FiO2 Research Articles

Chemical deposition of Cu2O films with ultra-low resistivity: correlation with the defect landscape

Cuprous oxide (Cu2O) is a promising p-type semiconductor material for many applications. So far, the lowest resistivity values are obtained for films deposited by physical methods and/or at high temperatures (~1000 °C), limiting their mass integration. Here, Cu2O thin films with ultra-low resistivity values of 0.4 Ω.cm were deposited at only 260 °C by atmospheric pressure spatial atomic layer deposition, a scalable chemical approach. The carrier concentration (7.1014−2.1018 cm−3), mobility (1–86 cm2/V.s), and optical bandgap (2.2–2.48 eV) are easily tuned by adjusting the fraction of oxygen used during deposition. The properties of the films are correlated to the defect landscape, as revealed by a combination of techniques (positron annihilation spectroscopy (PAS), Raman spectroscopy and photoluminescence). Our results reveal the existence of large complex defects and the decrease of the overall defect concentration in the films with increasing oxygen fraction used during deposition.

Liquid fragility maximum in lithium borate glass‐forming melts related to the local structure

AbstractThe structure of liquid lithium pyroborate, Li4B2O5 (J = Li/B = 2), has been measured over a wide temperature range by high‐energy X‐ray diffraction, and compared to that of its glass and borate liquids of other compositions. The results indicate a gradual increase in tetrahedral boron fraction from 3(1)% to 6(1)% during cooling from T = 1271(15) to 721(8) K, consistent with the larger N4 = 10(1)% found for the glass, and literature 11B nuclear magnetic resonance measurements. van't Hoff analysis based on a simple boron isomerization reaction BØ3O2– ⇌ BØO22– yields ΔH = 13(1) kJ mol–1 and ΔS = 40(1) J mol–1 K–1 for the boron coordination change from 4 to 3, which are, respectively, smaller and larger than found for singly charged isomers for J ≤ 1. With these, we extend our model for N4(J, T), nonbridging oxygen fraction fnbr(J, T), configurational heat capacity , and entropy Sconf(J, T) contributions up to J = 3. A maximum is revealed in at J = 1, and shown semi‐quantitatively to lead to a corresponding maximum in fragility contribution, akin to that observed in the total fragilities by temperature‐modulated differential scanning calorimetry. Lithium is bound to 4.6(2) oxygen in the pyroborate liquid, with 2.7(1) bonds centered around 1.946(8) Å and 1.9(1) around 2.42(1) Å. In the glass, nLiO = 5.4(4), the increase being due to an increase in the number of short Li–O bonds.

Role of Oxidizer Mixture Composition on Stabilizing Stratified Oxy-Flames in Dual Lean Premixed Combustors for Gas Turbines

Abstract This study investigates the effects of oxidizer composition on stability and combustion and emission characteristics of stratified premixed CH4-O2-CO2 flames in a dual annular counter-rotating swirl (DACRS) burner for wider near blowout operability of gas turbines. Flame stratification was achieved by dividing the incoming reactants into primary and secondary streams of different oxygen fractions (OF). The effects of primary and secondary OFs (primary OFs: 60%, 50%, and 30%; and secondary OFs: 60%, 50%, 40%, and 30%) were numerically investigated at fixed inlet throat velocities and equivalence ratios (φ) of the primary and the secondary streams of 6 m/s and 2 m/s and of 0.9 and 0.55, respectively. The probability distribution function has been used to average the thermochemical properties and reaction rates. Two distinct flame shapes, the v-shaped and the conical-shaped were identified as a function of the oxidizer composition. V-shaped flames with enhanced flow mixing, strong inner and outer recirculation zones (IRZ and ORZ), and intensive interactions between both streams at lower Damkohler number (Da) were recorded for OFs within 30–50%. This indicates the ability of the DACRS burner to extend the lean blowout limit by holding stratified stable flames of lower OFs. The flame shape turned into a conical shape at OFs of 60–60% for both streams, the IRZ disappeared, intensive reaction rates of higher Da attained, and the flashback mechanism approached. Weak flame/flow interactions were observed at OFs higher than 50% with excessive combustion temperature near the burner tip. CH4 disappeared very close to the burner tip, indicating fast reactions.

Hypoxic Gas Therapy in Neonatology: Considerations in Practice.

