Unraveling aortic hemodynamics using fluid structure interaction: biomechanical insights into bicuspid aortic valve dynamics with multiple aortic lesions.

Aortic lesions, exemplified by bicuspid aortic valves (BAVs), can complicate congenital heart defects, particularly in Turner syndrome patients. The combination of BAV, dilated ascending aorta, and an elongated aortic arch presents complex hemodynamics, requiring detailed analysis for tailored treatment strategies. While current clinical decision-making relies on imaging modalities offering limited biomechanical insights, integrating high-performance computing and fluid-structure interaction algorithms with patient data enables comprehensive evaluation of diseased anatomy and planned intervention.

Biomechanical Evaluation of Aortic Valve Stenosis by Means of a Virtual Stress Test: A Fluid-Structure Interaction Study.

The impact of aortic valve stenosis (AS) extends beyond the vicinity of the narrowed leaflets into the left ventricle (LV) and into the systemic vasculature because of highly unpredictable valve behavior and complex blood flow in the ascending aorta that can be attributed to the strong interaction between the narrowed cusps and the ejected blood. These effects can become exacerbated during exercise and may have implications for disease progression, accurate diagnosis, and timing of intervention. In this 3-D patient-specific study, we employ strongly coupled fluid-structure interaction (FSI) modeling to perform a comprehensive biomechanical evaluation of systolic ejection dynamics in a stenosed aortic valve (AV) during increasing LV contraction.

Improving transcatheter aortic valve interventional predictability via fluid-structure interaction modelling using patient-specific anatomy.

Transcatheter aortic valve replacement (TAVR) is now a standard treatment for high-surgical-risk patients with severe aortic valve stenosis. TAVR is being explored for broader indications including degenerated bioprosthetic valves, bicuspid valves and for aortic valve (AV) insufficiency. It is, however, challenging to predict whether the chosen valve size, design or its orientation would produce the most-optimal haemodynamics in the patient.

Synergy between Diastolic Mitral Valve Function and Left Ventricular Flow Aids in Valve Closure and Blood Transport during Systole.

Highly resolved three-dimensional (3D) fluid structure interaction (FSI) simulation using patient-specific echocardiographic data can be a powerful tool for accurately and thoroughly elucidating the biomechanics of mitral valve (MV) function and left ventricular (LV) fluid dynamics. We developed and validated a strongly coupled FSI algorithm to fully characterize the LV flow field during diastolic MV opening under physiologic conditions. Our model revealed that distinct MV deformation and LV flow patterns developed during different diastolic stages.

Computational mitral valve evaluation and potential clinical applications.

The mitral valve (MV) apparatus consists of the two asymmetric leaflets, the saddle-shaped annulus, the chordae tendineae, and the papillary muscles. MV function over the cardiac cycle involves complex interaction between the MV apparatus components for efficient blood circulation. Common diseases of the MV include valvular stenosis, regurgitation, and prolapse.

The effect of patient-specific annular motion on dynamic simulation of mitral valve function.

Most surgical procedures for patients with mitral regurgitation (MR) focus on optimization of annular dimension and shape utilizing ring annuloplasty to restore normal annular geometry, increase leaflet coaptation, and reduce regurgitation. Computational studies may provide insight on the effect of annular motion on mitral valve (MV) function through the incorporation of patient-specific MV apparatus geometry from clinical imaging modalities such as echocardiography. In the present study, we have developed a novel algorithm for modeling patient-specific annular motion across the cardiac cycle to further improve our virtual MV modeling and simulation strategy.

Peak wall stress predicts expansion rate in descending thoracic aortic aneurysms.

Background: Aortic diseases, including aortic aneurysms, are the 12th leading cause of death in the United States. The incidence of descending thoracic aortic aneurysms is estimated at 10.4 per 100,000 patient-years.

Patient-specific bicuspid valve dynamics: overview of methods and challenges.

About 1-2 % of the babies are born with bicuspid aortic valves instead of the normal aortic valve with three leaflets. A significant portion of the patients with the congenital bicuspid valve morphology suffer from aortic valve stenosis and/or ascending aortic dilatation and dissection thus requiring surgical intervention when they are young adults. Patients with bicuspid aortic valves (BAVs) have also been found to develop valvular stenosis earlier than those with the normal aortic valve.

