1,720,957 research outputs found
Modelling arterial chemoreceptor neural afferent activity to changes in blood oxygen and carbon dioxide
No full textArterial chemoreceptor sensing and signalling to the brain is essential for homeostatic control of cardiorespiratory function. Measuring arterial chemoreceptor neural afferent responses in vivo to perturbations in blood oxygen and carbon dioxide is highly invasive and has only been conducted in animals. Mathematical models provide a unique perspective to better understand arterial chemoreceptor behaviour that is difficult to quantify experimentally. Lumped-parameter models were developed for the carotid and aortic chemoreceptors using an energy-based Bond Graph framework. Components were included for blood flow through vascular segments, diffusion and transport of chemical species between the blood and tissue compartments, hydration of carbon dioxide to hydrogen ions, carbon anhydrase inhibition, acid loading and extrusion mechanisms, and neural adaptation. Tissue unbound oxygen ([O2ub]t) and hydrogen ion ([H+]t) concentrations were linked with a unique neural firing rate equation characterised by steady-state and transient components. Models were calibrated to literature-derived experimental cat data for (1) steady-state responses to arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) and (2) dynamic responses to step changes in PaCO2 with and without carbonic anhydrase inhibition. Model simulations were able to reproduce the steady-state and dynamic calibration data, including data for carbonic anhydrase inhibition, with reasonable accuracy and display behavioural similarities to novel data. The simulation data, therefore, supports the importance of [O2ub]t and [H+]t on arterial chemoreceptor function. However, simulations did not support the almost exclusive role of [H+]t on firing rate following step changes in PaCO2 and, rather, highlighted the importance of neural adaptation, particularly for the transient over-shoot in neural activity following a step increase in PaCO2. The model performed less well in capturing the PaCO2 threshold (i.e. the PaCO2 above which neural activity commences), the time-delay until a peak in neural activity following a step increase in PaCO2 and the undershoot following a step decrease in PaCO2 during hypoxia. Additionally, modelling constraints for interchanging between gas total content and partial pressure prevented the calculation of blood pH via buffering equations, which necessitated the inclusion of a term removing capillary blood H+ from the gas exchange site. Despite these limitations, the models were able to pro- vide further insight into carotid and aortic chemoreceptor function, whilst highlighting the importance of neural adaptation in dynamic responses
Understanding Cardiovascular Remodelling Related to Preterm Birth: A Clinical and Computational Modelling Study
No full textBackground: Globally, one in ten children are born preterm. Babies born prematurely
may suffer from cardiovascular instability and also have an increased lifetime
cardiovascular risk. Our aim was two-fold: to collect ultrasound data on the structure
and function of the developing cardiovascular system in healthy late preterm
newborns and term controls; and to develop newborn clinical digital twins: personalisable
anatomical computational models of the neonatal cardiovascular system.
Methods: Single-centre, prospective, observational cohort study recruiting term
(born ≥37+0 weeks’ gestation) and late preterm (born between 34+0 and 36+6 weeks’
gestation) healthy babies. Ultrasound data were collected within 48 hours of birth
and again three to six weeks later. These data inform personalised 0D closed-loop
bond graph models that simulate blood pressure and flows in the newborn cardiovascular
system.
Results: 15 term and 10 preterm babies were assessed on day 2 of life and 12
(80%) term and 7 (70%) preterm babies underwent a second assessment at median
post-menstrual age 295 days (25 days old for term group and 38 days old for preterm
group). We found no evidence that late preterm birth is associated with structural
cardiovascular changes in early life, however, there were differences in postnatal
growth velocities. This suggests a window for intervention to prevent cardiovascular
remodelling in preterm babies through careful monitoring of growth and nutrition.
In keeping with the clinical data, our computational modelling outputs were
similar for the term and preterm groups. We found that although the term and
preterm models had similar lower body resistances at birth, by three to six weeks
of age, the preterm group showed evidence of greater vascular resistance. This is
a reasonable mechanistic finding in keeping with previous pre-clinical and clinical
literature and highlights a possible mechanism of cardiovascular remodelling in late
preterm neonates.
Conclusion: This thesis presents our newborn cardiovascular digital twins: the
first and largest patient-specific computational modelling study of the cardiovascular
system in early life. These can provide deeper insights into the complex physiology
of cardiovascular remodelling related to preterm birth through the synthesis of
clinical data and computational modelling than either on its own
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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