Subdiaphragmatic venous hemodynamics in the Fontan circulation

Objective: We investigated the subdiaphragmatic venous physiology in patien ts subjected to the Fontan operation to understand some of the early and la te problems of this circulation. Methods: Flows were evaluated by Doppler ultrasonography in the subhepatic inferior vena cava, hepatic vein, and portal vein during respiratory monito ring and with a tilt table. Twenty control subjects (group A) and 56 patien ts who had the Fontan operation, 27 in functional class I(group B) and 29 i n class III or IV (group C), were studied. Inspiratory/expiratory flow rati o was calculated to reflect respiratory effects, and upright/supine flow ra tio was calculated to assess gravity effects. Inferior vena caval, hepatic venous, and wedged hepatic venous pressures were measured during catheteriz ation in 21 control subjects and 25 Fontan patients. The difference between wedged and hepatic venous pressures represents the transhepatic venous pre ssure gradient. Results: Fontan hepatic venous flow depended more on inspiration than contr ol, but without difference between groups B and C (inspiratory/expiratory f low ratios: 1.7, 2.9, and 2.9, respectively; P < .02). Normal portal venous flow was higher in expiration; this effect was lost in group B and reverse d in group C (inspiratory/expiratory flow ratios: 0.8, 1.0, and 1.3; P < .0 005). Gravity reduced portal venous flow in groups A and B, but progression to functional class III or IV (group C) exacerbated this effect (upright/s upine flow ratios: 0.8, 0.7, and 0.5; P < .01). Inferior vena caval, hepati c venous, and wedged hepatic venous pressures tin millimeters of mercury) i n the Fontan groups were all elevated compared with the control group (infe rior vena cava, 14.4 <plus/minus> 4.4 vs 5.9 +/- 2.3; hepatic vein, 14.7 +/ - 4.5 vs 5.9 +/- 1.9; wedged hepatic vein, 14.7 +/- 4.0 vs 8.3 +/- 2.6; P < .0001). However, trans hepatic venous pressure gradient in the Fontan grou p was lower than in the control group (0.5 <plus/minus> 0.5 vs 2.3 +/- 2.0; P < .001). Univariate analysis of inferior vena caval pressure and transhe patic venous pressure gradient showed significant inverse correlation (r = 0.6, P < .002). Conclusions: In patients who are in functionally poorer condition after the Fontan operation, portal venous flow loses normal expiratory augmentation and adverse gravity influence is enhanced. These suboptimal flow dynamics, coupled with higher splanchnic venous pressures and lower transhepatic veno us pressure gradients, suggest that hepatic sinusoids are congested, acting as "open tubes." Transhepatic gradient loss is incrementally worse with hi gher caval pressures. These observations may be responsible for late gastro intestinal problems in patients who have had the Fontan operation.