The essence of hepatic gas in the lungs is hypoxemia caused by vasodilation and abnormal oxygenation of arterial blood in the lungs. The available research data show that the occurrence of hepatic gas in the lungs is associated with at least systemic hyperdynamic state, portal hypertension, hepatic encephalopathy, hepatorenal syndrome and pulmonary hypertension. Therefore, its occurrence is also caused by systemic metabolic and hemodynamic disorders, and it is also involved in the formation of systemic metabolic and hemodynamic disorders, which has important pathophysiological significance. The pathogenic factors of liver gas offending lung: 1, increased vasodilator activity: various acute and chronic liver disease hepatocyte failure, metabolic disorders, especially the reduction of vasoactive substances inactivation, and through the abnormal anastomosis of the collateral vessels directly into the body circulation, resulting in systemic hemodynamic disorders, the blood circulation vasodilator substances content increased, as in patients with portal hypertension visceral congestion, acting on the lung The pulmonary vasodilatation and pulmonary congestion are caused by the blood vessels. The substances that cause vasodilation are: hyperglycemia, prostaglandins, vasoactive intestinal peptide, nitric oxide, vasopressor, bradykinin and its endotoxin, etc. 2, reduction of vasoconstrictive substances or decreased sensitivity of the vascular bed in the lung to endogenous vasoconstrictive substances: such as norepinephrine, endothelin, cardiac natriuretic hormone, vasopressin, 5-hydroxytryptamine, tyrosine, etc. The content of these substances is not absolutely reduced, it is possible that the sensitivity of their action is reduced. Resulting in the original closed non-functional capillary pre-capillary traffic branch open, as well as the originally normal hypoxic pulmonary vasoconstriction dysfunction, only 75% of normal. 3, neurological factors: sympathetic nerve tone is hyperactive in patients with cirrhosis, but after the formation of portal hypertension, sympathetic nerve function is impaired in vivo, which may play an important role. . 4.Reduced responsiveness of intrapulmonary vessels to hypoxia: In recent years, it was found that patients with cirrhosis with more than 2 spider nevi not only showed impaired liver function, but also reduced systemic vascular and intrapulmonary vascular resistance, reduced vascular responsiveness to hypoxia, and dilated intrapulmonary vessels. However, some people apply pulmonary angiography although they find the vascular dilatation at the end of the artery, but the response to oxygen administration is almost normal, which does not support this view. 5, abnormal angiogenesis or development in the lung: it may also be one of the factors of liver qi offending the lung. So far, the mechanism of liver qi offending the lung is not clear. However, the long-term effect of vasoactive substances in the lung can cause a significant increase in intracellular cyclic adenosine monophosphate (cAMP) and/or cyclic guanosine monophosphate (cGMP), leading to hypoxic pulmonary vasodilatation and pulmonary artery dilation, which may be an important cause of the disease.