Cardiac arrest(CA)is considered a state of clinical death in which the heart suddenly loses its ability to effectively expel blood,resulting in circulatory and respiratory arrest.CA is often catastrophic for patients,...Cardiac arrest(CA)is considered a state of clinical death in which the heart suddenly loses its ability to effectively expel blood,resulting in circulatory and respiratory arrest.CA is often catastrophic for patients,as it can cause serious long-term cardiovascular and cerebrovascular complications that affect their quality of life[1].Survey data indicate that the overall incidence rate of intraoperative CA in patients undergoing thoracic surgery in China is currently 0.138%[2].This rate is expected to increase because of the increasing proportion of older individuals(age>60 years)in the population,as well as the increasing pulmonary surgery rates.However,the incidence rate during the perianesthetic period in older patients undergoing thoracic surgery has not yet been comprehensively reported.展开更多
BACKGROUND Gastroesophageal reflux disease(GERD)is common among neonates,particularly those requiring mechanical ventilation.Pepsin,a reliable marker of gastric aspi-ration,may help detect GER episodes in ventilated n...BACKGROUND Gastroesophageal reflux disease(GERD)is common among neonates,particularly those requiring mechanical ventilation.Pepsin,a reliable marker of gastric aspi-ration,may help detect GER episodes in ventilated neonates and assess associated clinical outcomes.AIM To determine the incidence of GERD,associated risk factors,and morbidities among full-term mechanically ventilated neonates by detecting pepsin in endo-tracheal aspirates(ETA).METHODS This study included 97 full-term neonates admitted to the neonatal intensive care unit at Cairo University Hospitals from April 2023 to March 2024.ETA samples were collected at three intervals:Immediately post-intubation(Sample A),48 hours after intubation(Sample B),and just before extubation(Sample C).Pepsin concentration was measured using enzyme-linked immunosorbent assay.Clinical data,including hospital stay duration and feeding parameters,were correlated with pepsin levels.RESULTS Pepsin was detected in 76(78.4%)of Sample A,78(81.3%)of Sample B,and 47(68.1%)of Sample C.A significant positive correlation was found between pepsin levels and FiO_(2) in Sample B(r=0.203,P=0.047).Prolonged hospital stay was also associated with pepsin detection in Samples B and C(P<0.05).A negative correlation was observed between feeding amount and pepsin levels across all samples(P<0.05).CONCLUSION The incidence of GERD in full-term mechanically ventilated neonates is high,correlating with pepsin levels,FiO_(2),feeding intolerance,and hospital stay,highlighting the importance of early detection.展开更多
The cavity topology and unsteady behavior of ventilated cavitating flow over a bluff body are investigated experimentally using high-speed imaging and particle image velocimetry measurements.It is observed that the ca...The cavity topology and unsteady behavior of ventilated cavitating flow over a bluff body are investigated experimentally using high-speed imaging and particle image velocimetry measurements.It is observed that the cavity topology shows a distinct variation at different Reynold numbers(Re)for a given gas flow rate Q.For gas flow rate Q=4.16 litres per minute(LPM),the cavity topology is substantially the same at different Re,and the separated shear layer forms the basis for the cavity breakup and shedding vortices.However,for Q=16.67 LPM,the cavity length decreases,and the cavity topology changes from supercavity to large-scale shedding with the increasing of Re.According to the observations,the balance of gas injection and the gas leakage capacity of shedding vortices,which can be estimated by the cavitation vortex size and the vortex shedding frequency,determines the cavity topology.In addition,the proper orthogonal decomposition analysis indicates that the existence of natural cavitation in the ventilated cavitating flow mainly affects the temporal variation of shedding and makes the periodic change of vortex dynamic more complicated.展开更多
Objective:To explore the application effect of stratified nursing intervention based on the background of misinspiration risk assessment in mechanically ventilated patients in intensive care unit(ICU).Methods:100 case...Objective:To explore the application effect of stratified nursing intervention based on the background of misinspiration risk assessment in mechanically ventilated patients in intensive care unit(ICU).Methods:100 cases of mechanically ventilated patients who were admitted to the ICU of our hospital from March 2022 to March 2023 were selected and divided into an observation group and a control group according to the random number table method,with 50 cases in each of the two groups.The control group was given routine care in ICU,and the observation group was given stratified nursing interventions based on the background of the risk of aspiration assessment on the basis of the control group,and both groups were cared for until they were transferred out of the ICU,and the mechanical ventilation time,ICU stay time,muscle strength score,complication rate,adherence,and satisfaction were observed and compared between the two groups.Results:The mechanical ventilation time and ICU stay time of the observation group were shorter than that of the control group after the intervention;the muscle strength score,compliance and satisfaction of the observation group were higher than that of the control group after the intervention;and the complication rate of the observation group was lower than that of the control group after the intervention,all of which were P<0.05.Conclusion:The application of stratified nursing intervention based on the background of misaspiration risk assessment in ICU mechanically ventilated patients can improve the patient's muscle strength,shorten the time of mechanical ventilation,promote the patient's recovery,reduce the occurrence of complications,and improve the patient's compliance and satisfaction.展开更多
Objective:To investigate the effect of Yiqi Huoxue decoction combined with neuromuscular electrical stimulation on improving intensive care unit(ICU)acquired debility in mechanically ventilated patients.Methods:50 pat...Objective:To investigate the effect of Yiqi Huoxue decoction combined with neuromuscular electrical stimulation on improving intensive care unit(ICU)acquired debility in mechanically ventilated patients.Methods:50 patients who were admitted to the ICU and received mechanical ventilation treatment in our hospital from June 2022 to June 2023 and were complicated with ICU-acquired neurasthenia were selected,and randomly grouped using the randomized envelope method into two groups:control group with 25 patients who received neuromuscular electrical stimulation alone;observation group with 25 patients who received the traditional Chinese medicine Yiqi Huoxue decoction.Comparison indexes:treatment efficiency,degree of emotional recovery(APACHEⅡscore),muscle strength status(MRC score),motor status(FAC rating),and self-care ability(BI index score).Results:The treatment efficiency of patients in the observation group patients was higher as compared to those in the control group(P<0.05).There was no significant difference in the comparison of the results of the scores(ratings)of each index between the two groups before treatment(P>0.05).After the treatment,the APACHEⅡscores of patients in the observation group were significantly lower as compared to those in the control group,while the MRC scores,FAC ratings,and BI index scores were higher in the observation group than those of the control group patients(P<0.05).Conclusion:The combined application of Yiqi Huoxue decoction and neuromuscular electrical stimulation in the treatment of patients with ICU-acquired neurasthenia complicated by mechanical ventilation significantly enhanced the clinical efficacy,the patient’s muscle strength,motor status,and ability of self-care.Hence,it has high application value and is worthy to be popularized.展开更多
