Nonparametric statistical tests: friend or foe?

The head of an ICU would like to assess if obese patients admitted for a COPD exacerbation have a longer hospital length of stay (LOS) than do non-obese patients. After recruiting 200 patients, she finds that the distribution of LOS is strongly skewed to the right (Figure 1A). If she were to perform a test of hypothesis, would it be appropriate to use a t-test to compare LOS between obese and non-obese patients with a COPD exacerbation? PARAMETRIC VS. NONPARAMETRIC TESTS IN STATISTICSParametric tests assume that the distribution of data is normal or bell-shaped (Figure 1B) to test hypotheses. For example, the t-test is a parametric test that assumes that the outcome of interest has a normal distribution, that can be characterized by two parameters(1): the mean and the standard deviation (Figure 1B). Nonparametric tests do not require that the data fulfill this restrictive distribution assumption for the outcome variable. Therefore, they are more flexible andcan be widely applied to various different distributions. Nonparametric techniques use ranks(1) instead of the actual values of the observations. For this reason, in addition to continuous data, they can be used to analyze ordinal data, for which parametric tests are usually inappropriate.(2) What are the pitfalls? If the outcome variable is normally distributed and the assumptions for using parametric tests are met, nonparametric techniques have lower statistical power than do the comparable parametric tests. This means that nonparametric tests are less likely to detect a statistically significant result (i.e., less likely to find a p-value < 0.05 than a parametric test). Additionally, parametric tests provide parameter estimations?in the case of the t test, the mean and the standard deviation are the calculated parameters?and a confidence interval for these parameters. For example, in our practical scenario, if the difference in LOS between the groupswere analyzed with a t-test, it would report a sample mean difference in LOS between the groups and the standard deviation of that difference in LOS. Finally, the 95% confidence interval of the sample mean difference could be reported to express the range of values for the mean difference in the population. Conversely, nonparametric tests do not estimate parameters such as mean, standard deviation, or confidence intervals. They only calculate a p-value.(2)HOW TO CHOOSE BETWEEN PARAMETRIC AND NONPARAMETRIC TESTS?When sample sizes are large, that is, greater than 100, parametric tests can usually be applied regardless of the outcome variable distribution. This is due to the central limit theorem, which states that if the sample size is large enough, the distribution of a given variable is approximately normal. The farther the distribution departs from being normal, the larger the sample size will be necessary to approximate normality. When sample sizes are small, and outcome variabledistributions are extremely non-normal, nonparametric tests are more appropriate. For example, some variables are naturally skewed, such as hospital LOS or number of asthma exacerbations per year. In these cases, extremely skewed variables should always be analyzed with nonparametric tests, even with large sample sizes.(2) In our practical scenario, because the distribution of LOS is strongly skewed to the right, the relationship between obesity and LOS among the patients hospitalized for COPD exacerbations should be analyzed with a nonparametric test (Wilcoxon rank sum test or Mann-Whitney test) instead of a t-test.Fil: Politi, Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Carvalho Ferreira, Juliana. Universidade de Sao Paulo; BrasilFil: Patino, Cecilia María. University of Southern California; Estados Unido

Human AQP1 is a constitutively open channel that closes by a membrane-tension-mediated mechanism

This work presents experimental results combined with model-dependent predictions regarding the osmotic-permeability regulation of human aquaporin 1 (hAQP1) expressed in Xenopus oocyte membranes. Membrane elastic properties were studied under fully controlled conditions to obtain a function that relates internal volume and pressure. This function was used to design a model in which osmotic permeability could be studied as a pressure-dependent variable. The model states that hAQP1 closes with membrane-tension increments. It is important to emphasize that the only parameter of the model is the initial osmotic permeability coefficient, which was obtained by model-dependent fitting. The model was contrasted with experimental records from emptied-out Xenopus laevis oocytes expressing hAQP1. Simulated results reproduce and predict volume changes in high-water-permeability membranes under hypoosmotic gradients of different magnitude, as well as under consecutive hypo- and hyperosmotic conditions. In all cases, the simulated permeability coefficients are similar to experimental values. Predicted pressure, volume, and permeability changes indicate that hAQP1 water channels can transit from a high-water-permeability state to a closed state. This behavior is reversible and occurs in a cooperative manner among monomers. We conclude that hAQP1 is a constitutively open channel that closes mediated by membrane-tension increments.Fil: Ozu, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay; Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina;Fil: Dorr, Ricardo Alfredo. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina;Fil: Gutiérrez, Facundo. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina;Fil: Politi, María Teresa. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina;Fil: Toriano, Roxana Mabel. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Cátedra de Fisiología; Argentina; Universidad de Buenos Aires. Facultad de Medicina. Departamento de Ciencias Fisiológicas. Laboratorio de Biomembranas; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

