We expose an efficient strategy to deal with shape optimization of dynamical systems exhibiting flutter-type instability induced by friction, such as the considered disc-pad system. The stability of ...such systems can be analyzed through complex eigenvalue analysis, through which we present a squeal noise criterion to be minimized as a computationally expensive black-box function. The computational domain is discretized through isogeometric formulation for its advantages in optimization and superior approximation properties which are well studied in structural dynamics. To be computationally efficient with the expensive black-box function, we defined the optimization based on efficient global optimization scheme in the context of multi-objective optimization, with the integration of Isogeometric design-through-analysis methodology. As gradient information is hard to access for such black-box functions, in addition to the presence of constraints, we relied on meta-heuristic approach as a more generic strategy for realizing optimization of such functions in multi-objective context. As one such scheme with its own advantages was observed to provide lack of resolution to define expected improvement (
EI
) with a single reference value, we propose a multi-reference acquisition strategy which can be defined through a fast and efficient algorithm with fewer adaptation to the existing scheme. Results show the efficiency of this approach for our applicative example, which can be extended to other such applications as well.
Long-term outcomes of patients treated with venoarterial-extracorporeal membrane oxygenation for acute decompensated heart failure (i.e., cardiogenic shock complicating chronic cardiomyopathy) have ...not yet been reported. This study was undertaken to describe their outcomes and determine mortality-associated factors.
Retrospective analysis of data prospectively collected.
Twenty-six-bed tertiary hospital ICU.
One hundred five patients implanted with venoarterial-extracorporeal membrane oxygenation for acute decompensated heart failure.
None.
From March 2007 to January 2015, 105 patients were implanted with venoarterial-extracorporeal membrane oxygenation for acute decompensated heart failure in our ICU (67% of them had an intraaortic balloon pump to unload the left ventricle). Their 1-year survival rate was 42%; most of the survivors were transplanted either directly or after switching to central bilateral centrifugal pump, ventricular-assist device, or total artificial heart. Most deaths occurred early after multiple organ failure. Multivariable analyses retained (odds ratio 95% CI) pre-extracorporeal membrane oxygenation Sequential Organ Failure Assessment score of more than 11 (3.3 1.3-8.3), idiopathic cardiomyopathy (0.4 0.2-1), cardiac disease duration greater than 2 years pre-extracorporeal membrane oxygenation (2.8 1.2-6.9), and pre-extracorporeal membrane oxygenation blood lactate greater than 4 mmol/L (2.6 1.03-6.4) as independent predictors of 1-year mortality. Only 17% of patients with pre-extracorporeal membrane oxygenation Sequential Organ Failure Assessment scores of 14 or more survived, whereas 52% of those with scores less than 7 and 60% of those with scores 7 or more and less than 11 were alive 1 year later.
Among this selected cohort of 105 patients implanted with venoarterial-extracorporeal membrane oxygenation for acute decompensated heart failure, 1-year survival was 42%, but better for patients with pre-extracorporeal membrane oxygenation Sequential Organ Failure Assessment scores of less than 11. Venoarterial-extracorporeal membrane oxygenation should be considered for patients with acute decompensated heart failure, but timing of implantation is crucial.
Background
Structural neurological complications (ischemic stroke and intracranial bleeding) and their risk factors in patients receiving venoarterial-extracorporeal membrane oxygenation (VA-ECMO) ...are poorly described. Our objective was to describe frequencies, outcomes and risk factors for neurological complications (ischemic stroke and intracranial bleeding) in patients receiving VA-ECMO.
Methods
Retrospective observational study conducted, from 2006 to 2014, in a tertiary referral center on patients who developed a neurological complication(s) on VA-ECMO.
Results
Among 878 VA-ECMO-treated patients, 65 (7.4%) developed an ECMO-related brain injury: 42 (5.3%) ischemic strokes and 20 (2.8%) intracranial bleeding, occurring after a median 25th;75th percentile of 11 6;18 and 5 2;9 days of support, respectively. Intracranial bleeding but not ischemic stroke was associated with higher mortality. Multivariable analysis retained only platelet level > 350 giga/L as being associated with ischemic stroke. Female sex, central VA-ECMO and platelets < 100 giga/L at ECMO start were independently associated with intracranial bleeding with respective odds ratios 95% CI of 2.9 1.1–7.5, 3.8 1.1–10.2 and 3.7 1.4–9.7. In a nested case–control study, rapid CO
2
-level change from before-to-after ECMO start also seemed to be associated with intracranial bleeding.
