Hepatopulmonary syndrome: proposed mediators of pulmonary vasodilation

Hepatopulmonary syndrome (HPS) is a severe complication seen in the advanced liver disease. It is characterized by the triad of abnormal arterial oxygenation caused by intrapulmonary vascular dilatations (IPVD) in the setting of advanced liver disease, portal hypertension, or congenital portosystemic shunts. Liver transplantation is the only curative option for HPS. Pulmonary vascular dilation and angiogenesis are two central pathogenic features that cause abnormal pulmonary gas exchange in experimental HPS, and thus might underlie HPS in humans. The vascular component includes diffuse or local dilation of the pulmonary capillaries, and less commonly includes pulmonary arteriovenous shunts. The mechanisms responsible for the vascular changes in HPS remain incompletely understood. Research into the underlying molecular mechanisms has mainly focused on the roles of nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S), ATP-sensitive K+ channels (KATP channels), endothelin-1 (ET-1), tumor necrosis factor-alpha (TNF-α), etc. and is summarised below