Adequate oxygenation is essential for sick newborns. Each disease determines the target of oxygenation. Nevertheless, hyperoxia and hypoxia are related to adverse outcomes. Most studies related to this aspect have been conducted in preterm infants or term babies with pulmonary pathology. Congenital heart diseases may also require careful oxygenation control and management of oxygen supply. Presurgical stabilization of complex heart diseases (CHD) may be difficult, especially after the physiological decrease of pulmonary resistance, which generates pulmonary edema (due to overcirculation) and systemic hypoperfusion. Several strategies have been described to avoid this phenomenon, such as prostaglandin, vasodilators, inotropes, positive airway pressure, and even hypoxic mixture (inspired fraction of oxygen (FiO2) below 21%). The latter therapy is mainly used in single ventricular physiology heart diseases, such as the hypoplasic left heart syndrome (HLHS) or systemic ductus-dependent flow CHD (interruption of the aortic arch and coarctation of the aorta). Alveolar oxygen affects pulmonary vascular resistance modifying lung flow. This modification could help the stabilization during the presurgical period of complex CDH. Many centers use hypoxic therapy to avoid hypotension, metabolic acidosis, coronarycerebral ischemia, and liver, renal and intestinal injury. Despite the theoretical benefits, there are doubts about how tissue oxygen supply would change during hypoxic gas ventilation. It is worrisome that FiO2 < 21% causes a decrease in brain oxygenation, adding neurological injury as a complication to the already established disease of CHD and other not modifiable factors. Brain monitoring through near-infrared spectroscopy (NIRS) during hypoxic gas therapy is mandatory. Recent studies have shown that hypoxic gas ventilation therapy in patients with HLHS in the preoperative period decreases the ratio between systemic and pulmonary circulation (Qp/Qs) but does not improve regional oxygenation delivery. The use of hypoxic gas ventilation therapy continues to be controversial. It could be an option in some complex CHD, mainly HLHS.

Cardiorespiratory Coordination Among Intermediate And Novice Female Collegiate Rowers

Elite rowers present high levels of cardiorespiratory performance. Rowers’ on-water performance can be predicted by a cardiopulmonary exercise test (CPET) and related measured parameters such as maximum oxygen uptake test (VO2max), ventilation (VE), heart rate (HR), expired fraction of oxygen (FeO2) and carbon dioxide (FeCO2). However, such testing provides little information about the non-linear dynamic interactions during rowing and the qualitative synergetic reconfigurations between cardiovascular and respiratory systems to adjust to the individual rowing performance. Cardiorespiratory coordination (CRC) has been proposed as a method to measure the co-variation among cardiorespiratory variables during a CPET. PURPOSE: To measure and compare the CRC through principal components analysis (PCA) between intermediate (9) and novice (9) rowers. METHODS: Eighteen females, members of NCAA Division II team, participated based on their off-water performance on 6000 m time trial and training status (i.e., Intermediate vs, Novice) in a discontinuous incremental rowing ergometer test to exhaustion. A variety of cardiorespiratory values were recorded. VE, HR, FeO2, and FeCO2 values during the last two stages before volitional fatigue between intermediate and novice rowers were analyzed by PCA on SPSS vs28. The number of principal components (PCs) and the first PC eigenvalues were computed for each group. RESULTS: While 67% of participants in the intermediate group showed one PC, only 22% of the novice group displayed 1 single PC. The formation of an additional PC in N rowers was the result of the shift of FeCO2 from the PC1 cluster of variables. CONCLUSIONS: Intermediate rowers showed a trend towards lower number of PCs compared to novice rowers, reflecting a higher degree of CRC. These findings point toward a higher efficiency of cardiorespiratory function in intermediate rowers, potentially as a result of improved bicarbonate buffering efficiency during high-intensity exercise. Intermediate rowers presented better gas exchange and relied less on ventilation for a given oxygen consumption. CRC appears as a complementary measure to assess aerobic fitness as well as cardiorespiratory interactions and their response to exercise in rowing may be useful to coaches, athletes and other stakeholders.

Postoperative complications and myocardial injury in patients receiving air or oxygen. Prospective, randomised and pilot study.

