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Impact of posture and gravity on the cardiovascular system: a validated multiscale modeling approach for ground-based and spaceflight applications
Get PDFL'abstract è presente nell'allegato / the abstract is in the attachmen
In silico study of the posture-dependent cardiovascular performance during parabolic flights
Get PDFSpace exploration plays a crucial role in research and technological advance. Yet, weightlessness entails severe risks for human life that are investigated through both Earth-based and on-orbit experiments. To this aim, parabolic flights are used to study the short-term response of the human cardiovascular system (CVS) to micro- (~0 g) and hypergravity (up to 1.8 g). However, the short flight duration and technical difficulties associated with invasive in vivo measurements allow for the acquisition of a very limited number of hemodynamic variables. To enrich the picture, numerical tools can represent a powerful alternative. In this work, a new validated multiscale model of the CVS is proposed to inquire into global and central hemodynamic alterations – including cardiac mechano-energetic balance – triggered by parabolic flight at different postures (supine, seated and standing). Our analyses show that: (i) gravity-induced CVS changes strongly depend on posture; (ii) central aortic pressure, cardiac work and oxygen consumption indexes are significantly influenced by blood migration between central and lower body regions elicited by gravity variation; and (iii) cardiac efficiency improves during 20 s microgravity, while worsening in both hypergravity phases. Finally, (iv) the role of mildly elevated intracranial pressure (ICP) encountered in 0 g is discussed as a potential risk factor for spaceflight-induced visual impairment
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
Linking cerebral hemodynamics and ocular microgravity-induced alterations through an in silico-in vivo head-down tilt framework
Get PDFAN IN SILICO-IN VIVO FRAMEWORK FOR THE ACUTE OCULAR AND CARDIOVASCULAR RESPONSE TO 6° HEAD-DOWN TILT
Get PDFEnsuring the healthiness of astronauts undergoing long-term missions in space is of primary importance for the aerospace community. Spaceflight associated neuro-ocular syndrome (SANS) has been widely acknowledged to cause severe ocular disorders in astronauts returning from long permanence in weightlessness [1].
In this context, head-down tilt (HDT) has gained large popularity to resemble the cardiovascular response to microgravity, as well as to study SANS [2].
We propose a novel multiscale numerical framework to simulate the acute response to 6° HDBR – with in vivo validation – to help shed light on SANS onset
Cardiovascular Response to Posture Changes: Multiscale Modeling and in vivo Validation During Head-Up Tilt
Get PDFIn spite of cardiovascular system (CVS) response to posture changes have been widely studied, a number of mechanisms and their interplay in regulating central blood pressure and organs perfusion upon orthostatic stress are not yet clear. We propose a novel multiscale 1D-0D mathematical model of the human CVS to investigate the effects of passive (i.e., through head-up tilt without muscular intervention) posture changes. The model includes the main short-term regulation mechanisms and is carefully validated against literature data and in vivo measures here carried out. The model is used to study the transient and steady-state response of the CVS to tilting, the effects of the tilting rate, and the differences between tilt-up and tilt-down. Passive upright tilt led to an increase of mean arterial pressure and heart rate, and a decrease of stroke volume and cardiac output, in agreement with literature data and present in vivo experiments. Pressure and flow rate waveform analysis along the arterial tree together with mechano-energetic and oxygen consumption parameters highlighted that the whole system approaches a less stressed condition at passive upright posture than supine, with a slight unbalance of the energy supply-demand ratio. The transient dynamics is not symmetric in tilt-up and tilt-down testing, and is non-linearly affected by the tilting rate, with stronger under- and overshoots of the hemodynamic parameters as the duration of tilt is reduced. By enriching the CVS response to posture changes, the present modeling approach shows promise in a number of applications, ranging from autonomic system disorders to spaceflight deconditioning
Atrial fibrillation effects on coronary perfusion across the different myocardial layers: a computational analysis
Get PDFVariations 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
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