| 1. |
- Altimira, Mireia, et al.
(författare)
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Teaching Research Methodologies
- 2016
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Ingår i: INTED2016 Proceedings. - : IATED. - 9788460856177 ; , s. 3019-3027
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Konferensbidrag (refereegranskat)abstract
- This paper presents the methodology employed in the Research Methodology course, part of the Master Program in Engineering Mechanics of the Royal Institute of Technology (KTH). As a higher education institution, KTH aims at excellence in both generation and dissemination of knowledge. Even though these two activities are traditionally seen as independent –or even mutually exclusive-, there is a positive correlation between performance in research andin pedagogical activities, reinforced by the fact that inquiry-based or researchbased learning activities enhance deep learning among the students. The course Research Methodology in Engineering Mechanics poses a unique opportunity to engage the students to research in different areas through diversity-oriented learning activities.The course’s main learning outcome is that the students become acquainted with the most common concepts and research methodologies used in the fields of Fundamental Mechanics, Solid Mechanics, Fluid Mechanics, Acoustics and Biomechanics. After the completion of the course, the student should also be able to identify and analyze the methodologies in a given published work.The course consists of 9 lectures and a group project, with an estimation of the total dedication time of 80h (3hp). One lecture is focused on research ethics;while in the other 8 researchers from KTH present their areas of expertise, introducing the most relevant methodologies applied. The attendance is about40 students.In the last two years, and based on the course assessment survey, the structure of the course has been continuously shifting from traditional lectures to cover a broader range of teaching activities. In this way, different learning styles are covered and the learning outcomes can be achieved by as many students as possible. In this regard, traditional lectures are combined with problem-based or case-based lectures, and role-play. Additionally, in the content of the lectures we also try to keep a balance between experimental and numerical research methods of the different disciplines, in such a way that the students get a holistic view of the research in that particular field.This project involves reading a research journal article in the subject of engineering mechanics and presenting, in written and oral form, a critical analysis of the methodologies employed. In the beginning of their project, the students give an oral presentation of their article to another group. At the end of this activity, each group is asked to mention a positive aspect of the presentation they just heard and something that they believe should be improved. As an additional task, each group is asked to peer-review another group’s report. To do so, the students are given a document with some guidelines and evaluation criteria. Special instructions are given to make sure positive feedback is also included in the review. With this, the students get to read the work of others, learn to apply quality criteria and give feedback, and self-reflect on their own work after the review process.
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| 2. |
- 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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| 3. |
- Belliato, M., et al.
(författare)
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An experimental model of veno-venous arterial extracorporeal membrane oxygenation
- 2019
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Ingår i: International Journal of Artificial Organs. - : SAGE Publications Ltd. - 0391-3988 .- 1724-6040.
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Veno-venous arterial extracorporeal membrane oxygenation is a hybrid-modality of extracorporeal membrane oxygenation combining veno-venous and veno-arterial extracorporeal membrane oxygenation. It may be applied to patients with both respiratory and cardio-circulatory failure. Aim: To describe a computational spreadsheet regarding an ex vivo experimental model of veno-venous arterial extracorporeal membrane oxygenation to determine the return of cannula pairs in a single pump–driven circuit. Methods: We developed an ex vivo model of veno-venous arterial extracorporeal membrane oxygenation with a single pump and two outflow cannulas, and a glucose solution was used to mimic the features of blood. We maintained a fixed aortic impedance and physiological pulmonary resistance. Both flow and pressure data were collected while testing different pairs of outflow cannulas. Six simulations of different cannula pairs were performed, and data were analysed by a custom-made spreadsheet, which was able to predict the flow partition at different flow levels. Results: In all simulations, the flow in the arterial cannula gradually increased differently depending on the cannula pair. The best cannula pair was a 19-Fr/18-cm arterial with a 17-Fr/50-cm venous cannula, where we observed an equal flow split and acceptable flow into the arterial cannula at a lower flow rate of 4 L/min. Conclusion: Our computational spreadsheet identifies the suitable cannula pairing set for correctly splitting the outlet blood flow into the arterial and venous return cannulas in a veno-venous arterial extracorporeal membrane oxygenation configuration without the use of external throttles. Several limitations were reported regarding fixed aortic impedance, central venous pressure and the types of cannulas tested; therefore, further studies are mandatory to confirm our findings.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- Broman, Lars Mikael, et al.
(författare)
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Pressure and flow properties of cannulae for extracorporeal membrane oxygenation I : return (arterial) cannulae
- 2019
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Ingår i: Perfusion. - : SAGE PUBLICATIONS LTD. - 0267-6591 .- 1477-111X. ; 34, s. 58-64
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Tidskriftsartikel (refereegranskat)abstract
- Adequate extracorporeal membrane oxygenation support in the adult requires cannulae permitting blood flows up to 6-8 L/minute. In accordance with Poiseuille's law, flow is proportional to the fourth power of cannula inner diameter and inversely proportional to its length. Poiseuille's law can be applied to obtain the pressure drop of an incompressible, Newtonian fluid (such as water) flowing in a cylindrical tube. However, as blood is a pseudoplastic non-Newtonian fluid, the validity of Poiseuille's law is questionable for prediction of cannula properties in clinical practice. Pressure-flow charts with non-Newtonian fluids, such as blood, are typically not provided by the manufacturers. A standardized laboratory test of return (arterial) cannulae for extracorporeal membrane oxygenation was performed. The aim was to determine pressure-flow data with human whole blood in addition to manufacturers' water tests to facilitate an appropriate choice of cannula for the desired flow range. In total, 14 cannulae from three manufacturers were tested. Data concerning design, characteristics, and performance were graphically presented for each tested cannula. Measured blood flows were in most cases 3-21% lower than those provided by manufacturers. This was most pronounced in the narrow cannulae (15-17 Fr) where the reduction ranged from 27% to 40% at low flows and 5-15% in the upper flow range. These differences were less apparent with increasing cannula diameter. There was a marked disparity between manufacturers. Based on the measured results, testing of cannulae including whole blood flows in a standardized bench test would be recommended.
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| 10. |
- Broman, Lars Mikael, et al.
(författare)
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Pressure and flow properties of cannulae for extracorporeal membrane oxygenation II : drainage (venous) cannulae
- 2019
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Ingår i: Perfusion. - : SAGE PUBLICATIONS LTD. - 0267-6591 .- 1477-111X. ; 34, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- The use of extracorporeal life support devices such as extracorporeal membrane oxygenation in adults requires cannulation of the patient's vessels with comparatively large diameter cannulae to allow circulation of large volumes of blood (>5 L/min). The cannula diameter and length are the major determinants for extracorporeal membrane oxygenation flow. Manufacturing companies present pressure-flow charts for the cannulae; however, these tests are performed with water. Aims of this study were 1. to investigate the specified pressure-flow charts obtained when using human blood as the circulating medium and 2. to support extracorporeal membrane oxygenation providers with pressure-flow data for correct choice of the cannula to reach an optimal flow with optimal hydrodynamic performance. Eighteen extracorporeal membrane oxygenation drainage cannulae, donated by the manufacturers (n = 6), were studied in a centrifugal pump driven mock loop. Pressure-flow properties and cannula features were described. The results showed that when blood with a hematocrit of 27% was used, the drainage pressure was consistently higher for a given flow (range 10%-350%) than when water was used (data from each respective manufacturer's product information). It is concluded that the information provided by manufacturers in line with regulatory guidelines does not correspond to clinical performance and therefore may not provide the best guidance for clinicians.
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