1,720,971 research outputs found
COMBINED THROMBOXANE-A2 SYNTHETASE INHIBITION AND RECEPTOR BLOCKADE ARE EFFECTIVE IN PREVENTING SPONTANEOUS AND EPINEPHRINE-INDUCED CANINE CORONARY CYCLIC FLOW VARIATIONS
No full textFREQUENCY AND SEVERITY OF CYCLIC FLOW ALTERNATIONS AND PLATELET-AGGREGATION PREDICT THE SEVERITY OF NEOINTIMAL PROLIFERATION FOLLOWING EXPERIMENTAL CORONARY STENOSIS AND ENDOTHELIAL INJURY
No full textThe role of recurrent platelet aggregation in the development of neointimal proliferation of coronary arteries was explored in this study, and the hypothesis was evaluated that recurrent platelet aggregation and the consequent frequency and severity of cyclic coronary blood flow variations are important pathophysiologic factors in the subsequent development of neointimal proliferation. In 24 chronically instrumented dogs, variable degrees of coronary artery neointimal proliferation were observed 3 weeks after mechanical injury of the arterial endothelium and the placement of an external coronary artery constrictor. The severity of neointimal proliferation at 21 days was closely related to the frequency and severity of cyclic coronary blood flow variations during the initial 7 days after instrumentation of the animals, itself a manifestation of recurrent platelet aggregation and dislodgement. Pharmacological therapy with a dual thromboxane A2 synthetase inhibitor and receptor antagonist and with a serotonin S2 receptor antagonist frequently was successful in abolishing cyclic blood flow variations and in retarding neointimal proliferation
UNSTABLE ANGINA-PECTORIS AND THE PROGRESSION TO ACUTE MYOCARDIAL-INFARCTION - ROLE OF PLATELETS AND PLATELET-DERIVED MEDIATORS
No full textThe conversion from stable to unstable angina and the further progression to myocardial infarction are usually associated with atherosclerotic plaque fissuring or ulceration at sites of coronary artery stenosis and subsequent development of a thrombus. This thrombus formation is initiated by platelet adhesion and aggregation; these, in turn, are promoted by the local release and accumulation of thromboxane A2 and serotonin. This accumulation and the resulting platelet aggregation at sites of endothelial injury cause dynamic vasoconstriction. With time, the platelet-initiated thrombus expands to include white and red blood cells in a fibrin mesh. Thus, a fully occlusive coronary thrombus may develop and cause the progression from unstable angina to acute myocardial infarction, often Q-wave myocardial infarction. We believe that the connection between unstable angina and acute myocardial infarction is a continuum relative to the processes of coronary artery thrombosis and vasoconstriction. When the period of platelet aggregation or dynamic vasoconstriction at sites of endothelial injury and coronary stenosis lasts only a few minutes and is repetitive, unstable angina or non-Q wave myocardial infarction occurs. However, when complete coronary artery occlusion lasts for longer than 4 hours, a transmural or Q-wave myocardial infarction results. Recently, in experimental animal models with mechanically induced coronary artery stenoses and endothelial injury, we have found that other mediators, including adenosine diphosphate and thrombin, also contribute to coronary artery thrombosis. Moreover, in humans with limiting angina, we have identified spontaneous coronary blood flow variations in a pattern similar to the variations caused by alternating platelet attachment and dislodgement in experimental canine modes. In this review, we add information to our previous observations in order to present the possible mechanisms of conversion from chronic to acute coronary heart disease syndromes
ENDOGENOUS NITRIC-OXIDE PROTECTS AGAINST PLATELET-AGGREGATION AND CYCLIC FLOW VARIATIONS IN STENOSED AND ENDOTHELIUM-INJURED ARTERIES
No full textBackground. This study was designed to test the hypothesis that endogenously produced nitric oxide protects against platelet aggregation and cyclic flow variations in stenosed and endothelium-injured arteries of mongrel dogs. Methods and Results. N(G)-Monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide formation, was administered at 5 mg/kg to 15 dogs after the left anterior descending coronary artery was mechanically injured and narrowed by external constrictors and to nine dogs before endothelial injury of the femoral artery and after injury and moderate arterial constriction. Treatment with L-NMMA resulted in cyclic How variations (as detected by external Doppler flow probes) in the left anterior descending artery of seven of 15 dogs and in the femoral artery of four of nine dogs after endothelial injury. L-Arginine, the precursor for nitric oxide synthesis, was administered at 60 mg/kg and abolished cyclic flow variations in each of the 11 dogs. D-Arginine did not change the L-NMMA-induced cyclic flow variations. Saline infusion did not induce or change cyclic flow variations in any of the animals. Acetylcholine (1, 10, and 100 mug/min; n=9) was administered in the femoral artery of nine additional dogs before and after endothelial injury in moderately stenosed femoral arteries. Acetylcholine did not induce cyclic flow variations in any animal; however, it did increase the severity of cyclic flow variations that developed in severely stenosed arteries. The diameter of the femoral artery was measured by intravascular ultrasound imaging. L-NMMA caused vasoconstriction of normal arteries, but no change was detected in endothelium-injured arteries. In contraSt, L-arginine caused vasodilation of normal arteries, but, again, no change was noted in endothelium-injured arteries. Acetylcholine dilated normal femoral arteries but constricted arteries with endothelial injury. In both in vitro and ex vivo platelet studies, L-NMMA enhanced platelet aggregation, whereas L-arginine significantly reduced platelet aggregation. D-Arginine and acetylcholine showed no effect on platelet aggregation. Conclusions. Promotion of nitric oxide production decreases platelet aggregation and may eliminate cyclic flow variations, whereas a reduction in nitric oxide formation enhances platelet aggregation and may induce cyclic flow variations. Acetylcholine causes vasoconstriction at the femoral arterial site of endothelial injury and may increase the severity of cyclic flow variations
ROLE OF THROMBOXANE AND SEROTONIN AS MEDIATORS IN THE DEVELOPMENT OF SPONTANEOUS ALTERATIONS IN CORONARY BLOOD-FLOW AND NEOINTIMAL PROLIFERATION IN CANINE MODELS WITH CHRONIC CORONARY-ARTERY STENOSES AND ENDOTHELIAL INJURY
No full textPlatelet-mediated obstruction of stenotic and endothelium-injured coronary arteries may be important in the abrupt progression from chronic stable to unstable coronary heart disease syndromes in patients. Transcardiac accumulation of thromboxane A2 and serotonin has been demonstrated in patients as chronic stable angina is converted to unstable angina. In this study in anesthetized open chest dogs with coronary artery stenosis and endothelial injury, thromboxane A2 and serotonin were shown to be important mediators of intermittent coronary obstruction caused by platelet aggregation and dynamic vasoconstriction. Furthermore, thromboxane A2 synthesis inhibitors and receptor antagonists and serotonin receptor antagonists, singly and together, provided substantial protection against repetitive platelet aggregation and dislodgment in canine models with coronary artery stenosis and endothelial injury even when systemic catecholamine concentrations were markedly elevated. These same observations apply in chronically instrumented, awake, unsedated dogs with coronary artery stenosis and endothelial injury in which recurrent platelet attachment and dislodgment cause cyclic flow alterations that may be prevented by thromboxane A2 synthesis inhibitors and receptor antagonists and serotonin receptor antagonists. Chronically instrumented dogs with coronary stenosis and endothelial injury in which recurrent platelet attachment and dislodgment occurred also developed neointimal proliferation of varying severity within 10 days to 3 weeks; the morphologic appearance of the neointimal proliferation was identical to that found in patients who develop restenosis after coronary angioplasty
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
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