1,721,035 research outputs found
Anatomical adjustment of long-term ventricular assist devices through exploitation of Imaging and computer-assisted simulation
No full textLes assistances circulatoires mécaniques de longue durée (ACM) sont une stratégie de plus en plus répandue pour le traitement des patients porteurs d’insuffisance cardiaque avancée. Cependant, cette option thérapeutique reste associée à des complications immédiates at au suivi parfois particulièrement graves (telles que la thrombose de pompe, les évènements thromboemboliques et le dysfonctionnement du dispositif). Nous formulons l’hypothèse que l’analyse du positionnement postopératoire du dispositif (et notamment, de sa canule d’admission intraventriculaire) peut fournir des informations utiles à la prédiction des évènements cliniques cités ci-dessus. Nous formulons aussi l’hypothèse qu’il est possible d’optimiser la prise en charge de ces patients (choix du dispositif, choix du site ventriculaire et des modalités d’implantation) par le moyen d’une planification préopératoire assistée par ordinateur. Nous avons donc mis en place deux axes de recherche. Dans le premier, nous proposons un système original d’analyse d’orientation intraventriculaire de la canule d’admission (par rapport à la valve mitrale native) ; celui-ci démontre une association significative entre orientation de la canule en direction du septum interventriculaire et apparition clinique des complications. Ce moyen supplémentaire de prédiction spécifique-patient sera validé sur des cohortes plus large et testé dans le cadre d’une étude prospective. Dans le deuxième axe, nous proposons une solution d’implantation virtuelle spécifique patient. Elle est basée sur une segmentation semi-automatique des structures cardiaques, une visualisation augmentée du scanner préopératoire, un positionnement virtuel d’une représentation numérique des différents dispositifs, et une analyse de collision de celui-ci avec la paroi thoracique (ACM mono-ventriculaire et coeur artificiel total) ou le ventricule droit (ACM mono-ventriculaires). Nous ouvrons enfin les perspectives vers une approche d’analyse et prédiction physiologique basée sur la simulation par ordinateur de l’hémodynamique du ventricule gauche assisté.Long-term circulatory mechanical assist devices are increasingly employed in the management of patients with advanced heart failure. Nonetheless, this therapeutic strategy is still associated with immediate and long-term complications; among these, pump thrombosis, thromboembolic events and pump dysfunction are particularly dreadful. Mechanical factors are involved in their pathogenesis. We hypothesize that the analysis of the post-implantation positioning of the devices (and particularly of the admission cannula for left ventricular assist devices) might provide additional useful information for the prediction of the above events. We also hypothesize that it is possible to optimize the management of these patients (under the perspective of device selection, choice of the left ventricular implantation site and implantation modalities) through computer-assisted preoperative planning. We have therefore established two axes of research. With the first axis, we propose an original system for orientation analysis of the intraventricular admission cannula with respect to the mitral valve (postoperative CT scan). This analysis indicates a significant association between the cannula orientation towards the interventricular septum and the occurrence of early/delayed complications. This novel method will be validated in larger cohorts and tested in a prospective clinical investigation. With the second axis, we propose a virtual implantation solution (environment Cami-TK), based on semi-automatic segmentation of cardiac structures (preoperative CT scan), augmented visualization of the CT scan images, virtual positioning of a 3D mesh representing the devices, and collision analysis with the thoracic structures (left ventricular assist devices and total artificial heart) or the right ventricle (ventricular assist devices only). We finally indicate future investigations concerning the application of computational fluid dynamics to facilitate computer simulation of the hemodynamics within the assisted left ventricle, and refined prediction of adverse events
Analyse in sillico du risque de thrombose pour l’implantation d’un dispositif d’assistance ventriculaire gauche
No full textL’implantation d’un dispositif d’assistance ventriculaire gauche (DAVG) est envisagée au stade final de l’insuffisance cardiaque. Elle peut cependant entraîner des complications. L’objectif de cette thèse est d’étudier l’influence des caractéristiques (longueur et angulation) de la Canule Apicale (CA) sur le risque de thrombose en considérant l’anatomie ventriculaire par une approche de la Mécanique des Fluides Numérique (MFN). Nous proposons, un modèle simplifié. L’hypothèse 2D est d’abord vérifiée en comparant un modèle 3D et son modèle 2D correspondant, les mêmes tendances hémodynamiques ont été trouvées. Le modèle proposé est ensuite utilisé pour analyser l’hémodynamique ventriculaire en fonction des caractéristiques de la CA et construire un Marqueur du Potentiel Thrombogène Personalisé (MPTP) sur la base de la formation de vortex et de la morphologie ventriculaire. Pour évaluer l’efficacité du marqueur, plusieurs cas cliniques sont étudiés (19 patients implantés avec HM2 & HM3). Les résultats sont comparés aux résultats cliniques. Le marqueur semble capable de distinguer avec précision les patients avec et sans complications pour les deux types pompes. Un large intervalle d’angulations de la CA est étudié et les résultats obtenus révèlent que le marqueur proposé semble capable de mettre en évidence des configurations et des profils thrombogènes. Si les caractéristiques de la CA influencent le risque de thrombose, les simulations suggèrent également que l’anatomie ventriculaire semble être un facteur déterminant de l’étendue de cette influence. Le pipeline de simulation proposé est une piste prometteuse vers le développement d’un système d’aide à la décision clinique.In the context of end stage heart failure, implantation of a Left Ventricular Assist Device (LVAD) is associated with serious complications. The aim of this thesis is to investigate the influence of IC features (length and angulation) on thrombosis risk by considering ventricular anatomy through a Computational Fluids Dynamics (CFD) approach. We propose a simplified model. The 2D assumption is first verified by comparing a 3D model and its corresponding 2D model, same haemodynamic tendencies were found. The proposed model is then used to analyse the influence of IC features on LV haemodynamic which allowed proposing a Personolised Thrombogenic Potential Marker (PTPM) based on vortices formation and ventricular morphology. To assess the marker efficiency, several clinical cases are investigated (19 patients implanted with HM2 \& HM3). PTPM results are compared to clinical outcome. The marker seems able to accurately distinguish between patients with and without LVAD related complications. A wide range of IC angulation is investigated and obtained results reveal that the proposed marker seems able to recognise thrombogenic configurations and highlighted thrombogenic profiles. While IC features do influence the thrombosis risk, simulations also suggest that the ventricular anatomy seems to be a determining factor of the extent of this influence. The proposed pipeline of simulation is a promising lead towards the development of a clinical decision support system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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