1,720,968 research outputs found
Lung and chest wall mechanics in patients with acquired immunodeficiency syndrome and severe Pneumocystis carinii pneumonia
No full textThe aim of this study was to assess the mechanical characteristics of the respiratory system in patients with acquired immune deficiency syndrome (AIDS) and acute respiratory distress syndrome (ARDS) caused by Pneumocystis carinii pneumonia (PCP). In 12 mechanically ventilated patients, total respiratory system mechanics was assessed using the technique of rapid airway occlusion during constant flow inflation, and was partitioned into lung and chest wall components using the oesophageal balloon technique. We measured interrupter resistance (Rint), which mainly reflects airway resistance, additional resistance (ΔR) due to viscoelastic behaviour and time constant inequalities, and static elastance (Est). In addition, the static inflation volume-pressure (V-P) curve was assessed. In eight patients, computed tomography scans were performed within 2 days of the assessment of respiratory mechanics. Compared to values reported in the literature for normal subjects, Est and ΔR were markedly increased in AIDS patients with PCP, whilst Rint exhibited a relatively smaller increase. These changes, which involved only the lung and airways, were mainly due to the reduction of ventilated lung units, but additional factors were involved to cause independent modifications of lung stiffness, airway calibre, and viscoelastic properties. The changes in Rint, ΔR, and Est were similar to those observed in other studies on patients with ARDS of different aetiologies. At variance with common observations in the latter patients, none of the AIDS patients with PCP exhibited an inflection point on the static inflation V-P curve, suggesting little or no alveolar recruitment during lung inflation. This finding could be related to the distinctive histopathology of Pneumocystis carinii pneumonia. Indeed, computed tomography revealed homogeneous diffuse interstitial and alveolar infiltration rather than the dense, dependent opacities observed in other studies on acute respiratory distress syndrome of different aetiologies
Respiratory mechanics in anesthetized paralyzed humans: effects of flow, volume, and time
No full textThe effects of inspiratory flow rate and inflation volume on the resistive properties of the total respiratory system were investigated in 16 anesthetized paralyzed humans by using the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rmin,rs) and of the effective additional resistance (ΔRrs) as the results of viscoelastic pressure dissipations within the pulmonary and chest wall tissues. We observed that 1) at fixed inflation volume, Rmin,rs increased linearly with increasing flow although ΔRrs decreased according to an exponential function; 2) at fixed inflation flow, Rmin,rs decreased with increasing inflation volume although there was a concomitant increase in ΔRrs. This behavior could be explained in terms of a spring-and-dashpot model incorporating 1) the standard resistance and elastance and 2) a spring-and-dashpot in parallel with standard elastance, reflecting the stress adaptation units within the thoracic tissues
Insertional action of the abdominal muscles in rabbits and dogs
No full textThe insertional action of the abdominal muscles was studied in supine anesthetized, apneic rabbits and dogs by comparing the changes in esophageal pressure (Pes), upper and lower rib cage circumference (Crc,u and Crc,l) and lung volume (VL) in response to electrical stimulation of all abdominal muscles before and after evisceration. In eviscerated animals, abdominal muscle contraction increased Pes and decreased both VL and Crc,l, but had no effect on Crc,u. Maximal responses were obtained at submaximal intensities of stimulation, and became larger with increasing lung volume. Relative to the vital capacity in intact animals, maximal ΔVL for stimulation performed at FRC and TLC were 7.2 ± 2.9 (SD) and 39.5 ± 7% in rabbits, and 6.3 ± 0.8 and 18.3 ± 5.9% in dogs, respectively. Relative to the changes in lung volume occurring with maximal contraction of the abdominal muscles in intact animals, the values of ΔVL observed in the eviscerated animals amounted to ≃35 and ≃45% for stimulation performed at FRC and TLC, respectively. Hence, abdominal muscles exert substantial insertional action on the lower rib cage that can result in appreciable lung deflationary effects, particularly at elevated lung volumes
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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