Determinants of impairment of cardiac filling during progressive pericardial effusion.

The progressive reduction in cardiac output-and later in arterial pressures-that develops during advancing degrees of pericardial effusion is usually attributed to a steady decrease in the venoatrial pressure gradient. Evaluation of changes in instantaneous pressures in the right and left atria at the end of ventricular diastole (Z pressure) and systole (V pressure) indicates that as pericardial pressure rises other determinants enter in the following order: (1) reduction in diastolic capacities of the atriums and ventricles; (2) decrease in venoatrial pressure gradient and preponderant rise of left atrial pressures due to the higher elasticity coefficient of this chamber; (3) blockage of atrial inflow during ventricular diastole; (4) impairment of atrial inflow during ventricular systole as its stroke volume diminishes to an extreme degree; and (5) inauguration of a vicious cycle in which a diminishing venopressure gradient decreases ventricular filling, while the consequent reduction in stroke volume attenuates the facilitating effect of ventricular ejection on the venoatrial gradient. SINCE THE initial work of Cohnheim,l it has been known that the rapid introduction of fluid into the pericardial sac of experimental animals produces an increase of venous pressure and a fall of mean arterial pressure. The data later collected by Starling,2 Lewis,3 Kuno,4 and others demonstrated that the increased pericardial pressure acts as a barrier to the venous filling of the heart, resulting in a decrease in diastolic heart size when the gradient of pressure between the central veins and atrium is sufficiently diminished. The rise of central venous pressure results from pooling of venous blood which has failed to reach the right atrium, and the fall of mean arterial blood pressure is ascribed to the progressively decreasing cardiac output. It was the purpose of this investigation to subject the accepted dynamics of pericardial effusion to closer scrutiny and, if possible, to evaluate the importance and incidence of other suspected and unsuspected determinants of re