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.
An HVPG of ≥5 mmHg defines portal hypertension, and if the measurement exceeds 10 mmHg it is called clinically significant portal hypertension.
[5] While not widely performed, its assessment in people with chronic liver disease is recommended to monitor response to treatment.