1,720,988 research outputs found
Mechanical Performance of the Isolated and Perfused Heart of the Haemoglobinless Antarctic Icefish Chionodraco hamatus (Lonnberg): Effects of Loading Conditions and Temperature
No full textScaling of heart ventricle mass and body mass in the haemoglobinless Antarctic fish Chionodraco hamatus Lonnberg shows a relationship similar to those reported for other 'cardiomegalic' icefish (Chaenocephalus aceratus and Channichthys rhinoceratus). An in vitro preparation of the heart of C. hamatus was set up to investigate the mechanical performance of this heart at different preloads and afterloads. It appears that this heart is well adapted to working within a range of preloads varying from -0.07 to -0.04 kPa, while it is unable to sustain increases of afterloads higher than 3.0 kPa. As in other teleosts, heart rate is unaffected by changes in preload and afterload. Increase in temperature from 0.5 to 5.8-degrees-C affects heart rate whereas stroke volume is unaffected. On the whole, the in vitro data are similar to those in vivo measured in another icefish, C. aceratus and show that the heart of C. hamatus works as a typical volume pump. This is discussed in relation to both the structural constraints related to the cardiac design of this icefish and the biology of this unique vertebrate
In vitro cardiac performance in the sub-antarctic notothenioids Eleginops maclovinus (subfamily eleginopinae), Paranotothenia magellanica, and Patagonotothen tessellata (subfamily nototheniinae)
No full textThere is lack of information concerning species diversification in the Non-Antarctic Nototheniid fish both in relation with their variation in organismal performance and in the morphofunctional characteristics underlying this variation. This work was designed to study in three Sub-Antarctic Nototheniids, Eleginops maclovinus, Patagonotothen tessellata, and Paranotothenia magellanica, cardiocirculatory features that may reflect interspecific differences in organismal performance, which in rum may explain aspects of evolutionary and ecological diversity. Haematocrit values were similar in all three species (between 28 and 3?), being in the range of that observed in other red-blooded Notothenioids. In all species, the heart ventricle was fully trabeculated (Type I ventricle) with P. tessellata and P. magellanica having higher relative ventricle weights than E. maclovinus. The latter species was characterized by unique spindle-shaped ventricle, apparently caused by the insertion of a pair of respiratory muscles on either side of the pericardial cavity. Intrinsic cardiac performance was assessed using an in vitro isolated and perfused heart preparation working under loading conditions. Common trends in the three species were a) the intrinsic heart rate higher than that shown by the Antarctic counterparts, b) stroke volume positively related to preload and inversely to afterload, c) pressure work exhibiting higher cost (in terms of oxygen consumption) than volume work, and d) higher mechanical efficiency under volume loading than under pressure loading. There were clearly defined interspecific differences in cardiac mechanical performance between the two Nototheniinae and E. maclovinus. The heart of the latter differed from those of the Nototheniinae, particularly in its incapacity to maintain constant stroke volume and cardiac output under pressure loading. This finding may be relevant for evaluating organismal performance in light of Notothenioid diversification. (C) 1997 Elsevier Science Inc
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 Cardiodilatin 1-16 and Anf On the Coronary Flow In the Isolated Systemic Heart of Octopus-vulgaris
No full text1. The effects of cardiodilatin1–16 and atrial natriuretic factor (ANF) on the coronaryflow in the Octopusvulgaris were studied in vitro by using a preparation of the isolated and perfused systemicheart that produces physiological stroke volumes at physiological load conditions.
2. Both cardiodilatin1–16 and ANF have negative inotropic effects on the isolatedsystemicheart, and cause a significant increase of the coronary stroke volume.
3. The increase of coronary stroke volume is mainly the consequence of the reduction of coronary resistance in the presence of these peptides
Performance of the Isolated and Perfused Working Heart of the Teleost Conger-conger - Study of the Inotropic Effect of Prostacyclin
No full textAn in vitro preparation of the heart of the teleostConger conger, isolated without the pericardium, was set up. The procedure allowed subambient pressures to develop in the perfusion chamber during contraction, mimicking the in vivo situation with the pericardium intact. The ventricle produced a cardiac output of about 15 ml·min-1·kg wet body weight-1 at subambient input pressure, and was able to double the stroke work with an increase of preload up to about 0.2 kPa. Using this preparation it was found that prostacyclin has a positive inotropic effect on the atrium and ventricle, but it does not affect the heart rate. Semilogarithmic doseresponse curves of prostacyclin on the atrium are reported, showing a threshold concentration of about 10-9 M. The isolated and perfusedConger conger heart provides a useful model for a detailed analysis of the action of prostacyclin on myocardial contractility
Myoglobin enhances cardiac performance in antarctic icefish species that express the protein
No full textChannichthyid icefishes of Antarctica are unique among adult vertebrates. All icefish species lack hemoglobin and red blood cells in their circulating blood. All icefishes examined to date also lack the intracellular oxygen-binding protein myoglobin (Mb) in their oxidative skeletal muscles. However, some icefish species do express Mb in their heart ventricles. It is unknown whether Mb in those species in which it is present represents an evolutionary relic or has functional significance. To address this problem, we compared mechanical performance of isolated, perfused hearts from two species of icefish in which Mb is either present (Chionodraco rastrospinosus) or is absent (Chaenocephalus aceratus). Hearts were challenged with increasing afterload (2.5-4.0 kPa) under conditions of defined basal flow (similar to 100 ml . min(-1). kg(-1)), in both the presence and absence of 5 mM sodium nitrite, a Mb poison. Unlike hearts from C. aceratus, which were unable to maintain a constant cardiac output under pressure loading, those from C. rastrospinosus retained a constant flow up to 3.5 kPa afterload. At the upper range of power outputs, hearts of Mb-lacking C. aceratus display greater oxygen utilization than those of Mb-containing C. rastrospinosus. Poisoning of Mb significantly impaired the ability of C. rastrospinosus hearts to face pressure loading without reduction in flow, whereas those of C. aceratus were refractory to the treatment. The results strongly support a functional role for Mb in the former species
The Heart of the Icefish - Bioconstruction and Adaptation
No full textThe Channichthyidae or ''icefish'' represent an intriguing example of extreme adaptation to the stable low temperature and high oxygen content of the Antarctic waters. The lack of respiratory pigments (hemoglobin and myoglobin) in these teleosts is associated with relatively low oxygen consumption and relevant. cardio-circulatory adjustments which include large blood volume, increased relative heart weight (cardiomegaly), and very high cardiac output. The heart has the ability to displace large systolic volumes at a low rate and relatively low pressure, with large ventricular fillings (high ventricular compliance), whereas it is incapable effacing increased afterloads. These functional aspects of mechanical flexibility and restrictions of the cardiac pump have been tentatively related to some constructional aspects of the icefish cardiomegaly, particularly, at the whole ventricular level, to the trabeculate type of myo-architecture, and, at the subcellular level, to the conflict in space economy between the exceptionally high mitochondrial densities and the consequent severe reduction in myofibrillar volume. On the basis of this morphodynamic approach, we suggest that the icefish may illustrate how a certain feature (i.e., an architectural cardiac design) common to the suborder and to most teleosts, and apparently with ''irrelevant'' properties, can become useful for a specialized purpose (i.e., volume pump design); and how, in contrast, the internal machinery construction. because of structural and ultrastructural constraints, may pre;ent these stenothermal sedentary teleosts from conquering niches requiring more active locomotory habits
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
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