1,721,026 research outputs found
Pulse-wave Doppler interrogation of the abdominal aorta: A window to the left heart and vasculature
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Intermittent entrapment of a prosthetic mitral valve disc: What you see is not what you get
Full text linkAortic valve replacement. Doppler echocardiographic studies of prognosis, effects of valve replacement and assessment of prosthetic valve function
No full textBackground. Aortic valve replacement (AVR) due to aortic valve stenosis (AS) is the most common surgical procedure on cardiac valves in the adult population. The patients early mortality, occurrence of residual heart disease and prosthetic valve-related morbidity and mortality are important determinants of the outcome of AVR. The aims of the present thesis were to identify factors of importance for early mortality, describe the effects of AVR at two years of follow-up, determine the occurrence of residual heart disease and to study prosthetic valve function. Patients and Methods. The study comprised 303 patients who received either a mechanical valve of bileaflet (St. Jude Medical, SJM) or monoleaflet (Omnicarbon) design or a stented biological porcine valve (Biocor). They were investigated with Doppler echocardiography preoperatively, within the first week postoperatively (baseline) and after approximately two years. The prosthetic valves used in the clinical studies were also investigated in a steady-flow in vitro model with catheter pressure measurements and Doppler echocardiography. Results. Patients with severe AS who died within 30 days of the operation had a smaller left ventricular outflow tract (LVOT) than survivors, as well as a higher incidence of abnormal intraventricular flow velocity and increased relative wall thickness (RWT). An LVOT of = 22 mm identified 10 of 13 patients receiving a small prosthesis (size 19 or 21). At the two-year follow-up, patients displayed improved functional status, systolic and diastolic LV function and a regression in LV mass, but 14% still had severe symptomatology (NYHA class III/IV); 46% had an abnormally increased LV mass, 12% had systolic dysfunction with a reduced ejection fraction and 33% had signs of disturbed diastolic function. Reference Doppler echocardiographic findings at baseline and at the two-year follow-up were defined. The SJM and Omnicarbon valves displayed similar Doppler gradients both in vivo and in vitro, whereas the Biocor valve had significantly higher Doppler gradients. However, the pressure recovery (as a percentage of maximum catheter pressure) was most pronounced in the SJM central orifice (53±8.6%) compared with Omnicarbon (23±7.4%) and Biocor (18±9.3%). Valve size significantly influenced pressure recovery. Conclusions. The echocardiographic findings of a narrow LVOT, an abnormal increase in intraventricular velocity and an increase in RWT identified patients running an increased risk of early postoperative mortality. Patients undergoing AVR improved their functional status and systolic and diastolic LV function and displayed a reduction in LVM, but a fairly large proportion of the patients had severe symptomatology, LV hypertrophy and signs of disturbed systolic and diastolic function at the two-year follow-up. This indicates suboptimal timing of surgical intervention for many patients. When valve dysfunction is suspected, a previous investigation for comparison may be helpful and our data describes the changes that may normally be seen between an early baseline and a late investigation. Prosthetic valve design and size influence the degree of pressure recovery, making Doppler gradients potentially misleading in the assessment of hemodynamic performance and when comparing one design with another
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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