| 1. |
- Biasetti, Jacopo, et al.
(författare)
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Shear-induced migration of red blood cells in the abdominal aorta and thecarotid bifurcation : considerations on oxygen transport
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Shear-induced migration of red blood cells (RBCs) is a well known phenomenon characterizing blood flow in the small vessels (micron to mm size) of the cardiovascular system. In large vessels, like the abdominal aorta and the carotid artery (mm to cm size), the extent of this migration has not been fully elucidated. RBCs migration exerts its influence primarily on platelet concentration, oxygen transport and oxygen availability at the luminal surface; this being of primary importance in, for example, intra-luminal thrombus (ILT) growth, atherosclerosis and intima hyperplasia. Phillips’ shear-induced particle migration model coupled to the Quemada viscosity model was employed to simulate the macroscopic behavior of RBCs in four patient-specific geometries: a normal abdominal aorta, an abdominal aortic aneurysm (AAA), a normal carotid bifurcation and a stenotic carotid bifurcation. Simulations show a migration of RBCs from the near wall region with a lowering of wall hematocrit (volume fraction of RBCs) on the posterior side of the normal aorta and in the iliac arteries. A marked migration is observed on the outer wall of the carotid sinus, the inner curvature wall of the common carotid artery and in the carotid stenosis. No significant migration is observed in the AAA. The spatial and temporal patterns of wall hematocrit are correlated with the near-wall shear layer and with the secondary flow induced by the vessel curvature. The results reinforce data in literature showing a decrease in oxygen partial pressure on the inner curvature wall of the carotid sinus and, more in general, on the inner curvature wall. The lowering of wall hematocrit is postulated to induce a decrease in oxygen availability at the luminal surface through a diminished concentration of oxyhemoglobin, hence contributing, with the lowered oxygen partial pressure, to local hypoxia.
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| 2. |
- Grytsan, Andrii, 1986-, et al.
(författare)
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Growth description for vessel wall adaptation : a thick-walled mixture model of abdominal aortic aneurysm evolution
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Modeling the soft tissue volumetric growth has received considerable attention in the literature.However, due to the lack of experimental observations, the growth kinematics, that are reported in the literature, are based on a number of assumptions.The present study tested the plausibility of different growth descriptions when applied to the abdominal aortic aneurysm (AAA) evolution.A structurally motivated material model and the multi-constituent tissue growth descriptions were utilized. The mass increment of the individual constituents preserved either the density or the volume.Four different growth descriptions were tested, namely isotropic (IVG), in-plane (PVG), in-thickness (TVG) growth and no volume growth (NVG) models.Based on the model sensitivity to the increased collagen deposition, TVG and NVG models were found to be plausible scenarios, while IVG and PVG were found to be implausible. In addition, TVG and NVG models were less sensitive to the initial constituent volume fractions, than IVG and PVG models.In conclusion, the choice of the growth kinematics is of crucial importance when modeling the AAA growth and remodeling, and,probably, also for other soft biological tissues.
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| 3. |
- Stevens, Raoul, et al.
(författare)
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Biomechanical changes during abdominal aortic aneurysm growth
- 2016
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Rapport (refereegranskat)abstract
- The biomechanics-based Abdominal Aortic Aneurysm (AAA) rupture risk assessment has gainedconsiderable scientific and clinical momentum. However, such studies have mainly focused oninformation at a single time point, and little is known about how AAA properties change over time.Consequently, the present study explored how geometry, wall stress-related and blood flow-relatedbiomechanical properties change during AAA expansion. Four patients with a total of 23 ComputedTomography-Angiography (CT-A) scans at different time points were analyzed. At each time point,patient-specific properties were extracted from (i) the reconstructed geometry, (ii) the computedwall stress at Mean Arterial Pressure (MAP), and (iii) the computed blood flow velocity atstandardized in and out flow conditions. Testing correlations between these parameters identifiedseveral non-intuitive dependencies. Most interestingly, the Peak Wall Rupture Index (PWRI) and themaximum Wall Shear Stress (WSS) independently predicted AAA volume growth. Similarly, Intra-luminal Thrombus (ILT) volume growth depended on both the maximum WSS and the ILT volumeitself. In addition, ILT volume, ILT volume growth and maximum ILT layer thickness correlated withPWRI as well as AAA volume growth. Consequently, a large ILT volume as well as fast increase of ILTvolume over time may be a risk factor for AAA rupture. However, tailored clinical studies would berequired to test this hypothesis and to clarify whether monitoring ILT development has any clinicalbenefit.
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