(218h) Cell Distributions and Segregation during Blood Flow within Curved and Bifurcated Vascular Geometries in Blood Disorders

The spatial distribution of different cellular components of blood is nontrivial. Red blood cells (RBCs) migrate toward the vessel center leaving an RBC-depleted cell-free layer (CFL) near vessel walls, whereas white blood cells and platelets reside in the CFL, a flow-induced segregation termed margination. The margination may have significance in some blood cell disorders, such as sickle cell disease (SCD). A complication of SCD is chronic vasculopathy, in which the endothelial cells that line the vessels are dysfunctional and pro-inflammatory in the circulation. One might hypothesize that diseased cells strongly marginate, residing primarily in the CFL, and generating physical interactions that damage the endothelium.

We characterize cell distributions for mixtures of normal and aberrant RBC in straight, curved and bifurcated vascular geometries using an immersed boundary method. We test the hypothesis with a range of blood disorders, such as SCD, iron deficiency anemia, COVID-19, and spherocytosis. We find smaller and stiffer aberrant RBCs strongly marginate, suggesting the difference in cell size, shape, and deformability are adequate to induce cell segregation. We find marginated aberrant cells close to walls causing large shear stresses fluctuation, potentially leading to increased vascular inflammation. In curved vessels, we find a highly inhomogeneous distribution of marginated cells, highlighting the influence of vascular geometries on cell segregation. In addition, we examine the modified Zweifach-Fung (Z-F) effect at vessel bifurcations in blood disorders. Cell segregation results in a thinner CFL, which reduces the Z-F effect and leads to higher-than-normal hematocrits in low-flow branches, an observation of potential clinical importance for SCD.