Non-uniform plasma leakage affects local hematocrit and blood flow: implications for inflammation and tumor perfusion.

Vessel leakiness is a hallmark of inflammation and cancer. In inflammation, plasma extravasation and leukocyte adhesion occur in a coordinated manner to enable the immune response, but also to maintain tissue perfusion. In tumors, similar mechanisms operate, but they are not well regulated. Therefore, blood perfusion in tumors is non-uniform, and delivery of blood-borne therapeutics is difficult. In order to analyze the interplay among plasma leakage, blood viscosity, and vessel geometry, we developed a mathematical model that explicitly includes blood cells, vessel branching, and focal leakage. The results show that local hemoconcentration due to plasma leakage can greatly increase the flow resistance in individual vascular segments, diverting flow to other regions. Similarly, leukocyte rolling can increase flow resistance by partially blocking flow. Vessel dilation can counter these effects, and likely occurs in inflammation to maintain blood flow. These results suggest that potential strategies for improving perfusion through tumor networks include (i) eliminating non-uniform plasma leakage, (ii) inhibiting leukocyte interactions, and (iii) preventing RBC aggregation in sluggish vessels. Normalization of tumor vessels by anti-angiogenic therapy may improve tumor perfusion via the first two mechanisms.