| 1. |
- Ananthaseshan, S., et al.
(författare)
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Red blood cell distribution width is associated with increased interactions of blood cells with vascular wall
- 2022
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism underlying the association between elevated red cell distribution width (RDW) and poor prognosis in variety of diseases is unknown although many researchers consider RDW a marker of inflammation. We hypothesized that RDW directly affects intravascular hemodynamics, interactions between circulating cells and vessel wall, inducing local changes predisposing to atherothrombosis. We applied different human and animal models to verify our hypothesis. Carotid plaques harvested from patients with high RDW had increased expression of genes and proteins associated with accelerated atherosclerosis as compared to subjects with low RDW. In microfluidic channels samples of blood from high RDW subjects showed flow pattern facilitating direct interaction with vessel wall. Flow pattern was also dependent on RDW value in mouse carotid arteries analyzed with Magnetic Resonance Imaging. In different mouse models of elevated RDW accelerated development of atherosclerotic lesions in aortas was observed. Therefore, comprehensive biological, fluid physics and optics studies showed that variation of red blood cells size measured by RDW results in increased interactions between vascular wall and circulating morphotic elements which contribute to vascular pathology.
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| 2. |
- Berg, Niclas, 1988-
(författare)
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Blood flow and cell transport in arteries and medical assist devices
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cardiovascular system is responsible for transport of nutrients, oxygen, as well as the cells and molecules making up the immune system. Through the hemostatic system, the body maintains the integrity of the blood vessels, and prevents bleeding. The biochemical and physical processes governing the circulation interact, and take place at a large range of time and length scales - from those related to the individual cells up to the large scale flow structures. Dysfunctions of the heart or the circulatory system may have severe consequences. Cardiovascular diseases (CVD) is a heterogeneous group of diseases, responsible for about 50% of all death cases in the western world.Patients with severe but transient heart and/or lung disease may require the assistance of a heart-lung machine to bridge over the period required for the affected organ to recover. One such system is the Extracorporeal Membrane Oxygenator (ECMO) circuit, consting of a blood pump, a membrane oxygenator, cannulae and tubing system. While the therapy is life-saving, it is associated with relatively frequent thromboembolic (blood clotting and/or bleeding) events. Modeling of the flow in some components of the ECMO circuit was undertaken. The flow data was used together with models for platelet activation to assess the risk for thrombus formation. The results indicated locations of elevated risk of thrombosis in the centrifugal blood pump, the ECMO cannulae and the pipe connectors. The identified locations agreed well with clinical observations. The results lead to a direct recommendation to minimize the use of tube connectors. Further study of the sensitivity of the platelet activation models to uncertainties and errors was carried out. Some recommendations for improved modeling were proposed.Arteriosclerosis develops slowly over a long period of time (years or decades). It manifests initially at some common sites; arteries of certain sizes with relatively strong flow rate, as well as near artery bifurcations and locations of strong vessel curvature. The location specificity indicates that the blood flow plays a central role in the arteriosclerotic process. Being able to predict the future development of arteriosclerotic lesion and its location for an individual patient would imply that pre-emptive actions could be taken. This idea was the foundation of some of the numerical simulations in this thesis. A stenoted patient specific renal artery was considered, and was reconstructed to a non-pathological state by removing the stenosis using different segmentation methods. We could then evaluate if common stenosis markers based on functions of time-averages of the Wall Shear-Stress (WSS) could be use as predictive parameters. It was shown that these markers are not adequate as predictive tools. Furthermore, it was shown that the sensitivity to reconstruction technique was at least of the same order as the effect of the choice of blood rheology model. The rheology of blood was further studied through detailed simulations resolving the blood plasma flow and its interaction with the red blood cells (RBC) and the platelets. A hybrid Immersed boundary-Lattice Boltzmann method was applied, and the rheological data was compared to the Quemada model. It was found that the Quemada model could underpredict the effective viscosity by as much as 50%. The same methodology was applied to study the transport of RBCs and platelets, and the influence of RBC polydispersity. An increased degree of variability in RBC volume was found, under certain circumstances, to lead to an increase of the transport of platelets to the vessel wall (margination).
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| 3. |
- Berg, Niclas, 1988-, et al.
(författare)
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Blood flow simulations of the renal arteries - effect of segmentation and stenosis removal
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Ingår i: Flow Turbulence and Combustion. - 1386-6184 .- 1573-1987.
