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Portal Hypertension:
Discuss portal pressure?
Portal venous pressure is determined by the product of portal venous flow and the resistance to outflow from the portal venous system:
Portal pressure = Portal venous flow x portal venous outflow resistance
It is usually caused by an increase in resistance in the portal-hepatic vascular bed due to obstruction to flow, which in the vast majority of patients is related to cirrhosis.
However, a variety of disorders can cause portal hypertension in the absence of cirrhosis, a condition referred to as “noncirrhotic portal hypertension.”
In both the above cases the PH is because of increased resistance, but rarely PH can result because of increased portal flow in normal resistance, e.g. splanchnic AF fistula
Discuss portal vein anatomy?
Discuss the normal pressure and flows?
Hepatic vein pressure= 4mm Hg
Portal vein pressure= 7mm Hg
Hepatic artery pressure = 100 mm Hg
Hepatic vein flow = 1600ml/mt
Portal vein flow = 1200ml/mt
Hepatic artery flow = 400ml/mt
Portal pressure is 7 mm Hg (remember this is an average value – but absolute in nature rather than below)
Portal hypertension is defined by a hepatic venous pressure gradient (HVPG) greater than 5 mmHg.
When the portal circulation is obstructed, whether it is within or outside the liver, a remarkable collateral circulation develops to carry portal blood into the systemic circulation veins.
Collaterals usually imply PH although occasionally if the collateral circulation is very extensive portal pressure may fall.
Conversely PH of short duration can exist without a demonstrable collateral circulation
Haemodynamic of PH
Normally 100% of portal blood flow is recoverable from hepatic veins whereas in cirrhosis only 13% goes to hepatic vein and rest reaches the systemic circulation through the collaterals
Discuss portal pressure studies?
FHVP | WHVP | HV-PG | |
---|---|---|---|
Pre-sinusoidal
Eg. Schistosomiasis/ NCPF |
Normal | Normal | Normal |
Sinusoidal
Eg. Cirrhosis |
Normal | High | High |
Post- sinusoidal
Eg. Budd Chiari |
High | High | Normal |
Discuss the causes of portal hypertension?
Causes of presinusoidal portal hypertension – associated with relatively normal hepatocellular function and consequently if patient suffers a haemorrhage from varices liver failure is rarely a consequence in contrast patients with the intra-hepatic type frequently develop liver failure after bleeding
Causes of Sinusoidal portal hypertension
Causes of post sinusoidal portal hypertension
Discuss the mechanism of increased resistance in sinusoidal portal hypertension?
As a general rule, the clinical consequences of portal hypertension are similar regardless of the cause or site of obstruction. However, several pathophysiologic changes are related to specific types and causes of portal hypertension, which may influence their clinical presentation and therapy.
Liver Cirrhosis: pic shows destruction and fibrosis in centre, with remaining nodules of more normal liver at bottom right and top left. Note the irregular whorls of fibrosis around the nodules.
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