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

Etude des écoulements intra anévrismaux par PIV stéréoscopique.

Cette étude a pour objectif de décrire l'hydrodynamique instationnaire d'un fluide rhéofluidifiant dans un élargissement de section asymétrique représentant un anévrisme de l'aorte abdominale. La métrologie utilisée, PIV stéréoscopique, permet une analyse précise de l'anneau tourbillonnaire qui se développe et se propage dans le sac anévrismal au cours du cycle cardiaque

Risk Factor Analysis of Bird Beak Occurrence after Thoracic Endovascular Aortic Repair

ObjectivesThe aim was to analyze the role played by anatomy and stent graft in the incidence of incomplete apposition to aortic arch.MethodsBetween 2007 and 2014 data including available and suitable computed tomographic angiography (CTA) imaging of patients who had undergone thoracic endovascular aortic repair were reviewed. The study included 80 patients (65 men, 54 ± 21 years) treated for traumatic aortic rupture (n = 27), thoracic aortic aneurysm (n = 15), type B aortic dissection (n = 24), penetrating aortic ulcer (n = 5), intramural hematoma (n = 2), aorto-oesophageal fistula (n = 2), and aortic mural thrombus (n = 5). Pre- and post-operative CTA images were analyzed to characterize bird beak in terms of length and angle, and to calculate aortic angulation within a 30 mm range at the proximal deployment zone.ResultsBird beak configuration was detected in 46 patients (57%): mean stent protrusion length was 16 mm (range: 8–29 mm) and mean bird beak angle was 20° (range: 7–40°). The bird beak effect was significantly more frequent after traumatic aortic rupture treatment (p = .05) and in landing zone 2 (p = .01). No influence of either stent graft type or generation, or degree of oversizing was observed (p = .29, p = .28, p = .81 respectively). However, the mean aortic angle of patients with bird beak was higher in the Pro-form group than that in the Zenith TX2 group (62° vs. 48°, p = .13). Multivariate analysis identified the aortic angle of the deployment zone as the unique independent risk factor of malapposition (HR = 1.05, 95% CI 1–1.10, p = .005). The cutoff value of 51° was found to be predictive of bird beak occurrence with a sensitivity of 58% and a specificity of 85%.ConclusionsAssessment of proximal landing zone morphology to avoid deployment zones generating an aortic angle of over 50° can be recommended to improve aortic curvature apposition with the current available devices

Mesh management methods in finite element simulations of orthodontic tooth movement

In finite element simulations of orthodontic tooth movement, one of the challenges is to represent long term tooth movement. Large deformation of the periodontal ligament and large tooth displacement due to bone remodelling lead to large distortions of the finite element mesh when a Lagrangian formalism is used. We propose in this work to use an Arbitrary Lagrangian Eulerian (ALE) formalism to delay remeshing operations. A large tooth displacement is obtained including effect of remodelling without the need of remeshing steps but keeping a good-quality mesh. Very large deformations in soft tissues such as the periodontal ligament is obtained using a combination of the ALE formalism used continuously and a remeshing algorithm used when needed. This work demonstrates that the ALE formalism is a very efficient way to delay remeshing operations

Multiphysics simulation of the effect of leaflet thickness inhomogeneity and material anisotropy on the stress-strain distribution on the aortic valve

This study developed a realistic 3D FSI computational model of the aortic valve using the fixed-grid method, which was eventually employed to investigate the effect of the leaflet thickness inhomogeneity and leaflet mechanical nonlinearity and anisotropy on the simulation results. The leaflet anisotropy and thickness inhomogeneity were found to significantly affect the valve stress-strain distribution. However, their effect on valve dynamics and fluid flow through the valve were minor. Comparison of the simulation results against in-vivo and in-vitro data indicated good agreement between the computational models and experimental data. The study highlighted the importance of simulating multi-physics phenomena (such as fluid flow and structural deformation), regional leaflet thickness inhomogeneity and anisotropic nonlinear mechanical properties, to accurately predict the stress-strain distribution on the natural aortic valve

Geometric vascular singularities, hemodynamic markers and pathologies

International audienceVascular pathologies are numerous and varied, and their genesis and development are multifactorial. Nevertheless, it is now known that thecharacterization and analysis of the dynamics of fluids and structures involved in the functioning of certain segments of the vascular system allowtheir dysfunction to be better understood, and correlations to be established between these dynamics and the genesis and development of vascularpathologies. The purpose of this chapter is to describe flow behaviors in certain geometric singularities of the cardiovascular system, whether native or pathological, and to correlate their dynamics with the evolution of cardiovascular pathologies. These correlations can be made usingassociations between the spatiotemporal distributions of certain hemodynamic markers/indexes and in vivo observation of deleteriousclinical events. Certain in silico and in vitro works conducted within the IRPHE Biomechanics team, mostly over the period of the “Biomechanics offluids and transfers, biological structure-fluid interaction” and “MEChAnics of BIOlogical materials and fluids” research groups, will notably serve toillustrate the remarks, which will not necessarily be exhaustive

Fluid Structure Interaction in aortic dissections

International audienceAortic dissections (AD) result in two lumens of circulation separated by the neointimal membrane (NIF). Type A ADs requires replacement of the pathological segment but can still evolve in a residual dissection. There are currently no clinical criteria that are sufficiently discriminating to predict this evolution to optimize the patient management. The clinical relevance of numerical modeling to tackle these issues is obvious. However, the choice of the parameters of the elasto-hemodynamic models is decisive. Models including fluid-structure interaction (FSI) are developed. The results highlight that (i) rigid structure modeling overestimates velocities and high wall shear stresses (WSS) values, underestimates low WSS values compared to FSI modeling (ii) a deformable NIF with rigid aortic wall does not bring any significant difference on the flow behavior compared to full rigid modeling (iii) the relevance of FSI analysis is linked to the mechanical behavior of the NIF and dissected descending aorta

Influence of the presence of a porous thrombus on hemodynamics in a CFD model of a descending thoracic aneurysm

International audienc