Portopulmonary hypertension is reported to occur in 2%–5% of patients with liver cirrhosis
and portal hypertension. Three mechanisms are thought to play a causal role:
First, vasoactive substances such as serotonin, interleukin 1, endothelin 1, and thromboxane, which may cause vasoconstriction and mitogenesis in the pulmonary arteries, escape hepatic detoxifying mechanisms through portosystemic shunts or are not cleared as effectively by the diseased liver.