Hemodynamics of end-to-end anastomosis bypass: on the specific influnce of a stenosis in the host artery

Local hemodynamics is implicated in the failure of bypass graft surgery. Intimal thickening has been shown to occur at specific sites, namely the floor, the heel, the toe and the suture line. Nevertheless, the recipient artery has often been repre-sented in the literature as a simple flow rate reduction or as a complete obstruc-tion neglecting the perturbing presence of the stenosis. In addition, severe as well as moderate constrictions are sometimes bypassed without taking into account an existing residual flow through the host artery. The purpose of this chapter is therefore to investigate how competitive flows issued from the graft and the dis-eased artery could interact together, and thus to explain the restenosis process at an early stage. The velocity flow rates are issued from in vivo measurements for patients who had undergone coronary bypass surgery approximately three weeks before. 3D unsteady flows through idealized coronary bypass anastomoses are modeled by the finite element method. The influence of the inflows, and of the shape of the stenosis, are notably discussed. The experimental Doppler velocity fields corroborate well the numerical results. The post-stenotic recirculation zone is demonstrated to interact with the graft inflow during the cardiac cycle. These disturbed flow patterns due to the presence of a stenosis may have harmful con-sequences in terms of graft patenc

Towards New Aortic Tissues Analogue Materials: Micro-mechanical Modelling and Experiments

Human abdominal aortic tissue is a complex cylindrical soft sandwich structure, arranged in three different concentric layers. Within these layers, distribution and arrangement of all components display a double-helix architecture of wavy fibres, characterised by distinctive preferred orientations. The macroscopic mechanical behaviour of human healthy abdominal aorta (AA) and aneurysmal (AAA) tissues is highly non-linear, anisotropic and essentially hyperelastic. The global objective of this work is to design and process new artificial hy- perelastic and anisotropic membranes mimicking the macroscopic histological and mechanical features of AA and AAA tissues. These materials will be then used to build more realistic phantoms of AAA for in vitro experiments. The aim of the present study is (i) to develop a theoretical framework able to predict the optimal microstructure and mechanical behaviour of such AA/AAA analogues, and (ii) to provide experimental validation of micro-mechanical modelling

Modèle d’écoulement autour d’une prothèse valvulaire pour le diagnostic clinique

L'évaluation clinique de la performance valvulaire est basée sur la mesure de la vitesse maximale dans le jet transvalvulaire. Un modèle théorique basé sur la modélisation de profils minces et la théorie des écoulements potentiels est développé pour accéder aux vitesses dans ce jet. Les résultats sont validés par des simulations numériques. Ce modèle présente un excellent rapport  précision des résultats / temps CPU. On montrera comment son utilisation permet d'améliorer le diagnostic clinique

Comparison between the mechanical behavior of the human healthy AA and commercial prostheses under various mechanical loadings

International audienceStandard chirurgical treatment of abdominal aortic aneurysm (AAA) involves the placement of tubular synthetic aortic prostheses. Most of these implants are made up of polyester textiles or porous expanded polytetrafluoroethylene. Normalized tests are dedicated to their assessment (ISO7198:1998). However, such experiments are not sufficient to characterize the complete mechanical performance of these implants (Le Magnen et al., 2001) and to ensure their mechanical compatibility with the host artery. Thus, the design of mechanically compatible vascular prostheses still remains a challenge. Within this context, a full comparison of the mechanical behavior of the human healthy abdominal aorta (AA) with commercial prostheses is proposed. An original numerical database on the mechanical behavior of human AA subjected to various mechanical loadings is first built and then compared with experimental data obtained from mechanical tests performed on prostheses

De la dynamique des fluides aux anévrismes de l'aorte abdominale

National audienc

Modélisations expérimentales et numériques en biomécanique des fluides

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Biomécanique, modélisations et pathologies

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