Analysis of shear stress and hemodynamic factors in a model of coronary artery stenosis and thrombosis

Abstract

Shear stress and alterations in blood flow within a stenosed artery promote platelet-dependent thrombosis. Using the Folts model of coronary thrombosis, we evaluated morphology, histology, and the hemodynamic properties of the stenosed vessel in 18 animals. The average stenosis created was 58 +/- 8%, with stenosed vessel diameters ranging from 0.084 to 0.159 cm. Histological examination of the stenosed vessel demonstrated that thrombi were composed primarily of platelets and formation occurred 1.0 mm downstream from the apex of the constriction, propagating distally. Peak shear stress occurred just upstream from the apex of the stenosis and varied from 520 to 3,349 dyn/cm2. Only small differences in shear forces were noted when blood viscosity was calculated using Newtonian and non-Newtonian properties. In contrast, shear stress computed for Poiseuille flow with use of the stenosis diameter underestimated the apical shear stress. Blood flow remained laminar within the stenosis with a Reynolds number range of 292-534. Our data indicate that the geometry of the stenosis inflow region must be considered in the evaluation of platelet activation and thrombus formation within a stenosed artery.

Aggregation of blood components on a surface in a microfluidic environment

“…We hypothesize that the elevated density of platelet adhesion observed at the upstream elbow region ͑region K͒ is attributed to the variation of axial and radial velocities in this region. 10 The elevated axial velocity ͑35% higher than the velocity at the entrance region͒ computed at the upstream transition region will thus likely produce a higher density of deposited platelets downstream of the transition region. 10 Therefore, the density of platelet deposition at the elbow region ͑region K͒ is expected to be larger than the one at its upstream transition region ͑region J͒.…”

“…10 The elevated axial velocity ͑35% higher than the velocity at the entrance region͒ computed at the upstream transition region will thus likely produce a higher density of deposited platelets downstream of the transition region. 10 Therefore, the density of platelet deposition at the elbow region ͑region K͒ is expected to be larger than the one at its upstream transition region ͑region J͒. Another study also showed that significant near-wall excesses of platelets were found due to the migration of red blood cells toward the center of a laminar tube flow.…”

“…2 Moreover, since the axial velocity of blood flow influences the growth of thrombi as they grow toward the center, this could cause elevated deposition of blood components. 10 Contours of the axial and radial velocities as a function of distance along the tubing are shown in Fig. 7.…”

“…for each value of r. Previous works 5,[7][8][9][10][11] showed that the location of aggregation of blood components could be determined from variations in the flow field, i.e., acceleration, deceleration, and nonuniform patterns. In particular, the shear stress in the flow field can lead to the deformation and/or rolling of the blood components on the endothelial surface and/or a device wall.…”

“…13,14 Both these mechanisms can largely increase the size of the aggregate and thus could result in a significantly larger density of deposited blood components. 10 To proceed, a model system, which we represent as microfluidic blood-circulation loops connected together with tubings of different sizes, was examined experimentally for deposition of blood aggregates and then simulated with a computational fluid dynamics ͑CFD͒ code. This system was selected because it has local changes in geometry along its length that are very common in typical microfluidic devices.…”