Elucidating creating an entirely new flow-field causing abnormal

Elucidating blood flow and transport of macromoleculesin the human arterial system is crucial for the in depth understanding ofgenesis and progression of atherosclerotic plaques, 1. The Computational Fluid Dynamics (CFD)has proven to be an excellent tool for obtaining qualitative and detailedquantitative information on stent flow patterns, 2. Oscillating flow develops complex flow fieldand from computational point of view poses a difficult task.

Nowadays stent implantations are widely used to unblockarteries with stenosis. Stents are usually deployed in arteries with significantamount of stenosis (plaque). However, stent implantation drastically alters theblood flow characteristics creating an entirely new flow-field causing abnormalendothelium response. Furthermore, stent designsgreatly influence the reaction of the arterial wall.

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Questions arise as to howincreased heart rate affect Low Density Lipoprotein (LDL) distribution in stentedarteries. Of equal importance is the answer to the question: does diastole in relation to systole favorselevated LDL distribution at increased heart rates? Stentimplantation affects the Wall Shear Stress (WSS) in the surrounding upstreamand downstream strut flow regions 3. Considering oscillatory flow, low time-Averaged Wall ShearStress (AWSS) values give rise to atherosclerotic lesions at specific coronaryarterial regions as it is now widely accepted.

The developed highly complexlaminar flow yields low and oscillatory WSS, increase LDL uptake andpermeability, 4.Thus, the progressing of atherosclerosis is present. Oscillating WSS, lowerthan <1.

0-1.2 N/m2, is considered to be responsible for thrombusformation via endothelium injury, 5. Complex configuration of the vessel, after stentimplantation, promotes disturbances with low AWSS and high shear stresstemporal oscillations during accelerating, peak and decelerating flows 6. The strut spacing,strut diameter, longitudinal strut connectors and strut embedment may beresponsible for increased LDL concentration, 22. Struts oriented to flow direction reduce theflow recirculation, 23.

Instantaneous hemodynamic conditions have importantinfluence on LDL transmural transport in arteries with disturbed andcomplicated flow patterns 7.There have been very few studies investigating the fluid-wall coupled masstransport under oscillating flow condition 7, 8. Regional variations in the permeabilityof arterial endothelium may contribute to the localization of atherosclerosis 9, 10.

Luminalsurface level of LDL transport across the artery wall is considered to beimportant in atherogenesis 11,12. Elevated LDL nearly co-localize with known sites ofatherosclerotic plaque development, 13. Results indicate that lipids accumulate at the luminalsurface in areas where blood flow velocity and WSS are low and where the permeabilityof the endothelial layer is enhanced, 14. Few 3D oscillating CFD studieshave been carried out on stented arteries incorporating flow and mass transferelucidating at the same time the LDL concentration differentiation betweensystole and diastole at resting and/or at exercise condition (pulse wave). Ourobjective was to calculate the flow disturbance induced by the stent via the AWSS, Relative Residence Time (RRT) and the LDL transport distributions under resting and exercisecondition. Computational analysis is performed for the: half stent (strut) exposureinto lumen, while the other half is embedded into endothelium. In this researchwork the semi-permeable arterial wall treatment is incorporated.

No transmuralflow or mass transfer analysis within the stented arterial segment wall isintroduced. The infiltration velocity and the endothelial permeability aretreated as wall shear stress independent. Calculatedresults provide insight into how the fluid biomechanical factors, induced by acertain stent design, affect LDL concentration distribution during systole asit is compared to diastole at resting and exercise heart condition.