Effect of microvascular rarefaction on tissue oxygen delivery in hypertension

A mathematical model of oxygen transport in tissue was used to analyze the effects of microvessel rarefaction and nonhomogeneous oxygen consumption on tissue oxygen distribution. The model was based on the diffusion equation with a nonhomogeneous consumption term. Solutions were computed for several configurations of vessel and oxygen sink distributions on a finite domain using the finite element method. A microcirculatory unit consisting of a tissue slice of 100-microns depth and 40-microns width was chosen. Symmetry boundary conditions were applied so that the entire tissue consisted of a series of such microvascular units placed side by side. The boundary condition at the surface of the unit was chosen to simulate a tissue suffusion experiment in which the suffusion oxygen was varied from 0 to 37 mmHg. Results of the model, which were compared with direct measurements with oxygen microelectrodes, indicate that vascular oxygen delivery strongly dominates the tissue oxygen field for suffusion PO2 values of less than 20 mmHg, whereas above this level tissue oxygen is dominated by the suffusion PO2. Reduction of vessel density within the tissue was found to have the largest effect on tissue oxygen levels at low suffusion oxygen. Finally, under some configurations of oxygen sources (vessels) and sinks (mitochondria), extremely low PO2 levels may exist within the area of high consumption, which could limit the metabolic activity of the tissue.