FLOW RESISTANCE AND DRAG FORCES DUE TO MULTIPLE ADHERENT LEUKOCYTES IN POSTCAPILLARY VESSELS

Computational fluid dynamics was used to model flow past multiple adhe rent leukocytes in postcapillary size vessels. A finite-element packag e was used to solve the Navier-Stokes equations for low Reynolds numbe r flow of a Newtonian fluid past spheres adhering to the wall of a cyl indrical vessel. We determined the effects of sphere number, relative geometry, and spacing on the flow resistance in the vessel and the flu id flow drag force acting to sweep the sphere off the vessel wall. The computations show that when adherent leukocytes are aligned on the sa me side of the vessel, the drag force on each of the interacting leuko cytes is less than the drag force on an isolated adherent leukocyte an d can decrease by up to 50%. The magnitude of the reduction depends on the ratio of leukocyte to blood vessel diameter and distance between adherent leukocytes. However, there is an increase in the drag force w hen leukocytes adhere to opposite sides of the vessel wall. The increa se in resistance generated by adherent leukocytes in vessels of variou s sizes is calculated from the computational results. The resistance i ncreases with decreasing vessel size and is most pronounced when leuko cytes adhere to opposite sides of the vessel.