The normal poal venous pressure under normal physiological conditions is:

The poal venous system contributes approximately 75% of the blood and 72% of the oxygen supplied to the liver. In the average adult 1000 to 1500 mL/min of poal venous blood is supplied to the liver. The normal poal venous pressure is 5 to 10 mmHg, and at this pressure very little blood is shunted from the poal venous system into the systemic circulation. As poal venous pressure increases, however, the communications with the systemic circulation dilate, and a large amount of blood may be shunted around the liver and into the systemic circulation. Ref: Tsung A. (2010). Chapter 31. Liver. In T.R. Billiar, D.L. Dunn (Eds),Schwaz's Principles of Surgery, 9e.