Increased wall stress of saccular versus fusiform aneurysms of the descending thoracic aorta.

Background: Repair of fusiform descending thoracic aortic aneurysms (DTAs) is indicated when aneurysmal diameter exceeds a certain threshold; however, diameter-related indications for repair of saccular DTA are less well established.

Methods: Human subjects with fusiform (n = 17) and saccular (n = 17) DTAs who underwent computed tomographic angiography were identified. Patients with aneurysms related to connective tissue disease were excluded.

Effect of Geometry on the Leaflet Stresses in Simulated Models of Congenital Bicuspid Aortic Valves.

The aim of the study was to assess the effect of geometric variations on the stresses developed in the leaflets of congenital bicuspid aortic valves (CBAV). We developed a model for the human tri-leaflet aortic valve based on the geometry and dimensions published in the literature. We also developed simulated CBAV geometry based on the most common geometry present in patients with CBAV that is published in the literature.

Increased ascending aortic wall stress in patients with bicuspid aortic valves.

Background: Patients with bicuspid aortic valves (BAV) are at increased risk of ascending aortic dilatation, dissection, and rupture. We hypothesized that ascending aortic wall stress may be increased in patients with BAV compared with patients with tricuspid aortic valves (TAV).

Methods: Twenty patients with BAV and 20 patients with TAV underwent electrocardiogram-gated computed tomographic angiography.

Pathogenesis of acute aortic dissection: a finite element stress analysis.

Background: Type A and type B aortic dissections typically result from intimal tears above the sinotubular junction and distal to the left subclavian artery (LSA) ostium, respectively. We hypothesized that this pathology results from elevated pressure-induced regional wall stress.

Methods: We identified 47 individuals with normal thoracic aortas by electrocardiogram-gated computed tomography angiography.

Role of Computational Simulations in Heart Valve Dynamics and Design of Valvular Prostheses.

Computational simulations are playing an increasingly important role in enhancing our understanding of the normal human physiological function, etiology of diseased states, surgical and interventional planning, and in the design and evaluation of artificial implants. Researchers are taking advantage of computational simulations to speed up the initial design of implantable devices before a prototype is developed and hence able to reduce animal experimentation for the functional evaluation of the devices under development. A review of the reported studies to date relevant to the simulation of the native and prosthetic heart valve dynamics is the subject of the present paper.

Flow interactions with cells and tissues: cardiovascular flows and fluid-structure interactions. Sixth International Bio-Fluid Mechanics Symposium and Workshop, March 28-30, 2008, Pasadena, California.

Interactions between flow and biological cells and tissues are intrinsic to the circulatory, respiratory, digestive and genitourinary systems. In the circulatory system, an understanding of the complex interaction between the arterial wall (a living multi-component organ with anisotropic, nonlinear material properties) and blood (a shear-thinning fluid with 45% by volume consisting of red blood cells, platelets, and white blood cells) is vital to our understanding of the physiology of the human circulation and the etiology and development of arterial diseases, and to the design and development of prosthetic implants and tissue-engineered substitutes. Similarly, an understanding of the complex dynamics of flow past native human heart valves and the effect of that flow on the valvular tissue is necessary to elucidate the etiology of valvular diseases and in the design and development of valve replacements.

Impact of design parameters on bileaflet mechanical heart valve flow dynamics.

Background And Aim Of The Study: One significant problem encountered during surgery to implant mechanical heart valve prostheses is the propensity for thrombus formation near the valve leaflet and housing. This may be caused by the high shear stresses present in the leakage jet flows through small gaps between leaflets and the valve housing during the valve closure phase.

Methods: A two-dimensional (2D) study was undertaken to demonstrate that design changes in bileaflet mechanical valves result in notable changes in the flow-induced stresses and prediction of platelet activation.

A novel flex-stretch-flow bioreactor for the study of engineered heart valve tissue mechanobiology.

Tissue engineered heart valves (TEHV) have been observed to respond to mechanical conditioning in vitro by expression of activated myofibroblast phenotypes followed by improvements in tissue maturation. In separate studies, cyclic flexure, stretch, and flow (FSF) have been demonstrated to exhibit both independent and coupled stimulatory effects. Synthesis of these observations into a rational framework for TEHV mechanical conditioning has been limited, however, due to the functional complexity of tri-leaflet valves and the inherent differences of separate bioreactor systems.