Supplementary oxygen is administered during anaesthesia to increase oxygen delivery and prevent hypoxia. Recent studies have questioned this routine. In this pilot study, our main aim was to investigate if 21% oxygen compared to ≥50% reduces the risk of postoperative complications and myocardial injury. In this pragmatic, multicentre, single-blind study, patients undergoing vascular surgery were randomised to receive a fraction of inspired oxygen (Fi O2 ) ≥ 0.50 and oxygen saturation determined by pulse oximetry (SpO2 ) ≥ 98% (group H) or Fi O2 of 0.21 and SpO2 > 90% (group N) oxygen perioperatively. The primary outcome was a composite outcome of major pre-defined postoperative complications assessed at 30 days. Myocardial injury was determined by serial troponin measurements. Data were analysed using generalised estimating equation, Mann-Whitney U test or chi-squared test, as appropriate. The 191 patients were randomised, and per-protocol principle was used for analyses. At 30-day follow-up, 43 out of 94 patients (46%) had a postoperative complication in group H and 36 out of 90 patients (40%) in group N, p=.46. New myocardial injury was seen in 27% versus 22% in Groups H and N respectively (p=.41). No differences in other outcomes were observed between the groups. Twelve patients (13%) in Group N had SpO2 < 90%, six recovered spontaneously and six required supplemental oxygen. At 1-year follow-up, one patient in group H had died. In this pilot study, postoperative complications were similar between the groups in patients randomised to Fi O2 of 0.21 or ≥0.50 and no difference was found in the incidence of new myocardial injury. Larger, prospective adequately powered studies are needed.

Magnetocaloric La(Fe,Mn,Si)13Hz particles and their chemical stability in heat transfer fluids employed in magnetic refrigeration

La(Fe,Mn,Si)13Hz alloys are prominent solid-state refrigerants for magnetic refrigeration, given their outstanding magnetocaloric properties. However, their chemical stability is yet an issue to be further investigated, especially under the working conditions of magnetic refrigerators. These alloys should not corrode nor lose their magnetocaloric capabilities when in contact with the heat transfer fluids used in magnetic refrigeration. Such topics are addressed in this work by performing immersion tests with La(Fe,Mn,Si)13Hz particles in two kinds of media: deionized water and deionized water containing a corrosion inhibitor (Entek), the latter medium being an usual heat transfer fluid for magnetic refrigeration. Corrosion products were detected at the surface of the particles after just 15 min of exposure in water in the absence of the inhibitor, and corrosion progressed over time, increasing the pH in the surroundings of the particles. After 10 weeks, there were clear signs of surface damage, and the fraction of oxygen at the surface increased from about 2% wt. up to 12% wt. Consequently, the thermomagnetic properties changed as well: the Curie temperature of the particles was shifted to higher values (increased about 1.5%), and the magnetic transition was smeared out. A significant decrease in the variation of specific entropy was also observed: depending on the initial TC of the particles, such decrease was as high as 44,5% (from 8.1 J/kg∙K before the immersion test to 4.5 J/kg∙K after 10 weeks of immersion). In contrast, no changes were observed in the particles exposed to water containing the corrosion inhibitor for the same period: their microstructure remained stable, the pH of the exposure media did not vary significantly, and their thermomagnetic behaviour remained unchanged. Therefore, the presence of the inhibitor effectively avoided the occurrence of aqueous corrosion and preserved the microstructure and thermomagnetic properties of the La(Fe,Mn,Si)13Hz particles.

Cervical sympathetic trunk transection alleviates acute lung injury caused by intestinal obstruction via inhibition of phospholipase A2 in rats

BackgroundIntestinal obstruction can result in inflammatory injury to distant organs, especially the lungs. Stellate ganglion block (SGB) provides sympathetic nervous homeostasis and inhibits the systemic inflammatory response. This study aimed to investigate whether SGB can alleviate acute lung injury by inhibiting phospholipase A2 expression in rats.MethodsThirty healthy male Sprague–Dawley rats were divided into three groups: C group (sham-operated); CLP group (cecal ligation and puncture with intestinal obstruction), and cervical sympathetic trunk transection (CSTT) group (transection of the cervical sympathetic trunk following CLP).Arterial blood samples were obtained to determine the ratio of partial arterial pressure of oxygen (PaO2) to fraction of oxygen in inspired air (FiO2). Venous blood samples were used to evaluate the serum concentrations of chemokines, tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10 using enzyme-linked immunosorbent assays. Following euthanasia, the lungs were isolated to estimate the wet/dry lung weight (W/D) ratio, evaluate the pathological damage to lung tissues on microscopy, and determine secretory-type phospholipase A2 (sPLA2) expression using western blotting.ResultsRats in the CLP group showed increased fatigue, decreased activity levels, and coarse, gray hair. The levels of chemokines, TNF-α, and IL-6 in the CLP and CSTT groups were higher than those in the C group. However, the levels were lower in the CSTT group than those in the CLP group. IL-10 levels in the CLP group were higher and lower than those in the C and CSTT groups, respectively. W/D ratios and PaO2/FiO2 in the CLP and CSTT groups were higher than those in the C group, whereas these ratios in the CSTT group were lower than those in the CLP group. No lung injury was noted in group C, and the lung injury scores were lower in the CSTT group than those in the CLP group. sPLA2 expression levels in the CLP group were higher than those in the C group, whereas these levels in the CSTT group were lower than those in the CLP group.ConclusionssPLA2 overexpression in the lungs may be a pathogenic factor in acute lung injury. CSTT alleviated acute lung injury by inhibiting sPLA2 expression.

