Localized hydrodynamics of clustering leukocytes.

The recruitment of leukocytes to the endothelial walls is intensively investigated both experimentally and through three dimensional computer simulations. The shear dependent viscosity has been obtained from measured values in post-capillary venules of Wistar rats' cremaster muscle. Localized velocity fields and shear stresses on the surface of leukocytes and near vessel wall attachment points have been computed and discussed for a cluster of recruited leukocytes under generalized Newtonian blood flow with shear thinning viscosity. We have observed one region of maximum shear stress and two regions of minimum shear stress on the surface of the leukocytes close to the endothelial wall. This suggests that the accumulation of selectins attains a minimum value in two regions, rather than in one region, on the surface of the leukocytes. We have also verified that the collective hemodynamic behavior of the cluster of recruited leukocytes establishes a strong motive for additional leukocyte recruitment. From this study we claim that the influence of the leukocytes rolling on the endothelial wall increases the shear stress on both the leukocyte and the endothelial wall which results in activating more signaling mediators during inflammation.

Leukocytes rolling and recruitment by endothelial cells: hemorheological experiments and numerical simulations.

The recruitment of leukocytes from the blood stream and their subsequent adhesion to endothelial walls are essential stages to the immune response system during inflammation. The precise dynamic mechanisms by which molecular mediators facilitate leukocyte arrests are still unknown. In this study combined experimental results and computer simulations are used to investigate localized hydrodynamics of individual and collective behavior of clusters of leukocytes. Leukocyte-endothelial cell interactions in post-capillary venules of Wistar rats cremaster muscle were monitored by intravital microscopy. From these experiments the hemorheologic and hemodynamical measured parameters were used in time dependent three-dimensional computer simulations, using a mesoscopic lattice Boltzmann flow solver for shear thinning fluids. The dynamics of leukocyte clusters under generalized Newtonian blood flow with shear thinning viscosity was computed and discussed. In this paper we present quantified distributions of velocity and shear stress on the surface of leukocytes and near vessel wall attachment points. We have observed one region of maximum shear stress and two regions of minimum shear stress on the surface of leukocytes close to the endothelial wall. We verified that the collective hydrodynamic behavior of the cluster of recruited leukocytes establishes a strong motive for additional leukocyte recruitment. It was found that the lattice Boltzmann solver used here is fully adaptive to the measured experimental parameters. This study suggests that the influence of the leukocytes rolling on the increase of the endothelial wall shear stress may support the activation of more signalling mediators during inflammation.

Mesoscopic simulations of systolic flow in the human abdominal aorta.

The complex nature of blood flow in the human arterial system is still gaining more attention, as it has become clear that cardiovascular diseases localize in regions of complex geometry and complex flow fields. In this article, we demonstrate that the lattice Boltzmann method can serve as a mesoscopic computational hemodynamic solver. We argue that it may have benefits over the traditional Navier-Stokes techniques. The accuracy of the method is tested by studying time-dependent systolic flow in a 3D straight rigid tube at typical hemodynamic Reynolds and Womersley numbers as an unsteady flow benchmark. Simulation results of steady and unsteady flow in a model of the human aortic bifurcation reconstructed from magnetic resonance angiography, are presented as a typical hemodynamic application.