EVALITA Evaluation of NLP and Speech Tools for Italian - December 17th, 2020

Welcome to EVALITA 2020! EVALITA is the evaluation campaign of Natural Language Processing and Speech Tools for Italian. EVALITA is an initiative of the Italian Association for Computational Linguistics (AILC, http://www.ai-lc.it) and it is endorsed by the Italian Association for Artificial Intelligence (AIxIA, http://www.aixia.it) and the Italian Association for Speech Sciences (AISV, http://www.aisv.it)

Shone's syndrome: Insights from three-dimensional echocardiography

Shone's syndrome is a rare congenital anomaly defined as the presence of at least two of the following heart obstructions: a mitral supravalvular ring, a “parachute” mitral valve stenosis, subaortic stenosis, and aortic coarctation. A 58-year-old man presented with a mitral ring and a “parachute” mitral valve on two-dimensional transthoracic echocardiography, raising suspicion of Shone's syndrome. Three-dimensional transesophageal echocardiography revealed a subannular mitral ring inserted directly on the mitral leaflets, thus acting as a “valvar ring.” This distinction can have therapeutic implications as a “valvar” mitral ring could require valve repair or replacement, instead of simple resection.Fil: Vivas, Martín F.. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Politi, Teresa. Instituto Cardiovascular de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Riznyk, Laura M.. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Castro, María F.. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Avegliano, Gustavo. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Ronderos, Ricardo. Instituto Cardiovascular de Buenos Aires; Argentin

Shone's syndrome: Insights from three-dimensional echocardiography

Shone's syndrome is a rare congenital anomaly defined as the presence of at least two of the following heart obstructions: a mitral supravalvular ring, a “parachute” mitral valve stenosis, subaortic stenosis, and aortic coarctation. A 58-year-old man presented with a mitral ring and a “parachute” mitral valve on two-dimensional transthoracic echocardiography, raising suspicion of Shone's syndrome. Three-dimensional transesophageal echocardiography revealed a subannular mitral ring inserted directly on the mitral leaflets, thus acting as a “valvar ring.” This distinction can have therapeutic implications as a “valvar” mitral ring could require valve repair or replacement, instead of simple resection.Fil: Vivas, Martín F.. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Politi, Teresa. Instituto Cardiovascular de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Riznyk, Laura M.. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Castro, María F.. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Avegliano, Gustavo. Instituto Cardiovascular de Buenos Aires; ArgentinaFil: Ronderos, Ricardo. Instituto Cardiovascular de Buenos Aires; Argentin

Calculation of the aortic arch angles from three-dimensional reconstructions of computed tomography scans: Comparison between an automated program and visual assessment

Background: The curvature of the aortic arch is associated with the risk of endoleak formation after thoracic endovascular aortic repair (TEVAR). However, the adequate assessment of the angles of the aorta continues to represent a major difficulty. We developed a new program based on three-dimensional (3D) reconstructions of computed tomography (CT) scans to objectively identify the location of the aortic points of maximum curvature, and to automatically calculate the main aortic arch angles, comparing final values with visual assessment methods. Methods: This is a cross-sectional validation study of a convenience sample of subjects with multislice CT angiography scans of the thoracic aorta from an institutional imaging database. The center lumen line (CLL) of the aorta was determined semi-automatically using Endosize software. The points of maximum curvature on the CLL were determined by two methods: visually by two physicians and through a custom program. Results: The study enrolled 9 subjects: 4 with thoracic aneurysms and 5 with normal aortas. The inter-observer and inter-method correlation, agreement and reliability for each of the 3D spatial coordinates of the points of maximum curvature were appropriate. However, the aortic angles determined by visual assessment showed a very low to moderate correlation and reliability with those determined by our custom program. Conclusion: An automated custom program can reflect clinician's intuitive assessment of the location of points of maximum curvature and translate it into aortic angles with an apparently higher precision, reducing potential error and user time.Fil: Gaudric, Julien. Université Pierre et Marie Curie; Francia. Hôpitaux Universitaires La Pitié-Salpêtrière; Francia. Sorbonne University; FranciaFil: Politi, María Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Fernández, Juan Manuel Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Carre, Emmanuelle. Sorbonne University; FranciaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Fullana, Jose Maria. Sorbonne University; Franci

