Mechanisms and consequences of portal hypertension

Abstract

Portal hypertension is characterised by alterations in the splanchnic and systemic circulation resulting in the development of portosystemic collateral channels, the most important of which are found in the lower oesophagus and stomach. The major clinical complication of gastro-oesophageal varices is bleeding and over the last decade there has been considerable interest in the pharmacological management of this complication. The factors currently implicated in the development of gastro-oesophageal varices in patients with cirrhosis include a) increased portal vascular resistance, b) splanchnic and systemic vasodilatation and c) changes in the lower oesophageal venous anatomy [palisade and perforating venous zones]. In a patient with gastrointestinal bleeding, endoscopic examination of the upper gastrointestinal tract will confirm the diagnosis of portal hypertension by confirming the presence of gastro-oesophageal varices. Cirrhosis is the most common aetiological factor for gastro-oesophageal varices, but imaging techniques, including Doppler ultrasound, computerised tomography and venous phase angiography, may be required to exclude extrahepatic portal venous obstruction from the differential diagnosis. Although the pathogenesis of variceal rupture remains unclear, several risk factors for variceal haemorrhage have been identified, including a) increased size, b) high intravariceal-portal pressure, c) increased varix wall tension characterised by the presence of red spots observed at endoscopy (particularly in large varices since wall tension is related to variceal size), and d) poor liver function. Although oesophagitis may be observed at endoscopy, an erosive mechanism is no longer considered to be of pathogenic significance. A high portal pressure in the immediate postbleeding period is now recognised as predictive of rebleeding. Periodic elevations in intravariceal pressure, associated with the release of enhanced endogenous vasoactive compounds, or beta-adrenergic-mediated stress-related increases in portal pressure, may contribute to the rupture mechanism. Consequently, portal hypertension is now being more widely considered as a multiorgan disorder associated with changes in blood flow within both systemic and splanchnic vascular beds. This article reviews the factors currently implicated in the development of portal hypertension and the approach to diagnosis. The pathogenesis of variceal bleeding will also be considered.