Conclusions
Neurological events are frequent in VA-ECMO-treated patients. Ischemic stroke is the most frequent, occurs after 1 week on ECMO support, has no specific risk factor and is not associated with higher mortality. Intracranial bleeding occurs earlier and is associated with female sex, central VA-ECMO, low platelet count and rapid CO
2
change at ECMO start, and high mortality.
Level of evidence
This study provides Class IV evidence that central VA-ECMO, low platelet count and rapid CO
2
change at ECMO start are associated with intracranial bleeding and high mortality.
Delaying renal replacement therapy (RRT) for some time in critically ill patients with severe acute kidney injury and no severe complication is safe and allows optimisation of the use of medical ...devices. Major uncertainty remains concerning the duration for which RRT can be postponed without risk. Our aim was to test the hypothesis that a more-delayed initiation strategy would result in more RRT-free days, compared with a delayed strategy.
This was an unmasked, multicentre, prospective, open-label, randomised, controlled trial done in 39 intensive care units in France. We monitored critically ill patients with severe acute kidney injury (defined as Kidney Disease: Improving Global Outcomes stage 3) until they had oliguria for more than 72 h or a blood urea nitrogen concentration higher than 112 mg/dL. Patients were then randomly assigned (1:1) to either a strategy (delayed strategy) in which RRT was started just after randomisation or to a more-delayed strategy. With the more-delayed strategy, RRT initiation was postponed until mandatory indication (noticeable hyperkalaemia or metabolic acidosis or pulmonary oedema) or until blood urea nitrogen concentration reached 140 mg/dL. The primary outcome was the number of days alive and free of RRT between randomisation and day 28 and was done in the intention-to-treat population. The study is registered with ClinicalTrial.gov, NCT03396757 and is completed.
Between May 7, 2018, and Oct 11, 2019, of 5336 patients assessed, 278 patients underwent randomisation; 137 were assigned to the delayed strategy and 141 to the more-delayed strategy. The number of complications potentially related to acute kidney injury or to RRT were similar between groups. The median number of RRT-free days was 12 days (IQR 0–25) in the delayed strategy and 10 days (IQR 0–24) in the more-delayed strategy (p=0·93). In a multivariable analysis, the hazard ratio for death at 60 days was 1·65 (95% CI 1·09–2·50, p=0·018) with the more-delayed versus the delayed strategy. The number of complications potentially related to acute kidney injury or renal replacement therapy did not differ between groups.
In severe acute kidney injury patients with oliguria for more than 72 h or blood urea nitrogen concentration higher than 112 mg/dL and no severe complication that would mandate immediate RRT, longer postponing of RRT initiation did not confer additional benefit and was associated with potential harm.
Programme Hospitalier de Recherche Clinique.
Amikacin infusion requires targeting a peak serum concentration (C
) 8-10 times the minimal inhibitory concentration, corresponding to a C
of 60-80 mg/L for the least susceptible bacteria to ...theoretically prevent therapeutic failure. Because drug pharmacokinetics on extracorporeal membrane oxygenation (ECMO) are challenging, we undertook this study to assess the frequency of insufficient amikacin C
in critically ill patients on ECMO and to identify relative risk factors.
This was a prospective, observational, monocentric study in a university hospital. Patients on ECMO who received an amikacin loading dose for suspected Gram-negative infections were included. The amikacin loading dose of 25 mg/kg total body weight was administered intravenously and C
was measured 30 min after the end of the infusion. Independent predicators of C
< 60 mg/L after the first amikacin infusion were identified with mixed-model multivariable analyses. Various dosing simulations were performed to assess the probability of reaching 60 mg/L < C
< 80 mg/L.
A total of 106 patients on venoarterial ECMO (VA-ECMO) (68%) or venovenous-ECMO (32%) were included. At inclusion, their median (1st; 3rd quartile) Sequential Organ-Failure Assessment score was 15 (12; 18) and 54 patients (51%) were on renal replacement therapy. Overall ICU mortality was 54%. C
was < 60 mg/L in 41 patients (39%). Independent risk factors for amikacin under-dosing were body mass index (BMI) < 22 kg/m
and a positive 24-h fluid balance. Using dosing simulation, increasing the amikacin dosing regimen to 30 mg/kg and 35 mg/kg of body weight when the 24-h fluid balance is positive and the BMI is ≥ 22 kg/m
or < 22 kg/m
(Table 3), respectively, would have potentially led to the therapeutic target being reached in 42% of patients while reducing under-dosing to 23% of patients.
ECMO-treated patients were under-dosed for amikacin in one third of cases. Increasing the dose to 35 mg/kg of body weight in low-BMI patients and those with positive 24-h fluid balance on ECMO to reach adequate targeted concentrations should be investigated.