The dicrotic notch analyzed by a numerical model

Divergent concepts on the origin of the dicrotic notch are widespread in medical literature and education. Since most medical textbooks explain the origin of the dicrotic notch as caused by the aortic valve closure itself, this is commonly transmitted in medical physiology courses. We present clinical data and numerical simulations to demonstrate that reflected pressure waves could participate as one of the causes of the dicrotic notch. Our experimental data from continuous arterial pressure measurements from adult patients undergoing vascular surgery suggest that isolated changes in peripheral vascular resistance using an intravenous bolus of phenylephrine (a selective alpha 1-receptor agonist and thus a potent vasoconstrictor) modify the dicrotic notch. We then explore the mechanisms behind this phenomenon by using a numerical model based on integrated axisymmetric Navier-Stokes equations to compute the hemodynamic flow. Our model illustrates clearly how modifications in peripheral artery resistance may result in changes in the amplitude of the dicrotic notch by modifying reflected pressure waves. We believe that this could be a useful tool in teaching medical physiology courses.Fil: Politi, Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ghigo, Arthur. Universite de Paris VI; FranciaFil: Fernández, Juan Manuel Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Khelifa, Ismaïl. Hôpitaux Universitaires La Pitié-Salpêtrière; FranciaFil: Gaudric, Julien. Hôpitaux Universitaires La Pitié-Salpêtrière; Francia. Universite de Paris VI; FranciaFil: Fullana, José María. Universite de Paris VI; FranciaFil: Lagrée, Pierre Yves. Universite de Paris VI; Franci

Impact of arterial cross-clamping during vascular surgery on arterial stiffness measured by the augmentationindex and fractal dimension of arterial pressure

International audienceArterial cross-clamping is a common strategy used in vascular surgery and its duration is an independent predictor of surgical outcomes. The impact of arterial cross-clamping on the viscoelastic properties of the arterial system and its underlying mechanisms still remain unclear. The aim of this study was to evaluate the effect of arterial cross-clamping on arterial stiffness. A cross-sectional, observational, before-after study was designed to enroll adult patients undergoing vascular surgery. The Augmentation Index normalized to 75 beats-per-minute (AIx@75) and Fractal Dimension (FD) –indirect indicators of arterial stiffness– were calculated from radial arterial pressure tracings during surgery. The arterial pressure tracings from 8 patients were analyzed. Overall data included 4 aortic and 11 iliofemoral interventions. In both aortic and iliofemoral interven- tions, after arterial clamping, median AIx@75 rose and FD dropped significantly; the opposite occurred after arterial unclamping. Spearman’s correlation suggests a strong significant negative correlation between median AIx@75 and FD during each hemodynamic state for aortic interventions. Our results are consistent at many levels: a) opposite events (i.e., clamping and unclamping) produce changes in different directions, b) two different indicators (i.e., AIx@75 and FD) suggest the same underlying phenomenon, and c) similar results are observed at different vascular locations (i.e., aortic and iliofemoral). Overall, our data consistently suggests an increase in arterial stiffness during clamping and a reduction during unclamping. Despite the large distance from the aortic or iliofemoral intervention sites, radial artery pressure monitoring is still able to detect consistently these vascular events

Effects of Cross-Clamping on Vascular Mechanics: Comparing Waveform Analysis With a Numerical Model

