The resistance encountered by blood as it flows through the blood vessels is called blood flow resistance. As blood flows, it consumes energy due to friction, which is generally expressed as heat energy. This thermal energy cannot be converted into potential or kinetic energy of the blood, so the pressure of the blood gradually decreases as it flows through the blood vessels. In the case of turbulent flow, each mass in the blood constantly changes the direction of flow, so the energy consumed is more than in laminar flow, and the resistance to blood flow is greater. The increase in resistance to blood flow is mainly influenced by the viscosity of the blood. From the Poiseuille law can be seen, blood flow resistance and blood viscosity is directly proportional. Any factor that increases blood viscosity may increase peripheral resistance, increase blood pressure, and increase the burden on the heart. Blood pressure can be reduced by taking appropriate medications and foods that lower blood pressure. Blood viscosity: It is an important indicator to reflect the nature of blood flow. Normal blood viscosity is an important condition to ensure the normal operation of blood circulation, especially microcirculation. Once the blood viscosity increases, the blood flow slows down, and a large amount of lipids and shed endothelial cells are easily deposited on the intima, making the blood vessels narrow and the blood flow slow, and the oxygen and nutrients obtained by the body are relatively reduced. When the viscosity of blood increases to a certain degree, coagulation occurs, i.e., blood clots appear, causing vascular embolism, which leads to ischemic cardiovascular and cerebrovascular diseases. Portal hypertension is a group of syndromes caused by a persistent increase in portal venous pressure, which is caused by cirrhosis in the majority of patients, but in a minority of patients it is secondary to obstruction of the main portal vein or hepatic veins and some unexplained factors. Portal hypertension is divided into three categories according to the anatomical location: prehepatic, intrahepatic and posthepatic. The intrahepatic type is the most common in China, accounting for more than 90% of cases. The intrahepatic type is divided into sinusoidal, pre-sinusoidal and post-sinusoidal types according to the site of hepatic circulation disorder. Among them, sinusoidal type is the main cause of hepatic microcirculation disorder. The increase of portal vein pressure after the obstruction of portal blood return causes: ① the opening of portal traffic branch ② the increase of hepatic artery blood flow. Clinical manifestations of portal hypertension: ① splenomegaly and hypersplenism ② establishment of collateral circulation ③ ascites.