The hepatic haemodynamic response to acute portal venous blood flow reductions in the dog.

The hepatic haemodynamic response to acute reductions in portal venous blood flow was investigated in 14 anaesthetized normal dogs. A side-to-side mesocaval anastomosis was constructed to enable varying degrees of portal flow to be diverted into the inferior vena cava by suitable manipulations of the shunt diameter. Measurements of portal venous and hepatic arterial blood flow were made with electromagnetic flowmeters. A linear relationship was observed between the degree of reduction in portal flow and the magnitude of the resulting hepatic arterial hyperaemic response. Hepatic arterial vascular resistance showed a decrease which became more pronounced the greater the degree of reduction in portal flow. For every 1.0 ml X min-1 100 g-1 decrease in portal flow, the hepatic arterial flow increased by a mean of 0.24 ml X min-1 X 100 g-1, a value representing the average compensatory capacity of the arterial response. Arterial flow improvement therefore provided some degree of protection against severe falls in total liver blood flow. However, it provided even more effective protection against any fall in total hepatic oxygen consumption, which showed only a very gradual decrease with reduced hepatic portal blood flow.