Intraoperative respiratory and hemodynamic strategies for reducing nausea, vomiting, and pain after surgery: Systematic review and meta-analysis.

BackgroundDespite improved medical treatment strategies, postoperative pain, nausea, and vomiting remain major challenges. This systematic review investigated the relationship between perioperative respiratory and hemodynamic interventions and postoperative pain, nausea, and vomiting.MethodsPubMed and Embase were searched on March 8, 2021 for randomized clinical trials investigating the effect of perioperative respiratory or hemodynamic interventions in adults undergoing non‐cardiac surgery. Investigators reviewed trials for relevance, extracted data, and assessed risk of bias. Meta‐analyses were performed when feasible. GRADE was used to assess the certainty of the evidence.ResultsThis review included 65 original trials; of these 48% had pain, nausea, and/or vomiting as the primary focus. No reduction of postoperative pain was found in meta‐analyses when comparing recruitment maneuvers with no recruitment, high (80%) to low (30%) fraction of oxygen, low (5–7 ml/kg) to high (9–12 ml/kg) tidal volume, or goal‐directed hemodynamic therapy to standard care. In the meta‐analysis comparing recruitment maneuvers with no recruitment maneuvers, patients undergoing laparoscopic gynecological surgery had less shoulder pain 24 h postoperatively (mean difference in the numeric rating scale from 0 to 10: −1.1, 95% CI: −1.7, −0.5). In meta‐analyses, comparing high to low fraction of inspired oxygen and goal‐directed hemodynamic therapy to standard care in patients undergoing abdominal surgery, the risk of postoperative nausea and vomiting was reduced (odds ratio: 0.45, 95% CI: 0.24, 0.87 and 0.48, 95% CI: 0.27, 0.85). The certainty in the evidence was mostly very low to low. The results should be considered exploratory given the lack of prespecified hypotheses and corresponding risk of Type 1 errors.ConclusionThere is limited evidence regarding the impact of intraoperative respiratory and hemodynamic interventions on postoperative pain or nausea and vomiting. More definitive trials are needed to guide clinical care within this area.

Development and Validation of a Nomogram for Predicting Postoperative Pulmonary Infection in Patients Undergoing Lung Surgery

To develop and validate a nomogram for predicting postoperative pulmonary infection (PPI) in patients undergoing lung surgery. Single-center retrospective cohort analysis. A university-affiliated cancer hospital PARTICIPANTS: A total of 1,501 adult patients who underwent lung surgery from January 2018 to December 2020. Observation for PPI within 7 days after lung surgery. A complete set of demographics, preoperative variables, and postoperative follow-up data was recorded. The primary outcome was PPI; a total of 125 (8.3%) out of 1,501 patients developed PPI. The variables with p < 0.1 in univariate logistic regression were included in the multivariate regression, and multivariate logistic regression analysis showed that surgical procedure, surgical duration, the inspired fraction of oxygen in one-lung ventilation, and postoperative pain were independent risk factors for PPI. A nomogram based on these factors was constructed in the development cohort (area under the curve: 0.794, 95% CI 0.744-0.845) and validated in the validation cohort (area under the curve: 0.849, 95% CI 0.786-0.912). The calibration slope was 1 in the development and validation cohorts. Decision curve analysis indicated that when the threshold probability was within a range of 0.02-to-0.58 and 0.02-to-0.42 for the development and validation cohorts, respectively, the nomogram model could provide a clinical net benefit. The authors developed and validated a nomogram for predicting PPI in patients undergoing lung surgery. The prediction model can predict the development of PPI and identify high-risk groups.

Effect of flow rate on the end-expiratory lung volume in infants with bronchiolitis using high-flow nasal cannula evaluated through electrical impedance tomography.

