| 1. |
- Andersson, Magnus, et al.
(författare)
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Characterization of anisotropic turbulence behavior in pulsatile blood flow
- 2021
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Ingår i: Biomechanics and Modeling in Mechanobiology. - : SPRINGER HEIDELBERG. - 1617-7959 .- 1617-7940. ; 20, s. 491-506
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Tidskriftsartikel (refereegranskat)abstract
- Turbulent-like hemodynamics with prominent cycle-to-cycle flow variations have received increased attention as a potential stimulus for cardiovascular diseases. These turbulent conditions are typically evaluated in a statistical sense from single scalars extracted from ensemble-averaged tensors (such as the Reynolds stress tensor), limiting the amount of information that can be used for physical interpretations and quality assessments of numerical models. In this study, barycentric anisotropy invariant mapping was used to demonstrate an efficient and comprehensive approach to characterize turbulence-related tensor fields in patient-specific cardiovascular flows, obtained from scale-resolving large eddy simulations. These techniques were also used to analyze some common modeling compromises as well as MRI turbulence measurements through an idealized constriction. The proposed method found explicit sites of elevated turbulence anisotropy, including a broad but time-varying spectrum of characteristics over the flow deceleration phase, which was different for both the steady inflow and Reynolds-averaged Navier-Stokes modeling assumptions. Qualitatively, the MRI results showed overall expected post-stenotic turbulence characteristics, however, also with apparent regions of unrealizable or conceivably physically unrealistic conditions, including the highest turbulence intensity ranges. These findings suggest that more detailed studies of MRI-measured turbulence fields are needed, which hopefully can be assisted by more comprehensive evaluation tools such as the once described herein.
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| 2. |
- Andersson, Magnus, et al.
(författare)
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Model Verification and Error Sensitivity of Turbulence-Related Tensor Characteristics in Pulsatile Blood Flow Simulations
- 2021
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Ingår i: Fluids. - : MDPI. - 2311-5521. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Model verification, validation, and uncertainty quantification are essential procedures to estimate errors within cardiovascular flow modeling, where acceptable confidence levels are needed for clinical reliability. While more turbulent-like studies are frequently observed within the biofluid community, practical modeling guidelines are scarce. Verification procedures determine the agreement between the conceptual model and its numerical solution by comparing for example, discretization and phase-averaging-related errors of specific output parameters. This computational fluid dynamics (CFD) study presents a comprehensive and practical verification approach for pulsatile turbulent-like blood flow predictions by considering the amplitude and shape of the turbulence-related tensor field using anisotropic invariant mapping. These procedures were demonstrated by investigating the Reynolds stress tensor characteristics in a patient-specific aortic coarctation model, focusing on modeling-related errors associated with the spatiotemporal resolution and phase-averaging sampling size. Findings in this work suggest that attention should also be put on reducing phase-averaging related errors, as these could easily outweigh the errors associated with the spatiotemporal resolution when including too few cardiac cycles. Also, substantially more cycles are likely needed than typically reported for these flow regimes to sufficiently converge the phase-instant tensor characteristics. Here, higher degrees of active fluctuating directions, especially of lower amplitudes, appeared to be the most sensitive turbulence characteristics.
