1,720,962 research outputs found
Nutrient Transport Across the Intrauterine Growth-Restricted Placenta
No full textThis chapter is a brief review of the current literature on nutrient transport across the intrauterine growth restricted placenta in human pregnancies in vivo. These studies, performed at the time of fetal blood sampling or elective cesarean section, show that the placenta plays a very important role in the pathophysiology of intrauterine growth restriction, clarifying the mechanisms of impaired nutrient placental transport. Further studies are needed though to open new perspectives in the clinical management and in the prevention of the disease
Lactacidemia in intrauterine growth restricted (IUGR) pregnancies : relationship to clinical severity, oxygenation and placental weight
Full text linkThe aim of the study was to evaluate the impact of clinical severity and placental weight upon fetal lactacidemia in intrauterine growth restricted (IUGR) pregnancies. Seventy pregnancies complicated by IUGR were compared with 70 normal (appropriate for gestational age, AGA) pregnancies at the time of elective cesarean section. IUGR pregnancies were divided according to clinical severity in three groups: Group 1 had normal fetal heart rate (FHR) and normal pulsatility index of the umbilical artery (PI); Group 2 had normal FHR and abnormal PI; and Group 3 had abnormal FHR and PI. No cases with severe lactacidemia had placental weights >or=250 g. Forty-four fetuses had placental weight or=250 g exhibited an F/P ratio significantly lower than that in AGA fetuses suggesting that IUGR may be due to a reduction of placental function per gram of tissue
Umbilical amino acid uptake at increasing maternal amino acid concentrations : effect of a maternal amino acid infusate
No full textOBJECTIVE: Our purpose was to establish whether, in normal human pregnancies, the maternal intravenous infusion of amino acids can increase fetal amino acid uptake and amino acid concentrations. STUDY DESIGN: Twenty- six normal pregnancies were studied at the time of cesarean delivery (38-40 weeks' gestation). In 10 cases an amino acid formulation (Freamine 8,5% III, Baxter) was infused into a maternal vein before cesarean delivery. Maternal blood samples were obtained during the course of the study. Umbilical venous and arterial samples were obtained from the clamped segment of the cord. There were no differences between the 2 groups for fetal and placental weights and for fetal oxygenation and acid-base balance. RESULTS: Maternal amino acid concentrations increased significantly in the group receiving infusions. Significant increases in umbilical venous concentrations were observed for most amino acids, except for histidine and threonine. The amino acid umbilical arteriovenous differences per mole of oxygen (AA/O2 ratio) increased significantly for leucine, isoleucine, valine, methionine, phenylalanine, arginine, glycine serine, alanine, and proline. There were no significant increases for lysine, histidine, and threonine. CONCLUSION: An increase in maternal concentrations leads to an increase in the delivery of most amino acids to the fetus
Placental transport of leucine, phenylalanine, glycine and proline in intrauterine growth-restricted pregnancies
No full textL-[1-13C]Leucine, [1-13C]glycine, L-[1-13C]phenylalanine, and L-[1-13C]proline were infused as a bolus into the maternal circulation of seven appropriate for gestational age at 30.3 ± 3.0 wk and 7 intrauterine growth-restricted pregnancies at 26.5 ± 1.0 wk gestation to investigate placental transport in vivo. Umbilical venous samples were obtained at the time of in utero fetal blood sampling at 450 ± 74 sec from the bolus injection. In normal pregnancies the fetal/maternal (F/M) enrichment ratios for leucine (0.76 ± 0.06) and phenylalanine (0.77 ± 0.06) were higher (P < 0.01) than the F/M ratios for glycine (0.18 ± 0.04) and proline (0.22 ± 0.02). This suggests that these two essential amino acids rapidly cross the placenta in vivo. Compared with the essentials, both glycine and proline had significantly lower F/M enrichment ratios, which were not different from each other. The results support the hypothesis that amino acids with high affinity for exchange transporters cross the placenta most rapidly. In intrauterine growth-restricted pregnancies, the F/M enrichment ratio was significantly lower (P < 0.01) for L-[1-13C]leucine (0.76 ± 0.06 vs. 0.48 ± 0.07) and for L-[1-13C]phenylalanine (0.77 ± 0.06 vs. 0.46 ± 0.07) compared with appropriate for gestational age pregnancies reflecting impaired transplacental flux. The F/M enrichment ratio did not differ for [1-13C]glycine (0.18 ± 0.04 vs. 0.17 ± 0.03), and L-[1-13C]proline (0.22 ± 0.02 vs. 0.18 ± 0.04)
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
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