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Tidskriftsartikel (refereegranskat)abstract
- Patient specic based simulation of blood flows in arteries has been proposed as a future approach for better diagnostics and treatment of arterial diseases.The outcome of theoretical simulations strongly depends on the accuracy in describing the problem (the geometry, material properties of the artery and of the blood, flow conditions and the boundary conditions). In this study, the uncertainties associated with the approach for a priori assessment of reconstructive surgery of stenoted arteries are investigated. It is shown that strong curvature in the reconstructed artery leads to large spatial- and temporal-peaks in the wall shear-stress. Such peaks can be removed by appropriate reconstruction that also handles the post-stenotic dilatation of the artery. Moreover, it is shown that the effects of the segmentation approach can be equally important as the effects of using advanced rheological models. Unfortunately, this fact has not been recognized in the literature up to this point, making patient specic simulations potentially less reliable.
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| 4. |
- Berg, Niclas, 1988-, et al.
(författare)
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Blood Flow Simulations of the Renal Arteries - Effect of Segmentation and Stenosis Removal
- 2019
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Ingår i: Flow Turbulence and Combustion. - : SPRINGER. - 1386-6184 .- 1573-1987. ; 102:1, s. 27-41
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Tidskriftsartikel (refereegranskat)abstract
- Patient specific based simulation of blood flows in arteries has been proposed as a future approach for better diagnostics and treatment of arterial diseases. The outcome of theoretical simulations strongly depends on the accuracy in describing the problem (the geometry, material properties of the artery and of the blood, flow conditions and the boundary conditions). In this study, the uncertainties associated with the approach for a priori assessment of reconstructive surgery of stenoted arteries are investigated. It is shown that strong curvature in the reconstructed artery leads to large spatial- and temporal-peaks in the wall shear-stress. Such peaks can be removed by appropriate reconstruction that also handles the post-stenotic dilatation of the artery. Moreover, it is shown that the effects of the segmentation approach can be equally important as the effects of using advanced rheological models. This fact has not been recognized in the literature up to this point, making patient specific simulations potentially less reliable.
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| 5. |
- Berg, Niclas, 1988-, et al.
(författare)
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Flow characteristics and coherent structures in a centrifugal blood pump
- 2019
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Ingår i: Flow Turbulence and Combustion. - : Springer Nature. - 1386-6184 .- 1573-1987. ; 102:2, s. 469-483
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Tidskriftsartikel (refereegranskat)abstract
- Blood clot formation can be initiated by local flow conditions where regions of high shear and long residence time regions, such as flow separation and stagnation, have been identified as risk factors. This study highlights coherent structures,some of which not yet considered in the literature that may contribute to blood clot formation in the ECMO (Extra Corporeal Membrane Oxygenator) circuit. The centrifugal ECMO pump investigated in this study is compact and delivers adequate volume of blood with relatively high pressure in order to compensate for the large pressure drop in the membrane oxygenator. These requirements lead to regions with high shear in several different parts of the pump. In the narrow gap between the pump house and the impeller body (the magnet) a Taylor-Couette-like flow is observed with azimuthally aligned wavy vortices, which are also pushed towards the bottom of the pump-house by the flow generated by the blades. At the bottom gap between the impeller house and the pump house one finds spiraling flow structures, due to the rotation of the former structure. Separation bubbles are found near the tongue of the pump and at the lee sides of the blades. Such vortical structures have in literature been identified as regions where platelets may be activated whereby clots may develop.
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| 6. |
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| 7. |
- Drevhammar, T., et al.
(författare)
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Flows and function of the Infant Flow neonatal continuous positive airway pressure device investigated with computational fluid dynamics
- 2020
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Ingår i: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227.
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The first dedicated neonatal continuous positive airway pressure (CPAP) device using variable flow was the Infant Flow. The system was pressure stable with a low resistance to breathing. The aim of this study was to describe the flow and function of the Infant Flow geometry using simulated breathing and computational fluid dynamics. Method: The original Infant Flow geometry was used with simulated term infant breathing at three levels of CPAP. The large eddy simulation methodology was applied in combination with the WALE sub-grid scale model. Results: The simulation fully resolved the flow phenomena in the Infant Flow geometry. The main flow feature during inspiration was support by gas entrainment and mixing. During expiration, the jet deflected towards the outlet with unstable impingement of the jet at the opposing edge. Conclusion: The proposed mechanism has previously been based on theoretical reasoning, and our results present the first detailed description of the Infant Flow. The pressure stability was based on a jet supporting inspiration by gas entrainment and then being deflected during exhalation. This confirmed previously assumed principles of function and flows within the geometry and provided a base for further developments.
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| 8. |
- Fuchs, Alexander, 1985-, et al.