The smoke spreading law of urban transportation tunnels with multiple shafts under natural ventilation is studied.A full-scale burning experiment is conducted in an actual tunnel.The study shows that smoke temperature...The smoke spreading law of urban transportation tunnels with multiple shafts under natural ventilation is studied.A full-scale burning experiment is conducted in an actual tunnel.The study shows that smoke temperatures below the tunnel ceiling reduce rapidly along the longitudinal towards the tunnel exits. A noticeable temperature stratification is observed near the fire source.Most fire smoke is exhausted out of the shafts while the number of the smoke shafts in the downstream is more than that in the upstream.Large eddy simulation LES based on computational fluid dynamics CFD is carried out using the fire dynamics simulator FDS software with parallel processing in which the grid size of the fire-domain is set to be 0.083 m.The simulation results of temperatures under the ceiling the smoke fronts and the shafts＇smoke exhaust or air supply agree reasonably with the experimental data. Further simulations indicate that the decreasing ambient temperature or shaft spacing might reduce smoke temperatures under the tunnel ceiling and increase mass flow rates out of the shafts.This study provides technical scientific evidence and supports for the design and construction of such kinds of tunnels.展开更多
In order to assess the differences between the human body thermal sensation in naturally ventilated space and that in air-conditioned space,the fuzzy evaluation model was adopted in the research of thermal sensation i...In order to assess the differences between the human body thermal sensation in naturally ventilated space and that in air-conditioned space,the fuzzy evaluation model was adopted in the research of thermal sensation in naturally ventilated space.Based on the questionnaires and field measurements,the membership functions were presented by the statistic of the covering frequency to the fuzzy subset.Dry-bulb temperature was taken as the only independent variable for membership functions.The maximum values of membership grades are all at 0.5 or so,which is a distinction character on thermal comfort of naturally ventilated space.By the calculating results of membership grades value to different fuzzy evaluation subsets,the Predicted Mean Vote(PMV)was obtained.Furthermore,energy coefficient(Ea)was introduced to calculate the energy consumption,and the prediction methods of residential building energy consumption were also discussed.Finally,the importance of evaluation model of thermal sense is shown through the energy consumption prediction in a specific residential building.展开更多
Septic shock is a common critical condition, for which effective early fluid resuscitation is the therapeutic focus. According to the 2008 international guidelines for management of severe sepsis and septic shock, res...Septic shock is a common critical condition, for which effective early fluid resuscitation is the therapeutic focus. According to the 2008 international guidelines for management of severe sepsis and septic shock, resuscitation should achieve a central venous pressure （CVP） of 8-12 mmHg within the first 6 h. However, it is still uncertain about the sensitivity and specificity of CVP in reflecting the cardiac preload. Ultrasonography is a simple, rapid, non-invasive, and repeatable method for the measurement of sensitivity and specificity of CVP and has thus gradually attracted the increasing attention of physicians. It was reported that ultrasonography can show the inferior vena cava diameter, respiratory variability index, and blood volume in patients with sepsis or heart failure.展开更多
Ventilated cavitation has been successfully employed as ship drag reduction technology and potentially can mitigate flowinduced vibration. The obtained successes were based on solutions of design problems considered i...Ventilated cavitation has been successfully employed as ship drag reduction technology and potentially can mitigate flowinduced vibration. The obtained successes were based on solutions of design problems considered in the framework of ideal fluid theory with their following validation by towing tank tests. However, various aspects of the interaction of ventilated cavities with the viscous flows around the ship hulls remain unclear, whereas there is usually no possibility to simultaneously keep the full-scale Froude number and cavitation number in the test facilities. So, the further progress of the application of ventilated cavitation substantially depends on the ability of computational tools to predict this interaction. This paper briefly describes the state-of-the-art computation of ventilated cavitation and points out the most challenging unsolved problems that appeared in the model tests (prediction of air demand by cavities, ventilation effect on ship drag, on hydrofoil lift, and on the propagation of shock waves in cavities).展开更多
For some vehicles travelling through water, it is advantageous to cover the vehicle in a supercavity for the sake of reducing the drag acting on it. The method of artificial ventilation is most effective for generatin...For some vehicles travelling through water, it is advantageous to cover the vehicle in a supercavity for the sake of reducing the drag acting on it. The method of artificial ventilation is most effective for generating and dominating the supercavity. This paper focuses on the numerical simulation of flow field around three dimensional body. The method is based on the multiphase computational fluid dynamics （CFD） model combined with the turbulence model and the full cavity model. The flow field of cavity is simulated by solving the compressible Navier-Stokes equations. The fundamental similarity parameters of ventilated supercavitaty flows that include cavitation number, Froude number, ventilation rate and drag coefficient are all investigated numerically in the case of steady flow and gravity field. We discuss the following simulations results in section 3： The variations of the cavitation number and the supercavity＇s relative diameter with ventilation rate （subtopic 3.1）; The drag coefficient versus the cavitation number （subtopic 3.2）; Deformation of supercavity axis caused by gravitational effect for three different fixed Froude numbers-2.8, 3.4, 4.2 （subtopic 3.3）. In subtopic 3.2, we give the comparison results of the drag reduction ratio among numerical simulation and experiment conducted in hydrodynamic tunnel and towing tank respectively. In subtopic 3.3, we summarize our discussion of gravitational effect on the axis deformation of supercavity as follows： In the case of smaller Froude number, the inclination of the cavity axis increases monotonously with increasing horizontal length, and reaches its maximal value at the end of supercavity; This deformation can be almost completely negligible when the Froude number Fr〉7. The comparisons with the experimental data in the hydrodynamic tunnel and the towing tank indicate that the present method is effective for predicting the flows around ventilated supercavity; that the numerical results is in good agreement with the experimental ones and that the maximal value of the drag reduction ratio can reach 88% compared with that the condition of fully-wetted.展开更多