To evaluate the effects of four flow rates on the functional residual capacity (FRC) and pulmonary ventilation distribution while using a high-flow nasal cannula (HFNC). Our hypothesis is that flow rates below 1.5 L·kg-1 ·min-1 lead to FRC loss and respiratory distress. A single-center, prospective clinical study. Infants diagnosed with acute viral bronchiolitis were given HFNC. Through a prospective clinical study, the effects of four different flow rates, 2.0, 1.5, 1.0, and 0.5 L·kg-1 ·min-1 , on FRC and the pulmonary ventilation pattern were evaluated using electrical impedance tomography. The impedance variation (delta Z), end-expiratory lung volume (EELZ), respiratory rate, heart rate, respiratory distress score, and saturation/fraction of inspired oxygen ratio (SpO2 /FI O2 ), were also evaluated at each flow rate. Among the 11 infants included, There was a decrease in respiratory distress score at a flow rate of 1.5 L·kg-1 ·min-1 (*p = 0.021), and at a flow rate of 2.0 L·kg-1 ·min-1 (**p = 0.003) compared to 0.5 L·kg-1 ·min-1 . There was also a small but significant increase in SpO2 /FiO2 at flow rates of 1.5 (*p = 0.023), and 2.0 L·kg-1 ·min-1 (**p = 0.008) compared to 0.5 L·kg-1 ·min-1 . There were no other significant changes in the clinical parameters. In the global EELZ measurements, there was a significant increase under a flow rate of 2.0 L·kg-1 ·min-1 as compared to 0.5 L·kg-1 ·min-1 (p = 0.03). In delta Z values, there were no significant variations between the different flow rates. The ∆EELZ increases at the highest flow rates were accompanied by decreased distress scores and improved oxygenation.

Seven days of ischemic preconditioning augments hypoxic exercise ventilation and muscle oxygenation in recreationally trained males.

This investigation sought to assess whether single or repeated bouts of ischemic preconditioning (IPC) could improve oxyhemoglobin saturation ([Formula: see text]) and/or attenuate reductions in muscle tissue saturation index (TSI) during submaximal hypoxic exercise. Fifteen healthy young men completed submaximal graded exercise under four experimental conditions: 1) normoxia (NORM), 2) hypoxia (HYP) [oxygen fraction of inspired air ([Formula: see text]) = 0.14, ∼3,200 m], 3) hypoxia preceded by a single session of IPC (IPC1-HYP), and 4) hypoxia preceded by seven sessions of IPC, one a day for 7 consecutive days (IPC7-HYP). IPC7-HYP heightened minute ventilation (V̇e) at 80% HYP peak cycling power output (Wpeak) (+10.47 ± 3.35 L·min-1, P = 0.006), compared with HYP, as a function of increased breathing frequency. Both IPC1-HYP (+0.17 ± 0.04 L·min-1, P < 0.001) and IPC7-HYP (+0.16 ± 0.04 L·min-1, P < 0.001) elicited greater oxygen consumption (V̇o2) across exercise intensities compared with NORM, whereas V̇o2 was unchanged with HYP alone. [Formula: see text] was unchanged by either IPC condition at any exercise intensity, yet the reduction of muscle TSI during resting hypoxic exposure was attenuated by IPC7-HYP (+9.9 ± 3.6%, P = 0.040) compared with HYP, likely as a function of reduced local oxygen extraction. Considering all exercise intensities, IPC7-HYP attenuated reductions of TSI with HYP (+6.4 ± 1.8%, P = 0.001). Seven days of IPC heightens ventilation, posing a threat to ventilatory efficiency, during high-intensity submaximal hypoxic exercise and attenuates reductions in hypoxic resting and exercise muscle oxygenation in healthy young men. A single session of IPC may be capable of modulating hypoxic ventilation; however, our present population was unable to demonstrate this with certainty.

Application of Machine Learning in Hospitalized Patients with Severe COVID-19 Treated with Tocilizumab.

