Effect of non-linear leaflet material properties on aortic valve dynamics - A coupled fluid-structure approach (original) (raw)
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Cardiovascular Engineering and Technology, 2018
This paper describes a computational method to simulate the non-linear structural deformation of a polymeric aortic valve under physiological conditions. Arbitrary Lagrangian-Eulerian method is incorporated in the fluidstructure interaction simulation, and then validated by comparing the predicted kinematics of the valve's leaflets to in vitro measurements on a custom-made polymeric aortic valve. The predicted kinematics of the valve's leaflets was in good agreement with the experimental results with a maximum error of 15% in a single cardiac cycle. The fluidstructure interaction model presented in this study can simulate structural behaviour of a stented valve with flexible leaflets, providing insight into the haemodynamic performance of a polymeric aortic valve.
A three-dimensional computational analysis of fluid–structure interaction in the aortic valve
Journal of Biomechanics, 2003
Numerical analysis of the aortic valve has mainly been focused on the closing behaviour during the diastolic phase rather than the kinematic opening and closing behaviour during the systolic phase of the cardiac cycle. Moreover, the fluid-structure interaction in the aortic valve system is most frequently ignored in numerical modelling. The effect of this interaction on the valve's behaviour during systolic functioning is investigated. The large differences in material properties of fluid and structure and the finite motion of the leaflets complicate blood-valve interaction modelling. This has impeded numerical analyses of valves operating under physiological conditions. A numerical method, known as the Lagrange multiplier based fictitious domain method, is used to describe the large leaflet motion within the computational fluid domain. This method is applied to a three-dimensional finite element model of a stented aortic valve. The model provides both the mechanical behaviour of the valve and the blood flow through it. Results show that during systole the leaflets of the stented valve appear to be moving with the fluid in an essentially kinematical process governed by the fluid motion. r
Numerical Methods for Fluid–Structure Interaction Models of Aortic Valves
Archives of Computational Methods in Engineering, 2014
In the recent years, fluid structure interaction (FSI) models of the aortic valve and root have become increasingly common for two main reasons. The medical reason is that millions of patients suffer from aortic valve disorders. The second reason is that this challenging problem combines several fields of computational mechanics. The key motive for these modeling attempts is their potential to shed light on phenomena that cannot be captured in experiments or in simplified models of solely hemodynamics or structural mechanics. The aim of this paper is to review the state-of-theart FSI methods in general and their application to the aortic valve in particular. A brief overview of the medical background is provided. The numerical methods and appropriate assumptions are then presented with examples of previous aortic valve models, followed by a discussion of the limitation of current models and recommendations for overcoming them in future research. The methods presented in this paper could help readers to choose the modelling approach and assumptions that are most suitable for their goals.
A fluid–structure interaction model of the aortic valve with coaptation and compliant aortic root
Medical & Biological Engineering & Computing, 2012
Native aortic valve cusps are composed of collagen fibers embedded in their layers. Each valve cusp has its own distinctive fiber alignment with varying orientations and sizes of its fiber bundles. However, prior mechanical behavior models have not been able to account for the valve-specific collagen fiber networks (CFN) or for their differences between the cusps. This study investigates the influence of this asymmetry on the hemodynamics by employing two fully coupled fluid-structure interaction (FSI) models, one with asymmetricmapped CFN from measurements of porcine valve and the other with simplified-symmetric CFN. The FSI models are based on coupled structural and fluid dynamic solvers. The partitioned solver has nonconformal meshes and the flow is modeled by employing the Eulerian approach. The collagen in the CFNs, the surrounding elastin matrix, and the aortic sinus tissues have hyperelastic mechanical behavior. The coaptation is modeled with a masterslave contact algorithm. A full cardiac cycle is simulated by imposing the same physiological blood pressure at the upstream and downstream boundaries for both models. The mapped case showed highly asymmetric valve kinematics and hemodynamics even though there were only small differences between the opening areas and cardiac outputs of the two cases. The regions with a less dense fiber network are more prone to damage since they are subjected to higher principal stress in the tissues and a higher level of flow shear stress. This asymmetric flow leeward of the valve might damage not only the valve itself but also the ascending aorta.
Dynamic analysis of the aortic valve using a finite element model
The Annals of Thoracic Surgery, 2002
Background. The major aim of this study was to examine the leaflet/aortic root interaction during the cardiac cycle, including the stresses developed during the interaction. Methods. Dynamic finite element analysis was used along with a geometrically accurate model of the aortic valve and the sinuses. Shell elements along with proper contact conditions were also used in the model. Pressure patterns during the cardiac cycle were given as an input, and a linear elastic model was assumed for the material. Results. We found that aortic root dilation starts before the opening of the leaflet and is substantial by the time leaflet opens. Dilation of the root alone helps in opening the leaflet to about 20%. The equivalent stress pattern shows an instantaneous increase in stress at the coaptation surface during closure. Stresses increase as the point of attachment is approached from the free surface. Conclusions. The complex interplay of the geometry of the valve system can be effectively analyzed using a sophisticated dynamic finite element model. Results not previously brought out by the earlier static analysis shed new light on the root/valve interaction.
