These results suggest that differences between transient and steady-state end-systolic pressure-volume relationships are largely explained by direct interaction and that direct end-systolic interaction is important for maintaining balanced right and left heart outputs.