Among the IL-6 inhibitors, tocilizumab is the most widely used therapeutic option in patients with SARS-CoV-2-associated severe respiratory failure (SRF). The aim of our study was to provide evidence on predictors of poor outcome in patients with COVID-19 treated with tocilizumab, using machine learning (ML) techniques. We conducted a retrospective study, analyzing the clinical, laboratory and sociodemographic data of patients admitted for severe COVID-19 with SRF, treated with tocilizumab. The extreme gradient boost (XGB) method had the highest balanced accuracy (93.16%). The factors associated with a worse outcome of tocilizumab use in terms of mortality were: baseline situation at the start of tocilizumab treatment requiring invasive mechanical ventilation (IMV), elevated ferritin, lactate dehydrogenase (LDH) and glutamate-pyruvate transaminase (GPT), lymphopenia, and low PaFi [ratio between arterial oxygen pressure and inspired oxygen fraction (PaO2/FiO2)] values. The factors associated with a worse outcome of tocilizumab use in terms of hospital stay were: baseline situation at the start of tocilizumab treatment requiring IMV or supplemental oxygen, elevated levels of ferritin, glutamate-oxaloacetate transaminase (GOT), GPT, C-reactive protein (CRP), LDH, lymphopenia, and low PaFi values. In our study focused on patients with severe COVID-19 treated with tocilizumab, the factors that were weighted most strongly in predicting worse clinical outcome were baseline status at the start of tocilizumab treatment requiring IMV and hyperferritinemia.

Comparison of apnoeic oxygen techniques in term pregnant subjects: a computational modelling study

BackgroundHypoxaemia during general anaesthesia can cause harm. Apnoeic oxygenation extends safe apnoea time, reducing risk during airway management. We hypothesised that low-flow nasal oxygenation (LFNO) would extend safe apnoea time similarly to high-flow nasal oxygenation (HFNO), whilst allowing face-mask preoxygenation and rescue. MethodsA high-fidelity, computational, physiological model was used to examine the progression of hypoxaemia during apnoea in virtual models of pregnant women in and out of labour, with BMI of 24–50 kg m−2. Subjects were preoxygenated with oxygen 100% to reach end-tidal oxygen fraction (FE'O2) of 60%, 70%, 80%, or 90%. When apnoea started, HFNO or LFNO was commenced. To simulate varying degrees of effectiveness of LFNO, periglottic oxygen fraction (FgO2) of 21%, 60%, or 100% was configured. HFNO provided FgO2 100% and oscillating positive pharyngeal pressure. ResultsApplication of LFNO (FgO2 100%) after optimal preoxygenation (FE'O2 90%) resulted in similar or longer safe apnoea times than HFNO FE'O2 80% in all subjects in labour. For BMI of 24, the time to reach SaO2 90% with LFNO was 25.4 min (FE'O2 90%/FgO2 100%) vs 25.4 min with HFNO (FE'O2 80%). For BMI of 50, the time was 9.9 min with LFNO (FE'O2 90%/FgO2 100%) vs 4.3 min with HFNO (FE'O2 80%). A similar finding was seen in subjects with BMI ≥40 kg m−2 not in labour. ConclusionsThere is likely to be clinical benefit to using LFNO, given that LFNO and HFNO extend safe apnoea time similarly, particularly when BMI ≥40 kg m−2. Additional benefits to LFNO include the facilitation of rescue face-mask ventilation and ability to monitor FE'O2 during preoxygenation.

Experimental study on the oxygen-enriched biogas explosion characteristics by co-firing propane in a duct

To demonstrate the effect of propane co-firing on the explosion characteristics of the oxygen-enriched biogas, deflagration experiments were conducted in a semi-open duct. The results show that the tulip flame transforms from an existence to a disappearance with increasing oxygen fraction. The increasing brightness of the flame indicates that the increase in oxygen fraction can enhance the explosion strength and accelerate flame propagation. A clear backward motion of the burnt gas is clearly distinguished in the direct imaging of flame propagations. The propane effect is discernible when the flame evolves in a dynamic manner shortly after the flame skirt is in touch with the sidewalls. Moreover, the oxygen fraction impacts the extent of this dynamic feature and thus the magnitude of the propane effect. The laminar burning velocity SL can be singled out to forecast the flame propagation speed. The propane effect on SL and [H+OH+O]max gradually strengthens with increasing oxygen enrichment. [H+OH+O]max is well related to the fundamental properties of the mixture, such as SL, the expansion ratio, initial temperature and flame thickness, which in turn dominate flame propagations in the duct.