Ventilated cavitation could be applied to underwater vehicles to achieve a high drag-reduction ratio.The ventilated supercavity may experience deformation,fluctuation,and instability under the influence of the high-sp...Ventilated cavitation could be applied to underwater vehicles to achieve a high drag-reduction ratio.The ventilated supercavity may experience deformation,fluctuation,and instability under the influence of the high-speed jetting flow generated by the propulsion system.This study focuses on understanding the transient dynamics of a ventilated supercavity with jetting flow at the tail.Experiments are performed in an open water tunnel system with a high degassing rate.The evolution of the gas-liquid interface under different jetting flow rates is recorded in detail.A compressible multiphase model coupled with shear stress turbulence(SST)and surface capturing models is adopted herein to study the flow pattern in depth.As the jet velocity increases from subsonic to sonic speed,the flow field presents three different modes that could be identified as the transparent cavity(TC),transparent cavityjetting(TC-J),and deformed cavity-jetting(DC-J)modes.A new gas shedding scheme that couples twinvortex shedding with surface fluctuation shedding is observed in the TC mode.The variations in the internal flow structure and the local pressure vibration are discussed in detail.The transition of the flow pattern with dimensionless jetting momentum ratio and kinetic energy ratio is obtained.The obtained results could provide valuable insights into the control of the ventilated supercavity.展开更多
A computational model is established to investigate the effects of a periodic gust flow on the wake structure of ventilated supercavities.The effectiveness of the computational model is validated by comparing with ava...A computational model is established to investigate the effects of a periodic gust flow on the wake structure of ventilated supercavities.The effectiveness of the computational model is validated by comparing with available experimental data.Benefited from this numerical model,the vertical velocity characteristics in the entire flow field can be easily monitored and analyzed under the action of a gust generator;further,the unsteady evolution of the flow parameters of the closed region of the supercavity can be captured in any location.To avoid the adverse effects of mounting struts in the experiments and to obtain more realistic results,the wake structure of a ventilated supercavity without mounting struts is investigated.Unsteady changes in the wake morphology and vorticity distribution pattern of the ventilated supercavity are determined.The results demonstrate that the periodic swing of the gust generator can generate a gust flow and,therefore,generate a periodic variation of the ventilated cavitation numberσ.At the peakσ,a re-entrant jet closure appears in the wake of the ventilated supercavity.At the valleyσ,a twin-vortex closure appears in the wake of the ventilated supercavity.For the forward facing model,the twin vortex appears as a pair of centrally rolled-up vortices,due to the closure of vortex is affected by the structure.For the backward facing model,however,the twin vortex appears alternately as a pair of centrally rolled-up vortices and a pair of centrally rolled-down vortices,against the periodic gust flow.展开更多
The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the homogeneous equilibrium flow assumption,a mixture model is applied to simulate the multiphase cavitating ...The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the homogeneous equilibrium flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation.The transport equation cavitating model and a local linear low-Reynolds-number turbulence model are incorporated to the equation system.The calculations are executed based on a suite of computational fluid dynamics code.The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation are analyzed.The results indicate that the ventilated cavitation numbers and the drag coefficient are relative to the natural cavitation numbers and gas flow rate in the multiphase cavitating flows.展开更多
The collapse of the ventilated cavitation occurring on a cylindrical vehicle during the water-exit is numerically researched. The numerical model employs the finite volume method to solve the multiphase Reynoldsaverag...The collapse of the ventilated cavitation occurring on a cylindrical vehicle during the water-exit is numerically researched. The numerical model employs the finite volume method to solve the multiphase Reynoldsaveraged Navier-Stokes(RNNS) equations and uses the volume of fluid(VOF) method to capture the free surface.A practical water wave environment that the vehicle usually encounters is reproduced in a numerical wave flume,so that the water wave's effect on the cavity collapse flow regime is investigated. The main feature of the waterexit collapse of a ventilated cavity is studied under the wave-free condition. The result indicates that a collapsing ventilated cavity experiences two stages, in which the pattern of cavity evolution is different. In the early stage,the cavity undergoes a rapid shrinkage as a closed body. In the late stage, the cavity releases gas from the front due to the increase of the cavity pressure. The water wave effect is investigated at three typical wave phases: the wave crest, the wave trough and the wave node. Results show that when the vehicle is launched under the wave node, the cavity collapse regime remains fairly axisymmetric and is similar to the wave-free case. However, when the vehicle is launched under the wave crest and trough, the cavity evolution presents highly three-dimensional(3D) features. The results of predicted cavity size, pressure distributions and hydrodynamic forces at different wave phases show that the wave effect is relatively weak at the wave node but becomes apparent at the wave crest and trough.展开更多
Based on a suite of computational fluid dynamics code, the pulsation characteristics are studied for turbulent supercavitating flows over a 2D base-vented symmetric hydrofoil using a pressure-based Navier-Stokes solve...Based on a suite of computational fluid dynamics code, the pulsation characteristics are studied for turbulent supercavitating flows over a 2D base-vented symmetric hydrofoil using a pressure-based Navier-Stokes solver coupled with a phase mass fraction transport cavitation model and local linear low-Reynolds-number k-ε turbulence model. It is found that there exists a critical air supply flow under certain inflow condition. When the gas supply flow exceeds the critical value, the cavity begins to pulsate. Pulsating cavity has a visually wavy surface, and air leakage shows as a mass of air-water mixture detaching from the rear part of the cavity periodically.展开更多
