Pulmonary–Hepatic vascular Disorders (PHD)

⇓“The tantalizing problem of the connective link in cirrhotic patients between oxygen unsaturation and possible arteriovenous shunting in the lungs remains unsolved, and any relation between arterial unsaturation and pulmonary vasodilation remains obscure.” Fig. 1.— Working model of molecular alterations in the pulmonary microcirculation in experimental hepatopulmonary syndrome (HPS). a) In the normal microvasculature, a balance of vasoconstrictive and vasodilatory factors, including paracrine endothelin (ET)-1-mediated vasoconstriction through the ETA receptor (▪) on smooth muscle cells (SMCs) and ET-1-mediated vasodilatation mediated through the ETB receptor (□) linked to endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs), maintain tone. b) During the development of HPS, a number of alterations, both directly and indirectly related to hepatic injury and portal hypertension, result in the production or release of mediators into the venous circulation, where they influence the pulmonary microcirculation. Increased expression of pulmonary endothelial ETB receptors and increased hepatic production and release of ET-1 contribute to an increase in eNOS expression and enhanced nitric oxide (NO) production in the microvascular endothelium during the initiation of HPS. Tumour necrosis factor (TNF)-α-mediated accumulation of intravascular macrophage-like cells also occurs after chronic common bile duct ligation. Haem oxygenase (HO)-1 and inducible nitric oxide synthase (iNOS) expression increase in these cells and contribute to the progression of HPS. CO: carbon monoxide. Fig. 2.— Algorithm for screening and therapeutic decisions in hepatopulmonary syndrome (HPS). OLT: orthotopic liver transplantation; P a,O2: arterial oxygen tension; P A–a,O2: alveolar–arterial oxygen tension difference; CEE: contrast-enhanced echocardiography; PFT: pulmonary function test; MAA: macroaggregated albumin. #: high-resolution thoracic computed tomographic scanning is highly recommended in order to exclude chronic respiratory comorbid conditions; ¶: high risk for post-operative OLT mortality. 1 mmHg=0.133 kPa. Fig. 3.— Plot demonstrating the relationship between cardiac output ( Q ') and transpulmonary pressure gradient (TPG; mean pulmonary arterial …