Time-varying intensity of oxygen exposure is associated with mortality in critically ill patients with mechanical ventilation

BackgroundThere is no consensus exists regarding the association between oxygen exposure (arterial oxygen tension or fraction of inspired oxygen) and outcomes for patients with mechanical ventilation. Additionally, whether the association remains persistent over time is unknown. We aimed to explore the association between exposure to different intensities of oxygen exposure over time and 28-day mortality in patients with mechanical ventilation.MethodsWe obtained data from the Medical Information Mart for Intensive Care IV (MIMIC-IV), which included adult (≥ 18 years) patients who received invasive mechanical ventilation for at least 48 h. We excluded patients who received extracorporeal membrane oxygenation (ECMO) or who initiated ventilation more than 24 h after ICU admission. The primary outcome was 28-day mortality. Piece-wise exponential additive mixed models were employed to estimate the strength of associations over time.ResultsA total of 7784 patients were included in the final analysis. Patients had a median duration of invasive mechanical ventilation of 8.1 days (IQR: 3.8–28 days), and the overall 28-day mortality rate was 26.3%. After adjustment for baseline and time-dependent confounders, both daily time-weighted average (TWA) arterial oxygen tension (PaO2) and fraction of inspired oxygen (FiO2) were associated with increased 28-day mortality, and the strength of the association manifested predominantly in the early-middle course of illness. A significant increase in the hazard of death was found to be associated with daily exposure to TWA-PaO2 ≥ 120 mmHg (Hazard ratio 1.166, 95% CI 1.059–1.284) or TWA-FiO2 ≥ 0.5 (Hazard ratio 1.496, 95% CI 1.363–1.641) during the entire course. A cumulative effect of harmful exposure (TWA-PaO2 ≥ 120 mmHg or TWA-FiO2 ≥ 0.5) was also observed.ConclusionPaO2 and FiO2 should be carefully monitored in patients with mechanical ventilation, especially during the early-middle course after ICU admission. Cumulative exposure to higher intensities of oxygen exposure was associated with an increased risk of death.

Experimental observation on the end-gas autoignition and detonation affected by chemical reactivity in confined space

The deflagration-to-detonation transition remains one of the most interesting and mysterious physical phenomena in the combustion of energetic materials, which contains substantial complicated and nonlinear characteristics. In the present work, the effect of the chemical reactivity of different fuels and diluent gases on the end-gas autoignition and detonation development in a confined space was investigated. Five fuels (hydrogen, methane, iso-octane, n-heptane, and PRF50) and three diluent gases (argon, nitrogen, and carbon dioxide) were used to change the chemical reactivity. The results showed that both the chemical reactivity and shock wave had a significant influence on the end-gas autoignition and detonation development. For mixtures with different diluent gases, it was observed that the transition thresholds (denoted by critical oxygen fraction) increased in the order of argon, nitrogen, and carbon dioxide. Different detonation modes with varying shock compressions were observed under different diluents for n-heptane. Although the flame propagation of different fuels differs at 21% oxygen fraction, end-gas autoignition and detonation development processes can still be observed in all kinds of fuels when the oxygen fraction was elevated to a certain value. The transition thresholds increased in the order of hydrogen, n-heptane, PRF50, iso-octane, and methane. Further analysis revealed that the fuel with a shorter ignition delay usually required a lower flame tip velocity, accomplished with a delayed occurrence of detonation. In addition, the transition threshold was determined by the chemical reactivity and flame speed.

Capnodynamic monitoring of lung volume and blood flow in response to increased positive end-expiratory pressure in moderate to severe COVID-19 pneumonia: an observational study

