Analysis of Haemodynamics and Biomechanics of Different Aortic Valve and Root Prostheses

Lead Research Organisation: Imperial College London
Department Name: Department of Chemical Engineering

Abstract

This project will have two main themes; processing and analysing patient-specific medical imaging data and numerical modelling in OpenFOAM using transitional LES. The processed medical imaging data will be used to generate geometries of patients having undergone various procedures involving aortic valve replacement and those of healthy aortas. Furthermore, MRI data will also be used to extract patient-specific flow information, such as pulsatile velocity profiles which can be implemented in CFD simulations as boundary conditions. In order to complete these tasks, the student will gain familiarity and understanding of processing medical images, as well as being able to analyse the data. In the early stages of this project, simplified geometries will be modelled in OpenFOAM using transitional LES methods, progressing to more realistic geometries where laminar and LES results can be compared.

Further on in the project, numerical models will progress to include the fluid-structure interaction between leaflet dynamics and blood flow. This interaction will allow better understanding of the influence of the dynamic valves on transition and turbulence. Dependent on progress, fluid-structure interactions could be broadened to include the relationship between blood flow and arterial wall, to account for the changes in vessel shape during a cardiac cycle as done in previous work by (Lantz, Renner and Karlsson, 2011). This numerical model could also be of interest in order to better understand the interaction with prostheses materials which have different elastomechanical and compliance characteristics to arterial tissues (Spadaccio et al., 2016), as well as understanding the effects of different aortic valves on dilatation and aneurysms. The project could also be developed to include a mathematical model for thrombus formation which would be of particular interest for better understanding mechanical heart valves, as they are well known for being highly thrombogenic. Incorporating this model could help with the understanding of thrombus formation in relation to mechanical heart valves.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 30/09/2021
1966633 Studentship EP/N509486/1 01/10/2017 30/09/2021 Emily Louise Manchester
 
Description This work is focused on conducting high-resolution computational fluid dynamic simulations of blood flow through patient-specific aortas with both aortic valve disease and aortic valve replacements. In the healthy population blood flow is generally expected to remain laminar throughout the cardiac cycle, however, in the presence of aortic valve disease and aortic valve replacements, complex flow features are produced and blood may transition to turbulence. To better understand the mechanisms of transition in relation to this disease, as well as the effects of turbulence on native haemodynamics and biomechanics, large-eddy simulations will be conducted. Large-eddy simulations (LES) are a numerical (computational) method capable of modelling laminar, transitional and turbulent flows.

The first aim of this work was to validate the complex numerical methodology. This was done by conducting LES simulations of flow through the FDA's benchmark nozzle model (doi:10.17917/C78G69), which was designed to mimic flow behaviours experienced in blood-contacting medical devices. This model produces laminar, transitional and turbulent flow features - providing a challenging numerical test case. Numerous experimental and numerical studies have previously been conducted using the FDA benchmark nozzle model - providing sufficient data for validation. Key findings show that transitional flows are highly sensitive to numerous parameters and with correct application, accurate results can be achieved.

The second aim was to apply the validated methodology to a patient-specific aorta with aortic valve disease. This was done by using 4D magnetic resonance imaging data (4D MRI) from a patient with severe aortic stenosis to construct the patient's own aortic geometry. At the computational inlet time-varying 3D velocity profiles from an entire cardiac cycle were extracted from the 4D MRI data. At the outlets, the pressure base 3-element Windkessel model was applied to provide physiological wave-forms. Results from the simulation have been statistically correlated against 4D MRI data, showing excellent agreement. This work presented results for turbulence kinetic energy, both mean and turbulent contributions towards wall shear stress and energy losses. This is the first study to analyse these turbulence-based parameters for aortic valve disease. Key findings from this patient show that turbulent contributions to wall shear stress alone are large enough to potentially promote arterial wall diseases, highlighting the importance in considering turbulent effects. Further work is needed to better understand the correlations between aortic valve disease, turbulence production and aortic pathologies, however it is clear that severe aortic valve stenosis is capable of producing detrimental levels of turbulence.

Future work, expected to be completed as part of this project will conduct LES simulations of patients with various aortic valve replacements; including mechanical heart valves and bioprosthetic valves. Similar parameters will be looked at to assess the performance of these valves.
Exploitation Route The results from the FDA nozzle validation study will be published and can be used by other researchers towards the validation of their numerical methodologies.

Based on the initial findings, this work can be used to better understand the correlation between aortic valve disease/aortic valve prostheses, turbulence and subsequent aortic pathologies such as arterial wall disease. Based on these understandings, we can better evaluate the performance of current aortic valve prostheses. This work may also be used to improve the design of both current and new aortic valve prostheses.
Sectors Healthcare,Pharmaceuticals and Medical Biotechnology

 
Description EPCC Tier-2 HPC Service
Amount £10,000 (GBP)
Funding ID EP/P020267/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 07/2019 
End 07/2020