Simulations of blood as a suspension predicts a depth dependent hematocrit in the circulation throughout the cerebral cortex
Fig 8
Schematic of the depth dependent hematocrit network effect.
At the microcirculatory level, blood is a suspension of red blood cells in plasma with a thin boundary layer close to the vascular wall which contains little or no red blood cells. When red blood cells suspended in plasma flow through a bifurcation of a penetrating artery, they tend to concentrate in the thicker daughter branch, while the thinner side branch syphons a comparatively higher fraction of plasma from the cell free layer near the wall of the parent branch. This effect is known as plasma skimming. When plasma skimming repeats over many bifurcations of the cortical microcirculation, deeper reaching paths through the capillary bed tend to have higher hematocrit than surface paths. Longer path length incurs higher flow resistance leading to less bulk flow. In effect, total RBC flux, which is the product of hematocrit times flow, is more balanced than if RBC splits were even. The network effect also reduces variability in RBC fluxes, so that deeper layers are more evenly perfused. Our simulations implicated network effects due to biphasic blood rheology for the predicted hematocrit gradients and increased RBC flux homogenization.