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.