Normal portal pressure is about 9 mmHg and a normal inferior vena cava pressure is about 2-6 mmHg. This creates a normal pressure gradient of 3-7 mmHg. If the portal pressure rises above 12 mmHg, th gradient rises to more than 5 mm Hg. A gradient greater than 5 mmHg is defined as portal hypertension. Once gradient becomes greater than 10 mmHg, blood flowing though the hepatic portal system gets redirected from the liver into areas with lower venous pressures. This creates collateral circulation in the lower esophagus, abdominal wall, stomach, and rectum.
AWV = abdominal wall vein, GEV = gastroesophageal vein, IMV = inferior mesenteric vein, IVC = inferior vena cava, LGV = left gastric vein, LPV = left portal vein, LRV = left renal vein, MV = mesenteric vein, PDV = pancreaticoduodenal vein, PEV = paraesophageal vein, PV = portal vein, RPPV = retroperitoneal-paravertebral vein, SMV = superior mesenteric vein, SRV = splenorenal vein, SV = splenic vein, UV = umbilical vein.
