1,720,975 research outputs found
Adenosine produces changes in cerebral hemodynamics and metabolism as assessed by near-infrared spectroscopy in late-gestation fetal sheep in utero
No full textRises in fetal adenosine during hypoxia may have a metabolic inhibitory role that helps the fetus adapt to periods of low arterial partial pressure of oxygen (PaO2). We examined the fetal cerebral hemodynamic and metabolic responses to exogenous adenosine infusion and compared this with previous studies. Six fetal sheep at ca. 125 d gestation were instrumented under general anesthesia with catheters, flow probes, and near-infrared optodes and allowed to recover. After 3 d, adenosine was infused at a level known to reproduce fetal levels during hypoxia. Fetal hemodynamics and cerebral near-infrared spectroscopic (NIRS) variables were monitored and paired blood samples taken for oxygen delivery and consumption calculation. Fetal heart rate, mean arterial pressure, and carotid flow showed no change during adenosine infusion. Cerebral oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and blood volume rose, suggesting venous pooling in the brain. Cerebral cytochrome oxidase (CcO) became more oxidized, indicating reduction in electron flow down the mitochondrial electron transfer chain and, thus, a fall in metabolic rate. Blood sample analysis revealed that there was no change in oxygen delivery to the head but that cerebral oxygen consumption fell during adenosine infusion. These data indicate that fetal cerebral metabolism fell during infusion of adenosine at a level known to reproduce fetal plasma concentrations during hypoxia
The effect of systemic administration of lipopolysaccharide on cerebral haemodynamics and oxygenation in the 0.65 gestation ovine fetus in utero
No full textObjective: To investigate the effect of intravenous lipopolysaccharide on systemic and cerebral haemodynamics and oxygenation in the preterm ovine fetus.Design: Prospective observational study.Setting: Research centre for perinatal brain injury.Sample: Nine fetal sheep at circa 93 days of gestation (0.65).Methods: Fetal sheep were chronically instrumented with arterial and venous catheters and a flow probe in the carotid artery. Near-infrared spectroscopy was used to measure changes in cerebral oxygenation and total haemoglobin concentration. Three days after surgery, each fetus was given 100 ng/kg Escherichia coli lipopolysaccharide. Observations were continued for 48 hours post-injection and compared with baseline control values.Main outcome measures: Fetal heart rate, mean arterial pressure, carotid blood flow.Results: Three fetuses died after administration of the lipopolysaccharide. In the survivors fetal heart rate rose from 193 (SEM 7) to a mean maximal level of 226 (SEM 31 bpm) (P= 0.01) after 6.5 (SEM 1.0) hours. The mean arterial pressure decreased from 40.5 (SEM 4.2) to 29.4 (SEM 1.6) mmHg (P< 0.05) after 7.0 (SEM 2.0) hours, and carotid blood flow increased from 29.6 (SEM 1.6) to 45.8 (SEM 5.7) mL/min (P= 0.0002) at 12 (SEM 3) hours. All values returned to control levels by 48 hours. Histological assessment showed evidence of periventricular leucomalacia in three out of six brains studied.Conclusion: These data do not suggest that cerebral ischaemia is the main aetiological factor in endotoxin-related fetal brain injury. Fetal tachycardia and cerebral vasodilation may indicate endotoxaemia in fetuses exposed to prenatal infection
Effects of chronic hypoxia and protein malnutrition on growth in the developing chick
No full textObjective: the purpose of this study was to determine how chronic hypoxia and/or protein malnutrition in ovo affect growth in developing chicks. Study Design: chicken eggs were incubated under normoxic (21% oxygen; N = 30 eggs) or hypoxic (14% oxygen; N = 80 eggs) conditions. Hypoxia was imposed from day 0 (n = 38 eggs), day 10 (n = 22 eggs), or from day 0 to 10 (n = 20 eggs). Protein malnutrition alone (n = 20 eggs) or in combination with hypoxia (n = 24 eggs) was induced by removal of 10% of the estimated total albumin content of the egg. Embryos/chicks were killed and weighed at day 10, 15, or immediately after hatch; organs were removed and weighed.Results: embryos to which hypoxia was imposed from day 0 weighed less than control embryos at day 10, which stayed the same until hatch (64.67% ± 3.56% egg mass vs 69.36% ± 3.90% [mean ± SD]; P <.05). Malnourished chicks at day 15 and at hatch (63.42% ± 4.28%; P <.05) weighed less than control chicks, as did malnourished plus hypoxia chicks (59.74% ± 3.41%; P <.001). Malnourished plus hypoxia chicks weighed less than malnourished chicks alone (P <.05). Embryos that were hypoxic from day 0 to 10 weighed less than control embryos at day 15 (P <.05), but not at hatch. At hatch, neither hypoxia nor malnutrition decreased crown-rump length. Brain and heart weights were increased in both malnourished groups, but not chicks that were hypoxic from day 0. Conclusion: chick embryos exposed to malnutrition show asymmetric growth restriction with relative "sparing" of the brain and heart. Early growth restriction that was induced by hypoxia from the beginning of incubation is reversed by the restoration of normoxia at mid incubation. (Am J Obstet Gynecol 2002;186:261-7.
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
- …