Contrary to natural cavitation,ventilated cavitation is controllable and is not harmful.It is particularly used to reduce the drag of the hydraulic vehicles.The ventilated cavitation is characterized by various gas re...Contrary to natural cavitation,ventilated cavitation is controllable and is not harmful.It is particularly used to reduce the drag of the hydraulic vehicles.The ventilated cavitation is characterized by various gas regimes.The mechanisms of ventilated cavitation are investigated in the present work with CFD based on a 2D solver.The attention is especially focused on the transition between the reentrant jet and twin vortex regimes.The results confirmthat the product of ventilated cavitation number and Froude number is lower than 1(σcFr<1)in the twin vortex regime,while it is higher than 1(σcFr>1)in the reentrant jet regime,as reported in the literature.Further analysis shows that ventilated cavitation is significantly influenced by the natural cavitation number.展开更多
Ventilated cavitation plays an important role on the drag reduction of underwater vehicles and surface ships. For the modelling of ventilated cavitation, the minimum speed of the pressure wave is a crucial parameter f...Ventilated cavitation plays an important role on the drag reduction of underwater vehicles and surface ships. For the modelling of ventilated cavitation, the minimum speed of the pressure wave is a crucial parameter for the closure of the pressure-density coupling relationship. In this study, the minimum wave speed is determined based on a theoretical model coupling the wave equation and the bubble interface motion equation. The influences of several paramount parameters （e.g., frequency, bubble radius and void fraction） on the minimum wave speed are quantitatively demonstrated and discussed. Compared with the minimum wave speed in the traditional cavitation, values for the ventilated cavitation are much higher. The physical mechanisms for the above difference are briefly discussed with the suggestions on the usage of the present findings.展开更多
A semi-empirical gas entrainment model was proposed for the ventilated cavity in vertical pipe, based on which, a complete numerical scheme was established by coupling with the Eulerian-Eulerian two-fluid model to pre...A semi-empirical gas entrainment model was proposed for the ventilated cavity in vertical pipe, based on which, a complete numerical scheme was established by coupling with the Eulerian-Eulerian two-fluid model to predict the multiscale flow field created by ventilated cavity. Model predictions were validated against experimental measurements on void fraction and bubble size distributions. Simulations were carried out to explore the effect of ventilation rate and inlet turbulence intensity on the macroscale cavity shape and the bubbly flow downstream of the ventilated cavity. As the ventilation rate increasing, a reverse trend was observed for the void fraction and bub-ble size distributions. It is concluded that the average void fraction in the pipe flow region is determined by the vo-lumetric ratio between liquid and gas. However, the bubble size evolution is dominated by the breakage effect induced by turbulence in the vortex region. Furthermore, simulations were conducted to analyze geometric scale effect based upon Froude similitude. The results imply that the velocity distributions were properly scaled. Slight scale effect was seen for the void fraction caused by faster dispersion of bubbles in the larger size model. The comparatively greater bubble size was predicted in the smaller model, implying significant scale effects in terms of tur-bulence and surface tension effect. It reveals that empirical correlations valid in wide range are required for the extrapolation from small-size laboratory models.展开更多
BACKGROUND Patients with critical coronavirus disease 2019(COVID-19),characterized by respiratory failure requiring mechanical ventilation(MV),are at high risk of mortality.An effective and practical MV weaning protoc...BACKGROUND Patients with critical coronavirus disease 2019(COVID-19),characterized by respiratory failure requiring mechanical ventilation(MV),are at high risk of mortality.An effective and practical MV weaning protocol is needed for these fragile cases.CASE SUMMARY Here,we present two critical COVID-19 patients who presented with fever,cough and fatigue.COVID-19 diagnosis was confirmed based on blood cell counts,chest computed tomography(CT)imaging,and nuclei acid test results.To address the patients’respiratory failure,they first received noninvasive ventilation(NIV).When their condition did not improve after 2 h of NIV,each patient was advanced to MV[tidal volume(Vt),6 mL/kg ideal body weight(IBW);8-10 cmH2 O of positive end-expiratory pressure;respiratory rate,20 breaths/min;and 40%-80%FiO2]with prone positioning for 12 h/day for the first 5 d of MV.Extensive infection control measures were conducted to minimize morbidity,and pharmacotherapy consisting of an antiviral,immune-enhancer,and thrombosis prophylactic was administered in both cases.Upon resolution of lung changes evidenced by CT,the patients were sequentially weaned using a weaning screening test,spontaneous breathing test,and airbag leak test.After withdrawal of MV,the patients were transitioned through NIV and high-flow nasal cannula oxygen support.Both patients recovered well.CONCLUSION A MV protocol attentive to intubation/extubation timing,prone positioning early in MV,infection control,and sequential withdrawal of respiratory support,may be an effective regimen for patients with critical COVID-19.展开更多
The characteristic of flow and heat transfer of A12Oa-water nanofluids flowing through a horizontal ventilated cavity is investigated numerically. The bottom wall is subjected to a linearly varying increasing heating ...The characteristic of flow and heat transfer of A12Oa-water nanofluids flowing through a horizontal ventilated cavity is investigated numerically. The bottom wall is subjected to a linearly varying increasing heating temperature profile, whereas the other boundaries are assumed to be thermally insulated. The enclosure is cooled by an injected or sucked imposed flow. The simulations are focused specifically on the effects of different key parameters such as Reynolds number, 200 〈 Re 〈 5,000, nanoparticles concentration, 0 〈 φ 〈 0.1, and mode of imposed flow, on the flow and thermal patterns and heat transfer performances. The findings demonstrate clearly the positive role of the nanoparticles addition on the improvement of the heat transfer rate and the mean temperature within the cavity. Also, the results presented show that, the suction mode is more favorable to the heat transfer in comparison with the case of the injection mode. The cooling efficiency is found to be more pronounced by applying the suction mode.展开更多
基金supported by the Regional Science Foundation Project of the National Natural Science Foundation of China(Project No:82160157)the Beijing High-Level Public Health Technology Talent Construction Project(Project No.:Leading Talents-03-10).
