Changes in venous return parameters associated with univentricular Fontan circulations

To clarify the physiology of venous return (Qvr) in Fontan circulations, venous return conductance ( G vr) and mean circulatory filling pressure (Pmcf) were determined in pentobarbital sodium-anesthetized pigs. Relationships between Qvr and right (biventricular, n = 8) or left (Fontan, n = 8) filling pressures are described by straight lines with significant correlation coefficients. Estimated Pmcf values were correlated with observed Pmcfvalues 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 Pmcf (20.5 ± 1.4 vs. 11.1 ± 0.9 mmHg, P = 0.001) and observed Pmcf (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 Pmcf ( P ≤ 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 Pmcf(similar to pulmonary artery pressure), allows the gradient for Qvr to increase and maintains systemic blood flow at a biventricular level.