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Schematic representation of the anatomic classification of portal hypertension (PH). Portal hypertension can be because of prehepatic, intrahepatic (presinusoidal, sinusoidal or postsinusoidal) and posthepatic causes. Indirect evaluation of portal venous pressure (PVP) can be obtained by catheterization of the caudal vena cava and advancement of the catheter into the hepatic veins. This permits measurement of the free hepatic vein pressure (FHVP), which reflects caudal vena cava pressure. Measurement of the wedged hepatic vein pressure (WHVP) is accomplished by occluding the hepatic vein by inflation of the catheter balloon. WHVP is a measure of sinusoidal pressure which in the normal state is slightly lower (about 1 mmHg) than PVP. The hepatic venous pressure gradient (HVPG) is calculated as the difference between the WHVP and FHVP. This gradient is increased with intrahepatic sinusoidal and postsinusoidal PH, but not with prehepatic and presinusoidal intrahepatic PH (where both WHVP and FHVP are usually normal) or with posthepatic PH (where WHVP, FHVP and central venous pressure, CVP, are elevated). | Buob, S., Johnston, A. N., & Webster, C. R. L. (2011). Portal Hypertension: Pathophysiology, Diagnosis, and Treatment. Journal of Veterinary Internal Medicine, 25(2), 169–186. https://doi.org/10.1111/j.1939-1676.2011.00691.x

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