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| 3. |
- Andersson, Magnus, 1983-
(författare)
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Turbulence Descriptors in Arterial Flows : Patient-Specific Computational Hemodynamics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- At this very moment, there are literally millions of people who suffer from various types of cardiovascular diseases (CVDs), many of whom will experience reduced quality of life or premature lift expectancy. The detailed underlying pathogenic processes behind many of these disorders are not well understood, but were abnormal dynamics of the blood flow (hemodynamics) are believed to play an important role, especially atypical flow-mediated frictional forces on the intraluminal wall (i.e. the wall shear stress, WSS). Under normal physiological conditions, the flow is relatively stable and regular (smooth and laminar), which helps to maintain critical vascular functions. When these flows encounter various unfavorable anatomical obstructions, the flow can become highly unstable and irregular (turbulent), giving rise to abnormal fluctuating hemodynamic forces, which increase the bloodstream pressure losses, can damage the cells within the blood, as well as impair essential structural and functional regulatory mechanisms. Over a prolonged time, these disturbed flow conditions may promote severe pathological responses and are therefore essential to foresee as early as possible.Clinical measurements of blood flow characteristics are often performed non-invasively by modalities such as ultrasound and magnetic resonance imaging (MRI). High-fidelity MRI techniques may be used to attain a general view of the overall large-scale flow features in the heart and larger vessels but cannot be used for estimating small-scale flow variations nor capture the WSS characteristics. Since the era of modern computers, fluid motion can now also be predicted by computational fluid dynamics (CFD)simulations, which can provide discrete mathematical approximations of the flow field with much higher details (resolution) and accuracy compared to other modalities. CFD simulations rely on the same fundamental principles as weather forecasts, the physical laws of fluid motion, and thus can not only be used to assess the current flow state but also to predict (foresee) important outcome scenarios in e.g. intervention planning. To enable blood flow simulations within certain cardiovascular segments, these CFD models are usually reconstructed from MRI-based anatomical and flow image-data. Today, patient-specific computational hemodynamics are essentially only performed within the research field, where much emphasis is dedicated towards understanding normal/abnormal blood flow physiology, developing better individual-based diagnostics/treatments, and evaluating the results reliability/generality in order to approach clinical applicability.In this thesis, advanced CFD methods were adopted to simulate realistic patient-specific turbulent hemodynamics in constricted arteries reconstructed from MRI data. The main focus was to investigate novel, comprehensive ways to characterize these abnormal flow conditions, in the pursuit of better clinical decision-making tools; from more in-depth analyzes of various turbulence-related tensor characteristics to descriptors that evaluate the hemodynamics more globally in the domain. Results from the studies in this thesis suggest that these turbulence descriptors can be useful to: i) target cardiovascular sites prone to specific turbulence characteristics, both in the bulk flow and on the intraluminal wall, ii) provide a more extensive view of the general flow severity within malformed vascular regions, and iii) evaluated and potentially improve cardiovascular modeling strategies and MRI-measured turbulence data.The benefit of these descriptors is that they all, in principle, can be measured by different MRI procedures, making them more accessible from a clinical perspective. Although the significance of these suggested flow-mediated phenotypes has not yet been evaluated clinically, this work opens many doors of opportunities for making more thorough and longitudinal patient-specific studies, including large cohorts of patients with various CVDs susceptible to turbulent-like conditions, as well as performing more in-depth CFD-MRI validation analyzes.
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| 4. |
- Balgård, Matts, et al.
(författare)
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Inclusion of pharmacy students in an interprofessional training ward placement for health care students in Sweden
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- What was done?: Final year undergraduate pharmacy students, specialising clinical pharmacy,were given the opportunity to spend two weeks of their six months pharmacypractice to participate in an interprofessional training ward placement(ITWP) together with medical, nursing and physiotherapy students. During thistwo-week clinical placement, the students were collaboratively responsiblefor managing the care of geriatric inpatients while under supervision oflicensed practitioners.Why was it done?: ITWP for health care students is established at various teaching hospitals.However, to our knowledge, no such program in Scandinavia has includedpharmacy students. Clinical pharmacy is a growing profession in Sweden andother health care students will in the future work alongside with clinicalpharmacists. Therefore we set out to add pharmacy students to the ITWP team,believing that it would be a valuable experience for them to collaborate andshare knowledge with students from other health care professions. Equallyimportant, it is a way to promote the pharmacist’s competence andcontribution to the multiprofessional health care team, prior to graduation.How was it done?: A working group was formed consisting of teachers from the faculty ofpharmacy, a student representative and a working clinical pharmacist. Thegroup developed the initiative, including among other things, prerequisites,an evaluation plan, a workflow tool for clinical rounds and suggested tasksfor pharmacy students during the placement.What has been achieved?: The program has been running for three semesters and 6–8 pharmacy studentshave participated in the ITWP each semester. The initiative has beenevaluated using surveys. Participating pharmacy students expressed gainingnew knowledge and better insight into nursing care and the roles of the otherprofessions. Nursing students appreciated the support in medicationmanagement and medical students found the pharmacy students to be valuablediscussion partners that could challenge their drug-related decisions. Tutorsexpressed that the pharmacy students brought a beneficial dynamic to the ITWPteam.What next?: The opportunity for students from different professions to work together witha common objective in a real-life setting gives them valuable insight in eachother’s professional roles early in their careers. This good practiceinitiative could be used in other interprofessional training ward placementswishing to involve pharmacy students.
