Effect of cytosol viscosity on the flow behavior of red blood cell suspensions in microvessels

Objective The flow behavior of blood is strongly affected by red blood cell (RBC) properties, such as the viscosity ratio C between cytosol and suspending medium, which can significantly be altered in several pathologies (e.g. sickle-cell disease, malaria). The main objective of this study is to understand the effect of C on macroscopic blood flow properties such as flow resistance in microvessels, and to link it to the deformation and dynamics of single RBCs. Methods We employ mesoscopic hydrodynamic simulations to investigate flow properties of RBC suspensions with different cytosol viscosities for various flow conditions in cylindrical microchannels. Results Starting from a dispersed cell configuration which approximates RBC dispersion at vessel bifurcations in the microvasculature, we find that the flow convergence and development of RBC-free layer (RBC-FL) depend only weakly on C, and require a convergence length in the range of 25D-50D, where D is channel diameter. In vessels with D <= 20 mu m, the final resistance of developed flow is nearly the same for C = 5 and C = 1, while for D=40 mu m, the flow resistance for C = 5 is about 10% larger than for C = 1. The similarities and differences in flow resistance can be explained by viscosity-dependent RBC-FL thicknesses, which are associated with the viscosity-dependent dynamics of single RBCs. Conclusions The weak effect on the flow resistance and RBC-FL explains why RBCs can contain a high concentration of hemoglobin for efficient oxygen delivery, without a pronounced increase in the flow resistance. Furthermore, our results suggest that significant alterations in microvascular flow in various pathologies are likely not due to mere changes in cytosolic viscosity.

Automated summary

The viscosity ratio C between cytosol and suspending medium has a weak effect on flow resistance and RBC-FL development, with a required convergence length. Although in certain diameter vessels, flow resistance is nearly the same for different C values, in larger vessels, a 10% difference in flow resistance is observed. This suggests that alterations in microvascular flow in pathologies are not solely due to changes in cytosolic viscosity.