Abstract

The objective of this work is to analyze the local hemodynamic changes caused in a coronary bifurcation by three different stenting techniques: simple stenting of the main vessel, simple stenting of the main vessel with kissing balloon in the side branch and culotte. To carry out this study an idealized geometry of a coronary bifurcation is used, and two bifurcation angles, 45° and 90°, are chosen as representative of the wide variety of real configurations. Both numerical simulations and experimental measurements are performed. First, steady simulations are carried out with the commercial code ANSYS Fluent, then, experimental measurements with PIV (Particle Image Velocimetry), obtained in the laboratory, are used to validate the numerical simulations. The steady computational simulations show a good overall agreement with the experimental data. Second, pulsatile flow is considered to take into account the transient effects. The time averaged wall shear stress, oscillatory shear index (OSI) and pressure drop obtained numerically are used to compare the behavior of the stenting techniques. As conclusions obtained, simple stenting technique shows the worst results in terms of pressure drop, and kissing the best ones. This criterion could be applied for DES (Drug Eluting Stents) where the restenosis is not as critical as the reestablishment of the blood flow. But considering the regions of low wall shear stress (< 0.4 Pa) and elevated OSI (> 0.1), the culotte procedure shows the worst performance and the simple stent, the best. This could be applied to BMS (Bare Metal Stents).

Abstract

Introduction

In patients with moderate symptomatic or severe asymptomatic carotid stenosis, prior to an endarterectomy it is recommended to do a detailed study, in which the complet set of morphological and hemodynamic parameters are included.

In this work the effect that the location and shape of the stenosis has on the distribution of wall shear stresses and their impact on clinical diagnosis in these cases is analyzed.

Materials and methods

First the model of the area to study is generated and the numerical simulation is done. Then the wall shear stress, the oscilation index and the wall shear stress exposure time are established, and the impact of the results for embolization risk or the growth of arterial plaque because of intimal hiperpasia are analysed. The methodology is applied to three idealized carotids with different localization and geometrical slope of the stenosis.

Results

For the idealized carotids it is obtained that stenosis close to bifurcation present a higher embolization risk that the most distant one and has more risk as more stenosis slope it has. For the clinical case, the results show a high risk of embolization by break located near the atheromatous plaque. As well, it is obtained that the risk the arterial plaque to continue growing is low.

Conclusions

The results show that the location of a moderate stenosis related to carotid bifurcation and their geometry they are factors that aid to complete the diagnosis of lesion.

Abstract

The aim of this study is to assess how the shape of the abdominal aortic aneurysms (AAA) affects the hemodynamic wall stresses. With this purpose, different AAAs are studied through simplified models based on geometrical parameters of the aneurism such as its maximum and minimum diameter, length and asymmetry. Then, a computational fluid dynamics analysis is performed on the simplified models in order to compute pressure and wall shear stresses on the aneurysm sac. The results obtained show that blood pressure is the main dynamic load acting on the artery wall, and that the morphology of the aneurysm could be a good indicator of risk of failure. Furthermore, the computational results are compared with patient-specific real models with the objective to assess the reliability of the proposed simplified approach.

Abstract

The development length needed for tube flows to re-adjust from a uniform to the fully-developed velocity profile is usually defined as the length required for the centerline velocity to reach 99% of its fully-developed value. This definition, however, may be quite inaccurate in non-Newtonian flows with almost flat velocity distributions near the centerline, since the velocity far from the axis of symmetry develops more slowly. Shear-thinning and viscoplasticity may cause the flow close to the centerline to evolve faster than that closer to the walls. Thus, alternative definitions of the development length have been proposed for viscoplastic flows. Given that blood exhibits shear thinning, we numerically solve the flow development of power-law fluids in pipes and calculate the development length as a function of the radius, determining the global development length along with the standard centerline estimate. We also consider an alternative definition, based on the evolution of the wall shear stress. Results have been obtained for values of the power-law exponent ranging from 0.