Effect of suspending viscosity on red blood cell dynamics and blood flows in microvessels.

To obtain a better understanding of the beneficial effect of high plasma viscosity observed in hemodilution and resuscitation experiments, we conducted a computational study to investigate the suspending viscosity effect on red blood cell (RBC) dynamics and blood flow behaviors in microvessels. For single RBCs in simple shear or channel flows, RBCs appear more flexible as indicated by the tank-treading motion in shear flows and the strong transverse migration in channel flows. For the multiple RBC flows in straight channels, our results indicate no significant change with the suspending viscosity in stable flow structure and hemorheologic behaviors, under both constant flow and forcing conditions. However, due to the increase in apparent cell deformability in a more viscous medium, the cell-free layer (CFL) can be established in a shorter distance along the channel. Considering the multilevel bifurcated structure of the microvascular network, this change in CFL development distance may affect the phase skimming and RBC separation processes at the downstream bifurcation, and therefore the microcirculation performance in the tissue. This may suggest a possible mechanism for the high functional capillary density associated with a high suspending viscosity observed in experiments.