1,721,068 research outputs found
Effect of stochastic heterogeneity on lung impedance during acute bronchoconstriction: a model analysis
No full text Thorpe, C. William, and Jason H. T. Bates. Effect of stochastic heterogeneity on lung impedance during acute bronchoconstriction: a model analysis. J. Appl. Physiol. 82(5): 1616–1625, 1997.—In a previous study (J. H. T. Bates, A. M. Lauzon, G. S. Dechman, G. N. Maksym, and T. F. Schuessler. J. Appl. Physiol. 76: 616–626, 1994), we investigated the acute changes in isovolume lung mechanics immediately after a bolus injection of histamine. We found that dynamic resistance and elastance increased progressively in the 80-s period after injection, whereas the estimated tissue hysteresivity reached a stable plateau after ∼25 s. In the present study, we developed a computer model of the lung to investigate the mechanisms responsible for these observations. The model conforms to Horsfield’s morphometry, with the addition of compliant airways and structural damping tissue units. Using this model, we simulated the time course of acute bronchoconstriction after intravenous administration of a bolus of bronchial agonist. Heterogeneity was induced by randomly varying the values of the maximal airway smooth muscle contraction and the tissue response to the agonist. Our results demonstrate that much of the increase in lung impedance observed in our previous study can be produced purely by the effects of airway heterogeneity. However, we were only able to reproduce the plateauing of hysteresivity by assigning a minimum radius to each airway, beyond which it would immediately snap completely shut. We propose that airway closure played an important role in our experimental observations. </jats:p
A distributed nonlinear model of lung tissue elasticity
No full text Maksym, Geoffrey N., and Jason H. T. Bates. A distributed nonlinear model of lung tissue elasticity. J. Appl. Physiol. 82(1): 32–41, 1997.—- We present a theory relating the static stress-strain properties of lung tissue strips to the stress-bearing constituents, collagen and elastin. The fiber pair is modeled as a Hookean spring (elastin) in parallel with a nonlinear string element (collagen), which extends to a maximum stop length. Based on a series of fiber pairs, we develop both analytical and numerical models with distributed constituent properties that account for nonlinear tissue elasticity. The models were fit to measured stretched stress-strain curves of five uniaxially stretched tissue strips, each from a different dog lung. We found that the distributions of stop length and spring stiffness follow inverse power laws, and we hypothesize that this results from the complex fractal-like structure of the constituent fiber matrices in lung tissue. We applied the models to representative pressure-volume (PV) curves from patients with normal, emphysematous, and fibrotic lungs. The PV curves were fit to the equation V = A − Bexp(− KP), where V is volume, P is transpulmonary pressure, and A, B, and K are constants. Our models lead to a possible mechanistic explanation of the shape factor K in terms of the structural organization of collagen and elastin fibers. </jats:p
A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing
No full textSchuessler, Thomas F., Stewart B. Gottfried, and Jason H. T. Bates. A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing. J. Appl. Physiol. 82(5): 1694–1703, 1997.—Intrinsic positive end-expiratory pressure (PEEPi) and inspiratory work of breathing (Wi) are important factors in the management of severe obstructive respiratory disease. We used a computer model of spontaneously breathing patients with chronic obstructive pulmonary disease to assess the sensitivity of measurement techniques for dynamic PEEPi(PEEPi dyn) and Wi to expiratory muscle activity (EMA) and cardiogenic oscillations (CGO) on esophageal pressure. Without EMA and CGO, both PEEPi dynand Wi were accurately estimated ( r = 0.999 and 0.95, respectively). Addition of moderate EMA caused PEEPi dynand Wi to be systematically overestimated by 141 and 52%, respectively. Furthermore, CGO introduced large random errors, obliterating the correlation between the true and estimated values for both PEEPi dyn( r = 0.29) and Wi( r = 0.38). Thus the accurate estimation of PEEPi dynand Wi requires steps to be taken to ameliorate the adverse effects of both EMA and CGO. Taking advantage of our simulations, we also investigated the relationship between PEEPi dynand static PEEPi(PEEPi stat). The PEEPi dyn/PEEPi statratio decreased as stress adaptation in the lung was increased, suggesting that heterogeneity of expiratory flow limitation is responsible for the discrepancies between PEEPi dynand PEEPi statthat have been reported in patients with severe airway obstruction.</jats:p
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
Electrical impedance tomography can monitor dynamic hyperinflation in dogs
No full textAdler, Andy, Norihiro Shinozuka, Yves Berthiaume, Robert Guardo, and Jason H. T. Bates. Electrical impedance tomography can monitor dynamic hyperinflation in dogs. J. Appl. Physiol. 84(2): 726–732, 1998.—We assessed in eight dogs the accuracy with which electrical impedance tomography (EIT) can monitor changes in lung volume by comparing the changes in mean lung conductivity obtained with EIT to changes in esophageal pressure (Pes) and to airway opening pressure (Pao) measured after airway occlusion. The average volume measurement errors were determined: 26 ml for EIT; 35 ml for Pao; and 54 ml for Pes. Subsequently, lung inflation due to applied positive end-expiratory pressure was measured by EIT (ΔVEIT) and Pao (ΔVPao) under both inflation and deflation conditions. Whereas ΔVPaowas equal under both conditions, ΔVEITwas 28 ml greater during deflation than inflation, indicating that EIT is sensitive to lung volume history. The average inflation ΔVEITwas 67.7 ± 78 ml greater than ΔVPao, for an average volume increase of 418 ml. Lung inflation due to external expiratory resistance was measured during ventilation by EIT (ΔVEIT,vent) and Pes (ΔVPes,vent) and at occlusion by EIT (ΔVEIT,occl), Pes, and Pao. The average differences between EIT estimates and ΔVEIT,occlwere 5.8 ± 44 ml for ΔVEIT,ventand 49.5 ± 34 ml for ΔVEIT,occl. The average volume increase for all dogs was 442.2 ml. These results show that EIT can provide usefully accurate estimates of changes in lung volume over an extended time period and that the technique has promise as a means of conveniently and noninvasively monitoring lung hyperinflation.</jats:p
- …
