| 31. |
- Man, V., et al.
(författare)
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Impact of isotropic constitutive descriptions on the predicted peak wall stress in abdominal aortic aneurysms
- 2018
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Ingår i: Medical Engineering and Physics. - : Elsevier. - 1350-4533 .- 1873-4030. ; 53, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- Biomechanics-based assessment of Abdominal Aortic Aneurysm (AAA) rupture risk has gained considerable scientific and clinical momentum. However, computation of peak wall stress (PWS) using state-ofthe-art finite element models is time demanding. This study investigates which features of the constitutive description of AAA wall are decisive for achieving acceptable stress predictions in it. Influence of five different isotropic constitutive descriptions of AAA wall is tested; models reflect realistic non-linear, artificially stiff non-linear, or artificially stiff pseudo-linear constitutive descriptions of AAA wall. Influence of the AAA wall model is tested on idealized (n = 4) and patient-specific (n = 16) AAA geometries. Wall stress computations consider a (hypothetical) load-free configuration and include residual stresses homogenizing the stresses across the wall. Wall stress differences amongst the different descriptions were statistically analyzed. When the qualitatively similar non-linear response of the AAA wall with low initial stiffness and subsequent strain stiffening was taken into consideration, wall stress (and PWS) predictions did not change significantly. Keeping this non-linear feature when using an artificially stiff wall can save up to 30% of the computational time, without significant change in PWS. In contrast, a stiff pseudo-linear elastic model may underestimate the PWS and is not reliable for AAA wall stress computations.
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| 32. |
- Martufi, Giampaolo, et al.
(författare)
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Review : The role of biomechanical modeling in the rupture risk assessment for abdominal aortic aneurysms
- 2013
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Ingår i: Journal of Biomechanical Engineering. - : ASME International. - 0148-0731 .- 1528-8951. ; 135:2, s. 021010-
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Forskningsöversikt (refereegranskat)abstract
- AAA disease is a serious condition and a multidisciplinary approach including biomechanics is needed to better understand and more effectively treat this disease. A rupture risk assessment is central to the management of AAA patients, and biomechanical simulation is a powerful tool to assist clinical decisions. Central to such a simulation approach is a need for robust and physiologically relevant models. Vascular tissue senses and responds actively to changes in its mechanical environment, a crucial tissue property that might also improve the biomechanical AAA rupture risk assessment. Specifically, constitutive modeling should not only focus on the (passive) interaction of structural components within the vascular wall, but also how cells dynamically maintain such a structure. In this article, after specifying the objectives of an AAA rupture risk assessment, the histology and mechanical properties of AAA tissue, with emphasis on the wall, are reviewed. Then a histomechanical constitutive description of the AAA wall is introduced that specifically accounts for collagen turnover. A test case simulation clearly emphasizes the need for constitutive descriptions that remodels with respect to the mechanical loading state. Finally, remarks regarding modeling of realistic clinical problems and possible future trends conclude the article.
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| 33. |
- Matthews, Evan O., et al.
(författare)
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Athero-occlusive Disease Appears to be Associated with Slower Abdominal Aortic Aneurysm Growth : An Exploratory Analysis of the TEDY Trial
- 2022
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 63:4, s. 632-640
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The role of atherosclerosis in abdominal aortic aneurysm (AAA) pathogenesis is controversial. The aim of this study was to compare AAA growth in patients who did and did not have concurrent athero-occlusive disease (AOD). Methods: Patients with an AAA measuring 35 - 49 mm in maximum diameter were recruited as part of the TElmisartan in the management of abdominal aortic aneurysm (TEDY) trial. TEDY participants who had infrarenal aortic volume and orthogonal diameter assessed by computed tomography at entry and at least one other time point during the trial (12 and/or 24 months) were included. AOD was defined by prior diagnoses of coronary heart disease, stroke, or peripheral arterial disease or an ankle brachial pressure index < 0.90. The increase in AAA volume and diameter from entry for participants who did and did not have AOD was assessed using linear mixed effects models; 131 of the 210 participants recruited to TEDY were included. Results: In an unadjusted analysis, the mean (95% confidence interval) annual increases in AAA volume and diameter for participants with AOD were 3.26 (0.82 - 5.70) cm(3) and 0.70 (0.19 - 1.22) mm slower than those without AOD, p = .008 and.007 respectively. The association between AOD and significantly slower AAA growth was maintained after adjusting for risk factors and medications, significantly unequally distributed between participants with and without an AOD diagnosis. Conclusion: In an exploratory analysis of a selective cohort from the TEDY trial, AOD was associated with slower AAA growth. Validation of these findings in other cohorts is needed.
