1,720,990 research outputs found
Autonomic nervous system adaptations to short-term exercise training.
No full textSigns of sympathetic hyperactivity and low parasympathetic activity have been found during the acute and recovery phases of myocardial infarction and have been associated with an increased risk of cardiac mortality. Beneficial effects of physical training have been recently reported in postmyocardial infarction patients. We tested the hypothesis that physical training would be effective in improving the autonomic balance by studying 22 patients with a first and recent myocardial infarction who were randomly assigned to enter or not enter a 4-week in-hospital physical training program. Spectral indices of heart rate variability were analyzed at rest and during 70-degrees head-up tilt before and after the index training, not training period. As expected, physical training induced a significant increase in exercise duration (13.7 +/- 0.8 vs 17.1 +/- 0.1 min, p < 0.001) and in the anaerobic threshold (9.5 +/- 0.7 vs 12.0 +/- 1.0 min, p < 0.02) in trained patients, while no changes were observed in the untrained group. At entry, in both groups, spectral profile of heart rate variability was characterized by a predominant LF component and a smaller HF component with no further modification after head-up tilt. After 4 weeks, in resting conditions, no significant changes in spectral components were observed in both trained and untrained patients. After physical training, head-up tilt produced significant modifications in spectral profile with an increase in the LF component (84 +/- 3 vs 69 +/- 5 nu, p < 0.01) and a decrease in the HF component (7 +/- 1 vs 19 +/- 4 nu, p < 0.05) in trained patients, while no changes were observed in the untrained patients. Our data suggest that in postmyocardial infarction patients, 4 weeks of physical training may induce an improvement in the autonomic balance with a restoration toward normal in the reflex activity of the syste
Ab Inito Calculations on Possible Hard Materials Based on Interpenetrating Networks: SiO2.BeF2
No full textThe energetics and electronic behavior of SiO2·BeF2, based on interpenetrating diamondoid nets and recently proposed as a possible hard material, have been studied with ab initio periodic LCAO Hartree-Fock methods. The composite compound turns out to be unstable with respect to the precursors SiO2 and BeF2. The origin of the instability has been analyzed with the aid of crystal orbital displacement (COD) plots. A bulk modulus close to the sum of those of the two precursors is calculated for SiO2·BeF2. The additivity of the bulk moduli of subnets suggests that hard precursors should be required to obtain superhard materials
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
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
Analysis of the pressor sympathetic reflex produced by intracoronary injections of bradykinin in conscious dogs
No full textThe reflex hemodynamic effects of intracoronary bradykinin were tested in 20 conscious instrumented dogs. When the experiments were performed after full recovery from surgery and anesthesia, graded doses (10-300 ng/kg) of bradykinin always produced graded pressor responses, in the absence of any pain reaction. At the maximum pressor response obtained with 100 ng/kg, mean arterial pressure rose 28 +/- 3% from 89 +/- 4 mm Hg, left ventricular pressure 20 +/- 3% from 121 +/- 2 mm Hg, heart rate 30 +/- 4% from 88 +/- 5 beats/min, rate of change of left ventricular pressure 18 +/- 3% from 2812 +/- 65 mm Hg/sec (P less than 0.01). Higher doses of bradykinin did not produce greater responses. The magnitude of the response was similar when the injection was performed in either the left anterior descending (change in mean arterial pressure 29 +/- 3%) or circumflex (change in mean arterial pressure 27 +/- 2%) coronary artery. The reflex nature of the response was proved by its disappearance after appropriate pharmacological blockades; moreover, after vagotomy, the pressor rise was maintained, the heart rate response was reduced (change in heart rate 10 +/- 2%), and the inotropic response was enhanced (rate of change of left ventricular pressure 24 +/- 3%). This suggested that the afferent pathway of the pressor reflex was in the sympathetic nerves and that a subordinate vagal depressor reflex was also operative. No pain reaction was obtained even when injecting very large amounts (1000-2000 ng/kg) of bradykinin, which, instead, induced arterial hypotension.(ABSTRACT TRUNCATED AT 250 WORDS
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