Concurrent Topology Optimization of Composite Plates for Minimum Dynamic Compliance

This paper proposes a novel density-based concurrent topology optimization method to support the two-scale design of composite plates for vibration mitigation. To have exceptional damping performance, dynamic compliance of the composite plate is taken as the objective function. The complex stiffness model is used to describe the material damping and accurately consider the variation of structural response due to the change of damping composite material configurations. The mode superposition method is used to calculate the complex frequency response of the composite plates to reduce the heavy computational burden caused by a large number of sample points in the frequency range during each iteration. Both microstructural configurations and macroscopic distribution are optimized in an integrated manner. At the microscale, the damping layer consists of periodic composites with distinct damping and stiffness. The effective properties of the periodic composites are homogenized and then are fed into the complex frequency response analysis at the macroscale. To implement the concurrent topology optimization at two different scales, the design variables are assigned for both macro- and micro-scales. The adjoint sensitivity analysis is presented to compute the derivatives of dynamic compliance of composite plates with respect to the micro and macro design variables. Several numerical examples with different excitation inputs and boundary conditions are presented to confirm the validity of the proposed methodologies. This paper represents a first step towards designing two-scale composite plates with optional dynamic performance under harmonic loading using an inverse design method.

Mechanical Ventilation with Dynamic Compliance-Guided Positive End-Expiratory Pressure in Laparoscopic Surgery with Trendelenburg Positioning: A Eandomised Controlled Study

BACKGROUND: The intraoperative cardiorespiratory effect of ventilation with individualised positive end-expiratory pressure guided by dynamic compliance (Cdyn) remains undefined. We investigated whether individualised protective ventilation would protect the heart and lung more efficiently than standard protective ventilation during abdominal laparoscopic surgery with Trendelenburg positioning.METHODS: Forty patients undergoing abdominal laparoscopic surgery were randomly divided into two groups: Group T (titrimetric PEEP) and Group I (intentional PEEP, 5 cmH2O). Parameters of right ventricular function were measured via transoesophageal echocardiography, including tricuspid annular plane systolic excursion (TAPSE), early filling-to-late filling ratio of the right ventricle, and right ventricular end-diastolic area/left ventricular end-diastolic area (RVEDA/LVEDA) ratio. Cdyn, driving pressure (∆P), ratio of dead space to tidal volume (VD/VT), and partial pressure of arterial oxygen to inspiratory oxygen fraction (PF) ratio were measured during mechanical ventilation.RESULTS: The RVEDA/LVEDA ratio in all patients increased significantly at T2 compared with T0, but there were no significant differences in TAPSE or E/A ratio between groups during the whole procedure (P>0.05). Cdyn, ∆P, and VD/VT ratios in Group T were significantly improved compared to those in Group I at T2 (P<0.05). There was no significant difference in the PF ratio between groups (P>0.05).CONCLUSIONS: Intraoperative lung-protective ventilation with Cdyn-guided PEEP improved Cdyn, ∆P, and VD/VT ratio without obvious side effects on right ventricular function compared to standard protective ventilation during laparoscopic surgery with Trendelenburg positioning, which suggests that it is a circulation-friendly way to titrate PEEP for intraoperative lung protective ventilation.TRIAL REGISTRATION: Trial registration date: 13/09/2020; Trial registration number: ChiCTR2000038212.

Continuous fentanyl infusion reduces intra-abdominal pressure, postoperative pain and normalizes lungs’ mechanical changes in newborn with viscera-abdominal disproportion in early post-operative period