Dynamic simulation of bioprosthetic heart valves using a stress resultant shell model.

It is a widely accepted axiom that localized concentration of mechanical stress and large flexural deformation is closely related to the calcification and tissue degeneration in bioprosthetic heart valves (BHV). In order to investigate the complex BHV deformations and stress distributions throughout the cardiac cycle, it is necessary to perform an accurate dynamic analysis with a morphologically and physiologically realistic material specification for the leaflets. We have developed a stress resultant shell model for BHV leaflets incorporating a Fung-elastic constitutive model for in-plane and bending responses separately.

An experimentally derived stress resultant shell model for heart valve dynamic simulations.

In order to achieve a more realistic and accurate computational simulation of native and bioprosthetic heart valve dynamics, a finite shell element model was developed. Experimentally derived and uncoupled in-plane and bending behaviors were implemented into a fully nonlinear stress resultant shell element. Validation studies compared the planar biaxial extension and three-point bending simulations to the experimental data and demonstrated excellent fidelity.

Dynamic simulation pericardial bioprosthetic heart valve function.

While providing nearly trouble-free function for 10-12 years, current bioprosthetic heart valves (BHV) continue to suffer from limited long-term durability. This is usually a result of leaflet calcification and/or structural degeneration, which may be related to regions of stress concentration associated with complex leaflet deformations. In the current work, a dynamic three-dimensional finite element analysis of a pericardial BHV was performed with a recently developed FE implementation of the generalized nonlinear anisotropic Fung-type elastic constitutive model for pericardial BHV tissues (W.

Coronary arteries: imaging, reconstruction, and fluid dynamic analysis.

Atherosclerosis is the underlying cause of most cardiovascular-related deaths in industrialized nations. Determining the etiology of atherosclerosis and detecting lesions in the early stages of the disease for possible pharmacological or mechanical intervention have been challenges facing cardiovascular researchers. In addition to genetic and environmental factors, the formation and growth of atheroma have been linked to the complex fluid dynamics and mass transport in these arterial segments.

Plaque development, vessel curvature, and wall shear stress in coronary arteries assessed by X-ray angiography and intravascular ultrasound.

The relationships among vascular geometry, hemodynamics, and plaque development in the coronary arteries are complex and not yet well understood. This paper reports a methodology for the quantitative analysis of in vivo coronary morphology and hemodynamics, with particular emphasis placed on the critical issues of image segmentation and the automated classification of disease severity. We were motivated by the observation that plaque more often developed at the inner curvature of a vessel, presumably due to the relatively lower wall shear stress at these locations.

Regional material property alterations in porcine femoral arteries with atheroma development.

We have developed a novel methodology that permits assessment of regional vascular mechanical property alterations in the presence of atheroma in vivo employing a Yucatan miniswine model with induced lesions. Femoral arteries were imaged with intravascular ultrasound. Image data were segmented and, following three-dimensional reconstruction, underwent finite element and sensitivity analysis with optimization to identify regions with altered vascular mechanical properties.

Porcine carotid arterial material property alterations with induced atheroma: an in vivo study.

Objective: A novel methodology has been developed to evaluate regional alterations in arterial wall material properties with induced atheroma in an animal model.

Methods: Atheromatous lesions (fatty, fibro-fatty, and fibrous) were induced in the carotid arteries of a Yucatan miniswine model by endothelial cell denudation and high cholesterol diet. The images at base line and 8 weeks after denudation were obtained using intravascular ultrasound (IVUS) imaging along with hemodynamic data.

Three-dimensional fluid-structure interaction simulation of bileaflet mechanical heart valve flow dynamics.

The wall shear stress induced by the leaflet motion during the valve-closing phase has been implicated with thrombus initiation with prosthetic valves. Detailed flow dynamic analysis in the vicinity of the leaflets and the housing during the valve-closure phase is of interest in understanding this relationship. A three-dimensional unsteady flow analysis past bileaflet valve prosthesis in the mitral position is presented incorporating a fluid-structure interaction algorithm for leaflet motion during the valve-closing phase.