The Influence of Flow on the Concentration of Platelet Active Substances in the Vicinity of Mural Microthrombi

The flow effect on the concentration of platelet active substances in the vicinity of a mural microthrombus is investigated numerically. A three-dimensional model is employed in which the mural microthrombus is modelled as a semisphere attached to a plane surface. The description of the blood flow uses the three-dimensional incompressible Navier-Stokes equations for Newtonian fluids, and the mass transport and reaction kinetics are modelled applying a system of coupled convection-diffusion equations with reaction terms. The numerical approach employs the finite element method and a streamline upwind stabilization due to the high Peclet numbers. To verify the calculated concentrations a random walk model for the simulation of the convective diffusion of thrombogenic substances is employed. The results show flow recirculations directly upstream and downstream of the microthrombus which cause local concentration maxima in these regions. The resulting thrombin concentration exceeds the required level for platelet activation at shear rates and thrombus sizes under consideration. The resulting concentrations of thromboxane A(2) (TxA(2) ) and adenosine diphosphate (ADP) exceed the corresponding activation levels only at low shear rates and for large aggregates. For an aggregate diameter of 20 µm at the shear rate [formula: see text] the maximum TxA(2) concentration at a distance from the wall of 3 µm is 0.69 µM, which exceeds the required level of 0.6 µM. Increasing the shear rate to [formula: see text] causes a decrease of the maximum concentration to 0.43 µM.