Blood cell distribution in small and large vessels: Effects of wall and rotating motion of red blood cells

Abstract

A two-dimensional computer simulation of blood flow between two parallel plates as the tube was performed to understand the distribution of red blood cells (RBCs) and platelets (PLTs) according to the blood vessel size. The motion of the blood cells (BCs) was directly calculated using the particle method. The tube diameter and hematocrit were set as 20-500 µm and 0-0.4, respectively. In simulations with tank-treading (TT) RBCs under the planar Poiseuille flow, RBCs moved from the tube wall to form a cell-free layer (CFL). Then, the PLTs moved into the CFL, and the RBCs concentrated around the tube center, excluding the PLTs. By comparing the BC distribution between the Couette and Poiseuille flows, the range of the wall effect was estimated to be ≤50-100 µm at the hematocrit of 0.4. Tumbling (TB) RBCs uniformly distributed inside the tube, while forming rouleaux-like aggregates on the wall at 0.4 in hematocrit; at hematocrit ≤0.3, the TB RBCs tended to be excluded from the tube center as known to the tubular pinch effect. The mechanical interaction among the RBCs and tube wall facilitated TT motion even if the apparent shear rate was so small that an RBC in a dilute suspension would exhibit TB motion. These results indicate that the TT motion of RBCs combined with the wall effect plays a major role in forming CFL and avoiding aggregation of BCs and that TB motion helps BCs to distribute uniformly in large vessels where the shear rate is relatively low.

Keywords: Biomechanics; Blood flow; Particle method; Red blood cells, Platelets; Tank-treading motion; Tumbling motion.