1,720,959 research outputs found
Modelling of thrombus formation, growth and embolisation in the left atrial appendage under atrial fibrillation
Get PDFLeft atrial appendage (LAA) thrombosis is a frequent and serious complication associated with atrial fibrillation (AF), which significantly increases the risk of ischemic events. The presence of a thrombus within the LAA can disrupt normal blood flow and eventually embolise, leading to impaired circulation and severe complications.
An innovative fluid-structure interaction model, based on the smoothed particle hydrodynamics method, is used to simulate the formation and behaviour of thrombi in a patient-specific LAA morphology under AF condition. The clotting process is modelled by tracking the concentrations of key components involved in the coagulation cascade. The approach transforms fluid particles into a solid phase by applying internal spring forces when specific biochemical and haemodynamic conditions occur.
The findings shed light on the haemodynamic and biochemical mechanisms driving thrombus formation and migration within the LAA, highlighting regions of clot growth and subsequent embolisation. Thrombus formation begins at the LAA tip, gradually expanding through lobes and trabeculae, and ultimately progressing internally to high-recirculation regions, increasing the risk of embolisation and of potential clinical complications.
By accurately predicting thrombus formation, growth and fragmentation, this study offers valuable insight into the mechanisms associated with the thromboembolic risk in AF. These are crucial for developing targeted therapeutic strategies to minimise the risk of thromboembolic events in patient with AF
Mitral Regurgitation And Atrial Fibrillation: An Explorative Fluid-Structure Interaction Study
Get PDFAtrial fibrillation (AF) is a common cardiac arrhythmia which promotes blood stagnation into the left atrial appendage (LAA), a muscular sac attached to the left atrium of the heart. This stasis increases the risk of blood clot formation and ischaemic complications [1]. This pathology strongly increases with age, affecting about 8% of octogenarians. This implies that it is often concomitant with other common age elated cardiac pathologies such as mitral regurgitation (MR), a condition where the mitral valve does not close properly, allowing blood to flow back from the left ventricle into the left atrium. Some clinical studies have explored the association between AF and MR, suggesting that MR might have some protective effect, reducing the probability of clot formation [2-4]. This study aims to investigates how the interaction between AF and MR may alter the haemodynamics into the LAA, to identify the biomechanics of the phenomenon [5]. To this end, computational approaches are adopted, which have already demonstrated their efficacy in investigating the complex relationship between the LAA anatomy and operative function and the risk of thromboembolism in AF patients [6-9]. These computational tools, mentioned above, have demonstrated significant effectiveness in elucidating the underlying mechanisms of thromboembolic risk in patients with AF. In particular, a fluid-structure interaction approach is used to simulate blood flow in the LAA under three different conditions: healthy, AF and MR. Results indicate that MR has a significant impact on the motility of LAA, improve the wash out and reduce stagnation. Moreover, the blood stasis factor (BSF), a factor recently identified to quantify the risk of clot formation in LAA, reduces of two folds [9]. This supports the protective effect of MR observed clinically, clarifying the mechanism. These findings suggest that both LAA features and MR should be taken into consideration when assessing the thromboembolic risk in patients with AF. A combined approach, both numerical and clinical, could potentially improve patient management strategies and lead to a reduction in stroke events
The role of patient specific morphology and contractility of the left atrial appendage on the thromboembolic risk in atrial fibrillation
Get PDFThe vast majority of thrombi that cause ischemic complications in atrial fibrillation originate in the left atrial appendage. The left atrial appendage is an anatomical structure that starts from the left atrium, characterized by a wide morphological variability between individuals. This work analyses simulated hemodynamic for different patient-specific models of the left atrial appendage, using computational fluid-structure interaction studies, modelling the effect of changes in contractility and shape resulting from atrial fibrillation.
Three operating conditions were analysed: sinus rhythm, acute atrial fibrillation, and chronic atrial fibrillation. These were simulated on four patient-specific left atrial appendage morphologies, each associated with one of the major morphological variants identified by the common classification: chicken wing, cactus, windsock, and cauliflower.
The active contractility of the wall muscle was calibrated on the basis of clinical assessments of the filling and emptying volumes and boundary conditions were imposed on the fluid to replicate physiological and pathological atrial pressures, typical of the different operating conditions.
The volume of the left atrial appendage and the shear strain rates were analysed over time and space for the different models.
Globally, under conditions of atrial fibrillation, all models were found to be well aligned in terms of shear rate values and expected risk level.
Regions of low shear velocity, typically associated with an increased risk of clot, appeared to be promoted by sudden turns and focused on the trabeculae and lobes. These become substantially more pronounced and extensive with atrial fibrillation, especially in acute conditions.
This work clarifies the role of active and passive contraction on healthy hemodynamic in the left atrial appendage, analysing the changes produced by atrial fibrillation that produce hemodynamic conditions that promote clot formation.
The study indicates that the local topological features of the left atrial appendage are more directly associated with the onset of risk than the global form of the appendage, suggesting that more effective classification criteria should be identified
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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