Methods for assessing hepatic distending pressure and changes in hepatic capacitance in pigs

The equilibrium pressure obtained during simultaneous occlusion of hepatic vascular inflow and outflow was taken as the reference estimate of hepatic vascular distending pressure (P-hd). P-hd at baseline was 1.1 +/- 0.2 (mean +/- SE) mmHg higher than hepatic vein pressure (P-hv) and 0.7 +/- 0.3 mmHg lower than portal vein pressure (P-pv). Norepinephrine (NE) infusion incre ased P-hd by 1.5 +/- 0.5 mmHg and P-pv by 3.7 +/- 0.6 mmHg but did not sign ificantly increase P-hv. Hepatic lobar vein pressure (P-hlv) measured by a micromanometer tipped 2-Fr catheter closely resembled P-hd both at baseline and during NE-infusion. Dynamic pressure-volume (PV) curves were construct ed from continuous measurements of P-hv and hepatic blood volume increases (estimated by sonomicrometry) during brief occlusions of hepatic vascular o utflow and compared with static PV curves constructed from P-hd determinati ons at five different hepatic volumes. Estimates of hepatic vascular compli ance and changes in unstressed blood volume from the two methods were in cl ose agreement with hepatic compliance averaging 32 +/- 2 ml.mmHg(-1).kg liv er(-1). NE infusion reduced unstressed blood volume by 110 +/- 38 ml/ kg li ver but did not alter compliance. In conclusion, P-hlv reflects hepatic dis tending pressure, and the construction of dynamic PV curves is a fast and v alid method for assessing hepatic compliance and changes in unstressed bloo d volume.