文摘Cardiac arrest(CA)is considered a state of clinical death in which the heart suddenly loses its ability to effectively expel blood,resulting in circulatory and respiratory arrest.CA is often catastrophic for patients,as it can cause serious long-term cardiovascular and cerebrovascular complications that affect their quality of life[1].Survey data indicate that the overall incidence rate of intraoperative CA in patients undergoing thoracic surgery in China is currently 0.138%[2].This rate is expected to increase because of the increasing proportion of older individuals(age>60 years)in the population,as well as the increasing pulmonary surgery rates.However,the incidence rate during the perianesthetic period in older patients undergoing thoracic surgery has not yet been comprehensively reported.
文摘BACKGROUND Gastroesophageal reflux disease(GERD)is common among neonates,particularly those requiring mechanical ventilation.Pepsin,a reliable marker of gastric aspi-ration,may help detect GER episodes in ventilated neonates and assess associated clinical outcomes.AIM To determine the incidence of GERD,associated risk factors,and morbidities among full-term mechanically ventilated neonates by detecting pepsin in endo-tracheal aspirates(ETA).METHODS This study included 97 full-term neonates admitted to the neonatal intensive care unit at Cairo University Hospitals from April 2023 to March 2024.ETA samples were collected at three intervals:Immediately post-intubation(Sample A),48 hours after intubation(Sample B),and just before extubation(Sample C).Pepsin concentration was measured using enzyme-linked immunosorbent assay.Clinical data,including hospital stay duration and feeding parameters,were correlated with pepsin levels.RESULTS Pepsin was detected in 76(78.4%)of Sample A,78(81.3%)of Sample B,and 47(68.1%)of Sample C.A significant positive correlation was found between pepsin levels and FiO_(2) in Sample B(r=0.203,P=0.047).Prolonged hospital stay was also associated with pepsin detection in Samples B and C(P<0.05).A negative correlation was observed between feeding amount and pepsin levels across all samples(P<0.05).CONCLUSION The incidence of GERD in full-term mechanically ventilated neonates is high,correlating with pepsin levels,FiO_(2),feeding intolerance,and hospital stay,highlighting the importance of early detection.
基金supported by the National Natural Science Foundation of China(Grant Nos.12372243,11902323,12122214,62371453,1229300,12293003,and 12293004).
文摘The cavity topology and unsteady behavior of ventilated cavitating flow over a bluff body are investigated experimentally using high-speed imaging and particle image velocimetry measurements.It is observed that the cavity topology shows a distinct variation at different Reynold numbers(Re)for a given gas flow rate Q.For gas flow rate Q=4.16 litres per minute(LPM),the cavity topology is substantially the same at different Re,and the separated shear layer forms the basis for the cavity breakup and shedding vortices.However,for Q=16.67 LPM,the cavity length decreases,and the cavity topology changes from supercavity to large-scale shedding with the increasing of Re.According to the observations,the balance of gas injection and the gas leakage capacity of shedding vortices,which can be estimated by the cavitation vortex size and the vortex shedding frequency,determines the cavity topology.In addition,the proper orthogonal decomposition analysis indicates that the existence of natural cavitation in the ventilated cavitating flow mainly affects the temporal variation of shedding and makes the periodic change of vortex dynamic more complicated.
文摘Objective:To explore the application effect of stratified nursing intervention based on the background of misinspiration risk assessment in mechanically ventilated patients in intensive care unit(ICU).Methods:100 cases of mechanically ventilated patients who were admitted to the ICU of our hospital from March 2022 to March 2023 were selected and divided into an observation group and a control group according to the random number table method,with 50 cases in each of the two groups.The control group was given routine care in ICU,and the observation group was given stratified nursing interventions based on the background of the risk of aspiration assessment on the basis of the control group,and both groups were cared for until they were transferred out of the ICU,and the mechanical ventilation time,ICU stay time,muscle strength score,complication rate,adherence,and satisfaction were observed and compared between the two groups.Results:The mechanical ventilation time and ICU stay time of the observation group were shorter than that of the control group after the intervention;the muscle strength score,compliance and satisfaction of the observation group were higher than that of the control group after the intervention;and the complication rate of the observation group was lower than that of the control group after the intervention,all of which were P<0.05.Conclusion:The application of stratified nursing intervention based on the background of misaspiration risk assessment in ICU mechanically ventilated patients can improve the patient's muscle strength,shorten the time of mechanical ventilation,promote the patient's recovery,reduce the occurrence of complications,and improve the patient's compliance and satisfaction.