Background: Immediate changes in vascular mechanics during aortic cross-clamping remain widely unknown. By using a numerical model of the arterial network, vascular compliance and resistance can be estimated and the time constant of pressure waves can be calculated and compared with results from the classic arterial waveform analysis. Methods: Experimental data were registered from continuous invasive radial artery pressure measurements from 11 patients undergoing vascular surgery. A stable set of beats were chosen immediately before and after each clamping event. Through the arterial waveform analysis, the time constant was calculated for each individual beat and for a mean beat of each condition as to compare with numerical simulations. Overall proportional changes in resistance and compliance during clamping and unclamping were calculated using the numerical model. Results: Arterial waveform analysis of individual beats indicated a significant 10% median reduction in the time constant after clamping, and a significant 17% median increase in the time constant after unclamping. There was a positive correlation between waveform analysis and numerical values of the time constant, which was moderate (ρ = 0.51; P = 0.01486) during clamping and strong (ρ = 0.77; P ≤ 0.0001) during unclamping. After clamping, there was a significant 16% increase in the mean resistance and a significant 23% decrease in the mean compliance. After unclamping, there was a significant 19% decrease in the mean resistance and a significant 56% increase in the mean compliance. Conclusions: There are significant hemodynamic changes in vascular compliance and resistance during aortic clamping and unclamping. Numerical computer models can add information on the mechanisms of injury due to aortic clamping.Fil: Politi, María Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ventre, Jeanne. Sorbonne University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Fernández, Juan Manuel Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Ghigo, Arthur. Universite Paul Sabatier. Institut de Mathematiques de Toulouse; Francia. Centre National de la Recherche Scientifique; FranciaFil: Gaudric, Julien. Sorbonne University; Francia. Hôpitaux Universitaires La Pitié-Salpêtrière; FranciaFil: Armentano, Ricardo Luis. Universidad de Buenos Aires; ArgentinaFil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Lagrée, Pierre Yves. Universidad de Buenos Aires; Argentina. Sorbonne University; Franci

Changes in cardiac Aquaporin expression during aortic valve replacement surgery with cardiopulmonary bypass

OBJECTIVES: Cardiopulmonary bypass (CPB) use is an essential strategy for many cardiovascular surgeries. However, its use and duration have been associated with a higher rate of postoperative complications, such as low cardiac output syndrome due to myocardial oedema and dysfunction. Though Aquaporin water channels have been implicated in myocardial water balance, their specific role in this clinical scenario has not been established. METHODS: In a consecutive study of 17 patients with severe aortic stenosis undergoing aortic valve replacement surgery, 2 myocardial biopsies of the left ventricle were taken: 1 before and 1 after CPB use. Sociodemographic, clinical and laboratory data were collected. Western blot and immunohistochemistry studies were performed. RESULTS: After CPB use, there was a mean increase of ∼62% in Aquaporin 1 protein levels (P = 0.001) and a mean reduction of ∼38% in Aquaporin 4 protein levels (P = 0.030). In immunohistochemistry assays, Aquaporin 1 was found lining small blood vessels, while Aquaporin 4 formed a circular label in cardiomyocytes. There were no changes in the localization of either protein following CPB use. During the observed on-pump time interval, there was a 1.7%/min mean increase in Aquaporin 1 (P = 0.021) and a 2.5%/min mean decrease in Aquaporin 4 (P = 0.018). Myocardial interstitial oedema increased by 42% (95% confidence interval 31-54%) after CPB use. Patients who developed low cardiac output syndrome were in the upper half of the median percentage change of Aquaporin expression. CONCLUSION: Time-dependent changes in cardiac Aquaporin expression may be associated with myocardial oedema and dysfunction related to CPB use.Fil: Politi, María Teresa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ochoa, Federico Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Netti, Vanina Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ferreyra, Raúl. No especifíca;Fil: Bortman, Guillermo. No especifíca;Fil: Sanjuan, Norberto Aníbal. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones en Microbiología y Parasitología Médica. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones en Microbiología y Parasitología Médica; ArgentinaFil: Morales, Celina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiopatología Cardiovascular; ArgentinaFil: Piazza, Antonio. No especifíca;Fil: Capurro, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentin