1,721,199 research outputs found
Vasomotion and insulin-mediated capillary recruitment - part of the explanation?
No full textIn the 1990s, Baron and colleagues were among the first to report that insulin dilated resistance vessels and increased skeletal muscle blood flow. They further suggested that a defect in insulin's action to increase blood flow to insulin-sensitive tissues contributed to insulin resistance (Baron et al. 2000). More recently it has been shown that insulin increases microvascular perfusion in skin and skeletal muscle, and that impairment of insulin-mediated microvascular dilator responses in skeletal muscle decreases glucose uptake. The functional increase in microvascular flow has been investigated extensively by Clark and colleagues (for review see Clark, 2008) who have argued that insulin-mediated recruitment of capillaries, in the absence of increases in bulk flow, is indicative of a redirection of blood flow from a non-nutritive to a nutritive route, an argument that has been hotly disputed in recent years (Poole et al. 2008).In the most recent paper from this group in The Journal of Physiology (Newman et al. 2009), insulin-induced changes in muscle blood flux have been explored in an animal model of acute insulin resistance, using laser Doppler flowmetry (LDF), a widely used and generally non-invasive technique, to measure intramuscular blood flow. They go on to explore vasomotor activity in the microvascular bed by analysis of the component frequencies of the LDF signal using a Wavelet transform. These periodic oscillations in the LDF signal have been attributed to the influence of heart beat (spectral peaks at 0.6–2 Hz), respiration (0.15–0.6 Hz), myogenic activity in the vessel wall (?0.05–0.15 Hz), sympathetic activity (?0.02–0.05 Hz), and endothelial activity (?0.008–0.02 Hz) (Kvandal et al. 2006). Using this analysis Newman et al. find that insulin acts to increase the ?0.1 Hz, assumed myogenic component of vasomotor activity in muscle. They further show that both muscle microvascular flow and myogenic activity are depressed in the ?-methylserotonin-induced acute insulin resistant state, and that this attenuation in insulin-induced microvascular flow is accompanied by reductions in glucose uptake in the muscle. From this, Newman et al. suggest that recruitment of microvascular flow by insulin may in part involve action on the vascular smooth muscle to increase vasomotion to thereby enhance perfusion and glucose uptake in skeletal muscle, and that this is impaired in acute insulin resistance. These new data are among the first to show a direct link with vasomotion and insulin, though others have drawn this conclusion from studies in insulin-resistant states such as obesity (e.g. O'Brien et al. 1999; de Jongh et al. 2008).Vasomotion was originally defined as the rhythmic oscillations in vascular tone due to changes in smooth muscle constriction and dilatation. It has been commented upon since the earliest days of microscopical observation (Jones, 1852), and its assessment in muscle, indirectly using LDF, is well established (Oude Vrielink et al. 1987). In contrast to the recent work of Newman et al., these authors, using a similar preparation but using intravital microscopy as well as LDF to identify red cell-perfused capillaries at rest and during reactive hyperaemia, showed no evidence for recruitment of arterioles or capillaries. To evaluate these findings we may need to return to the concept of recruitment and its definition – perfusion of a greater number of vessels (physical recruitment) or reduced periodicity of cyclic perfusion (temporal recruitment), both of which would lead to greater blood flow, substrate delivery, and effective capillary exchange surface area. It can be argued that with a minimal 10-fold range in red blood cell velocity among capillaries together with increased microvascular diameter during hyperaemia, changes in volume flow to explain substrate delivery/effective exchange surface may be accommodated by the existing capillary bed without the need to ‘recruit' more vessels. The physical characteristics of the muscle in question may affect the extent of perfusion heterogeneity, e.g. being maximal in phasically active muscles with regional differences in intramuscular pressure. However, the mainstay of the argument for recruitment is the assumption of nutritive and non-nutritive vascular (capillary?) beds – an increasingly common assumption, for which there is little or no anatomical evidence (Grant & Wright 1970). In addition, to be functionally relevant this would require metabolic control to be located within vessels rather than mitochondria of the host tissue, in violation of most biochemical evidence.Notwithstanding this, the association between insulin-mediated increases in muscle blood flow, by whatever means, and ‘downstream' glucose uptake remains controversial. As described above, it is accepted by many that insulin at physiological levels acts to increase capillary exchange surface area. Whether this is a result of capillary ‘recruitment' and/or alterations in flow pattern due to vasomotion has yet to be fully elucidated. The work by Newman et al. published recently in The Journal of Physiology provides a further insight into this phenomenon, and suggests a novel role for the myogenic response in an animal model of acute insulin resistance. However, the important question that remains to be answered is how, in insulin-resistant individuals, does impaired insulin action result in a decreased delivery of glucose, insulin and other metabolites to muscle fibres? Whether microvascular dysfunction contributes to and exacerbates insulin resistance, or whether microvascular dysfunction has an insulin sensitivity-independent action, to regulate glucose concentrations, is presently uncertain
Egginton, Stuart
No full textStuart Egginton - Faculty/Staff.https://digitalcommons.library.umaine.edu/univ_photos/2301/thumbnail.jp
J Appl Physiol, Al-Shammari et. al. supplementary material
No full textThis data provides executables to accompany the J Appl Physiol paper authored by AA. Al-Shammari, RWP Kissane, S Holbek, AL Mackey, TR Andersen, EA Gaffney, MK Kjaer and S Egginton, entitled "Integrated method for quantitative morphometry and oxygen transport modeling in striated muscle".
This has been successfully tested on (i) 64 bit Windows 10, which has been the intended platform (ii) Mac platforms using the parallels PC emulator (https://www.parallels.com/uk/)
Installation instruction are contained within the zip, including the OTM subfolder for the OTM (Oxygen Transport Modeller) standalone
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
Local capillary supply in muscle is not determined by local oxidative capacity
Full text linkIt is thought that the prime determinant of global muscle capillary density is the mean oxidative capacity. However, feedback control during maturational growth or adaptive remodelling of local muscle capillarisation is likely to be more complex than simply matching O2 supply and demand in response to integrated tissue function. We tested the hypothesis that the maximal oxygen consumption (MO2,max) supported by a capillary is relatively constant, and independent of the volume of tissue supplied (capillary domain). We demonstrate that local MO2,max assessed by succinate dehydrogenase histochemistry: (1) varied more than 100-fold between individual capillaries and (2) was positively correlated to capillary domain area in both human vastus lateralis (R=0.750, P<0.001) and soleus (R=0.697, P<0.001) muscles. This suggests that, in contrast to common assumptions, capillarisation is not primarily dictated by local oxidative capacity, but rather by factors such as fibre size, or consequences of differences in fibre size such as substrate delivery and metabolite removal
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