文摘Objective:To investigate the effect of Yiqi Huoxue decoction combined with neuromuscular electrical stimulation on improving intensive care unit(ICU)acquired debility in mechanically ventilated patients.Methods:50 patients who were admitted to the ICU and received mechanical ventilation treatment in our hospital from June 2022 to June 2023 and were complicated with ICU-acquired neurasthenia were selected,and randomly grouped using the randomized envelope method into two groups:control group with 25 patients who received neuromuscular electrical stimulation alone;observation group with 25 patients who received the traditional Chinese medicine Yiqi Huoxue decoction.Comparison indexes:treatment efficiency,degree of emotional recovery(APACHEⅡscore),muscle strength status(MRC score),motor status(FAC rating),and self-care ability(BI index score).Results:The treatment efficiency of patients in the observation group patients was higher as compared to those in the control group(P<0.05).There was no significant difference in the comparison of the results of the scores(ratings)of each index between the two groups before treatment(P>0.05).After the treatment,the APACHEⅡscores of patients in the observation group were significantly lower as compared to those in the control group,while the MRC scores,FAC ratings,and BI index scores were higher in the observation group than those of the control group patients(P<0.05).Conclusion:The combined application of Yiqi Huoxue decoction and neuromuscular electrical stimulation in the treatment of patients with ICU-acquired neurasthenia complicated by mechanical ventilation significantly enhanced the clinical efficacy,the patient’s muscle strength,motor status,and ability of self-care.Hence,it has high application value and is worthy to be popularized.
基金The National Natural Science Foundation of China(No.51178217)the Natural Science Foundation of Jiangsu Province(No.BK2011804)
文摘The smoke spreading law of urban transportation tunnels with multiple shafts under natural ventilation is studied.A full-scale burning experiment is conducted in an actual tunnel.The study shows that smoke temperatures below the tunnel ceiling reduce rapidly along the longitudinal towards the tunnel exits. A noticeable temperature stratification is observed near the fire source.Most fire smoke is exhausted out of the shafts while the number of the smoke shafts in the downstream is more than that in the upstream.Large eddy simulation LES based on computational fluid dynamics CFD is carried out using the fire dynamics simulator FDS software with parallel processing in which the grid size of the fire-domain is set to be 0.083 m.The simulation results of temperatures under the ceiling the smoke fronts and the shafts＇smoke exhaust or air supply agree reasonably with the experimental data. Further simulations indicate that the decreasing ambient temperature or shaft spacing might reduce smoke temperatures under the tunnel ceiling and increase mass flow rates out of the shafts.This study provides technical scientific evidence and supports for the design and construction of such kinds of tunnels.
基金Supported by National Natural Science Foundation of China(50508035)the National Science Foundation for Post-doctoral Scientists of China(20070411121)
文摘In order to assess the differences between the human body thermal sensation in naturally ventilated space and that in air-conditioned space,the fuzzy evaluation model was adopted in the research of thermal sensation in naturally ventilated space.Based on the questionnaires and field measurements,the membership functions were presented by the statistic of the covering frequency to the fuzzy subset.Dry-bulb temperature was taken as the only independent variable for membership functions.The maximum values of membership grades are all at 0.5 or so,which is a distinction character on thermal comfort of naturally ventilated space.By the calculating results of membership grades value to different fuzzy evaluation subsets,the Predicted Mean Vote(PMV)was obtained.Furthermore,energy coefficient(Ea)was introduced to calculate the energy consumption,and the prediction methods of residential building energy consumption were also discussed.Finally,the importance of evaluation model of thermal sense is shown through the energy consumption prediction in a specific residential building.
文摘Septic shock is a common critical condition, for which effective early fluid resuscitation is the therapeutic focus. According to the 2008 international guidelines for management of severe sepsis and septic shock, resuscitation should achieve a central venous pressure （CVP） of 8-12 mmHg within the first 6 h. However, it is still uncertain about the sensitivity and specificity of CVP in reflecting the cardiac preload. Ultrasonography is a simple, rapid, non-invasive, and repeatable method for the measurement of sensitivity and specificity of CVP and has thus gradually attracted the increasing attention of physicians. It was reported that ultrasonography can show the inferior vena cava diameter, respiratory variability index, and blood volume in patients with sepsis or heart failure.
文摘Ventilated cavitation has been successfully employed as ship drag reduction technology and potentially can mitigate flowinduced vibration. The obtained successes were based on solutions of design problems considered in the framework of ideal fluid theory with their following validation by towing tank tests. However, various aspects of the interaction of ventilated cavities with the viscous flows around the ship hulls remain unclear, whereas there is usually no possibility to simultaneously keep the full-scale Froude number and cavitation number in the test facilities. So, the further progress of the application of ventilated cavitation substantially depends on the ability of computational tools to predict this interaction. This paper briefly describes the state-of-the-art computation of ventilated cavitation and points out the most challenging unsolved problems that appeared in the model tests (prediction of air demand by cavities, ventilation effect on ship drag, on hydrofoil lift, and on the propagation of shock waves in cavities).
基金supported by National Defense Basic Research Foundation of China(No.K1800060604).
文摘For some vehicles travelling through water, it is advantageous to cover the vehicle in a supercavity for the sake of reducing the drag acting on it. The method of artificial ventilation is most effective for generating and dominating the supercavity. This paper focuses on the numerical simulation of flow field around three dimensional body. The method is based on the multiphase computational fluid dynamics （CFD） model combined with the turbulence model and the full cavity model. The flow field of cavity is simulated by solving the compressible Navier-Stokes equations. The fundamental similarity parameters of ventilated supercavitaty flows that include cavitation number, Froude number, ventilation rate and drag coefficient are all investigated numerically in the case of steady flow and gravity field. We discuss the following simulations results in section 3： The variations of the cavitation number and the supercavity＇s relative diameter with ventilation rate （subtopic 3.1）; The drag coefficient versus the cavitation number （subtopic 3.2）; Deformation of supercavity axis caused by gravitational effect for three different fixed Froude numbers-2.8, 3.4, 4.2 （subtopic 3.3）. In subtopic 3.2, we give the comparison results of the drag reduction ratio among numerical simulation and experiment conducted in hydrodynamic tunnel and towing tank respectively. In subtopic 3.3, we summarize our discussion of gravitational effect on the axis deformation of supercavity as follows： In the case of smaller Froude number, the inclination of the cavity axis increases monotonously with increasing horizontal length, and reaches its maximal value at the end of supercavity; This deformation can be almost completely negligible when the Froude number Fr〉7. The comparisons with the experimental data in the hydrodynamic tunnel and the towing tank indicate that the present method is effective for predicting the flows around ventilated supercavity; that the numerical results is in good agreement with the experimental ones and that the maximal value of the drag reduction ratio can reach 88% compared with that the condition of fully-wetted.
