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Wall shear stress variations and unsteadiness of pulsatile blood-like flows in 90-degree bifurcations
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-9976-8316
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
2013 (English)In: Computers in Biology and Medicine, ISSN 0010-4825, E-ISSN 1879-0534, Vol. 43, no 8, 1025-1036 p.Article in journal (Refereed) Published
Abstract [en]

Complex and slow interaction of different mechanical and biochemical processes in hemodynamics is believed to govern atherogenesis. Over the last decades studies have shown that fluid mechanical factors such as the Wall Shear Stress (WSS) and WSS gradients can play an important role in the pathological changes of the endothelium. This study provides further indications that the effects of fluid mechanical aspects are correlated with the diseased regions of the larger arteries. Unsteady high temporal WSS gradients (TWSSG), a function of the shear-thinning property of the non-Newtonian viscosity, move with the separation bubble. Red Blood Cell (RBC) dilution due to the secondary flows determines the magnitudes of the WSS and TWSSG. The results indicate that the focal nature of the TWSSG may have implications on the response of the endothelium.

Place, publisher, year, edition, pages
2013. Vol. 43, no 8, 1025-1036 p.
Keyword [en]
Wall shear stress, Wall shear stress gradients, CFD, Blood, Atherosclerosis, Endothelium, Non-Newtonian
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-51553DOI: 10.1016/j.compbiomed.2013.05.008ISI: 000321994800007Scopus ID: 2-s2.0-84879423922OAI: oai:DiVA.org:kth-51553DiVA: diva2:464519
Funder
Swedish Research Council
Note

QC 20130815. Updated from submitted to published.

Available from: 2011-12-13 Created: 2011-12-13 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Unsteadiness of blood flow in 90-degree bifurcations
Open this publication in new window or tab >>Unsteadiness of blood flow in 90-degree bifurcations
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vii, 39 p.
Series
Trita-MEK, ISSN 0348-467X ; 2011:16
Keyword
blood rheology, viscosity, CFD, bifurcations, unsteadiness, wall shear stress
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-51585 (URN)978-91-7501-194-3 (ISBN)
Presentation
2011-12-08, Sal E3, KTH, Osquars Backe 14, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20111214Available from: 2011-12-14 Created: 2011-12-14Bibliographically approved
2. Blood Flow variations in Large Arteries due to non-Newtonian rheology
Open this publication in new window or tab >>Blood Flow variations in Large Arteries due to non-Newtonian rheology
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The blood is a complex fluid that contains, in addition to water, cells, macro-molecules and a large number of smaller molecules. The physical properties of the blood are therefore the result of non-linear interactions of its constituents, which are influenced by the local flow field conditions. Hence, the local blood viscosity is a function of the local concentration of the blood constituents and the local flow field itself. This study considers the flow of blood-like fluids in generalised 90-degree bifurcating pipes and patient-specific arterial bifurcations relevant to the large aortic branches in humans. It is shown that the Red Blood Cell (RBC) distribution in the region of bifurcations may lead to large changes in the viscosity, with implications on the concentrations of the various cells in the blood plasma. This in turn implies that the flow in the near wall regions is more difficult to estimate and predict than that under the assumption of a homogeneous fluid. The rheological properties of blood are complex and are difficult to measure, since the results depend on the measuring equipment and the inherent flow conditions. We attempt to model the viscosity of water containing different volume fractions of non-deforming RBC-like particles in tubes. The apparent viscosities of the mixtures obtained from these model experiments have been compared to the predictions of the different rheological models found in the literature. The same rheological models have also been used in the different simulations, where the local RBC concentration and local shear rate are used in the viscosity models. The flow simulations account for the non-linearity due to coupling between the flow and fluid rheology. Furthermore, from a physiological perspective, it is shown that oscillatory wall shear stresses are affected by changes in RBC concentration in the regions of the bifurcation associated with atherogenesis. The intrinsic shear thinning rheological property of the blood, in conjunction with stagnation in separated flows, may be responsible for elevated temporal wall shear stress gradients (TWSSG) influencing endothelial cell behaviour, which has been postulated to play a role in the development of atherosclerosis. The blood-like fluid properties along with variations in the RBC concentration could also lead to variations in the developing flow structures in the larger arteries that could influence the work the heart has to bear.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xx, 98 p.
Series
Trita-MEK, ISSN 0348-467X ; 2013:18
Keyword
Blood, Rheology, Viscosity, non-Newtonian, CFD, Bifurcations, Unsteadiness, Wall Shear Stress, Atherosclerosis
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-136594 (URN)978-91-7501-952-9 (ISBN)
Public defence
2013-12-19, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20131206

Available from: 2013-12-06 Created: 2013-12-06 Last updated: 2013-12-06Bibliographically approved

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Prahl Wittberg, Lisa

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