20 The results showed a significant inverse correlation between Doppler measurements and HVPG values. However, a correlation between the portal vein velocity and the HVPG was not confirmed in a recent study.21 Surprisingly, in these studies, neither hepatic artery resistance nor mesenteric artery resistance was correlated with the severity of portal hypertension. It should be noted that this method may not accurately characterize the portal blood flow because it measures only the peak velocity, whereas the flow is known

to be parabolic. Furthermore, Cyclopamine this method is operator-dependent and has poor reproducibility in obese patients. Thus, further studies are needed to confirm these results, and studies should be performed in patients with asymptomatic cirrhosis to determine the portal vein velocity or flow values that correspond to the presence Dabrafenib datasheet of severe portal hypertension. Different factors contribute to the increased vascular resistance of the liver in patients with cirrhosis.22 One component is the hyperproduction of endogenous vasoconstrictors. For example, serum endothelin levels have

been shown to be significantly correlated with HVPG values in patients with cirrhosis.23 Thus, serum endothelin levels could be used to evaluate the degree of portal hypertension; however, further studies are needed to determine whether this dosage can be used in clinical practice. Recently, peripheral circulating cells associated with vascular injury were evaluated in patients with cirrhosis.24 The results showed

that the circulating endothelial cell count or the ratio of circulating endothelial cells to the platelet count is potentially a new biomarker of portal hypertension, but further clinical investigations are needed to confirm these results. Increased hepatic vascular resistance in patients with cirrhosis is also influenced by the presence and extent of fibrosis.4, 5 In one recent study, the area of liver collagen, which is Protein kinase N1 the major component of fibrous tissue, was measured by computer-assisted image analysis and was found to be significantly correlated with the HVPG in patients with cirrhosis.5 Accordingly, an evaluation of the extent of hepatic fibrosis may provide information about the presence and severity of portal hypertension. The noninvasive estimation of hepatic fibrosis has been a subject of extensive research in the last 10 years. However, only a few of these procedures have been evaluated for the noninvasive diagnosis of portal hypertension (Table 2). Only the methods that have evaluated the relationship between hepatic fibrosis and portal hypertension are reported in this review. Different markers of hepatic fibrosis have been studied to assess portal hypertension.