We aimed to study the influence of prolonged administration of fentanyl on postoperative pain, intra­ab­dominal pressure and mechanical lungs’ changes that may happen in neonates in early post­operative period. 30 newborns (in the period from January 2017 to May 2021) with gastroschisis were divided into two groups ac­cordingly to the method of analgesia (14 – morphine hydrochloride; 16 – prolonged infusion of fentanyl). Lungs’ mechanical characteristics, effectiveness of post­operative analgesia, abdominal wall relaxation was studied by monitoring of dynamic compliance (Cdyn), pressure and flow­volume loops, capnography. Apprising analgesia sta­tus, we measured hemodynamic, SаO2, blood level of cortizol, C­reactive protein (CRP), glucose, analyzed post­operative pain syndrome using visual analogue scales (VAS). Intra­abdominal pressure (IAP) was controlled by Cron. For statistic analysis we used Student’s t­test. In the group with morphine, thete was the increase of IAP by 11–12 cm H2O, being stable during some period of time, and also variable levels of pain according to VAS, the in­creasing of CRP from 0.8 ± 0.25 mg/dl by 5 mg/dl, cortisol by 674.4 nmol/l, and blood glucosae rate – 7.4 mmol/l. Periods with high traumatic effects and poor analgesia (morphine group) reasoned the increasing IAP, step by step dynamic compliance decreasing in 3.4 times, resistance increasing in 2.42 times and PIP rising till 22 cm H2O. Di­rect correlation between IAP increase and lungs’ mechanical changes took place. The study has demonstrated that prolonged administration of fentanyl prevented high increase of IAP, CRP, levels of glucose and cortizol and changes of VAS data, lungs’ mechanical characteristics.

Effects of individualized positive end-expiratory pressure combined with recruitment maneuver on intraoperative ventilation during abdominal surgery: a systematic review and network meta-analysis of randomized controlled trials

Low tidal volume ventilation strategy may lead to atelectasis without proper positive end-expiratory pressure (PEEP) and recruitment maneuver (RM) settings. RM followed by individualized PEEP was a new method to optimize the intraoperative pulmonary function. We conducted a systematic review and network meta-analysis of randomized clinical trials to compare the effects of individualized PEEP + RM on intraoperative pulmonary function and hemodynamic with other PEEP and RM settings. The primary outcomes were intraoperative oxygenation index and dynamic compliance, while the secondary outcomes were intraoperative heart rate and mean arterial pressure. In total, we identified 15 clinical trials containing 36 randomized groups with 3634 participants. Ventilation strategies were divided into eight groups by four PEEP (L: low, M: moderate, H: high, and I: individualized) and two RM (yes or no) settings. The main results showed that IPEEP + RM group was superior to all other groups regarding to both oxygenation index and dynamic compliance. LPEEP group was inferior to LPEEP + RM, MPEEP, MPEEP + RM, and IPEEP + RM in terms of oxygenation index and LPEEP + RM, MPEEP, MPEEP + RM, HPEEP + RM, IPEEP, and IPEEP + RM in terms of dynamic compliance. All comparisons were similar for secondary outcomes. Our analysis suggested that individualized PEEP and RM may be the optimal low tidal volume ventilation strategy at present, while low PEEP without RM is not suggested.

Lung-protective Ventilation Combined With Pressure-controlled Ventilation Volume-guaranteed in Children Undergoing One-lung Ventilation: A Randomised Controlled Trial

The purpose of study was to evaluate the effect of lung-protective ventilation (LPV) combined with PCV-VG in children undergoing OLV. Patients were randomly assigned to the LPV combined with PCV-VG group (PCV-VG) or LPV group (volume-controlled ventilation). Both groups received tidal-volume ventilation of 8 ml kg-1 body weight during two-lung ventilation, 6 ml kg‑1 during OLV, with sustained 5 cmH2O positive end-expiratory pressure.The PCV-VG group exhibited lower PIP than the LPV group at T1 (16.8±2.3 vs. 18.7±2.7, P=0.001), T2 (20.2±2.7 vs. 22.4±3.3, P=0.001), and T3 (23.8±3.2 vs. 26.36±3.7, P=0.01). Dynamic compliance was higher in the PCV-VG group at T1, T2 , and T3 (P=0.01). After anaesthesia induction, lung aeration deteriorated, but with no immediate postoperative difference in both groups. Postoperative lung aeration improved and returned to normal from 2.5 h postextubation in both groups. No differences were observed in postoperative pulmonary complications, intra-operative desaturation, hospital stay. In paediatric patients, who underwent thoracoscopic surgery, PCV-VG combined with LPV was superior to LPV in its ability to provide ventilation with lower PIP and higher dynamic compliance. However, the long-term benefits of different ventilation strategies should be further investigated.

