Impact of Red Blood Cell Deformability and Local Hematocrit on Microvascular Flow Resistance: Insights from In Vitro Microfluidic Measurements and Viscosity Modeling.

Altered red blood cell (RBC) deformability can impact microvascular flow resistance through changes in cell partitioning at bifurcations, and local hematocrit distribution, a key determinant of the effective viscosity of blood. In this work we report on resistance-relevant viscosity distributions extracted from in vitro microfluidic observations of a Y-junction type blood flow. Spatially resolved hematocrit distributions in the parent channel and daughter branches, determined by experimental measurements in earlier work, for healthy and stiffened RBC suspensions over a range of daughter to parent flow-split ratios, Q*, are combined with a recently proposed viscosity model enabling the estimation of the local relative viscosity profiles ηr. The maximum of the RBC elongation index EI, was utilized to define of the deformability parameter λ, which with the local RBC volume fraction, Φ(y), were used as inputs in the relative viscosity, ηr. The latter is a modified Krieger-Dougherty viscosity expression, accounting explicitly for deformability and RBC concentration. The resulting viscosity profiles are averaged in the channel regions of interest to provide an apparent viscosity in the branches, used here as an indicator of microvascular flow resistance. The results illustrate that deformability and hematocrit-dependent RBC enrichment or depletion in the branches of a vascular junction may amplify or attenuate the resistance asymmetry in the daughters of the Y-junction.