Chapter 9 - Shear Stress Variation and Plasma Viscosity Effect in Microcirculation

Abstract

Blood is a multiphase fluid that is comprised of several cellular components suspended in plasma. Red blood cells (RBCs) make up the most important component due to their large number density, crucial role in oxygen transport and direct influence on blood flow behaviors. In this chapter, we employ the immersed-boundary lattice-Boltzmann method (IB-LBM) to investigate shear stress variation induced by blood flows and the effect of plasma viscosity on RBC dynamics and blood flows in microvessels. This two-dimensional model accounts for RBC membrane deformability, intercellular aggregation and fluid-membrane interaction. Numerical simulations have been conducted for several flow configurations to address their effects on wall shear stress (WSS) variation. The results show that lower WSS values are typically observed at locations with narrower cell-wall gaps, while higher WSS values are observed at locations where cells are relatively far away from the wall. It is shown that the linear shear assumption is not valid since the velocity profiles across the cell-wall gap exhibit strong nonlinear features. In addition, numerical simulations are presented to investigate the motion and deformation of a single RBC and multiple RBCs in straight and bifurcated microvessels with different values of suspending viscosity. Our results show that RBCs exhibit a higher flexibility in a more viscous medium and, therefore, a higher suspending viscosity can facilitate the cell-free layer development and enhance the hematocrit phase separation. These findings provide helpful insight to better understand the complex physics underlying blood flow processes in microcirculation, and could be valuable for relevant biomedical applications.