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On the interplay between hemodynamics and biochemsitry of the normal and aneurysmatic abdominal aorta
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , vii p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0512
National Category
Medical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-44538ISBN: 978-91-7501-139-4 (print)OAI: oai:DiVA.org:kth-44538DiVA: diva2:451028
Presentation
2011-10-14, Sal D41, KTH, Lindstedtvägen 17, Stockholm, 10:15
Opponent
Supervisors
Note

QC 20111024

Available from: 2011-10-24 Created: 2011-10-24 Last updated: 2013-01-15Bibliographically approved
List of papers
1. Hemodynamics of the Normal Aorta Compared to Fusiform and Saccular Abdominal Aortic Aneurysms with Emphasis on a Potential Thrombus Formation Mechanism
Open this publication in new window or tab >>Hemodynamics of the Normal Aorta Compared to Fusiform and Saccular Abdominal Aortic Aneurysms with Emphasis on a Potential Thrombus Formation Mechanism
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2010 (English)In: Annals of Biomedical Engineering, ISSN 0090-6964, E-ISSN 1573-9686, Vol. 38, no 2, 380-390 p.Article in journal (Refereed) Published
Abstract [en]

Abdominal Aortic Aneurysms (AAAs), i.e., focal enlargements of the aorta in the abdomen are frequently observed in the elderly population and their rupture is highly mortal. An intra-luminal thrombus is found in nearly all aneurysms of clinically relevant size and multiply affects the underlying wall. However, from a biomechanical perspective thrombus development and its relation to aneurysm rupture is still not clearly understood. In order to explore the impact of blood flow on thrombus development, normal aortas (n = 4), fusiform AAAs (n = 3), and saccular AAAs (n = 2) were compared on the basis of unsteady Computational Fluid Dynamics simulations. To this end patient-specific luminal geometries were segmented from Computerized Tomography Angiography data and five full heart cycles using physiologically realistic boundary conditions were analyzed. Simulations were carried out with computational grids of about half a million finite volume elements and the Carreau-Yasuda model captured the non-Newtonian behavior of blood. In contrast to the normal aorta the flow in aneurysm was highly disturbed and, particularly right after the neck, flow separation involving regions of high streaming velocities and high shear stresses were observed. Naturally, at the expanded sites of the aneurysm average flow velocity and wall shear stress were much lower compared to normal aortas. These findings suggest platelets activation right after the neck, i.e., within zones of pronounced recirculation, and platelet adhesion, i.e., thrombus formation, downstream. This mechanism is supported by recirculation zones promoting the advection of activated platelets to the wall.

Keyword
Intra-luminal thrombus, Aortic aneurysm, Computational Fluid Dynamics, Saccular, Fusiform, Aorta, fluid-structure interaction, intraluminal thrombus, wall stress, rupture, flow, biomechanics, blood, diameter, models, tissue
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-19176 (URN)10.1007/s10439-009-9843-6 (DOI)000274237000014 ()2-s2.0-77249088121 (Scopus ID)
Funder
Swedish Research Council, 20067568
Note

QC 20110124

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Blood flow and coherent vortices in the normal and aneurysmatic aortas: a fluid dynamical approach to intraluminal thrombus formation
Open this publication in new window or tab >>Blood flow and coherent vortices in the normal and aneurysmatic aortas: a fluid dynamical approach to intraluminal thrombus formation
2011 (English)In: Journal of the Royal Society Interface, ISSN 1742-5689, E-ISSN 1742-5662, Vol. 8, no 63, 1449-1461 p.Article in journal (Refereed) Published
Abstract [en]

Abdominal aortic aneurysms (AAAs) are frequently characterized by the development of an intra-luminal thrombus (ILT), which is known to have multiple biochemical and biomechanical implications. Development of the ILT is not well understood, and shear-stress-triggered activation of platelets could be the first step in its evolution. Vortical structures (VSs) in the flow affect platelet dynamics, which motivated the present study of a possible correlation between VS and ILT formation in AAAs. VSs educed by the lambda(2)-method using computational fluid dynamics simulations of the backward-facing step problem, normal aorta, fusiform AAA and saccular AAA were investigated. Patient-specific luminal geometries were reconstructed from computed tomography scans, and Newtonian and Carreau-Yasuda models were used to capture salient rheological features of blood flow. Particularly in complex flow domains, results depended on the constitutive model. VSs developed all along the normal aorta, showing that a clear correlation between VSs and high wall shear stress (WSS) existed, and that VSs started to break up during late systole. In contrast, in the fusiform AAA, large VSs developed at sites of tortuous geometry and high WSS, occupying the entire lumen, and lasting over the entire cardiac cycle. Downward motion of VSs in the AAA was in the range of a few centimetres per cardiac cycle, and with a VS burst at that location, the release (from VSs) of shear-stress-activated platelets and their deposition to the wall was within the lower part of the diseased artery, i.e. where the thickest ILT layer is typically observed. In the saccular AAA, only one VS was found near the healthy portion of the aorta, while in the aneurysmatic bulge, no VSs occurred. We present a fluid-dynamics-motivated mechanism for platelet activation, convection and deposition in AAAs that has the potential of improving our current understanding of the pathophysiology of fluid-driven ILT growth.

Keyword
coherent vortices, intra-luminal thrombus, aortic aneurysm, platelets, computational fluid dynamics, aorta
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-39504 (URN)10.1098/rsif.2011.0041 (DOI)000294208100009 ()2-s2.0-80052252526 (Scopus ID)
Funder
Swedish Research Council, 2006-7568
Note

QC 20111024

Available from: 2011-09-26 Created: 2011-09-12 Last updated: 2017-12-08Bibliographically approved
3. An integrated fluido-chemical model towards modeling the formation of intra-luminal thrombus in abdominal aortic aneurysms
Open this publication in new window or tab >>An integrated fluido-chemical model towards modeling the formation of intra-luminal thrombus in abdominal aortic aneurysms
2011 (English)Article in journal (Other academic) Submitted
Abstract [en]

Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-Luminal Thrombus (ILT) known to influence biochemically and biomechanically their evolution. ILT progression mechanism is still unclear and little is known regarding the impact of chemicals transported by blood flow. It is expected that chemical agonists and antagonists of platelets activation, aggregation, and adhesion play an important role in ILT development. Starting fromthis assumption, the evolution of chemical species related to the coagulation cascade (CC), their relation to coherent vortical structures (VSs) and their effect on ILT evolution have been studied. To this end a fluido-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations and considers blood as a non-Newtonian incompressible fluid has been developed. In addition to the relation between VSs and thrombin distribution, high thrombin concentrations at the distal portion of the AAA were observed, i.e. the region where the thickest ILT is usually seen. The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could unveil mechanisms of ILT formation and development.

National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-44536 (URN)
Note
QS 20120316Available from: 2011-10-24 Created: 2011-10-24 Last updated: 2012-03-16Bibliographically approved

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