Portal venous pressure is the blood pressure in the hepatic portal vein, and is normally between 5-10 mmHg. Raised portal venous pressure is termed portal hypertension, and has numerous sequelae such as ascites and hepatic encephalopathy.
Wedged Hepatic Venous Pressure (WHVP) 
WHVP is used to estimate the portal venous pressure by reflecting not the actual hepatic portal vein pressure but the hepatic sinusoidal pressure. It is determined by wedging a catheter in a hepatic vein, to occlude it, and then measuring the pressure of proximal static blood (which is reflective of pressure in the sinusoids). WHVP in fact slightly underestimates portal pressure due to sinusoidal equilibration in patients without cirrhosis, but the difference between the two is clinically insignificant. In patients with cirrhotic livers intersinusoidal communication is disrupted such that sinusoidal pressure equilibrium cannot be maintained, and so WHVP becomes a far more accurate measure of portal venous pressure.
Hepatic Venous Pressure Gradient (HPVG) 
HVPG is a clinical measurement of the pressure gradient between the wedged hepatic venous pressure (WHVP) and the free hepatic venous pressures, and thus is an estimate of the pressure gradient between the portal vein and the inferior vena cava. An HPVG of ≥10 mmHg defines clinically significant portal hypertension, and if the measurement exceeds 12 mmHg variceal haemorrhaging may occur.
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