Changes in venous return parameters associated with univentricular Fontan circulations.

To clarify the physiology of venous return (Q(vr)) in Fontan circulations, venous return conductance (G(vr)) and mean circulatory filling pressure (P(mcf)) were determined in pentobarbital sodium-anesthetized pigs. Relationships between Q(vr) and right (biventricular, n = 8) or left (Fontan, n = 8) filling pressures are described by straight lines with significant correlation coefficients. Estimated P(mcf) values were correlated with observed P(mcf) values in either circulations (P </= 0.02). G(vr) was smaller in Fontan than in biventricular circulations (4.51 +/- 0.36 vs. 7.83 +/- 0.69 ml. min(-1). kg(-1). mmHg(-1), P = 0.002) and inversely correlated with pulmonary vascular resistances in Fontan circulations (P = 0.01). Estimated P(mcf) (20.5 +/- 1.4 vs. 11.1 +/- 0.9 mmHg, P = 0.001) and observed P(mcf) (21.8 +/- 1.3 vs. 10.6 +/- 0.8 mmHg, P < 0.001) were higher in Fontan versus biventricular circulations, respectively. Pulmonary artery pressure in Fontan circulations was correlated with either P(mcf) (P < or = 0.04). We conclude that in Fontan circulations 1) pulmonary vascular resistances induce a proportional decrease in G(vr); and 2) volume loading, while increasing P(mcf) (similar to pulmonary artery pressure), allows the gradient for Q(vr) to increase and maintains systemic blood flow at a biventricular level.