סמינר מחלקה של עדי מורני - ביומכניקה של תיקונים בריאים, חולים ותותבות של מסתמי אבי העורקים באמצעות CFD סריג בולצמן בשילוב עם שיטות FE מרובות קנה מידה
School of Mechanical Engineering Seminar
Wednesday 31.05.2023 at 14:00
Wolfson Building of Mechanical Engineering, Room 206
Biomechanics of Healthy, Diseased, and Prosthetic-Repairs of Aortic Valves using the Lattice Boltzmann CFD Coupled with Multiscale FE Methods
PhD student under the supervision of Prof. Rami Haj-Ali
School of Mechanical Engineering, Tel Aviv University, Tel Aviv, Israel
The aortic valve (AV) between the left ventricle and the aorta maintains an outward unidirectional flow. A common AV congenital disease is the form of a bicuspid aortic valve (BAV). This anatomical abnormality (~2% of the population) elevates leaflet stress that can lead to aortic stenosis (AS), one of the most common valvular heart diseases in the developed world. AS usually affects about 5% of people who are over 65 years of age. The latter is a progressive disease based on calcification (CAS) or fibrosis (FAS), ultimately leading to valve repair and replacement. Currently, a balloon aortic valvuloplasty procedure precedes surgical aortic valve replacement. In the last decade, a new transcatheter aortic valve replacement (TAVR) procedure has matured and gained recognition due to its positive long-term outcomes, partly due to the prevention of open heart surgery.
This study examines a new hemodynamic-structural co-modeling approach using Lattice-Boltzmann (LBM) and multiscale-tissue Finite-Element (FE) methods of compliant aortic valves independently and in a full electro-mechanical heart model. The applied LBM, a grid-based mesh-less method, uses the kinetic gas theory of particles to simulate fluid flow. Four parametric AV models were introduced and investigated: pathology-free models of tri-and-bi cuspid AVs with healthy collagen fiber network (CFN) and without calcification deposits embedded within the tissue. A FAS model includes thickened CFN with small calcification volumes, and the last CAS model employs healthy CFN with embedded high calcification volumes based on a representative CT scan taken from pre-TAVR patients. In addition, a multiscale FE structural approach has been employed to explicitly recognize the heterogeneous leaflet tissues as CFN constituents embedded within the elastin matrix of the leaflets. The proposed LBM-FE fluid-structure interaction (FSI) framework is examined in its ability to resolve local hemodynamic and structural responses. In particular, the diastolic fluctuating velocity phenomenon near the leaflets is explicitly predicted, providing vital information on the flow transient nature. The full closure of the contacting leaflet forces in BAV is also demonstrated. Accordingly, good structural kinematics and deformations are captured for the entire cardiac cycle and correlate well with those reported in the literature. Moreover, the results from these models point to the interplay between calcium bulks with the surrounding tissue and fibers, where the dominancy of the fibers in the FAS, was demonstrated. Next, simulation of the TAVR procedure and its post-outcomes were examined for both CAS and FAS. TAVR-CAS has a higher maximum pressure and smaller contact area than TAVR-FAS, making it prone to aortic tissue damage. Finally, the paravalvular leakage was predicted to be higher in TAVR-CAS despite its larger opening area and may be attributed to a similar thrombogenicity potential that characterizes both models.
The clinical part of this study focuses on the calcification evolution and routes of type-1 BAVs based on CT scans and the effect of the unique geometrical shapes of calcium deposits on their fragmentation under balloon valvuloplasty procedures. Subsequently, calcification fragmentation biomechanical models of six representative stenotic BAVs of different calcification patterns were introduced. Towards this goal, the novel Reverse Calcification Technique (RCT), which can predict the calcification progression leading to the current state based on CT scans, is utilized. Two main calcification patterns of type-1 bicuspid aortic valves were identified; asymmetric and symmetric with partial or complete arcs and circles. It was found that the distinct geometrical shape of the calcium deposits had a significant effect on the cracks' initiations.
The proposed computational framework highlights the importance of biomechanical simulations and the need to generate refined multiscale modeling, which can serve as a platform for designing and implementing new prosthetic valves to improve treatment approaches in stenotic aortic valve patients.
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