Impact of aortic acceleration on haemodynamics
File(s)
Author(s)
Abou-Gamrah, Mazen Mohamed
Type
Thesis
Abstract
The aortic valve apparatus (AVA) is a complicated structure continuously moving throughout
the cardiac cycle such that it may be regarded as a live organ. Different studies previously
focused on analysing the dynamism or local deformations of the AVA; however, the effect of
the axial movement of the AVA on blood flow or aortic valve loading remains uncharted. In
this study we propose analysing the axial acceleration of the AVA and its effect on blood flow.
After mathematically decomposing the deformations of healthy AVA’s from CT image tracking,
it was deduced that the dominant component is the axial movement towards and away from
the left ventricle. Using the 1D water hammer approximation we hypothesised a theory tying
the previously inexplicable dicrotic notch seen on the arterial pressure waveform to the AVA
acceleration during valve closure.
The next intermediate step was to use an idealised model replicating the anatomy of the AVA
in order to study the effect of axial acceleration on blood flow combined with steady inflow
conditions. A series of non-dimensional parameters describing the underlying physics were
derived in order to enable an appropriate comparison with a patient specific anatomy.
The final step was to analyse a stationary and an accelerating patient specific AVA using
high fidelity Fluid-Structure Interaction (FSI) simulations. The results showed qualitative and
quantitative differences between both cases especially in valvular dynamics and loading.
Moreover, the FSI simulation results confirmed the presence of a sudden reactive force on the
aortic valve in the accelerating AVA case at the time of peak acceleration during valve closure;
where the same phenomenon was not present in the stationary AVA case. The calculated force
of 0.6 N along with the aortic valve wetted area of 0.0013 m2 yield ≈ 3.5 mmHg which is in
the same ball park as previously measured dicrotic notch pressure rises.
As a result, we propose that the axial acceleration of the AVA may be a crucial parameter in
diagnosing aortic or ventricular disease since it has a significant effect on aortic valve function.
We also propose a future plan of investigation in order to strengthen our hypothesis and enable
the use of the acceleration of the AVA as a non-invasive diagnostic parameter.
the cardiac cycle such that it may be regarded as a live organ. Different studies previously
focused on analysing the dynamism or local deformations of the AVA; however, the effect of
the axial movement of the AVA on blood flow or aortic valve loading remains uncharted. In
this study we propose analysing the axial acceleration of the AVA and its effect on blood flow.
After mathematically decomposing the deformations of healthy AVA’s from CT image tracking,
it was deduced that the dominant component is the axial movement towards and away from
the left ventricle. Using the 1D water hammer approximation we hypothesised a theory tying
the previously inexplicable dicrotic notch seen on the arterial pressure waveform to the AVA
acceleration during valve closure.
The next intermediate step was to use an idealised model replicating the anatomy of the AVA
in order to study the effect of axial acceleration on blood flow combined with steady inflow
conditions. A series of non-dimensional parameters describing the underlying physics were
derived in order to enable an appropriate comparison with a patient specific anatomy.
The final step was to analyse a stationary and an accelerating patient specific AVA using
high fidelity Fluid-Structure Interaction (FSI) simulations. The results showed qualitative and
quantitative differences between both cases especially in valvular dynamics and loading.
Moreover, the FSI simulation results confirmed the presence of a sudden reactive force on the
aortic valve in the accelerating AVA case at the time of peak acceleration during valve closure;
where the same phenomenon was not present in the stationary AVA case. The calculated force
of 0.6 N along with the aortic valve wetted area of 0.0013 m2 yield ≈ 3.5 mmHg which is in
the same ball park as previously measured dicrotic notch pressure rises.
As a result, we propose that the axial acceleration of the AVA may be a crucial parameter in
diagnosing aortic or ventricular disease since it has a significant effect on aortic valve function.
We also propose a future plan of investigation in order to strengthen our hypothesis and enable
the use of the acceleration of the AVA as a non-invasive diagnostic parameter.
Version
Open Access
Date Issued
2022-06
Date Awarded
2023-03
Copyright Statement
Creative Commons Attribution Licence
License URL
Advisor
Parker, Kim
Yacoub, Magdi
Publisher Department
Bioengineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)