Background Recent studies suggest that isolated sonographic assessment of the respiratory, cardiac, or neuromuscular functions in mechanically ventilated patients may assist in identifying patients at risk of postextubation distress. The aim of the present study was to prospectively investigate the value of an integrated thoracic ultrasound evaluation, encompassing bedside respiratory, cardiac, and diaphragm sonographic data in predicting postextubation distress. Methods Longitudinal ultrasound data from 136 patients who were extubated after passing a trial of pressure support ventilation were measured immediately after the start and at the end of this trial. In case of postextubation distress (31 of 136 patients), an additional combined ultrasound assessment was performed while the patient was still in acute respiratory failure. We applied machine-learning methods to improve the accuracy of the related predictive assessments. Results Overall, integrated thoracic ultrasound models accurately predict postextubation distress when applied to thoracic ultrasound data immediately recorded before the start and at the end of the trial of pressure support ventilation (learning sample area under the curve: start, 0.921; end, 0.951; test sample area under the curve: start, 0.972; end, 0.920). Among integrated thoracic ultrasound data, the recognition of lung interstitial edema and the increased telediastolic left ventricular pressure were the most relevant predictive factors. In addition, the use of thoracic ultrasound appeared to be highly accurate in identifying the causes of postextubation distress. Conclusions The decision to attempt extubation could be significantly assisted by an integrative, dynamic, and fully bedside ultrasonographic assessment of cardiac, lung, and diaphragm functions.

In critically ill patients, the performance of the esCCO monitor was not clinically acceptable, and this monitor cannot be recommended in this setting. Moreover, the esCCO failed to trend CO data reliably.

Extravascular lung water (EVLW) could increase by permeability pulmonary oedema, cardiogenic oedema, or both. Transthoracic echocardiography examination of a patient allows quantifying B-lines, originating from water-thickened interlobular septa, and the E/Ea ratio, related to pulmonary capillary wedge pressure. The aim of our study was to assess the correlation and the trending ability between EVLW measured by transpulmonary thermodilution and the B-lines score or the E/Ea ratio in patients with ARDS. Twenty-six intensive care unit patients were prospectively included. B-lines score was obtained from four ultrasound zones (anterior and lateral chest on left and right hemithorax). E/Ea was measured from the apical four-chamber view. EVLW was compared with the B-lines score and the E/Ea ratio. A linear mixed effect model was used to take account the repeated measurements. A p value<0.05 was considered significant. A total of 73 measurements were collected. The correlation coefficient between EVLW and B-lines score was 0.66 (EVLW=0.71 B-lines+7.64, R2=0.44, p=0.001), versus 0.31 for E/Ea (p=0.06). The correlation between EVLW changes and B-lines variations was significant (R2=0.26, p<0.01), with a concordance rate of 74%. A B-lines score≥6 had a sensitivity of 82% and a specificity of 77% to predict EVLW>10 ml/kg, with an AUC equal to 0.86 (0.76-0.93). The gray zone approach identified a range of B-lines between four and seven for which EVLW>10 ml/kg could not be predicted reliably. The correlation between ultrasound B-lines and EVLW was significant, but the B-lines score was not able to track EVLW changes reliably.

The shifted Helmholtz operator has received a lot of attention over the past decade as a preconditioner for the iterative solution of the Helmholtz equation. The idea is that if one uses a small complex shift, the shifted Helmholtz operator is still close to the original Helmholtz operator and could thus be an effective preconditioner. It was shown in [M. J. Gander, I. G. Graham, and E. A. Spence, Numer. Math., 53 (2015), pp. 573-579] that the shift can be at most O(k) to prove rigorously wave number independent convergence of the preconditioned system solved with GMRES, provided the preconditioner is inverted exactly. In practice, however, the preconditioner is inverted only approximately, and if one shifts enough, this can be done effectively by standard multigrid methods. We show in this paper that for a finite element discretization, the shift has to be at least O(k 2) to be able to invert the shifted Helmholtz preconditioner using multigrid. There is therefore a gap between being a good preconditioning operator (shift at most O(k)) and being able to effectively invert the preconditioner by multigrid (shift at least O(k 2)). So what shift should be chosen in practice, and when is the preconditioner not inverted exactly? By studying the numerical range of the preconditioned operator, we show that one cannot obtain analytical results for this case with currently available tools. We thus test the preconditioner extensively numerically for a wave guide type square domain in the range of shifts between O(√ k) and O(k 2) with approximate inversion by one multigrid V-cycle. We find in our experiments that preconditioned GMRES iteration numbers will then inevitably grow like O(k 2). We also see that in contrast to common practice where shifts of O(k 2) are used, it might be beneficial for the wave guide to use a smaller shift, e.g., O(k 3/2), especially when several smoothing steps are used.

A new interpolation technique to deal with fluid-porous media interfaces for topology optimization of heat transfer. Computers and Fluids, Abstract This paper proposes a new interpolation technique based on density approach to solve topology optimization problems for heat transfer. Problems are modeled under the assumptions of steady-state laminar flow using the incompressible Navier-Stokes equations coupled to the convection-diffusion equation through the Boussinesq approximation. The governing equations are discretized using finite volume elements and topology optimization is performed using adjoint sensitivity analysis. Material distribution and effective conductivity are interpolated by two sigmoid functions respectively h τ (α) and k τ (α) in order to provide a continuous transition between the solid and the fluid domains. Comparison with standard interpolation function of the literature (RAMP function) shows a smaller transition zone between the fluid and the solid thereby, avoiding some regularization techniques. In order to validate the new method, numerical applications are investigated on some cases from the literature, namely the single pipe and the bend pipe. Lastly, as two new parameters are introduced thanks to the interpolation functions, we study their impact on results of the optimization problem. The study shows that the proposed technique is a viable approach for designing geometries and fluid-porous media interfaces are well-defined. 19 method, known as the Brinkman penalization, leads to a problem where flow 20 and (almost) non-flow regions are developed by allowing interpolation be-21 tween the lower and upper value of permeability. Generally, authors used 22 the density interpolation function proposed by Borrvall and Petersson [4] 23 or a reformulated version of their convex and q-parametrized interpolation 24function. The parameter q > 0 is a penalty parameter that is used to con-25 trol the level of 'gray' in the optimal design. However, authors had also 26 experienced problems with locally optimal solutions. Therefore, they con-27 sidered a two-steps solution procedure where the problem was first solved 28 with a small penalty value of q = 0.01 for example and then the result is 29 used as initial case for the problem with a penalty value of q = 0.1 [4, 8] 30 or q = 1 [15]. The mathematical foundation of the interpolation of α was 31 further investigated by Evgrafov [14] where the limiting cases of pure fluid 32 and solid were included. Brinkman approach has since been used for several 33 problems as transport problem [28], reactive [32] and transient flows [33, 3], 34 fluid-structure interaction [36] and also flows driven by body forces [37]. 35 A variation of the approach is presented by Guest and Prevost [2]. They 36 proposed to regularize the solid-fluid structure by treating the material phase 37 as a porous medium where fluid flow is governed by Darcy's law. In their 38 approach, flows through voids are governed by Stokes flow and, when the 39 solid phase is impermeable, discrete n...