A parametric model for analysing atherosclerotic arteries: On the FSI coupling

There are many evidences that coronary plaque is not only dependent on the formation and progression of atherosclerosis, but also on the vascular remodelling response. If the local wall shear stress is low, a proliferative plaque may develop. Local inflammatory response will stimulate the formation of a plaque prone to rupture with superimposed thrombus formation (vulnerable plaque). Furthermore, the role of the wall shear stress in the genesis and the development of atherosclerotic diseases has been recently intensively investigated, examining its relationship with the presence of lesions and the intima media thickness. Due to the important role of pulsating blood flow, pressure and hemodynamics factors in atheroma growth, a Fluid Structure Interaction (FSI) parametric study of a 3D atherosclerotic artery has been carried out, with aim of studying the main geometrical risk factors in terms of plaque vulnerability

Use of computational fluid dynamics to compare upper airway pressures and airflow resistance in brachycephalic, mesocephalic, and dolichocephalic dogs

Brachycephalic dog breeds are prone to breathing difficulties because of their upper airway anatomy. Several surgical techniques exist to correct anatomical pathologies and common surgical approaches aim to correct functional abnormalities in the nares and/or the soft palate. However, further research is needed to improve clinical outcomes. This study evaluated air pressure and airflow resistance in the upper airways and trachea in nine sedated, sternally recumbent dogs of different skull types (dolichocephalic, n = 3; mesocephalic, n = 3; brachycephalic, n = 3). CT images were acquired from the nostrils to the caudal border of the lungs and geometrical reconstruction of the upper airway and trachea was performed. Analysis of computational fluid dynamics was performed using inspiratory flow adapted to bodyweight for each dog. Flow (L/min) and pressure (cmH2O) were computed for the entire upper airway and trachea. Resistance (cmH2O/L/min) was calculated using pressure differences between the nose, larynx, and trachea. In this pilot study, statistical comparisons were not performed. Pressure maps, airflow, and resistance were similar in dolichocephalic and mesocephalic breeds. Median pressure difference (3.76 cmH2O) and resistance (0.154 cmH2O/L/min) between the nose and larynx were numerically higher in brachycephalic dogs than in other breeds (0.45 cmH2O and 0.016 cmH2O/L/min, respectively). Median pressure difference (0.205 cmH2O) and resistance (0.009 cmH2O/L/min) between the larynx and trachea was numerically similar in all dogs, except for the English bulldog. The methodology used in this preliminary study to quantify airflow characteristics such as pressure and resistance could improve the understanding of brachycephalic obstruction airway syndrome

Numerical and experimental study of the fluid flow through a medical device

The purpose of this paper is to verify a commercial software based fluid–structure interaction scheme for the inferior vena cava. Vena cava deep thrombosis (TVP) is a potentially deathly disease consequent to pulmonary thromboembolism (TEP). TEP consist in the obstruction of the pulmonary artery due to a blood clot traveling in the cardiovascular system and is treated with anticoagulants and inferior vena cava filters. Flow fields along the vena cava and an antithrombus filter were studied and compared with a Particle Image Velocimetry (PIV) based model to validate the numerical model. The results show that the fluid–structure interaction (FSI) models are valid and can be used to study the deformations in the inferior vena cava wall using patient-specific geometries

On studying the interaction between different stent models and rabbit tracheal tissue: numerical, endoscopic and histological comparison

Stenting technique is employed worldwide for treating atherosclerotic vessel and tracheal stenosis. Both diseases can be treated by means of metallic stents which present advantages but are affected by the main problem of restenosis of the stented area. In this study we have built a rabbit trachea numerical model and we have analyzed it before and after insertion and opening of two types of commercial stent: a Zilver® FlexTM Stent and a WallStentTM. In experimental parallel work, two types of stent were implanted in 30 New Zealand rabbits divided in two groups of 10 animals corresponding to each stent type and a third group made up of 10 animals without stent. The tracheal wall response was assessed by means of computerized tomography by endoscopy, macroscopic findings and histopathological study 90 days after stent deployment. Three idealized trachea models, one model for each group, were created in order to perform the computational study. The animal model was used to validate the numerical findings and to attempt to find qualitative correlations between numerical and experimental results. Experimental findings such as inflammation, granuloma and abnormal tissue growth, assessed from histomorphometric analyses were compared with derived numerical parameters such as wall shear stress (WSS) and maximum principal stress. The direct comparison of these parameters and the biological response supports the hypothesis that WSS and tensile stresses may lead to a greater tracheal epithelium response within the stented region, with the latter seeming to have the dominant role. This study may be helpful for improving stent design and demonstrates the feasibility offered by in-silico investigated tracheal structural and fluid dynamics

Computational methodology to determine fluid related parameters on non regular three-dimensional scaffolds

The application of three-dimensional (3D) biomaterials to facilitate the adhesion, proliferation, and differentiation of cells has been widely studied for tissue engineering purposes. The fabrication methods used to improve the mechanical response of the scaffold produce complex and non regular structures. Apart from the mechanical aspect, the fluid behavior in the inner part of the scaffold should also be considered. Parameters such as permeability (k) or wall shear stress (WSS) are important aspects in the provision of nutrients, the removal of metabolic waste products or the mechanically-induced differentiation of cells attached in the trabecular network of the scaffolds. Experimental measurements of these parameters are not available in all labs. However, fluid parameters should be known prior to other types of experiments. The present work compares an experimental study with a computational fluid dynamics (CFD) methodology to determine the related fluid parameters (k and WSS) of complex non regular poly(L-lactic acid) scaffolds based only on the treatment of microphotographic images obtained with a microCT (lCT). The CFD analysis shows similar tendencies and results with low relative difference compared to those of the experimental study, for high flow rates. For low flow rates the accuracy of this prediction reduces. The correlation between the computational and experimental results validates the robustness of the proposed methodology.The authors gratefully acknowledge research support from the Spanish Ministry of Science and Innovation through research project DPI2010-20399-C04-01. 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