Application of Computational Fluid Dynamics in Modeling Blood Flow in Human Thoracic Aorta
Vasava, Paritosh R. (2011-12-19)
Väitöskirja
Vasava, Paritosh R.
19.12.2011
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-265-197-6
https://urn.fi/URN:ISBN:978-952-265-197-6
Tiivistelmä
The aim of this study was to simulate blood flow in thoracic human aorta and
understand the role of flow dynamics in the initialization and localization of
atherosclerotic plaque in human thoracic aorta. The blood flow dynamics in
idealized and realistic models of human thoracic aorta were numerically simulated
in three idealized and two realistic thoracic aorta models. The idealized models of
thoracic aorta were reconstructed with measurements available from literature,
and the realistic models of thoracic aorta were constructed by image processing
Computed Tomographic (CT) images. The CT images were made available by
South Karelia Central Hospital in Lappeenranta. The reconstruction of thoracic
aorta consisted of operations, such as contrast adjustment, image segmentations,
and 3D surface rendering. Additional design operations were performed to make
the aorta model compatible for the numerical method based computer code. The
image processing and design operations were performed with specialized medical
image processing software. Pulsatile pressure and velocity boundary conditions
were deployed as inlet boundary conditions. The blood flow was assumed
homogeneous and incompressible. The blood was assumed to be a Newtonian
fluid. The simulations with idealized models of thoracic aorta were carried out
with Finite Element Method based computer code, while the simulations with
realistic models of thoracic aorta were carried out with Finite Volume Method
based computer code. Simulations were carried out for four cardiac cycles. The
distribution of flow, pressure and Wall Shear Stress (WSS) observed during the
fourth cardiac cycle were extensively analyzed.
The aim of carrying out the simulations with idealized model was to get an
estimate of flow dynamics in a realistic aorta model. The motive behind the
choice of three aorta models with distinct features was to understand the
dependence of flow dynamics on aorta anatomy. Highly disturbed and nonuniform
distribution of velocity and WSS was observed in aortic arch, near
brachiocephalic, left common artery, and left subclavian artery. On the other
hand, the WSS profiles at the roots of branches show significant differences with geometry variation of aorta and branches. The comparison of instantaneous WSS
profiles revealed that the model with straight branching arteries had relatively
lower WSS compared to that in the aorta model with curved branches. In addition
to this, significant differences were observed in the spatial and temporal profiles
of WSS, flow, and pressure. The study with idealized model was extended to
study blood flow in thoracic aorta under the effects of hypertension and
hypotension. One of the idealized aorta models was modified along with the
boundary conditions to mimic the thoracic aorta under the effects of hypertension
and hypotension.
The results of simulations with realistic models extracted from CT scans
demonstrated more realistic flow dynamics than that in the idealized models.
During systole, the velocity in ascending aorta was skewed towards the outer wall
of aortic arch. The flow develops secondary flow patterns as it moves downstream
towards aortic arch. Unlike idealized models, the distribution of flow was nonplanar
and heavily guided by the artery anatomy. Flow cavitation was observed in
the aorta model which was imaged giving longer branches. This could not be
properly observed in the model with imaging containing a shorter length for aortic
branches. The flow circulation was also observed in the inner wall of the aortic
arch. However, during the diastole, the flow profiles were almost flat and regular
due the acceleration of flow at the inlet. The flow profiles were weakly turbulent
during the flow reversal. The complex flow patterns caused a non-uniform
distribution of WSS. High WSS was distributed at the junction of branches and
aortic arch. Low WSS was distributed at the proximal part of the junction, while
intermedium WSS was distributed in the distal part of the junction. The pulsatile
nature of the inflow caused oscillating WSS at the branch entry region and inner
curvature of aortic arch. Based on the WSS distribution in the realistic model, one
of the aorta models was altered to induce artificial atherosclerotic plaque at the
branch entry region and inner curvature of aortic arch. Atherosclerotic plaque
causing 50% blockage of lumen was introduced in brachiocephalic artery,
common carotid artery, left subclavian artery, and aortic arch. The aim of this part
of the study was first to study the effect of stenosis on flow and WSS distribution,
understand the effect of shape of atherosclerotic plaque on flow and WSS
distribution, and finally to investigate the effect of lumen blockage severity on
flow and WSS distributions. The results revealed that the distribution of WSS is
significantly affected by plaque with mere 50% stenosis. The asymmetric shape of
stenosis causes higher WSS in branching arteries than in the cases with symmetric
plaque.