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| 34. |
- Riveros, F., et al.
(författare)
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Influence of intraluminal thrombus topology on AAA passive mechanics
- 2013
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Ingår i: 2013 40th Computing in Cardiology Conference, CinC 2013. - : IEEE Computer Society. - 9781479908844 ; , s. 899-902
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Konferensbidrag (refereegranskat)abstract
- An intraluminal thrombus (ILT) is found in most AAAs of clinically relevant size. Even though some studies seem to indicate a protective role of the ILT against AAA rupture, there is still great controversy on this regard. In addition, patient-specific AAA models are generated from gated medical images in which the artery is under pressure. Identification of the AAA zero pressure geometry would allow for a more realistic estimate of the aneurysmal wall mechanics and a better understanding of the role of the ILT. This study looks into the influence of the ILT on patient specific AAA accounting for the zero pressure geometry. Ten patient specific AAA of similar maximum diameter (4.8-5.2cm) and ILT volume were considered. For the stress analysis, the arterial wall is modeled as an anisotropic hyperelastic solid. Our results suggest that the geometrical configuration of the ILT relative to the arterial wall may be an influential factor not only on the ensuing peak wall stress, but also on its location within the lesion. The effects of the ILT topology are enhanced when the zero pressure configuration of the lesion is accounted for, where as the location of the peak wall stress in the lesion corresponds to the region of minimal ILT thickness. These suggest that the topology of the ILT, which greatly influence the zero-pressure geometry of the AAA, affects the stress field at the systolic pressure on AAA.
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| 35. |
- Rofes, Adrià, et al.
(författare)
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Survey on current cognitive practices within the European Low-Grade Glioma Network : towards a European assessment protocol.
- 2017
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Ingår i: Acta Neurochirurgica. - : Springer Science and Business Media LLC. - 0001-6268 .- 0942-0940. ; 159:7, s. 1167-1178
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The European Low-Grade Glioma network indicated a need to better understand common practices regarding the managing of diffuse low-grade gliomas. This area has experienced great advances in recent years.METHOD: A general survey on the managing of diffuse low-grade gliomas was answered by 21 centres in 11 European countries. Here we focused on specific questions regarding perioperative and intraoperative cognitive assessments.RESULTS: More centres referred to the same speech and language therapist and/or neuropsychologist across all assessments; a core of assessment tools was routinely used across centres; fluency tasks were commonly used in the perioperative stages, and object naming during surgery; tasks that tapped on attention, executive functions, visuospatial awareness, calculation and emotions were sparsely administered; preoperative assessments were performed 1 month or 1 week before surgery; timing for postoperative assessments varied; finally, more centres recommended early rehabilitation, whenever needed.CONCLUSIONS: There is an emerging trend towards following similar practices for the management of low-grade gliomas in Europe. Our results are descriptive and formalise current discussions in our group. Also, they contribute towards the development of a European assessment protocol.
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| 36. |
- Ross, Owen A., et al.