基金the National Natural Science Foundation of China(Grant Nos.52176164 and 51776221)the Research Project Foundation of National University of Defense Technology(Grant No.ZK18-02-07).
文摘Ventilated cavitation could be applied to underwater vehicles to achieve a high drag-reduction ratio.The ventilated supercavity may experience deformation,fluctuation,and instability under the influence of the high-speed jetting flow generated by the propulsion system.This study focuses on understanding the transient dynamics of a ventilated supercavity with jetting flow at the tail.Experiments are performed in an open water tunnel system with a high degassing rate.The evolution of the gas-liquid interface under different jetting flow rates is recorded in detail.A compressible multiphase model coupled with shear stress turbulence(SST)and surface capturing models is adopted herein to study the flow pattern in depth.As the jet velocity increases from subsonic to sonic speed,the flow field presents three different modes that could be identified as the transparent cavity(TC),transparent cavityjetting(TC-J),and deformed cavity-jetting(DC-J)modes.A new gas shedding scheme that couples twinvortex shedding with surface fluctuation shedding is observed in the TC mode.The variations in the internal flow structure and the local pressure vibration are discussed in detail.The transition of the flow pattern with dimensionless jetting momentum ratio and kinetic energy ratio is obtained.The obtained results could provide valuable insights into the control of the ventilated supercavity.
基金This study was financially supported by the Taishan Scholars Project of Shandong Province(tsqn201909172)the University Young Innovational Team Program of Shandong Province(2019KJN003)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,Weihai(2020)。
文摘A computational model is established to investigate the effects of a periodic gust flow on the wake structure of ventilated supercavities.The effectiveness of the computational model is validated by comparing with available experimental data.Benefited from this numerical model,the vertical velocity characteristics in the entire flow field can be easily monitored and analyzed under the action of a gust generator;further,the unsteady evolution of the flow parameters of the closed region of the supercavity can be captured in any location.To avoid the adverse effects of mounting struts in the experiments and to obtain more realistic results,the wake structure of a ventilated supercavity without mounting struts is investigated.Unsteady changes in the wake morphology and vorticity distribution pattern of the ventilated supercavity are determined.The results demonstrate that the periodic swing of the gust generator can generate a gust flow and,therefore,generate a periodic variation of the ventilated cavitation numberσ.At the peakσ,a re-entrant jet closure appears in the wake of the ventilated supercavity.At the valleyσ,a twin-vortex closure appears in the wake of the ventilated supercavity.For the forward facing model,the twin vortex appears as a pair of centrally rolled-up vortices,due to the closure of vortex is affected by the structure.For the backward facing model,however,the twin vortex appears alternately as a pair of centrally rolled-up vortices and a pair of centrally rolled-down vortices,against the periodic gust flow.
基金the National Natural Science Foundation of China (No.10832007)the Shanghai Leading Academic Discipline Project (No.B206)
文摘The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the homogeneous equilibrium flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation.The transport equation cavitating model and a local linear low-Reynolds-number turbulence model are incorporated to the equation system.The calculations are executed based on a suite of computational fluid dynamics code.The hydrodynamics characteristics of flow field under the interaction of natural cavitation and ventilated cavitation are analyzed.The results indicate that the ventilated cavitation numbers and the drag coefficient are relative to the natural cavitation numbers and gas flow rate in the multiphase cavitating flows.
基金the National Natural Science Foundation of China(Nos.11102109 and 11472174)
文摘The collapse of the ventilated cavitation occurring on a cylindrical vehicle during the water-exit is numerically researched. The numerical model employs the finite volume method to solve the multiphase Reynoldsaveraged Navier-Stokes(RNNS) equations and uses the volume of fluid(VOF) method to capture the free surface.A practical water wave environment that the vehicle usually encounters is reproduced in a numerical wave flume,so that the water wave's effect on the cavity collapse flow regime is investigated. The main feature of the waterexit collapse of a ventilated cavity is studied under the wave-free condition. The result indicates that a collapsing ventilated cavity experiences two stages, in which the pattern of cavity evolution is different. In the early stage,the cavity undergoes a rapid shrinkage as a closed body. In the late stage, the cavity releases gas from the front due to the increase of the cavity pressure. The water wave effect is investigated at three typical wave phases: the wave crest, the wave trough and the wave node. Results show that when the vehicle is launched under the wave node, the cavity collapse regime remains fairly axisymmetric and is similar to the wave-free case. However, when the vehicle is launched under the wave crest and trough, the cavity evolution presents highly three-dimensional(3D) features. The results of predicted cavity size, pressure distributions and hydrodynamic forces at different wave phases show that the wave effect is relatively weak at the wave node but becomes apparent at the wave crest and trough.
