1,721,038 research outputs found
Acute cardiovascular effects of exposure to airborne particulate matter : a study of possible pathogenetic mechanisms
Full text linkIntroduction
Increased levels of particulate matter air pollution (PM) have been associated with increased cardiovascular morbidity and mortality, especially in elderly adults and in people suffering from cardiovascular or lung diseases. The mechanisms behind these effects are still unknown, although some hypothesis have been postulated that include a modification of autonomic regulation of heart rhythm and the induction of arrhythmic events. Which fraction of PM is the most harmful is still controversial, and few studies investigated the role of personal exposure to different fractions, and in particular ultrafine particles.
*Aim
The aim of this thesis is to assess: i) the association between the individual exposure to PM and the modification of HRV (an index of autonomic regulation of heart rhythm) and QTec (an index of a pro-arrhythmic status), both in healthy subjects and in subjects suffering from chronic ischemic heart disease or chronic lung disease; ii) the potential role of inflammation and baseline health status in these associations; iii) the role of different PM fractions in these associations.
*Materials and methods
27 healthy individuals (“Healthy” group), 34 individuals with chronic ischemic heart disease (Heart group), 18 with chronic asthma or COPD (Lung group) underwent a 24-hour exposure/clinical evaluation protocol during their habitual activities, both in the warm season (Summer) and in the cold season (Winter). Individual exposure to UFPs, fine and coarse particles number concentration, gravimetric PM2.5 and PM10 was assessed for each subject, along with a 24-hour ambulatory ECG, for the assessment of heart rate variability and QT period. Mixed effects models were used to evaluate the associations between exposure to particles and clinical parameters, during 24-hour, day- and night-time.
*Results
The mean±SD age of the study population was 64±10 years and 65% were male. 24-hour individual exposure levels to UFPs, PM2.5 and PM10 (median (25th-75th) or mean±SD) were 19.643 (14.520-30.328) #/cm3, 41,53±22,52 μg/m3 and 51,97±24,31 μg/m3 respectively. Higher individual exposure was observed during day-time, except for particles in the accumulation mode (FP0,3-1). A -5,69% (95% C.I. -10,76 to -0,62) and -8,61% (-17,57 to 0,35) decrease in night-time SDNN (night-SDNN) in the total sample and in the Heart group respectively, was observed for an interquartile range (IQR) increase in FP0,3-1 during the night period (night-FP0,3-1). The same, even stronger, association was observed between day-FP0,3-1 and night-SDNN, and was confirmed in all groups. In subjects with higher levels of hsCRP, an increase in all night-time vagal indices (PNN50>HF>rMSSD) was observed in the totality of subjects for an IQR increase in day-FP2.5-10, and confirmed in healthy subjects only. In all subjects with lower levels of hsCRP, a +12,21% (95% C.I. 2,67 to 22,64) and +7,09 (0,12 to 14,55) increase in night-HF for an IQR increase in night-FP0,3-1 and in night-FP2,5-10 respectively was found, coupled to a decrease in the LF/HF ratio. These findings were confirmed in healthy subjects only. These associations were even stronger between day-FP and night-HRV in the total sample, and confirmed in the “Healthy” and the Heart groups.
*Discussion and conclusion
The observed results suggest a major role of fine particles leading to acute and delayed alteration in autonomic control of heart rhythm in healthy subjects and subjects with chronic ischemic heart disease, probably not related to the inflammatory status. On the other hand, coarse particles possibly need higher concentrations to exert their effects on autonomic control of heart rhythm, and these effects could be linked to inflammatory mechanisms in healthy subjects. Ultrafine particles appear to be less involved in the observed associations suggesting for these particles mechanisms other than those investigated in this study
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
- …
