1,721,010 research outputs found
Cardiovascular magnetic resonance of a hiatus hernia causing positional cardiac compression
No full textA69-year-old lady with intermittent breathlessness and chest pain underwent cardiovascular magnetic resonance (CMR) in the supine position. A large hiatus herniawas seen compressing the left ventricle, atrium, and mitral annulus. The CMR, including adenosine stress perfusion, was otherwise normal. The patient was immediately repositioned into the prone position and rescanned. In this position, the cardiac compression from the hiatus hernia was reduced, thus demonstrating its positional nature. Positional cardiac compression may in fact be an under-diagnosed phenomenon. Echocardiography in the left lateral decubitus position may not detect compression that occurs only when supine, unless an index of suspicion calls to reposition the patient, which is feasible with echocardiography. CMR may be more likely to detect this rare phenomenon given its supine nature
Is the orientation of the apical defibrillation paddle of importance during manual external defibrillation?
No full textObjective: Transthoracic impedance (TTI) is a factor determining the magnitude of the transmyocardial current during external defibrillation. Minimising TTI increases the chances of successful defibrillation. Most external defibrillation paddles are rectangular in shape and can, therefore, be placed in a transverse or longitudinal orientation. The apical paddle is often placed in a transverse orientation. This may theoretically result in a higher TTI than a longitudinal orientation because of poorer contact at the lateral paddle edges. We compared TTI with the apical paddle in both a transverse and longitudinal orientation. Materials and methods: Twenty sequential anaesthetised patients were studied. A pair of defibrillator paddles were instrumented to measure paddle force. TTI was recorded pre-operatively at end-expiration with the apical paddle in both longitudinal and transverse orientations. The sternal paddle was placed in a longitudinal orientation for all measurements. Results: TTI decreased in both transverse and longitudinal orientations as paddle force increased. Transverse paddle orientation resulted in a significantly (P<0.01) higher TTI than longitudinal orientation at all paddle forces below 12 kg force. Conclusion: The longitudinal orientation of a rectangular defibrillation paddle provides a lower TTI than orientation horizontally
Comparison of the effects of removal of chest hair with not doing so before external defibrillation on transthoracic impedance
No full textChest hair contributes significantly to transthoracic impedance (TTI) during defibrillation. The magnitude of this effect has not been established using external paddles. We compared TTI in 40 men before elective cardiac surgery, and before and after shaving their chests. Chest hair causes a significant increase in TTI during external defibrillation, the magnitude of the effect being related to both the quantity of hair and force applied to the defibrillation paddles. When the chests of nonhirsute patients were shaved, a decrease in TTI occurred, which was probably related to the creation of low-impedance pathways through skin abrasions
Differential contribution of skin impedance and thoracic volume to transthoracic impedance during external defibrillation
No full textBackground: Two mechanisms by which firm external paddle force decreases transthoracic impedance (TTI) have been proposed. Decreased impedance at the paddle-skin interface has been assumed to be the primary mechanism, but expulsion of air from the lungs, reducing lung volume is also likely to contribute. The relative contribution of each mechanism is unknown. Methods and results: Thirty five intubated patients undergoing general anaesthesia for cardiac surgery were studied. TTI across external defibrillation paddles was measured as paddle force was increased to 12 kgf. Measurements were performed twice; once allowing the volume of the lungs to change and once with lung volume held at functional residual capacity. TTI with constant lung volume was significantly higher at all paddle forces (P<0.001), confirming that a reduction in lung volume contributes to the decrease in TTI. At an optimal paddle force of 8 kg, the reduction in lung volume contributed to 16.2% of the overall decrease in TTI. Conclusion: The decrease in TTI seen with increasing external paddle force is due primarily to improved electrical contact at the paddle-skin interface, with a decrease in thoracic volume accounting for no more than 16% of the overall decrease at forces used clinically
Determining the optimal paddle force for external defibrillation.
No full textIn summary, 8-kg paddle force achieves 95% of the overall attainable decrease in TTI when using adult defibrillation paddles placed in an anterior-apical position. We recommend that this is the minimum force that should be applied, with a maximum force of 12 kg if physically possible
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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