1,720,987 research outputs found
Interplay between Geometry, Fluid Dynamics, and Structure in the Ventricles of the Human Heart
Full text linkNatural structures conveying fluid flow exhibit an interplay between flow-mediated forces and long-term adaptation. This phenomenon is relevant in the cardiovascular system where the geometric remodelling of the heart chambers is the main mechanism underlying pathological progression leading to hearth failure. Cardiac adaptation is analyzed here in children with a single right ventricle (SRV) in their heart. In these patients, the left ventricle (LV) is not well-developed and the healthy right ventricle (RV) is surgically reconnected, early after birth, to take the functional role of the systemic ventricle. Such a condition represents a special model to investigate cardiac adaptation and this study takes advantage of the availability of an uncommon dataset (64 normal RV, 64 normal LV, 64 SRV with clinically normal function).
The ventricular functional performance is analyzed in terms of fluid dynamics and tissue deformation with the objective of verifying to which degree the SRV configuration adapts from the original RV and progresses toward the function of a LV.
Results show that SRV immediately assumes a larger volume and a wider geometry due to the higher operating pressure. However, the fluid dynamics is weakly turbulent and produces a reduced propulsion. The surrounding tissue develops muscular thickening with multi-directional orientation of myofibers that mimic a LV. However, the reduced flow performance and a lower structural consistency makes the SRV at higher risk of progressive dysfunctional adaptations.
This study demonstrates how the interplay between cardiac flow and tissue response represents the driving macroscopic factor underlying the development of heart failure. More in general, the combined evaluation of fluid dynamics and structural functional properties can be a requirement for the exploration of of the adaptation processes across the different time-scales
Contraction Patterns of Post-Fontan Single Right Ventricle versus Normal Left and Right Ventricles in Children: Insights from Principal Strain Analysis
No full textBackground: Principal strain analysis (PSA) quantifies three-dimensional (3D) myocardial deformation using 3D speckle tracking echocardiography. It defines both amplitude and direction of the principal myocardial contraction, expressed as principal strain (PS), and a perpendicular secondary strain (SS) of lower intensity. We aim to apply PSA to describe the contractile pattern in the single right ventricle (SRV) functioning as a systemic chamber in hypoplastic left heart syndrome (HLHS), compared with normal left ventricle (LV) and right ventricle (RV), and to compare SRV function with conventional echocardiographic evaluations. Methods: Sixty-four post-Fontan HLHS patients and age-matched controls (LV: 64, RV: 48) underwent computation of PS-lines, ejection fraction (EF), end-diastolic volume indexed by body surface area (EDVi), PS, SS, circumferential strain (CS), and longitudinal strain (LS). The PS-lines were compared between groups. Linear regressions with coefficient determination (R2) of strains, fractional area change (FAC), and tricuspid annular plane excursion with EF and EDVi were assessed in SRV. Additionally, HLHS cohort was equally divided into two groups, higher and lower EF groups, followed by comparison of all parameters. Results: The pattern of PS-lines demonstrated a left-handed direction in anterior free wall, a right-handed direction in posterior free wall, and a circumferential direction in medial wall in SRV. In contrast, in the normal LV the principal contraction is in the circumferential direction whereas in the normal RV it is predominantly longitudinal. R2 of PS, SS, and CS on EF were high (0.88, 0.72, and 0.90, respectively), whereas R2 of LS was comparable with FAC (0.56 and 0.55). All parameters were independent of EDVi. PS-lines of higher EF group showed a more circumferential orientation than lower EF group in SRV. Conclusions: PSA provides a unique functional map of SRV contraction. This map differs from corresponding maps of normal LV and RV. This may be helpful in understanding the mechanisms of SRV function, although future longitudinal studies are needed
Simultaneous Volumetric and Functional Right Ventricular Assessment by Principal Strain Analysis in Children with Repaired Tetralogy of Fallot
No full textAims: Principal strain (PS) analysis using 3D speckle-tracking echocardiography enables us to simultaneously measure 3D ventricular volumes and strains. PS quantifies 3D deformation by defining not only amplitude but also direction of principal myocardial contraction (PS angle). This study aims (i) to validate volumetric and functional parameters using PS analysis in volume-overloaded right ventricle (RV) of repaired tetralogy of Fallot (rTOF) vs. cardiac magnetic resonance (CMR) and (ii) to describe PS analysis indices in patients undergoing pulmonary valve replacement (PVR). Methods and results: Sixty-four paediatric patients with rTOF (12.4 ± 5.2 years) and 58 age-matched healthy children (12.8 ± 3.7 years) were prospectively included. We calculated PS magnitude [global PS (GPS)] and angle, indexed RV end-diastolic and end-systolic volumes (EDVi and ESVi), RV ejection fraction (EF), and conventional strains. Among rTOF patients, 32 CMRs were available. First, we validated volumetric parameters obtained by PS analysis against CMR. Second, we compared these indices between rTOF patients and controls. Lastly, we evaluated the discriminative value of PS analysis in PVR. PS analysis and CMR measurements showed good correlations (EDVi, r = 0.80; ESVi, r = 0.74; and EF, r = 0.70, P < 0.001). GPS showed the highest correlation with 3D-EF (r = -0.84, P < 0.001). rTOF patients exhibited nearly doubled RV volume and significantly decreased 3D-EF and conventional strains. PS magnitude also decreased in rTOF patients, with altered PS angles in RV free wall. Volume measurements of RV showed the highest predictive value for discriminating PVR (+) by receiver operating characteristic analysis, followed by PS functional parameters. Conclusion: PS analysis is a reliable and reproducible method for both volumetric and functional analysis of volume-overloaded RV in rTOF, which can be of incremental value for defining the indications for PVR
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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