(författare)
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Assessment of Rheological Models Applied to Blood Flow in Human Thoracic Aorta
- 2023
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Ingår i: Bioengineering. - : MDPI AG. - 2306-5354. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this study is to assess the importance of non-Newtonian rheological models on blood flow in the human thoracic aorta. Methods: The pulsatile flow in the aorta is simulated using the models of Casson, Quemada and Walburn-Schneck in addition to a case of fixed (Newtonian) viscosity. The impact of the four rheological models (using constant hematocrit) was assessed with respect to (i) magnitude and deviation of the viscosity relative to a reference value (the Newtonian case); (ii) wall shear stress (WSS) and its time derivative; (iii) common WSS-related indicators, OSI, TAWSS and RRT; (iv) relative volume and surface-based retrograde flow; and (v) the impact of rheological models on the transport of small particles in the thoracic aorta. Results: The time-dependent flow in the thoracic aorta implies relatively large variations in the instantaneous WSS, due to variations in the instantaneous viscosity by as much as an order of magnitude. The largest effect was observed for low shear rates (tens s-1). The different viscosity models had a small impact in terms of time- and spaced-averaged quantities. The significance of the rheological models was clearly demonstrated in the instantaneous WSS, for the space-averaged WSS (about 10%) and the corresponding temporal derivative of WSS (up to 20%). The longer-term accumulated effect of the rheological model was observed for the transport of spherical particles of 2 mm and 2 mm in diameter (density of 1200 kg/m3). Large particles' total residence time in the brachiocephalic artery was 60% longer compared to the smaller particles. For the left common carotid artery, the opposite was observed: the smaller particles resided considerably longer than their larger counterparts. Conclusions: The dependence on the non-Newtonian properties of blood is mostly important at low shear regions (near walls, stagnation regions). Time- and space-averaging parameters of interest reduce the impact of the rheological model and may thereby lead to under-estimation of viscous effects. The rheological model affects the local WSS and its temporal derivative. In addition, the transport of small particles includes the accumulated effect of the blood rheological model as the several forces (e.g., drag, added mass and lift) acting on the particles are viscosity dependent. Mass transport is an essential factor for the development of pathologies in the arterial wall, implying that rheological models are important for assessing such risks.
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| 9. |
- Fuchs, Alexander, 1985-, et al.
(författare)
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Blood rheology modeling effects in aortic flow simulations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The purpose of the study is to assess the importance of non-Newtonian rheological models onblood flow in the human thoracic aorta.Methods: The pulsatile flow in the aorta is simulated using the models of Casson, Quemada and Walburn-Schneck in addition to a case of fixed (Newtonian) viscosity. The impact of the four rheological models wasassessed with respect to the following quantities:i. Magnitude of the viscosity relative to a reference value (the Newtonian case) and the relative mean deviation from that value.ii. Mechanical kinetic energy,vorticity, viscous dissipation rate.iii. WSS and its time derivative.iv. WSS-related indicators; OSI, TAWSS and RRT.Results: The flow in the thoracic aorta is characterized by shear-rates leading to an increase in viscosity by afactor of up to six. The different models had negligible impact on the kinetic energy and viscous dissipationrate. The effect on WSS related parameters was quantified and was found to be modest. Largest effect wasobserved for low shear-rates (below 100 s-2).Conclusions: The choice of a non-Newtonian model is important whenever the flow is viscosity dominated.Blood flow in larger arteries is weakly dependent on viscosity and can be handled by a model with weakdependence on shear-rate (e.g. Quemada or Newtonian). Blood flows with regions with low shear-rate andstrong temporal variation requires rheological models that better account for low shear and explicitlyincludes temporal variation effects.
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| 10. |
- Fuchs, Alexander, 1985-, et al.
(författare)
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Fluid mechanical aspects of blood flow in the thoracic aorta
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Arterial blood flow contains structures known to be associated with arterial wall pathologies (such as atherosclerosis and aneurysms) but also with helical motion reported to be atheroprotective. Numerical simulation of the flow in a typical human thoracic aorta model was carried out for several heart- and flow-rates. The aim was to explore the presence and the underlying mechanism of the formation of helical flow, retrograde motion and the formation of smaller scale unsteady flow structures. The main findings of the paper are as follows:- Retrograde flow is induced during flow deceleration. Reversed flow may persist throughout the cardiac cycle in parts of the descending aorta. Retrograde flow may lead enhanced risk of upstream transport of thrombi from the descending aorta to the branches of the aortic arch.- Helical flows are induced by bend and torsion of the aorta and through non-uniformity in the spatial distribution of the inlet flow (aortic valve plane).- Amplification of axial vorticity was shown to occur in the thoracic aorta. This convective instability is enhanced in the descending aorta.- Transitional and turbulent flow may occur in the thoracic aorta under elevated flow- and heart-rate conditions also in healthy individuals.- Under normal conditions, healthy individuals do not develop turbulent flow in the thoracic aorta.A hypothesis for a possible mechanism for the atheroprotective effect of helical flow is suggested.
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