Informatics in Medicine Unlocked
Aortic valve diseases are among the most common cardiovascular defects. Since a non-functioning valve results in disturbed blood flow conditions, the diagnosis of such defects is based on identification of stenosis via echocardiography. Calculation of disease parameters such as valve orifice area or transvalvular pressure gradient using echocardiography is associated with substantial errors. Computational fluid dynamics (CFD) modeling has emerged as an alternative approach for accurate assessment of aortic valve hemodynamics. Fluid-structure interaction (FSI) modeling is adapted in these models to account for counter-interacting forces of flowing blood and deforming leaflets for most accurate results. However, implementation of this approach is difficult using custom built codes and algorithms. In this paper, we present an FSI modeling methodology for aortic valve hemodynamics using a commercial modeling software, ANSYS. We simulated the problem using fluid flow solver FLUENT and structural solver MECHANICAL APDL under ANSYS and coupled the solutions using System Coupling Module to enable FSI. This approach minimized adaptation problems that would raise if separate solvers were used. As an example case, we investigated influence of leaflet calcification on hemodynamic stresses and flow patterns. Model geometries were generated using b-mode echocardiography images of an aortic valve. A Doppler velocity measurement was used as velocity inlet boundary condition in the models. Simulation results were validated by comparing leaflet movements in the simulations with b-mode echo recordings. Wall shear stress levels, pressure levels and flow patterns agree well with previous studies demonstrating the accuracy of our results. Our modeling methodology can be easily adopted by researchers that are familiar with ANSYS and other similar CFD software to investigate similar biomedical problems.
International Journal for Numerical Methods in Biomedical Engineering, 2010
There are numerous examples of fluid-structure interactions (FSIs) within the human body. In all cases, a computer model capable of simulating the phenomenon can aid in the understanding of organ function, failure, and implant design or improvement. In the current paper, two approaches are examined for use in simulating the FSI problem of the dynamics of tissue heart valves. Valve leaflets have nonlinear anisotropic material properties, and undergo complex deformation. Their motion affects-and is affected by-the surrounding blood. This two-way coupling necessitates a robust algorithm in order to overcome numerical stiffness, convergence challenges, and stability issues. A locally refined Cartesian mesh, sharp interface method has been developed for the fluid flow solution. In the structural domain, the valve leaflet is represented in a Lagrangian fashion and moves based on its experimentally determined material properties. In computing leaflet motion, the anisotropic, nonlinear material properties of the valve leaflet are incorporated using a finite element solver, which calculates the leaflet deformation and stresses based on the stress imparted by the surrounding fluid. Two FSI algorithms have been studied in the context of a sharp-interface Cartesian grid setting, and each has been validated with benchmark results. The two approaches are compared, and ultimately one is selected as most appropriate for simulating tissue heart valves. In the selected approach, a strongly coupled, partitioned method is used in which subiterations of the fluid and structure solutions are performed at each time step. During the subiterations, the leaflet motion is used as a boundary condition on the fluid, and the fluid stresses act as a boundary condition on the leaflet. In this way, continuity is ensured and two-way coupling is achieved. The selected approach has overcome the challenges faced by previous simulations reported in the literature, and a robust FSI solution is achieved using physiologic Reynolds numbers, realistic material properties, highly resolved grids, and a dynamic simulation. This approach has the advantage of handling both thin and volumetric embedded objects in a unified fashion, and of treating rigid and deformable structures in the same way, thus allowing a spectrum of potential applications.
Recorded about two million people worldwide have heart problems everyday. One was due to heart valve disease. The objectives of this study are to simulate the stress distribution and analyze the rigidity of heart valve leaflet during systole condition. Two-dimensional model of the heart valve were created in ADINA-Fluid Structure Interaction for computational simulations. The result shows rigidity of heart valve leaflet always opposite to degeneration and the simulated show stress distribution in this model corresponded to normal distribution in physical heart valve in systole condition. The conclusion is modeling simulation techniques are very useful in the study of degenerative valve disease and the findings would allow us to optimize feature and geometries to reduced stresses and rigidity of heart valve failure.
The dynamic finite element method with the fluidstructure interaction was used to investigate the deformation behavior of a newly developed artificial heart valve. To reproduce the opening movements of trileaflets of the valve during the half cardiac cycle, a timedependent blood velocity was used as the boundary condition of the fluid domain. The nonslip boundary condition was also chosen for the tri-leaflets to ensure the viscous effect between the blood and the leaflet surfaces, while the free slip boundary condition was chosen for the cylindrical wall to ignore such viscous effect. The valve was assumed to be made from a natural tissue and a linear elastic material was assumed as the material model. The blood was assumed to be incompressible and Newtonian fluid. It was found that the valve was easily open when it came into contact with blood flow, taking only 0.3 seconds to go from fully
A two-dimensional fluid–structure interaction model of the aortic value
Journal of Biomechanics, 2000
Failure of synthetic heart valves is usually caused by tearing and calci"cation of the lea#ets. Lea#et "ber-reinforcement increases the durability of these values by unloading the delicate parts of the lea#ets, maintaining their physiological functioning. The interaction of the valve with the surrounding #uid is essential when analyzing its functioning. However, the large di!erences in material properties of #uid and structure and the "nite motion of the lea#ets complicate blood}valve interaction modeling. This has, so far, obstructed numerical analyses of valves operating under physiological conditions. A two-dimensional #uid}structure interaction model is presented, which allows the Reynolds number to be within the physiological range, using a "ctitious domain method based on Lagrange multipliers to couple the two phases. The extension to the three-dimensional case is straightforward. The model has been validated experimentally using laser Doppler anemometry for measuring the #uid #ow and digitized high-speed video recordings to visualize the lea#et motion in corresponding geometries. Results show that both the #uid and lea#et behaviour are well predicted for di!erent lea#et thicknesses.