Dynamic modelling of a stented aortic valve
Date
2008-12
Authors
Van Aswegen, Karl
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
Aortic valve replacements are frequently performed during heart surgery. However,
since this is quite a stressful procedure, many patients are turned down for
medical reasons. Stented valves, designed and manufactured for percutaneous
insertion, eliminate many of the risks involved in open-heart surgery, thus providing
a solution to patients not deemed strong enough for open-chest aortic
valve replacements. The aortic valve is a complex structure, and therefore numerical
simulation is necessary to obtain flow and stress data to support the
design of a prosthetic heart valve in the absence of viable physical measuring
methods.
To aid in the design of a prosthetic heart valve, various finite element valve
models were created, and the fluid structure interaction (FSI) between the
valves and the blood was simulated using commercial finite element software.
The effect of the geometry of the leaflets on the haemodynamic behaviour over
the cardiac cycle was investigated. It was found that leaflet dimensions should
be chosen judiciously, because of their considerable effect on the stress distribution
and performance of the valve. A simple leaflet geometry optimisation
was done for a 20 mm and 26 mm valve, respectively, by means of existing
geometry relationships found in the literature. Simulations were done to obtain the maximum leaflet attachment forces
that can be used by a stent designer for fatigue loading, or to investigate the
structural strength of the stent. These simulations were numerically validated.
The effect of leaflet thickness and stiffness on resistance to opening, stress
distribution and strain were investigated. Results showed that leaflet thickness
has a greater effect on the performance of the valve than leaflet stiffness, and
thereby validated the results of similar tests contained in the literature. After
simulating over-, as well as under-dilation of a stented valve, it was found that
problems associated with over-dilation can be minimised to a certain extent
by increasing the coaptation1 region of the leaflets.
A simple pulse duplicator was designed based on a four-element Windkessel
model. The pulse duplicator was used to study the performance of the prototype
valves by means of high-speed photography, the results of which were
fed into one of the numerical finite element models and compared to real valve
performance. Some of the prototype valves showed efficiencies of 88%.
Description
Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008.
Keywords
Fluid structure interaction, Prosthetic heart valve -- Design, Aortic valve, Dissertations -- Mechanical engineering, Theses -- Mechanical engineering, Aortic valve -- Stenosis, Heart valve prosthesis