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| 5. |
- Bergengren, Lovisa, 1972-
(författare)
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Cervical screening with primary HPV : from research to clinical effectiveness
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organized cervical screening has greatly reduced the incidence of cervical cancer where implemented. Human papilloma virus (HPV) is the cause of cervical cancer, and in later years, convincing evidence has led to cervical screening with HPV as the primary method being implemented around the world. The overall aim of this thesis is to improve cervical screening, with focus on HPV screening.Papers I–III were performed with focus on postmenopausal women. Women aged, 55–59 years, excluded from the screening with a normal cytology cervical sample were found to have a high-risk HPV (hrHPV) prevalence of 5.5% in paper II. In a follow-up sample, 56% (71/126) had a persistent infection with the same genotype. Nineteen per cent of the women had dysplasia, where the majority of the high-grade squamous intraepithelial lesions (HSILs) were associated with HPV types other than HPV 16/18.Women 55-59 has a lower attendance rate in the study region, and since self-sample has been proven to increase attendance, paper I was performed to compare self-sample and professionally collected samples in these postmenopausal women. The concordance between the sampling methods was 83%, and both tests detected all histological HSILs. When including a study with older women (aged 70 years) in paper III, 23% of histological HSILs were found in hrHPV-positive women.Paper IV is a scientific evaluation of an implemented HPV-based screening programme, comparing clinical effectiveness and cost with cytology screening. More HSIL+ were detected in the new programme but at a higher cost than the old cytology-based programme. The screening visits for sampling accounted for two thirds of the costs.Altogether, the results indicate the importance of having a negative HPVtest before exiting screening. Data also present the necessity to find biomarkers that are more specific than cytology and HPV 16/18 for triaging women with hrHPV to further follow-up, both among postmenopausal women and other age groups when screening with HPV, since many women without HSIL are coming for clinical follow-up and treatment. Extending the screening interval between hrHPV-negative tests as well as implementing selfsampling to a greater extent can be important changes, since two thirds of the costs in the programme come from screening visits for sampling.
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| 6. |
- Bäck, Sophia, et al.
(författare)
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Assessment of transmitral and left atrial appendage flow rate from cardiac 4D-CT
- 2023
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Ingår i: Communications Medicine. - : Springer Nature. - 2730-664X. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Plain language summaryAssessing the blood flow inside the heart is important in diagnosis and treatment of various cardiovascular diseases, such as atrial fibrillation or heart failure. We developed a method to accurately track the motion of the heart walls over the course of a heartbeat in three-dimensional Computed Tomography (CT) images. Based on the motion, we calculated the amount of blood passing through the mitral valve and the left atrial appendage orifice, which are markers used in the diagnostic of heart failure and assessment of stroke risk in atrial fibrillation. The results agreed well with measurements from 4D flow MRI, an imaging technique that measures blood velocities. Our method could broaden the use of CT and make additional exams redundant. It can even be used to calculate the blood flow inside the heart. BackgroundCardiac time-resolved CT (4D-CT) acquisitions provide high quality anatomical images of the heart. However, some cardiac diseases require assessment of blood flow in the heart. Diastolic dysfunction, for instance, is diagnosed by measuring the flow through the mitral valve (MV), while in atrial fibrillation, the flow through the left atrial appendage (LAA) indicates the risk for thrombus formation. Accurate validated techniques to extract this information from 4D-CT have been lacking, however.MethodsTo measure the flow rate though the MV and the LAA from 4D-CT, we developed a motion tracking algorithm that performs a nonrigid deformation of the surface separating the blood pool from the myocardium. To improve the tracking of the LAA, this region was deformed separately from the left atrium and left ventricle. We compared the CT based flow with 4D flow and short axis MRI data from the same individual in 9 patients.ResultsFor the mitral valve flow, good agreement was found for the time span between the early and late diastolic peak flow (bias: <0.1 s). The ventricular stroke volume is similar compared to short-axis MRI (bias 3 ml). There are larger differences in the diastolic peak flow rates, with a larger bias for the early flow rate than the late flow rate. The peak LAA outflow rate measured with both modalities matches well (bias: -6 ml/s).ConclusionsOverall, the developed algorithm provides accurate tracking of dynamic cardiac geometries resulting in similar flow rates at the MV and LAA compared to 4D flow MRI. Back et al. describe a motion tracking algorithm to measure the flow rate through the mitral valve (MV) and the left atrial appendage (LAA) from 4D-CT data. The developed algorithm provided accurate tracking of dynamic cardiac geometries resulting in similar flow rates at the MV and LAA to those measured by 4D flow MRI.