The flow dynamics within thoracic aorta models has been extensively studied and
reported here. The effects of pressure and arterial anatomy on the flow dynamic
were investigated. The distribution of complex flow and WSS is correlated with the localization of atherosclerosis. With the available results we can conclude that
the thoracic aorta, with complex anatomy is the most vulnerable artery for the
localization and development of atherosclerosis. The flow dynamics and arterial
anatomy play a role in the localization of atherosclerosis. The patient specific
image based models can be used to diagnose the locations in the aorta vulnerable
to the development of arterial diseases such as atherosclerosis.
understand the role of flow dynamics in the initialization and localization of
atherosclerotic plaque in human thoracic aorta. The blood flow dynamics in
idealized and realistic models of human thoracic aorta were numerically simulated
in three idealized and two realistic thoracic aorta models. The idealized models of
thoracic aorta were reconstructed with measurements available from literature,
and the realistic models of thoracic aorta were constructed by image processing
Computed Tomographic (CT) images. The CT images were made available by
South Karelia Central Hospital in Lappeenranta. The reconstruction of thoracic
aorta consisted of operations, such as contrast adjustment, image segmentations,
and 3D surface rendering. Additional design operations were performed to make
the aorta model compatible for the numerical method based computer code. The
image processing and design operations were performed with specialized medical
image processing software. Pulsatile pressure and velocity boundary conditions
were deployed as inlet boundary conditions. The blood flow was assumed
homogeneous and incompressible. The blood was assumed to be a Newtonian
fluid. The simulations with idealized models of thoracic aorta were carried out
with Finite Element Method based computer code, while the simulations with
realistic models of thoracic aorta were carried out with Finite Volume Method
based computer code. Simulations were carried out for four cardiac cycles. The
distribution of flow, pressure and Wall Shear Stress (WSS) observed during the
fourth cardiac cycle were extensively analyzed.
The aim of carrying out the simulations with idealized model was to get an
estimate of flow dynamics in a realistic aorta model. The motive behind the
choice of three aorta models with distinct features was to understand the
dependence of flow dynamics on aorta anatomy. Highly disturbed and nonuniform
distribution of velocity and WSS was observed in aortic arch, near
brachiocephalic, left common artery, and left subclavian artery. On the other
hand, the WSS profiles at the roots of branches show significant differences with geometry variation of aorta and branches. The comparison of instantaneous WSS
profiles revealed that the model with straight branching arteries had relatively
lower WSS compared to that in the aorta model with curved branches. In addition
to this, significant differences were observed in the spatial and temporal profiles
of WSS, flow, and pressure. The study with idealized model was extended to
study blood flow in thoracic aorta under the effects of hypertension and
hypotension. One of the idealized aorta models was modified along with the
boundary conditions to mimic the thoracic aorta under the effects of hypertension
and hypotension.
The results of simulations with realistic models extracted from CT scans
demonstrated more realistic flow dynamics than that in the idealized models.
During systole, the velocity in ascending aorta was skewed towards the outer wall
of aortic arch. The flow develops secondary flow patterns as it moves downstream
towards aortic arch. Unlike idealized models, the distribution of flow was nonplanar
and heavily guided by the artery anatomy. Flow cavitation was observed in
the aorta model which was imaged giving longer branches. This could not be
properly observed in the model with imaging containing a shorter length for aortic
branches. The flow circulation was also observed in the inner wall of the aortic
arch. However, during the diastole, the flow profiles were almost flat and regular
due the acceleration of flow at the inlet. The flow profiles were weakly turbulent
during the flow reversal. The complex flow patterns caused a non-uniform
distribution of WSS. High WSS was distributed at the junction of branches and
aortic arch. Low WSS was distributed at the proximal part of the junction, while
intermedium WSS was distributed in the distal part of the junction. The pulsatile
nature of the inflow caused oscillating WSS at the branch entry region and inner
curvature of aortic arch. Based on the WSS distribution in the realistic model, one
of the aorta models was altered to induce artificial atherosclerotic plaque at the
branch entry region and inner curvature of aortic arch. Atherosclerotic plaque
causing 50% blockage of lumen was introduced in brachiocephalic artery,
common carotid artery, left subclavian artery, and aortic arch. The aim of this part
of the study was first to study the effect of stenosis on flow and WSS distribution,
understand the effect of shape of atherosclerotic plaque on flow and WSS
distribution, and finally to investigate the effect of lumen blockage severity on
flow and WSS distributions. The results revealed that the distribution of WSS is
significantly affected by plaque with mere 50% stenosis. The asymmetric shape of
stenosis causes higher WSS in branching arteries than in the cases with symmetric
plaque.
The flow dynamics within thoracic aorta models has been extensively studied and
reported here. The effects of pressure and arterial anatomy on the flow dynamic
were investigated. The distribution of complex flow and WSS is correlated with the localization of atherosclerosis. With the available results we can conclude that
the thoracic aorta, with complex anatomy is the most vulnerable artery for the
localization and development of atherosclerosis. The flow dynamics and arterial
anatomy play a role in the localization of atherosclerosis. The patient specific
image based models can be used to diagnose the locations in the aorta vulnerable
to the development of arterial diseases such as atherosclerosis.
Kokoelmat
- Väitöskirjat [1036]