基金the National Natural Science Foundation of China(No:10832007)the Shanghai Leading Academic Discipline Project(No.B206)
文摘Based on a suite of computational fluid dynamics code, the pulsation characteristics are studied for turbulent supercavitating flows over a 2D base-vented symmetric hydrofoil using a pressure-based Navier-Stokes solver coupled with a phase mass fraction transport cavitation model and local linear low-Reynolds-number k-ε turbulence model. It is found that there exists a critical air supply flow under certain inflow condition. When the gas supply flow exceeds the critical value, the cavity begins to pulsate. Pulsating cavity has a visually wavy surface, and air leakage shows as a mass of air-water mixture detaching from the rear part of the cavity periodically.
基金performed in the scope of project ANR-12-ASTR-0017-03 "BF-DRAINH" in collaboration with the IRENav Laboratory (French Naval Academy,Brest,France) and the IMFT laboratory (Toulouse,France)
文摘Contrary to natural cavitation,ventilated cavitation is controllable and is not harmful.It is particularly used to reduce the drag of the hydraulic vehicles.The ventilated cavitation is characterized by various gas regimes.The mechanisms of ventilated cavitation are investigated in the present work with CFD based on a 2D solver.The attention is especially focused on the transition between the reentrant jet and twin vortex regimes.The results confirmthat the product of ventilated cavitation number and Froude number is lower than 1(σcFr<1)in the twin vortex regime,while it is higher than 1(σcFr>1)in the reentrant jet regime,as reported in the literature.Further analysis shows that ventilated cavitation is significantly influenced by the natural cavitation number.
基金Supported by the National Natural Science Foundation of China under Grant No 51506051
文摘Ventilated cavitation plays an important role on the drag reduction of underwater vehicles and surface ships. For the modelling of ventilated cavitation, the minimum speed of the pressure wave is a crucial parameter for the closure of the pressure-density coupling relationship. In this study, the minimum wave speed is determined based on a theoretical model coupling the wave equation and the bubble interface motion equation. The influences of several paramount parameters （e.g., frequency, bubble radius and void fraction） on the minimum wave speed are quantitatively demonstrated and discussed. Compared with the minimum wave speed in the traditional cavitation, values for the ventilated cavitation are much higher. The physical mechanisms for the above difference are briefly discussed with the suggestions on the usage of the present findings.
基金Supported by the Research Project Foundation of National University of Defense Technology(JC12-01-04)the National Science Foundation for Post-doctoral Scientists of China(2012M520268)
文摘A semi-empirical gas entrainment model was proposed for the ventilated cavity in vertical pipe, based on which, a complete numerical scheme was established by coupling with the Eulerian-Eulerian two-fluid model to predict the multiscale flow field created by ventilated cavity. Model predictions were validated against experimental measurements on void fraction and bubble size distributions. Simulations were carried out to explore the effect of ventilation rate and inlet turbulence intensity on the macroscale cavity shape and the bubbly flow downstream of the ventilated cavity. As the ventilation rate increasing, a reverse trend was observed for the void fraction and bub-ble size distributions. It is concluded that the average void fraction in the pipe flow region is determined by the vo-lumetric ratio between liquid and gas. However, the bubble size evolution is dominated by the breakage effect induced by turbulence in the vortex region. Furthermore, simulations were conducted to analyze geometric scale effect based upon Froude similitude. The results imply that the velocity distributions were properly scaled. Slight scale effect was seen for the void fraction caused by faster dispersion of bubbles in the larger size model. The comparatively greater bubble size was predicted in the smaller model, implying significant scale effects in terms of tur-bulence and surface tension effect. It reveals that empirical correlations valid in wide range are required for the extrapolation from small-size laboratory models.
文摘BACKGROUND Patients with critical coronavirus disease 2019(COVID-19),characterized by respiratory failure requiring mechanical ventilation(MV),are at high risk of mortality.An effective and practical MV weaning protocol is needed for these fragile cases.CASE SUMMARY Here,we present two critical COVID-19 patients who presented with fever,cough and fatigue.COVID-19 diagnosis was confirmed based on blood cell counts,chest computed tomography(CT)imaging,and nuclei acid test results.To address the patients’respiratory failure,they first received noninvasive ventilation(NIV).When their condition did not improve after 2 h of NIV,each patient was advanced to MV[tidal volume(Vt),6 mL/kg ideal body weight(IBW);8-10 cmH2 O of positive end-expiratory pressure;respiratory rate,20 breaths/min;and 40%-80%FiO2]with prone positioning for 12 h/day for the first 5 d of MV.Extensive infection control measures were conducted to minimize morbidity,and pharmacotherapy consisting of an antiviral,immune-enhancer,and thrombosis prophylactic was administered in both cases.Upon resolution of lung changes evidenced by CT,the patients were sequentially weaned using a weaning screening test,spontaneous breathing test,and airbag leak test.After withdrawal of MV,the patients were transitioned through NIV and high-flow nasal cannula oxygen support.Both patients recovered well.CONCLUSION A MV protocol attentive to intubation/extubation timing,prone positioning early in MV,infection control,and sequential withdrawal of respiratory support,may be an effective regimen for patients with critical COVID-19.
文摘The characteristic of flow and heat transfer of A12Oa-water nanofluids flowing through a horizontal ventilated cavity is investigated numerically. The bottom wall is subjected to a linearly varying increasing heating temperature profile, whereas the other boundaries are assumed to be thermally insulated. The enclosure is cooled by an injected or sucked imposed flow. The simulations are focused specifically on the effects of different key parameters such as Reynolds number, 200 〈 Re 〈 5,000, nanoparticles concentration, 0 〈 φ 〈 0.1, and mode of imposed flow, on the flow and thermal patterns and heat transfer performances. The findings demonstrate clearly the positive role of the nanoparticles addition on the improvement of the heat transfer rate and the mean temperature within the cavity. Also, the results presented show that, the suction mode is more favorable to the heat transfer in comparison with the case of the injection mode. The cooling efficiency is found to be more pronounced by applying the suction mode.
