Reliability of the nitrogen washin-washout technique to assess end-expiratory lung volume at variable PEEP and tidal volumes

International audienceBackgroundEnd-expiratory lung volume measurement by the nitrogen washin-washout technique (EELVWI-WO) may help titrating positive end-expiratory pressure (PEEP) during acute respiratory distress syndrome (ARDS). Validation of this technique has been previously performed using computed tomography (EELVCT), but at mild PEEP levels, and relatively low fraction of inspired oxygen (FiO2), which may have insufficiently challenged the validity of this technique. The aims of this study were (1) to evaluate the reliability of EELVWI-WO measurements at different PEEP and V T during experimental ARDS and (2) to evaluate trending ability of EELVWI-WO to detect EELV changes over time.MethodsARDS was induced in 14 piglets by saline lavage. Optimal PEEP was selected during a decremental PEEP trial, based on best compliance, best EELVWI-WO, or a PEEP-FiO2 table. Eight V T (4 to 20 mL * kg-1) were finally applied at optimal PEEP. EELVWI-WO and EELVCT were determined after ARDS onset, at variable PEEP and V T.ResultsEELVWI-WO underestimated EELVCT with a non-constant linear bias, as it decreased with increasing EELV. Limits of agreement for bias were ±398 mL. Bias between methods was greater at high PEEP, and further increased when high PEEP was combined with low V T. Concordance rate of EELV changes between consecutive measurements was fair (79%). Diagnostic accuracy was good for detection of absolute EELV changes above 200 mL (AUC = 0.79).ConclusionsThe reliability of the WI-WO technique is critically dependent on ventilatory settings, but sufficient to accurately detect EELV change greater than 200 mL

Pole-weapons in the Sagas of Icelanders: a comparison of literary and archaeological sources

The Icelandic sagas are a major source of information on the Vikings and their fighting prowess. In these stories, several mysterious pole-weapons appear, which are often called “halberds”, for lack of a better word. In order to better identify what these weapons could have been, and to provide a better understanding of how the sagas relate to the Viking-age events they describe, we confront textual and archaeological evidence for several of these weapons (the höggspjót, the atgeirr, the kesja, the krókspjót, the bryntroll and the fleinn), keeping in mind the contextualisation of their appearances in sagas. The description of the use of each weapon allows to pick several candidates likely to correspond to the studied word. Without a perfect knowledge of what context the authors of the sagas wanted to describe, it appears to be impossible to give a final answer. However, we show that some specific types of spears are good candidates for some of the studied weapons

The impact of pelvicalyceal anatomy on the stone formation in patients with lower pole renal stones

Background: The aim of our study was to determine whether various anatomic factors constitute a predisposition to a lower pole renal stones. Materials and methods: We analysed the computed tomography (CT) urography of 75 patients with a single lower pole stone. Measurements were taken of the infundibulopelvic angle (IPA), infundibular width (IW), infundibular length (IL) and calyceopelvic height (CPH). Results: The mean patient age was 50 years (range 17–79 years). The mean stone size was 11.9 mm. The mean IPA using Sampaio method in affected kidney was 113.4 ± 15.3o (range 80–139o), 59.5 ± 17.3o using Elbahnasy method. The values of IPA on the contralateral kidney were 119.86 ± 15.37o (range 79–141o; p = = 0.001) using Sampaio method of measurement and 59.78 ± 12o (range 34–90 o; p = 0.465) using the method described by Elbahnasy. We reported statistically significant differences between stone-bearing kidney and contralateral kidney in measurement IPA using only Sampaio method. The mean infundibular width was 4.22 ± 1.81 mm on the affected kidney and 3.72 ± 2.5 mm on the contralateral side (p = 0.164). The mean infundibular length was 15.37 ± 4.57 mm on the affected kidney and 14.66 ± 4.35 mm on the unaffected side (p = 0.329). The CPH was 10.19 ± 4.05 mm on the affected kidney and 10.44 ± 3.83 mm on the normal side (p = 0.688). Conclusions: Pelvicalyceal morphology of the kidney is one of the factors that determine the risk of developing kidney stones. Out of the analysed morphological parameters of kidney IPA is a statistically significant risk factor to form lower pole kidney stones. Other anatomic parameters did not seem to have a significant role in predisposing to form lower pole kidney stone. (Folia Morphol 2018; 77, 1: 16–21)

Estimation of A Posteriori Computational Error by the Higher Order Multipoint Meshless FDM