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| 7. |
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| 8. |
- Danielsson, Örjan, et al.
(författare)
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A Systematic Method for Predictive In Silico Chemical Vapor Deposition
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:14, s. 7725-7736
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive systematic method for chemical vapor deposition modeling consisting of seven well-defined steps is presented. The method is general in the sense that it is not adapted to a certain type of chemistry or reactor configuration. The method is demonstrated using silicon carbide (SiC) as a model system, with accurate matching to measured data without tuning of the model. We investigate the cause of several experimental observations for which previous research reports only have had speculative explanations. In contrast to previous assumptions, we can show that SiCl2 does not contribute to SiC deposition. We can confirm the presence of larger molecules at both low and high C/Si ratios, which have been thought to cause so-called step-bunching. We can also show that high concentrations of Si lead to other Si molecules other than the ones contributing to growth, which also explains why the C/Si ratio needs to be lower at these conditions to maintain high material quality as well as the observed saturation in deposition rates. Due to its independence of a chemical system and reactor configuration, the method paves the way for a general predictive CVD modeling tool.
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| 9. |
- Ekman, Petter, 1988-, et al.
(författare)
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Assessment of hybrid RANS-LES methods for accurate automotive aerodynamic simulations
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105 .- 1872-8197. ; 206
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Tidskriftsartikel (refereegranskat)abstract
- The introduction of the Harmonized Light Vehicles Test Procedure causes a significant challenge for the automotive industry, as it increases the importance of efficient aerodynamics and demands how variations of optional extras affect the car’s fuel consumption and emissions. This may lead to a huge number of combinations of optional extras that may need to be aerodynamically analyzed and possibly optimized, being to resource-consuming to be done with wind tunnel testing merely. Reynolds Average Navier-Stoles (RANS) coupled with Large Eddy Simulations (LES) have shown potential for accurate simulation for automotive applications for reasonable computational cost. In this paper, three hybrid RANS-LES models are investigated on the DrivAer notchback and fastback car bodies and compared to wind tunnel measurements. Several yaw angles are investigated to see the model’s ability to capture small and large changes of the flow field. It is seen that the models generally are in good agreement with the measurement, but only one model is able to capture the behavior seen in the measurements consistently. This is connected to the complex flow over the rear window, which is important to capture for accurate force predictions.
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| 10. |
- Ekman, Petter, 1988-, et al.
(författare)
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Importance of Sub-Grid Scale Modeling for Accurate Aerodynamic Simulations
- 2021
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Ingår i: Journal of Fluids Engineering. - : ASME. - 0098-2202 .- 1528-901X. ; 143:1
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Tidskriftsartikel (refereegranskat)abstract
- The Ahmed body is one of the most well-investigated vehicle bodies for aerodynamic purposes. Despite its simple geometry, the flow around the body, especially at the rear, is very complex as it is dominated by a large wake with strong interaction between vortical structures. In this study, the flow around the 25 deg Ahmed body has been investigated using large eddy simulations and compared to high-resolution particle image velocimetry (PIV) measurements. Special emphasis was put on studying three commonly used sub-grid scale (SGS) models and their ability to capture vortical structures around the Ahmed body. The ability of the SGS models to capture the near-wall behavior and small-scale dissipation is crucial for capturing the correct flow field. Very good agreement between simulations and PIV measurements were seen when using the dynamic Smagorinsky-Lilly and the wall-adopting local eddy-viscosity SGS models, respectively. However, the standard Smagorinsky-Lilly model was not able to capture the flow patterns when compared to the PIV measurements due to shortcomings in the near-wall modeling in the standard Smagorinsky-Lilly model, resulting in overpredicted separation.
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