1,721,101 research outputs found
The many faces of myocardial ischemia and angina
No full textObstructive disease of the epicardial coronary arteries is the main cause of angina. However, a number of patients with anginal symptoms have normal coronaries or non-obstructive coronary artery disease despite electrocardiographic evidence of ischemia during stress testing. In addition to limited microvascular vasodilator capacity, the coronary microcirculation of these patients is particularly sensitive to vasoconstrictor stimuli, in a condition known as microvascular angina. This review briefly summarizes the determinants and control of coronary blood flow and myocardial perfusion. It subsequently analyzes the mechanisms responsible for transient myocardial ischemia: obstructive coronary artery disease, coronary spasm and coronary microvascular dysfunction in the absence of epicardial coronary lesions, and variable combinations of structural anomalies, impaired endothelium-dependent and/or -independent vasodilation, and enhanced perception of pain. Lastly, we exemplify mechanism of angina during tachycardia. Distal to a coronary stenosis, coronary dilator reserve is already recruited and can be nearly exhausted at rest distal to a severe stenosis. Increased heart rate reduces the duration of diastole and thus coronary blood flow when metabolic vasodilation is no longer able to increase coronary blood flow. The increase in myocardial oxygen consumption and resulting metabolic vasodilation in adjacent myocardium without stenotic coronary arteries further acts to divert blood flow away from the post-stenotic coronary vascular bed through collaterals
Prevention of TNF alpha-associated myocardial dysfunction resulting from cardiopulmonary bypass and cardioplegic arrest by glucocorticoid treatment
No full textObjective: Cardiac surgery on cardiopulmonary bypass (CPB) results in progressive myocardial dysfunction, despite unimpaired coronary blood flow, and is associated with increased myocardial tumor necrosis factor-alpha (TNF alpha) expression. We investigated whether anti-inflammatory treatment prevents increased TNF alpha expression and myocardial dysfunction after CPB. Methods and results: Baseline systemic hemodynamics, myocardial contractile function, aortic and coronary blood flow were measured in anesthetized pigs. Then, placebo (PLA; saline; n = 7) or methylprednisolone (MP; 30 mg/kg; n = 6) was infused intravenously and CPB was instituted. Global ischemia was induced for 10 min by aortic cross-clamping, followed by 1 h of cardioplegic cardiac arrest. After declamping and reperfusion, CPB was terminated after a total of 3 h. Measurements were repeated at 15 min, 4 h, and 8 h following termination of CPB. Systemic TNF alpha-plasma concentrations and left ventricular TNF alpha expression were analyzed. With unchanged coronary blood flow in both groups, a progressive toss of myocardial contractile function to 38 +/- 2% of baseline (p < 0.01) and cardiac index to 48 +/- 6% of baseline (p < 0.01) at 8 h after CPB in PLA was attenuated in MP (myocardial function: 72 +/- 3%, p < 0.01 vs PLA; cardiac index: 78 +/- 6%, p < 0.05 vs PLA). Systemic TNFa was increased at 8 h in PLA compared to MP (243 +/- 34 vs 90 +/- 34 pg/ml, p < 0.05). Myocardial TNF alpha was increased at 8 h after CPB compared to baseline and MP (p < 0.05). Myocardial TNF alpha immunostaining was more pronounced in PLA than in MP (p < 0.05), with TNF alpha-mRNA localization predominantly to cardiomyocytes. Conclusions: Methylprednisolone attenuates both systemic and myocardial TNF alpha increases and progressive myocardial dysfunction induced by cardiac surgery, suggesting a key rote for TNF alpha. (c) 2006 Elsevier B.V. All rights reserved
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
Vascular (dys)function in the failing heart
No full textHeart failure (HF) is not confined to contractile failure of cardiomyocytes or myocardial fibrosis. Coronary and systemic vascular dysfunction contributes to the initiation and progression of HF with or without reduced ejection fraction. Furthermore, HF compromises vascular function, creating and sustaining a vicious cycle with deranging effects on coronary blood flow, cardiac metabolism and cardiac function. In HF, systemic arterial dysfunction, characterized by increased arterial stiffness and resistance, raises cardiac afterload and impedes myocardial contractile function. Reduced coronary blood flow impairs myocardial oxygen delivery and consequently cardiomyocyte metabolism and function. Coronary microvascular dysfunction is heterogeneous in its pathogenesis and manifestations, complicating the diagnosis and management across different HF phenotypes. Understanding the alterations in function in different segments of the vasculature, from the aorta to the capillary level, offers mechanistic insights into disease drivers and therapeutic interventions. Interventional approaches can improve vascular haemodynamics, whereas established and emerging pharmacotherapies target the neurohumoral axis and reduce extravascular compression, inflammation, and oxidative stress, thereby improving vascular function and HF-related outcomes. In this Review, we provide a mechanistic framework of vascular dysfunction in the pathogenesis of HF with or without reduced ejection fraction, pointing towards integrated therapies that consider the vascular implications of contemporary HF management across HF phenotypes
- …