BackgroundThe optimal level of positive end-expiratory pressure (PEEP) during mechanical ventilation for COVID-19 pneumonia remains debated and should ideally be guided by responses in both lung volume and perfusion. Capnodynamic monitoring allows both end-expiratory lung volume ({text{EELV}}_{{{text{CO}}_{2} }}) and effective pulmonary blood flow (EPBF) to be determined at the bedside with ongoing ventilation.MethodsPatients with COVID-19-related moderate to severe respiratory failure underwent capnodynamic monitoring of {text{EELV}}_{{{text{CO}}_{2} }} and EPBF during a step increase in PEEP by 50% above the baseline (PEEPlow to PEEPhigh). The primary outcome was a > 20 mm Hg increase in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio to define responders versus non-responders. Secondary outcomes included changes in physiological dead space and correlations with independently determined recruited lung volume and the recruitment-to-inflation ratio at an instantaneous, single breath decrease in PEEP. Mixed factor ANOVA for group mean differences and correlations by Pearson’s correlation coefficient are reported including their 95% confidence intervals.ResultsOf 27 patients studied, 15 responders increased the P/F ratio by 55 [24–86] mm Hg compared to 12 non-responders (p < 0.01) as PEEPlow (11 ± 2.7 cm H2O) was increased to PEEPhigh (18 ± 3.0 cm H2O). The {text{EELV}}_{{{text{CO}}_{2} }} was 461 [82–839] ml less in responders at PEEPlow (p = 0.02) but not statistically different between groups at PEEPhigh. Responders increased both {text{EELV}}_{{{text{CO}}_{2} }} and EPBF at PEEPhigh (r = 0.56 [0.18–0.83], p = 0.03). In contrast, non-responders demonstrated a negative correlation (r = − 0.65 [− 0.12 to − 0.89], p = 0.02) with increased lung volume associated with decreased pulmonary perfusion. Decreased (− 0.06 [− 0.02 to − 0.09] %, p < 0.01) dead space was observed in responders. The change in {text{EELV}}_{{{text{CO}}_{2} }} correlated with both the recruited lung volume (r = 0.85 [0.69–0.93], p < 0.01) and the recruitment-to-inflation ratio (r = 0.87 [0.74–0.94], p < 0.01).ConclusionsIn mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to increased PEEP was associated with increased end-expiratory lung volume and pulmonary perfusion. The change in end-expiratory lung volume was positively correlated with the lung volume recruited and the recruitment-to-inflation ratio. This study demonstrates the feasibility of capnodynamic monitoring to assess physiological responses to PEEP at the bedside to facilitate an individualised setting of PEEP.Trial registration: NCT05082168 (18th October 2021).

Energy recovery evaluation and temperature field research of underground coal gasification under different oxygen concentrations

In this paper, UCG simulation experiments were carried out on selected coal samples to study the effects of the gasification agent ratio on the product gas composition and calorific value under different oxygen concentrations. Moreover, an energy recovery evaluation method based on stoichiometric theory was established based on the carbon (C) balance in the generated gas content, and the energy recovery rate and coal consumption of the underground gasification process were evaluated. Based on the composition of the produced gas and the thermodynamic law of conservation, an evaluation model of the underground coal gasification temperature field was established. The gasification chamber temperature in each stage was evaluated by calculating the reaction heat and sensible heat. The experimental and research results showed that when the volume fraction of oxygen in a gasification agent was in the range 40–70 % and the calorific value of the produced gas increased from 10.48 MJ/m3 to 12.48 MJ/m3. The calorific value of the produced gas increased with an increasing oxygen concentration. Furthermore, the energy recovery rate increased from 69.63 % to 83.88 %, indicating that the gasification efficiency of the UCG experiment can be significantly improved with an increasing oxygen concentration. The error between the theoretical value of the coal consumption and the actual monitoring value was within 10 %, which effectively evaluates the coal consumption in the gasification process. The theoretical calculation temperature was consistent with the experimental monitoring temperature results, and the reaction heat was found to also be linearly correlated with the gasification temperature. Therefore, this method can effectively determine the gasification chamber temperature. These monitoring and evaluation methods are expected to guide the analysis of subsurface field experiments.

Two-lung ventilation in video-assisted thoracoscopic esophagectomy in prone position: a systematic review

Esophageal cancer surgery is still carrying a high risk of morbidity and mortality. That is why some anesthesia strategies have tried to reduce those postoperative complications. In this systematic review performed in accordance with the PRISMA-S guidelines (PROSPERO (ID: CRD42022310385)), we aimed to investigate the safety and advantages of two-lung ventilation (TLV) over one-lung ventilation (OLV) in minimally invasive esophagectomy (MIE) in the prone position. Seven trials, with a total number of 1710 patients (765 patients with TLV versus 945 patients with OLV) were included. Postoperative mortality and morbidity rates were similar between TLV and OLV when realised for esophagectomy. Interestingly, we observed no difference in changes in intraoperative respiratory parameters, operative duration, thoraco-conversion rate, number of harvested lymph nodes, postoperative heart rate and respiratory rate between TLV and OLV. TLV brings better results in terms of intraoperative oxygen arterial pressure (PaO2) during the thoracic time, postoperative oxygenation, PaO2 on inspired fraction of oxygen (FiO2) ratio, duration of thoracic surgery, preoperative time, blood loss, temperature on postoperative day-1, and C-reactive protein dosage. Our study highlighted the safety of TLV for MIE in prone position when compared to OLV. Interestingly, we found better intra and postoperative ventilation parameters. The choice of ventilation modality did not influence clinical outcome after surgery and the quality of oncological resection. Large randomised controlled trials are needed to confirm these results.