Does the oxygen concentration equilibrate between red blood cells in the liver sinusoids? In the sinusoids of the liver, venous blood from the hepatic portal system mixes with arterial blood from the hepatic arteries. Do oxygen molecules move between oxygenated RBCs and non-oxygenated RBCs, so that the partial oxygen saturation of the blood in the sinusoids reflect partial saturation of the RBCs? Or do RBCs retain their initial oxygen saturation, so that the partial saturation of the blood in the sinusoids reflects a mixture of saturated and unsaturated RBCs?

The **oxygen saturation** (in lungs) and desaturation (in target organs) **takes place via diffusion** along the concentration gradient (i.e. partial pressure for gases). Therefore as long as **RBCs** from two different sources and **having different partial pressure** of oxygen mix up, the oxygen level **starts to equilibrate** between these cells.

But **diffusion** as a passive mechanism **is not very fast** and can take some time. So the only possibility for the second variant (there is a mixture of two types of RBCs) is if the mixture exists for very short time in liver sinusoids, so that the blood leaves them without really mixing completely up.

This is not true, **at leastin some animal models the blood within the liver seems to reach equilibrium very quickly** and its resulting partial pressure can be influenced by adjusting the blood flow from different sources (using vasoactive substances injected directly, as in the referenced paper).