Fluid mechanics of arterial stenosis: Relationship to the development of mural thrombus

Abstract

AbstFact--In this study, we analyzed blood flow through a model stenosis with Reynolds numbers ranging from 300 to 3,600 using both experimental and numerical methods. The jet produced at the throat was turbulent, leading to an axisymmetric region of slowly recirculating flow. For higher Reynolds numbers, this region became more disturbed and its length was reduced. The numerical predictions were confirmed by digital particle image velocimetry and used to describe the fluid dynamics mechanisms relevant to prior measurements of platelet deposition in canine blood flow (R. T. Schoephoerster et al., Atheroscleros& and Thromboshr 12:1806-1813. Actual deposition onto the wall was dependent on the wall shear stress distribution along the stenosis, increasing in areas of flow recirculation and reattachment. Platelet activation potential was analyzed under laminar and turbulent flow conditions in terms of the cumulative effect of the varying shear and elongational stresses, and the duration platelets are exposed to them along individual platelet paths. The cumulative product of shear rate and exposure time along a platelet path reached a value of 500, half the value needed for platelet activation under constant shear (J. M. Ramstack et al., Journal of Biomechanics 12: 113-125, 1979).

Aggregation of blood components on a surface in a microfluidic environment

“…4 and 5͒ and is defined by numerically integrating ͐␥ ͑t͒dt along a platelet trajectory. Since other studies 5,7,8 suggest that flow separation and reattachment due to recirculation can also enhance platelet deposition, examination of the flow patterns and determination of their relationship to the activation level in the peristaltic recirculation system was also performed.…”

“…1 as a locus plot for the shear stress required for platelet activation. The amount of stimulation 4 ͑level of activation͒, 5 which is proportional to the product of local shear stress and exposure time to that stress, is widely accepted as the index that determines platelet activation in shear flows. The loci for incipient shearrelated platelet serotonin release and red-blood-cell hemolysis are displayed in the figure on a shear-stress-exposuretime phase plane plot.…”

“…Accordingly, the blood was assumed to be an incom- pressible Newtonian fluid with a density of 1050 kg m −3 and a viscosity of 3.5ϫ 10 −3 kg m −1 s −1 . 5,6 For simple shear flow or laminar flow of a Newtonian fluid in a tube, the shear stress reduces to the velocity gradient times the viscosity. The wall shear stress for a Newtonian fluid is thus given as…”

“…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.…”

“…To develop a predictive model, the CFD simulation was conducted to calculate the blood-flow parameters in the microfluidic recirculating loop system. A numerical threshold criterion 4,5 for platelet aggregation that depends on flow parameters will be introduced.…”