1,720,965 research outputs found
Analysis of oscillatory components of short-term heart rate variability in hemodynamically stable and unstable patients during hemodialysis
No full textShort period oscillatory components embedded in heart rate variability (HRV) were studied during hemodialysis induced hypovolemia in 15 hypotension- resistant (stable) and 15 hypotension-prone (unstable) patients. Hemodialysis was undertaken so that a similar blood volume reduction was induced in all patients (p > 0.05) without causing acute hypotension events. Autoregressive HRV power spectrums were calculated using an eigenanalysis-based approach. The frequencies of the main HRV rhythmic components were estimated through the Pisarenko harmonic decomposition. Percent changes during the hemodialysis in both heart rate and arterial pressure were similar in the stable and unstable groups (p > 0.05). The HRV spectral density showed markedly different power distributions. In the stable patients, power was mainly in the low frequency band (74 ± 7 nU in the low frequency [LF] band vs. 21 ± 6 nU in the high frequency [HF] band) whereas in stable patients, it was mainly in the high frequency band (39 ± 10 nU in the LF band vs. 47 ± 7 nU in the HF band). The frequency of the main oscillation was 0.1 P 0.02 Hz in stable patients and 0.18 ± 0.04 Hz in unstable ones (p < 0.01). These HRV spectral parameters have a clear diagnostic value in discriminating between stable and unstable patients when their hemodynamic behaviors are similar
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
Neuroinflammation in Bacterial Meningitis
No full textUnder physiologic conditions, the brain is a microbiologically sterile site
and is protected from infection by highly specialized barriers, including the hard
bony skull, the tough dura mater, and the restrictive blood–brain barrier (BBB).
Host defense mechanisms in the central nervous system (CNS) are limited and
tightly regulated. Peripheral immune cells and plasma proteins are largely excluded from the brain parenchyma. Once they have breached the protective barriers and entered the CNS, bacteria multiply within the cerebrospinal fluid space (CSF) highly efficiently exhibiting similar kinetics as in vitro and reaching concentrations of up to 109 CFU/mL. In response to the multiplying bacteria and their components, i.e., cell wall fragments, lipopolysaccharides, teichoic and lipoteichoic acids, peptidoglycans, bacterial DNA, and other cytosolic factors, resident cells in the perivascular space and the meninges release pro-inflammatory signaling molecules. Tumor necrosis factor-α, interleukin-1β, and IL-6 are released early on and trigger a cascade of other inflammatory
mediators, including a variety of cytokines, chemokines, platelet-activating
factor, antimicrobial peptides, prostaglandins, matrix metalloproteinases, nitric oxide, and reactive oxygen species initiating a self-perpetuating inflammatory cascade. The immediate consequences of the intense inflammatory reaction are a massive influx of leukocytes, the breakdown of the blood–brain barrier with the formation of brain edema, and alterations of the cerebral blood flow. This overshooting inflammatory reaction to the invading pathogens causes damage to the brain parenchyma as collateral damage and is the driving pathophysiologic mechanism of inflammatory inner ear damage, brain cortical ischemic injury, and hippocampal apoptosis, the most frequent histopathological correlates of the neurofunctional sequelae of bacterial meningitis
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
Parametric analysis of heart rate variability during hemodialysis
No full textThe problem of evaluating short-term autonomic response to hypovolemia in patients under chronic hemodialysis treatment is considered. Power spectra of the beat-to-beat heart rate variability were evaluated during the dialysis treatment in twenty hemodynamically stable and unstable patients, using a parametric technique. The autoregressive model coefficients were calculated by the modified covariance method, while model order was selected according to the minimum description length criterion. Reported results demonstrate that stable and unstable patients present markedly different spectral patterns. The efficiency of the compensatory response to hemodialysis-induced hypovolemia was evaluated through the ratio between the powers in LF and HF bands. Stable patients exhibit a LF/HF ratio greater than one with large fluctuations over the whole dialysis session. In contrast, all the unstable patients are characterized by a value of LF/HF lower than one and with a reduced time variability. This result suggests that the hemodynamic instability of the hypotension-prone patients may be due to a deficiency in the short-term compensatory response to the hemodialysis-induced hypovolemia
Autonomic nervous function during haemodialysis assessed by spectral analysis of heart-rate variability
No full text1. Short-term autonomic response to haemodialysis-induced hypovolaemia was studied in 30 patients undergoing chronic haemodialysis by analysing power spectra of heart-period variability. Patients were classified as haemodynamically stable (15 patients) and unstable (15 patients) according to their past history of cardiovascular collapse during the treatment. Blood volume, systolic arterial pressure and heart period were measured during sessions that ended without the occurrence of collapse. 2. No significant differences were observed when comparing blood volume, heart rate and arterial pressure of stable and unstable patients during the dialysis, and the two groups could not be distinguished merely on the basis of these haemodynamic parameters. Conversely, spectral analysis of beat-to-beat heart-period variability showed markedly different power patterns: in stable patients power was mainly in the low-frequency (LF) band (0.06-0.15 Hz), whereas in unstable patients it was mainly in the high-frequency (HF) band (0.15-0.4 Hz). 3. The efficiency of the autonomic response to hypovolaemia was evaluated by the ratio between the powers in the LF and HF bands. Stable patients exhibited an LF/HF power ratio systematically greater than unstable patients during the entire dialysis, and on the basis of this index the two groups were clearly separated. 4. Results obtained with spectral analysis lead us to conclude that reduced efficiency in the autonomic control of cardiovascular functions could be the main cause of the haemodynamic instability of patients prone to collapse
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