1,720,959 research outputs found
A mechanistic analysis of the force-frequency relation in non-failing and progressively failing human myocardium
No full textThis review focuses on the role of the myocardial force-frequency relation (FFR) in human ventricular performance and how changes in the FFR can reduce cardiac output and, ultimately, can contribute to altering the stability of the in-vivo cardiovascular system in a way that contributes to the progression of heart failure. Changes in the amplitude, shape, and position of the myocardial FFR occurring in various forms of heart failure are characterized in terms of maximal isometric twitch tension, slope of the ascending limb (myocardial reserve), and position of the peak of the FFR on the frequency axis (optimum stimulation frequency). All three of these parameters decline according to severity of myocardial disease in the following order: non-failing atrial septal defect, non-failing coronary artery disease, non-failing coronary artery disease with diabetes mellitus, failing mitral regurgitation, failing viral myocarditis, failing idiopathic dilated cardiomyopathy. Evidence is presented supporting a sarcoplasmic reticulum Ca-pump based mechanism for this progressive depression of the FFR. Intracellular calcium cycling and concentration and Ca-pump content all diminish in proportion to degree of depression of the FFR. Additional evidence from myocyte culture studies suggests a cause of diminished Ca-pump content is sustained, elevated levels of plasma norepinephrine. A hypothesis is presented to explain the mechanism of myocardial failure and its progression in terms of changes in the cardiovascular feedback control system that are triggered by reduced myocardial reserve. Sustained elevation of plasma norepinephrine levels depresses expression of sarcoplasmic reticulum Ca-pump protein causing depression of the FFR and this causes a compensatory further increase in norepinephrine levels and a further depression of Ca-pump protein
A Mechanistic Analysis of Reduced Mechanical Performance in Human Heart Failure
No full textIn failing human hearts (FHH) (NYHA IV) the cardiac output is inadequate to meet the metabolic needs of the peripheral systems. By means of thermo-mechanical analysis we have shown that epicardial strips from FHH (37 °C) have a depressed tension independent heat (TIH) and tension independent heat rate (dTIH/dt) liberation that correlates with depression in peak isometric force and the rate of relaxation. Furthermore, in response to a change in frequency of stimulation, FHH shows a severe blunting of the force-frequency relationship resulting in a decrease in myocardial reserve and in the frequency at which optimum force is obtained. We used ventricular ANF as an index of the severity of myocardial disease and demonstrated an inverse relationship between ANF mRNA and the sarcoplasmic reticulum (SR) calcium cycling proteins (SERCA 2, Phospholamban, Ryanodine Receptor) while these latter proteins all had a positive correlation with each other. At the same time there was an increase in sarcolemmal sodium calcium exchange protein. The decrease in SR pump proteins correlates with the decrease in myocardial reserve and optimum frequency of contraction. The latter mechanical changes are explainable in terms of a frequency dependent decrease in calcium concentration (aequorin light) in FHH
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
