A note on the interpretation of tracer dispersion in the liver

The transit time distribution of intravascular markers and highly diffusible solutes is determined by the mixing process within the network of interconnected sinusoids. Based on the role of the relative dispersion or coefficient of variation (CV2) of transit times as a measure of distribution dynamics (macromixing) various intrahepatic mixing processes are discussed, which are implied by current models of hepatic elimination. The opposite extremes of perfect micromixing and complete segregation are reflected by the dispersion model and the distributed parallel tube model, respectively. Assuming various capillary structures-including that of a fractal network-the dispersion models differ with regard to the predicted scaling behaviour of CV2. The observed flow independence of CV2 suggests that molecular diffusion and Taylor dispersion can be neglected but does not allow discrimination between mixing models.