The main objective of this paper is to present a possibility of high quality a posteriori error evaluation based on reference solutions obtained by means of the new multipoint meshless finite difference method. Due to its higher order approximation, the multipoint results may be used as improved reference solution instead of the true analytical one to estimate the errors. Several types of a posteriori error estimators which can be used to evaluate the calculation error are described here. The results of selected numerical benchmarks are considered

Improvements in the Global A-Posteriori Error Estimation of the FEM and MFDM Solutions

The present paper deals with the estimation of the solution error of the boundary value problems of mechanics science. The well-known ideas of error estimators are presented, as well as new original ones, which use the concept of the improved HO reference solution, obtained using the Meshless Finite Difference Method analysis. Such HO estimators may be applied not only in the MFDM, but also in the Finite Element Method error analysis. This issue is presented here for the first time ever. The approach is tested on chosen 2D benchmark problems. The results are very encouraging

On Acceleration of Evolutionary Algorithms Taking Advantage of A Posteriori Error Analysis

A variety of important engineering and scientific tasks may be formulated as non-linear, constrained optimization problems. Their solution often demands high computational power. It may be reached by means of appropriate hardware, software or algorithm improvements. The Evolutionary Algorithms (EA) approach to solution of such problems is considered here. The EA are rather slow methods; however, the main advantage of their application is observed in the case of non-convex problems. Particularly high efficiency is demanded in the case of solving large optimization problems. Examples of such problems in engineering include analysis of residual stresses in railroad rails and vehicle wheels, as well as the Physically Based Approximation (PBA) approach to smoothing experimental and/or numerical data. Having in mind such analysis in the future, we focus our current research on the significant EA efficiency increase. Acceleration of the EA is understood here, first of all, as decreasing the total computational time required to solve an optimization problem. Such acceleration may be obtained in various ways. There are at least two gains from the EA acceleration, namely i) saving computational time, and ii) opening a possibility of solving larger optimization problems, than it would be possible with the standard EA. In our recent research we have preliminarily proposed several new speed-up techniques based on simple concepts. In this paper we mainly develop acceleration techniques based on simultaneous solutions averaging well supported by a non-standard application of parallel calculations, and a posteriori solution error analysis. The knowledge about the solution error is used to EA acceleration by means of appropriately modified standard evolutionary operators like selection, crossover, and mutation. Efficiency of the proposed techniques is evaluated using several benchmark tests. These tests indicate significant speed-up of the involved optimization process. Further concepts and improvements are also currently being developed and tested

Bird’s eye view of molecular clouds in the Milky Way: II. Cloud kinematics from subparsec to kiloparsec scales

Context. The kinematics of molecular gas are crucial for setting the stage for star formation. One key question related to the kinematic properties of gas is how they depend on the spatial scale.Aims. We aim to describe the CO spectra, velocity dispersions, and especially the linewidth-size relation of molecular gas from cloud (parsec) scales to kiloparsec scales in a complete region within the Milky Way disk.Methods. We used the census of molecular clouds within 2 kpc from our earlier work, together with CO emission data for them from the literature. We studied the kinematics and the Larson relations for the sample of individual clouds. We also mimicked a face-on view of the Milky Way and analysed the kinematics of the clouds within apertures of 0.25–2 kpc in size. In this way, we describe the scale-dependence of the CO gas kinematics and Larson’s relations.Results. We describe the spectra of CO gas at cloud scales and in apertures between 0.25 and 2 kpc in our survey area. The spectra within the apertures are relatively symmetric, but show non-Gaussian high-velocity wings. At cloud scales, our sample shows a linewidth-size relation\ua0σv\ua0= 1.5 \ub7\ua0R0.3\ub10.1\ua0with a large scatter. The mass-size relation in the sample of clouds is\ua0MCO\ua0= 794 \ub7 R1.5\ub10.5. The relations are also present for the apertures at kiloparsec-scales. The best-fit linewidth-size relation for the apertures is\ua0σv\ua0= 0.5 \ub7\ua0R0.35\ub10.01, and the best-fit mass-size relation is\ua0MCO\ua0= 229 \ub7\ua0R1.4\ub10.1. A suggestive dependence on Galactic environment is seen. Apertures closer to the Galactic centre and the Sagittarius spiral arm have slightly higher velocity dispersions. We explore the possible effect of a diffuse component in the survey area and find that such a component would widen the CO spectra and could flatten the linewidth-size relation. Understanding the nature of the possible diffuse CO component and its effects on observations is crucial for connecting Galactic and extragalactic data