1,720,957 research outputs found
Adrenergic effects on force-frequency relationship: a pivotal role for the cardiac intrinsic systems.
No full textAim: The force-frequency relationship (F-FR) is an important intrinsic regulatory mechanism of cardiac contractility. The involvement of autonomic nervous system in this physiological aspect of cardiac control remains unclear. The aim of the study was to evaluate the role of extrinsic and intrinsic cardiac adrenergic innervations on the heart rate (HR)-related positive inotropic response.
Methods: Twenty-four dogs were anesthetized and acutely instrumented to monitor and record ECG, systemic and left ventricular pressures and derivatives, and to pace the heart at 130, 150, 170, 190 and 210 bpm, in order to construct the F-FR curve. Animals were randomly assigned to four groups (n = 6 each): vehicle (V), ganglion-blocked (G-B), beta-blocked (beta-B) and ganglion-blocked plus beta-blocked (G-B + beta-B).
Results: Vehicle treated animals presented the classical F-FR. In the beta-B group F-FR was blunted, but never fully suppressed. The G-B treated animals showed a bell-shape response curve of the induced inotropic effect with the zenith at 170 bpm: the first part of the curve resembling the control one, followed by a rapid decline toward baseline value. The co-administration of G-B and beta-B agents reversed the contractile response to HR rise with a curve resembling the negative F-FR curve observed in the failing heart.
Conclusion: The F-FR appeared to be constituted by two consecutive mechanisms: first depolarization-rate dependent, and a second catecholamine-dependent. The natural consequence of these observations is that the full expression of F-FR needs an intact adrenergic syste
Sympathomimetic inefficiency in restoring contractility in the acute or chronic beta-blocker-treated ischaemic heart: comparison with a new agent.
Full text linkBackground: Adequate pharmacologic cardiac support in acute myocardial infarction (MI), as well as in chronic MI patients under β-blocker therapy, is problematic due to the impaired cardiac response to β-adrenergic agonists. New therapeutic approaches could resolve this problem. Istaroxime (ISTA) is a new Na+,K+-ATPase inhibitor and SERCA2 agonist.
Aims: To evaluate: 1) the effects of dobutamine (DOB) on left ventricular function in early (48–72 h) and late (14 days) phases of a post-MI canine model, compared to ISTA, and 2) the efficacy of DOB in chronic left ventricular dysfunction (6 months post-MI) in dogs pre-treated or not with a β-blocker, compared with ISTA and milrinone (MIL).
Results: When compared to the effects in healthy animals, DOB increased contractility only slightly in the first 48–72 h post-MI, whereas its efficacy recovered partially by day 14 and fully by 6 months after MI. ISTA had a greater effect on contractility than DOB and improved relaxation, while DOB did not. Moreover, ß-adrenergic blockade inhibited the inotropic action of DOB, without altering the effect of ISTA. Surprisingly, ß-adrenergic blockade blunted the effects of MIL.
Conclusion: ISTA may represent a novel strategy for enhancing left ventricular performance even in the context of acute MI and/or concomitant β-adrenergic blockade
ANTI STUNNING EFFECT OF POST 2744 IN AN HIGT AFTER LOAD, ISCHEMIA /REPERFUSION CANINE MODEL
No full textIstaroxime: a new luso-inotropic agent for heart failure
Full text linkIstaroxime is a new luso-inotropic compound selected for the treatment of acute heart failure syndromes, which reduces sodium-potassium adenosine triphosphatase (ATPase) activity and stimulates the sarcoplasmic calcium ATPase isoform 2 reuptake func- tion. The aim of this study was to evaluate the safety profile of istaroxime. For this purpose, istaroxime was administered during a 24-hour infusion to conscious dogs with chronic heart failure and to genetically cardiomyopathic BIO TO.2 hamsters for 34 weeks orally. The parameters recorded were arrhythmic events and hemodynamic effects in dogs and mortality in hamsters. In dogs, istaroxime at 1, 3, and 4 g/kg per min did not trigger arrhythmic events or magnify preexisting events. It increased left ventricular (LV) dP/dtmax (about 50% at 3 g/kg per min) and LV dP/dtmax (about 20% at 3 g/kg per min) without changing heart rate, blood pressure, or double product. At 4 g/kg per min, istaroxime increased dP/dtmax >100% but induced intense emesis in all animals. In cardiomyopathic hamsters, the dose of 30 mg/kg prolonged the survival rate to 32%. In conclusion, istaroxime seems to be a promising and safe new drug for improving cardiac performance in the failing heart
Hemodynamic effects of a new inotropic compound, PST-2744, in dogs with chronic ischemic heart failure.
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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
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