Modeling of oxygen transport in blood-perfluorocarbon emulsion mixtures: Part II: tissue oxygenation

The models developed in the accompanying article in this issue for oxygen transport in uniform (pseudo-homogeneous model) and non-uniform (core annulus model) dispersions of erythrocytes and perfluorocarbons (PFCs) have been analyzed with a fixed wall flux boundary condition. Such a situation arises in the case of oxygen transport from a capillary to the surrounding tissue. The results reveal that PFCs are extremely effective in increasing the tissue oxygen tension during enriched air breathing. The increased oxygen capacity of blood on the addition of PFC emulsion is the main contributor toward this increase. If the contribution of the accompanying increase in the arterial oxygen tension also is considered, the resulting increase in the tissue oxygen tension was even larger than that observed by Braun et al, and hence other factors, such as an increase in the cardiac output or service of erythrocyte free capillaries, need not be invoked. A near wall excess of PFC droplets, if it occurs, has been shown to have a negligible effect on the tissue oxygen tension during normal rates of tissue oxygen consumption when the intracapillary gradients are small. In these conditions, the capillary phase may be taken to be uniform. A criterion has been developed to assess the magnitude of the gradients within the capillary. Accordingly, in cases of elevated rates of tissue oxygen consumption or low arterial oxygen tensions, the internal gradients become important and the capillary phase can no longer be taken to be uniform.