In this paper, the vibratory dynamics of a system consists of a rotor and a stator with friction at the interface is studied. The main goal is to study how taking into account the deviation of the ...relative velocities associated with each point of the interface (rotor/stator) influences the model. The inclusion of this deviation, not usually modeled for this type of system, allows taking the friction plane into account. However, introducing this mechanism in a model with a friction interface leads to damping that in turn has an impact on the values and the convergence of the amplitudes of vibration. In addition, the deviation has a significant impact only when the rotation frequency of the rotating part is low. Thus this paper also focuses on the separation occurring at the interface. The method used to take this separation into account is presented. The addition of this separation in the model makes it possible to obtain more physically realistic limit cycles in the case of high rotation frequency. These two phenomena are combined in order to obtain physical amplitudes.
The objective of this paper is to present a numerical scheme for applying nonlinear modal synthesis to study the dynamic performance of assembled structures with a frictional interface. A generalized ...Masing model is introduced to describe the frictional mechanism in steady state to enable obtaining the harmonic components of the friction force. By employing the concept of nonlinear modes based on normal form theory, a reduction technique based on branch modes can be applied to obtain a reduced order model. Both complex nonlinear modes and real nonlinear modes depending on the modal amplitude are used in the nonlinear modal synthesis approach, leading to a particular damping term representing energy dissipation due to friction. The implementation of the nonlinear modal synthesis combined with the generalized Masing model provides a simple, fast and efficient numerical method for describing the nonlinear performance of structures with dry friction devices. The proposed approach is applied to three increasingly complex case studies. Numerical simulations are carried out to demonstrate the efficiency and reliability of the method.
Simulating the full dynamic response of a rolling sculpted tire requires not only taking into account various non-linearities but also considering the multi-scale nature of the dynamic response ...itself. On one hand, there is the macroscopic rolling dynamic behavior that operates around the rotating frequency with relatively high amplitudes. On the other hand, the vibratory response operates in a larger frequency window with relatively low amplitudes. In contrast to a straightforward strategy that consists of using an energy-conserving stable time integrator to predict the multi-scale dynamic response, the proposed strategy is based on a two-steps approach to separate the dynamics operating at different scales. This methodology is applied to simulate the nonlinear vibrations of a hyperelastic solid undergoing large deformations in contact with a rigid plane. In order to illustrate the potential of the proposed numerical method, the nonlinear vibrations response of a grooved cylinder rolling on a rigid plane is investigated.
This paper provides a description of a phenomenological model representing a mechanical system consisting of a stator disk fixed to a clamped beam and a rotor disk. When the rotor is in contact with ...the stator, the rotation gives rise to friction leading to a self-sustaining vibratory instability called whirl. This instability confers a two-beam bending mode to the coupling. Moreover, adding detachment at the rotor/stator interface leads to the disappearance of whirl instability and the onset of another mode known as squeal. The main goal of this paper is to study the conditions of occurrence of the squeal mode. This is the first time a study has been performed to observe 3 different behaviors as a function of the parameters imposed. A limit cycle is associated with each behavior. Then, each limit cycle is studied using spectrograms and state space representation. Attention is then focused on the limit cycle bifurcation and limit cycle stability is studied using the monodromy matrix. Finally, a contact bounce is introduced in the model to observe a limit cycle consisting of alternating whirl and squeal modes.
This paper presents a methodology for the multi-objective (MO) robust optimization of plate structures under stress criteria, based on Mixed Super-Elements (MSEs). The optimization is performed with ...a classical Genetic Algorithm (GA) method based on Pareto-optimal solutions. It considers antagonist objectives among them stress criteria and thickness parameters distributed along the plate. This work aims at providing fast and efficient objective calculations. Our method is based on the implementation of MSEs for each zone of the plate featured by its own thickness. They are constructed with a Mixed Finite Element Model (MFEM) based on a displacement-stress mechanical formulation, and is enhanced with a sub-structuring modal reduction method in order to reduce the size of each constant thickness MSE. Those methods combined enable a fast and stress-wise efficient structure analysis, which improves the performance of the repetitive GA. A few cases minimizing the mass and the maximum Von Mises stress within a plate structure under dynamic loads put forward the relevance of our method with promising results. For the sake of robustness, both discrete frequencies and frequency bands are studied. The MO optimization is able to satisfy multiple damage criteria with different thickness distributions. It brings simplicity, saves computational time and the Pareto-front presentation with stress objective provides a good overview of the possibilities for the designers.
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