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The objective of this paper was to evaluate the ability of the peak systolic velocity ratio (PSVR) and pressure drop (DeltaP) to detect and grade multiple stenoses in lower limb mimicking arteries. Numerical simulations and experiments in vascular phantoms allowing ultrasound duplex scanning and pressure measurements were used to investigate simple and double stenotic arterial segments. Inter-stenotic distance, severity of the distal stenosis, flow rate and flow profile (steady or pulsatile) were the tested parameters. The three-dimensional simulations considered the turbulent two-equation Wilcox model. Agreements were observed between the experimental and numerical results for DeltaP and PSVR. The maximum PSVR along the artery was shown to be mainly influenced by the severity of the most important stenosis. However, mutual interactions of both stenoses on hemodynamics were noted. By using the clinical PSVR threshold used to diagnose critical lesions (PSVR > or = 2), its longitudinal evolution along the artery poorly reflected the length of the lesion or the impact of surrounding stenoses. This investigation confirms the interaction between adjacent stenoses on hemodynamics and its impact on the Doppler ultrasound index PSVR.

Using the finite element method, physiological blood flows through a three-dimensional model of a coronary graft are numerically analysed. The model includes a stenosis shape in the host artery upstream from the anastomosis. Recirculating areas, secondary flows, wall shear stress (WSS) and spatial wall shear stress gradients (WSSGs) are studied for different flow repartitions and at different times in the cycle. The temporal and spatial evolutions of the recirculating areas downstream from the stenosis, their interactions with the flow issued from the graft and their associated WSSs highlight that the presence of the stenosis in the recipient artery is essential for prediction of the evolution of a grafting at the beginning of its implantation. The areas downstream from the stenosis expansion, non-existent for a host artery without stenosis, are submitted to low and oscillating WSS between -0.5 and 0 Nm(-2). The stagnation point on the recipient artery floor is subjected to high positive and negative WSSGnd values, and its location is dependent on the residual flow through the stenosis.

When atherosclerotic lesions are found within a coronary bifurcation, a double stent implantation is sometimes required to treat the disease of each branch. The clinical procedure can result in the positioning of several stents in the bifurcation. In the study, physiological flows in typical configurations of such stented coronary bifurcations were numerically modelled using the finite volumes method. Two deployed Palmaz stents were inserted in a 90 degrees coronary bifurcation, simulating a double stent implantation. As the geometric position of the metallic stent cells can vary, several models of broken cells were proposed and compared to characterise the influence of the stent struts protruding into the collateral branch. Flow features in the bifurcation surroundings changed from one model to another. These changes could lead to the occurrence of flow stasis and also of recirculation areas downstream from the struts, depending on the way the strut was opened. The stent struts protruding into the lumen of the collateral branch induced high values of shear stress at the stent wall of about 20 N m(-2), which could stimulate platelet activation. In addition, these areas of high shear stress values were concomitant with areas of low shear stress values of about 0.5 Nm(-2). These regions could be prone to platelet adhesion and so to thrombo-embolic complications. The analysis of the flow field indicated that it would be judicious to use dedicated bifurcated stents to treat bifurcation lesions.