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Blood flow and coherent vortices in the normal and aneurysmatic aortas: a fluid dynamical approach to intraluminal thrombus formation
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
Department of Mechanical Engineering, University of Houston, Houstohn, TX, USA.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
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.

Place, publisher, year, edition, pages
2011. Vol. 8, no 63, 1449-1461 p.
Keyword [en]
coherent vortices, intra-luminal thrombus, aortic aneurysm, platelets, computational fluid dynamics, aorta
National Category
Medical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-39504DOI: 10.1098/rsif.2011.0041ISI: 000294208100009Scopus ID: 2-s2.0-80052252526OAI: oai:DiVA.org:kth-39504DiVA: diva2:443708
Funder
Swedish Research Council, 2006-7568
Note

QC 20111024

Available from: 2011-09-26 Created: 2011-09-12 Last updated: 2017-12-08Bibliographically approved
In thesis
1. On the interplay between hemodynamics and biochemsitry of the normal and aneurysmatic abdominal aorta
Open this publication in new window or tab >>On the interplay between hemodynamics and biochemsitry of the normal and aneurysmatic abdominal aorta
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:nbn:se:kth:diva-44538 (URN)978-91-7501-139-4 (ISBN)
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
2. Physics of blood flow in arteries and its relation to intra-luminal thrombus and atherosclerosis
Open this publication in new window or tab >>Physics of blood flow in arteries and its relation to intra-luminal thrombus and atherosclerosis
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Vascular pathologies such as Abdominal Aortic Aneurysm (AAA) and atherosclerosis are complex vascular diseases involving biological, mechanical, and fluid-dynamical factors. This thesis follows a multidisciplinary approach and presents an integrated fluid-chemical theory of ILT growth and analyzes the shear-induced migration of red blood cells (RBCs) in large arteries with respect to hypoxia and its possible role in atherosclerosis. The concept of Vortical Structures (VSs) is employed, with which a theory of uid-chemically-driven ILT growth is formulated. The theory proposes that VSs play an important role in convecting and activating platelets in the aneurysmatic bulge. In particular, platelets are convected toward the distal aneurysm region inside vortex cores and are activated via a combination of high residence times and relatively high shear stress at the vortex boundary. After vortex breakup, platelets are free to adhere to the thrombogenic wall surface. VSs also convect thrombin, a potent procoagulant enzyme, captured in their core, through the aneurysmatic lumen and force its accumulation in the distal portion of the AAA. This framework is in line with the clinical observation that the thickest ILT is usually seen in the distal AAA region. The investigation of the fluid-dynamics in arteries led to the study of the shear-induced migration of RBCs in large vessels such as the abdominal aorta and the carotid artery. Marked RBCs migration is observed in the region of the carotid sinus and in the iliac arteries, regions prone to atherogenesis. This leads to the hypothesis that oxyhemoglobin availability can decrease in the near-wall region thus contributing to wall hypoxia, a factor implicated in atherosclerosis. The thesis proposes a new potential mechanism of ILT growth, driven by fluid and chemical stimuli, which can be used to study ILT progression over physiologically relevant timeframes and be used as a framework to test new hypotheses; the thesis also provides new insights on the oxyhemoglobin availability in the near-wall region with direct inuence on atherosclerosis.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 43 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0546
National Category
Other Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-125810 (URN)978-91-7501-836-2 (ISBN)
Public defence
2013-08-22, sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130813

Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2013-08-13Bibliographically approved

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