Perfluorocarbon-Based Oxygen Carriers and Subnormothermic Lung Machine Perfusion Decrease Production of Pro-Inflammatory Mediators

The quality of marginal donor lungs is clinically assessed with normothermic machine perfusion. Although subnormothermic temperature and perfluorocarbon-based oxygen carriers (PFCOC) have proven favourable for other organ transplants, their beneficial use for ex vivo lung perfusion (EVLP) still requires further investigation. In a rat model, we evaluated on a 4 h EVLP time the effects of PFCOC with either 28 °C or 37 °C perfusion temperatures. During EVLP at 28 °C with PFCOC, we recorded significantly lower lung pulmonary vascular resistance (PVR), higher dynamic compliance (Cdyn), significantly lower potassium and lactate levels, higher lung tissue ATP content, and significantly lower myeloperoxidase tissue activity when compared to the 37 °C EVLP with PFCOC. In the subnormothermic EVLP with or without PFCOC, the pro-inflammatory mediator TNFα, the cytokines IL-6 and IL-7, the chemokines MIP-3α, MIP-1α, MCP-1, GRO/KC as well as GM-CSF, G-CSF and the anti-inflammatory cytokines IL-4 and IL-10 were significantly lower. The 28 °C EVLP improved both Cdyn and PVR and decreased pro-inflammatory cytokines and pCO2 levels compared to the 37 °C EVLP. In addition, the 28 °C EVLP with PFCOC produced a significantly lower level of myeloperoxidase activity in lung tissue. Subnormothermic EVLP with PFCOC significantly improves lung donor physiology and ameliorates lung tissue biochemical and inflammatory parameters.

Design of Two-Axial Actuator for Controlled Vibration Damper for Large Rams

Machine tool rams are important constructional elements found on vertical lathes as well as on many other machines. In most cases, a machine tool ram constitutes an assembly with significant dynamic compliance that affects the machine’s ability to achieve stable cutting conditions. There are various solutions for increasing a machine tool ram’s stiffness and damping. This paper describes an innovative concept of a two-axial electromagnetic actuator for controlled vibration dampers with high dynamic force values. The described solution is purposefully based on the use of standard electric drives. As a result, the size of the actuator is easier to scale to the required application. The solution is designed as a spacer between the end of the ram and the head. The paper presents the actuator concept, construction design, current control loop solution and experimental verification of the controlled vibration damper’s function on the test ram in detail. The presented position measurement concept will enable the use of non-contact position sensors for motor commutation as well as for possible use in vibration suppression control. Applications can be expected mainly in the field of vibration suppression of vertical rams of large machine tools.

Right Ventricular Dysfunction in Ventilated Patients with COVID-19 (COVID-RV)

Purpose COVID-19 is associated with cardiovascular complications, with right ventricular dysfunction (RVD) commonly reported. The combination of acute respiratory distress syndrome (ARDS), injurious invasive ventilation, micro/macro thrombi and the potential for direct myocardial injury create conditions where RVD is likely to occur. No study has prospectively explored the prevalence of RVD, and its association with mortality, in a cohort requiring mechanical ventilation. Methods Prospective, multi-centre, trans-thoracic echocardiographic, cohort study of ventilated patients with COVID-19 in Scottish intensive care units. RVD was defined as the presence of severe RV dilatation and interventricular septal flattening. To explore role of myocardial injury, high sensitivity troponin and N-terminal pro B-type natriuretic peptide (NT-proBNP) were measured in all patients. Results One hundred and twenty-one patients were recruited to COVID-RV, 118 underwent imaging and it was possible to determine the primary outcome in 112. RVD was present in seven (6.2% [95%CI; 2.5%, 12.5%]) patients. Thirty-day mortality was 85.7% in those with RVD, compared to 44.8% in those without (p=0.051). Patients with RVD were more likely to have; pulmonary thromboembolism (p<0.001), higher plateau pressure (p=0.048), lower dynamic compliance (p=0.031), higher NT-proBNP (p<0.006) and more frequent abnormal troponin (p=0.048). Abnormal NT-proBNP (OR 4.77 [1.22, 21.32], p=0.03) and abnormal Troponin (16.54 [4.98, 67.12], p<0.001) independently predicted 30-day mortality. Conclusion COVID-RV demonstrates a prevalence of RVD in ventilated patients with COVID-19 of 6.2% and is associated with a mortality of 85.7%. Association is observed between RVD and each of the aetiological domains of; ARDS, ventilation, micro/macro thrombi and myocardial injury.