1,720,983 research outputs found
Spectral analysis of RR and RT variabilities in patients with coronary artery disease
No full textBackground: As the duration of the Q-T interval is dependent upon the length of the preceding cardiac cycle, changes in QT interval duration mainly reflect, in normal subjects, the physiological beat-by-beat variability of the sinus node. However, little information is available on short-term QT variability in patients with an abnormal neural modulation of the sinus node. Methods: We analyzed, with autoregressive techniques, RR and R-T(apex), and R-T(end) variabilities in 12 patients after myocardial infarction, in 13 patients before and after percutaneous transluminal coronary angioplasty (PTCA), and in 10 age-matched controls. Results: No significant differences in mean value and variance of RR, R-T(apex), and R-T(end) interval among the three groups of subjects were observed. Spectral analysis of RR variability was characterized by signs of sympathetic activation with a predominance of low frequency (LF) component in patients after myocardial infarction (69 ± 5 nu) and before PTCA (74 ± 5 nu) in comparison to controls (50 ± 4 nu). Instead, spectral energy was equally distributed within LF and HF (high frequency) components of R-T(apex) and R-T(end) variabilities in the three groups of subjects. Conclusions: These data indicate that the predominance of LF(RR) in normalized units, indicating an increase of sympathetic modulation of sinus node activity in patients with coronary artery disease, are not accompanied by a parallel predominance of the LF component of R-T(apex) and R-T(end) variabilities. This difference reflects, in our opinion, a minor dependency of duration of ventricular repolarization from the preceding cardiac cycle in patients with coronary artery disease
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
Effects of beta blockers (atenolol or metroprolol) on heart rate variability after acute myocardial infarction
No full textThis study analyzed, with spectral techniques, the effects of atenolol or metroprolol on RR interval variability in 20 patients 4 weeks after the first uncomplicated myocardial infarction. Beta blocker-induced bradycardia was associated with a significant increase in the average 24 hour values of RR variance (from 13,886 ± 1,479 to 16,728 ± 1,891 ms2) and of the normalized power of the high-frequency component (from 22 ± 1 to 28 ± 2 normalized units), whereas the low-frequency component was greatly reduced (from 60 ± 3 to 50 ± 3 normalized units). When considering day and nighttime separately, the effects of both drugs were more pronounced in the daytime. In addition, a marked attenuation was observed in the circadian variation of the low-frequency component after β blockade. As a result, the early morning increase of the spectral index of sympathetic modulation was no longer detectable. These results indicate that β-blocker administration has important effects on RR interval variability and on its spectral components. The observed reduction in signs of sympathetic activation and the increase in vagal tone after β blockade help to explain the beneficial effects of these drugs after myocardial infarction. However, the potential clinical relevance of the increase in RR variance remains to be established
Beta blocking effect of propafenone based on spectral analysis of heart rate variability
No full textRR variability was analyzed in 15 patients with ventricular arrhythamias to evaluate whether the antiarrhythmic action of propafenone is associated with alteration of neural control mechanisms. Before drug administration, spectral analysis of RR variability was characterized by 2 major components at low and high frequency, which are considered to reflect sympathetic and parasympathetic modulation of the heart period. After propafenone (600 to 900 mg/day), there was a marked reduction in RR variance (826 +/- 184 to 412 +/-77 ms2; p < 0.05), although the mean RR interval was unchanged. The drug significantly reduced the low-frequency component (52 +/- 6 to 28 +/- 4 nu) and augmented the high-frequency component (39 +/- 6 to 55 +/- 5 nu). As a result, the low-/high-frequency ratio (an index of sympathovagal balance) decreased from 2.0 +/- 0.4 to 0.6 +/- 0.1. A positive correlation between serum levels and drug-induced changes in the low-frequency component was also observed. Furthermore, the increase in the low-frequency component induced by tilt (53 +/- 5 to 79 +/- 3 nu) was markedly attenuated after drug administration (27 +/- 5 to 54 +/- 7 nu). Thus, propafenone administration is associated with changes in spectral components that are consistent with a beta-blocking effect of the drug
Brain natriuretic peptide as a marker of cardiac toxicity during mitoxantrone treatment in patients with multiple sclerosis
No full textVariations 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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