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. Relationshi ps between Q(vr) and right (biventricular, n = 8) or left (Fontan, n = 8) f illing pressures are described by straight lines with significant correlati on coefficients. Estimated P-mcf values were correlated with observed P-mcf values in either circulations (P less than or equal to 0.02). G(vr) was sm aller 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 wi th pulmonary vascular resistances in Fontan circulations (P = 0.01). Estima ted P-mcf (20.5 +/- 1.4 vs. 11.1 +/- 0.9 mmHg, P = 0.001) and observed P-mc f (21.8 +/- 1.3 vs. 10.6 +/- 0.8 mmHg, P < 0.001) were higher in Fontan ver sus biventricular circulations, respectively. Pulmonary artery pressure in Fontan circulations was correlated with either P-mcf (P <less than or equal to> 0.04). We conclude that in Fontan circulations 1) pulmonary vascular r esistances induce a proportional decrease in G(vr); and 2) volume loading, while increasing P-mcf (similar to pulmonary artery pressure), allows the g radient for Q(vr) to increase and maintains systemic blood flow at a bivent ricular level.