(författare)
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Genomic investigation of alpha-synuclein multiplication and parkinsonism
- 2008
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Ingår i: Annals of Neurology. - : Wiley. - 1531-8249 .- 0364-5134. ; 63:6, s. 743-750
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Copy number variation is a common polymorphic phenomenon within the human genome. Although the majority of these events are non-deleterious they can also be highly pathogenic. Herein we characterize five families with parkinsonism that have been identified to harbor multiplication of the chromosomal 4q21 locus containing the a-synuclein gene (SNCA). Methods: A methodological approach using fluorescent in situ hybridization and Affymetrix (Santa Clara, CA) 250K SNP microarrays was used to characterize the multiplication in each family and to identify the genes encoded within the region. The telomeric and centromeric breakpoints of each family were further narrowed using semiquantitative polymerase chain reaction with microsatellite markers and then screened for transposable repeat elements. Results: The severity of clinical presentation is correlated with SNCA dosage and does not appear to be overtly affected by the presence of other genes in the multiplicated region. With the exception of the Lister kindred, in each family the multiplication event appears de novo. The type and position of Alu/LINE repeats are also different at each breakpoint. Microsatellite analysis demonstrates two genomic mechanisms are responsible for chromosome 4q21 multiplications, including both SNCA duplication and recombination. Interpretation: SNCA dosage is responsible for parkinsonism, autonomic dysfunction, and dementia observed within each family. We hypothesize dysregulated expression of wild-type (alpha-synuclein results in parkinsonism and may explain the recent association of common SNCA variants in sporadic Parkinson's disease. SNCA genomic duplication results from intraallelic (segmental duplication) or interallelic recombination with unequal crossing over, whereas both mechanisms appear to be required for genomic SNCA triplication.
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| 37. |
- Sailer, Anna, et al.
(författare)
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A genome-wide association study in multiple system atrophy
- 2016
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Ingår i: Neurology. - 0028-3878. ; 87:15, s. 1591-1598
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To identify genetic variants that play a role in the pathogenesis of multiple system atrophy (MSA), we undertook a genome-wide association study (GWAS). Methods: We performed a GWAS with >5 million genotyped and imputed single nucleotide polymorphisms (SNPs) in 918 patients with MSA of European ancestry and 3,864 controls. MSA cases were collected from North American and European centers, one third of which were neuropathologically confirmed. Results: We found no significant loci after stringent multiple testing correction. A number of regions emerged as potentially interesting for follow-up at p < 1 × 10-6, including SNPs in the genes FBXO47, ELOVL7, EDN1, and MAPT. Contrary to previous reports, we found no association of the genes SNCA and COQ2 with MSA. Conclusions: We present a GWAS in MSA. We have identified several potentially interesting gene loci, including the MAPT locus, whose significance will have to be evaluated in a larger sample set. Common genetic variation in SNCA and COQ2 does not seem to be associated with MSA. In the future, additional samples of well-characterized patients with MSA will need to be collected to perform a larger MSA GWAS, but this initial study forms the basis for these next steps.
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| 38. |
- Sproll, Véronique, et al.
(författare)
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Radiostation Grafted Ion-Conducting Membranes: The Influence of Variations in Base Film Nanostructure
- 2016
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 49:11, s. 4253-4264
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Tidskriftsartikel (refereegranskat)abstract
- The proton exchange membrane (PEM) is a key element of a polymer electrolyte fuel cell, and radiation-grafting is an attractive option for the synthesis of PEMs. Via a systematic investigation of a well-defined model material, sulfonated polystyrene grafted poly(ethylene-alt-tetrafluoroethylene), ETFE-g-PS(SA), we show that the performance and stability of radiation-grafted PEMs in fuel cells strongly depends on the microstructure of the underlying base polymer. The nanoscale structure of the base polymers, grafted films, and membranes is probed by small-angle scattering, and the nanoscale proton dynamics is probed by quasi-elastic neutron scattering. The results of these techniques correlated with fuel cell relevant properties—including proton conductivity and water uptake—and fuel cell performance clearly indicate that differences in the arrangement of the crystalline phase in the otherwise chemically identical semicrystalline base films can have considerable impact, representing an essential aspect to consider in the development of proton exchange membranes prepared via preirradiation grafting.
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| 39. |
- Sproll, Veronique, et al.
(författare)
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Structure-property correlations of ion-containing polymers for fuel cell applications
- 2016
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 118, s. 120-123
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the structure-property correlations of grafted proton conducting membranes, the model system consisting of an ETFE base film grafted with polystyrene and subsequent sulfonation (ETFE-g-PSSA) along with crosslinked derivatives ETFE-g-P(SSA-co-DiPB) were synthesized. The characteristics of the final membranes were characterized by PFG-NMR diffusometry, in-plane conductivity and by investigations of the dimensional changes of the grafted membranes. The collected data were correlated with the inherent anisotropy of the ETFE base film. (C) 2015 Elsevier Ltd. All rights reserved.
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| 40. |
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