Ventilation Strategies Research Articles

Analysis of ventilation and infiltration rates using physics-informed neural networks: Impact of space operation and meteorological factors

This study presents the development and application of a Physics-Informed Neural Network (PINN) model to estimate ventilation and infiltration rates using long-term observation data, addressing the challenge of dynamically varying space operations and meteorological conditions. A central research equestion is: How can we accurately estimate ventilation rates while accounting for these time-varying factors? Traditional tracer gas methods require numerous measurements to accurately characterize air change rates (ACR) under dynamic space operations and varying meteorological conditions. Our PINN model integrates these fluctuating factors, providing a more precise analysis of their transient effects on ACR. We employed Shapley Additive Explanations (SHAP) to interpret the sensitivity and contributions of each influencing factor. Our findings indicate that the state of windows and doors significantly affects spatial operations, while wind speed and direction are the most impactful meteorological factors. The interaction between open windows and doors results in higher ventilation rates compared to their individual effects. Wind-related factors cause ACR variations exceeding 200 %, with the wind direction relative to the office window playing a crucial role. Additionally, external temperature and indoor-outdoor temperature differences show a strong correlation with ACR. However, limitations include the lack of outdoor CO2 measurements and the assumption of uniform indoor CO2 levels, which may affect accuracy. Generalizability is also limited due to the specificity of the space studied. Future work should incorporate outdoor CO2 data and multiple spaces to enhance model applicability. This study contributes to optimizing ventilation strategies for better indoor air quality and energy efficiency.

Use of extracorporeal membrane oxygenation during a decompressive hemicraniectomy for severe traumatic brain injury: illustrative case.

Decompressive hemicraniectomy (DHC) can be a life-saving treatment for patients with severe traumatic brain injury (TBI) with a focal mass lesion who develop refractory elevated intracranial pressure (ICP). Nonetheless, successful completion of this procedure requires maintaining hemodynamic and respiratory stability. Extracorporeal membrane oxygenation (ECMO) use in patients with respiratory or cardiac failure is well described in the literature and has become routinely used in patients with refractory hypoxia unresponsive to traditional mechanical ventilation strategies, but few cases of its use have been reported in the neurosurgical literature. Herein, the authors describe a unique case in which a man presented after an unwitnessed fall that caused severe TBI without a focal mass lesion. The patient subsequently developed medically refractory elevated ICP secondary to traumatic cerebral edema. He required DHC, but the procedure could only be completed safely with the utilization of intraoperative ECMO. As more is learned about the techniques and pitfalls of ECMO, its indications are rapidly expanding. The case presented describes the safe use of ECMO during a major neurosurgical procedure, showing that the technique can be completed safely and offering a therapeutic option for effectively addressing refractory hypoxia and hypercarbia in patients with severe TBI who require urgent or emergency neurosurgical procedures. https://thejns.org/doi/10.3171/CASE24264.

Driving pressure during general anesthesia for minimally invasive abdominal surgery (GENERATOR)—study protocol of a randomized clinical trial

BackgroundIntraoperative driving pressure (ΔP) has an independent association with the development of postoperative pulmonary complications (PPCs) in patients receiving ventilation during general anesthesia for major surgery. Ventilation with high intraoperative positive end–expiratory pressure (PEEP) with recruitment maneuvers (RMs) that result in a low ΔP has the potential to prevent PPCs. This trial tests the hypothesis that compared to standard low PEEP without RMs, an individualized high PEEP strategy, titrated to the lowest ΔP, with RMs prevents PPCs in patients receiving intraoperative protective ventilation during anesthesia for minimally invasive abdominal surgery.Methods“DrivinG prEssure duriNg gEneRal AnesThesia fOr minimally invasive abdominal suRgery (GENERATOR)” is an international, multicenter, two–group, patient and outcome–assessor blinded randomized clinical trial. In total, 1806 adult patients scheduled for minimally invasive abdominal surgery and with an increased risk of PPCs based on (i) the ARISCAT risk score for PPCs (≥ 26 points) and/or (ii) a combination of age > 40 years and scheduled surgery lasting > 2 h and planned to receive an intra–arterial catheter for blood pressure monitoring during the surgery will be included. Patients are assigned to either an intraoperative ventilation strategy with individualized high PEEP, titrated to the lowest ΔP, with RMs or one with a standard low PEEP of 5 cm H2O without RMs. The primary outcome is a collapsed composite endpoint of PPCs until postoperative day 5.DiscussionGENERATOR will be the first adequately powered randomized clinical trial to compare the effects of individualized high PEEP with RMs versus standard low PEEP without RMs on the occurrence of PPCs after minimally invasive abdominal surgery. The results of the GENERATOR trial will support anesthesiologists in their decisions regarding PEEP settings during minimally invasive abdominal surgery.Trial registrationGENERATOR is registered at ClinicalTrials.gov (study identifier: NCT06101511) on 26 October 2023.

Modelling of Indoor Air Quality and Thermal Comfort in Passive Buildings Subjected to External Warm Climate Conditions

Air renewal rate is an important parameter for both indoor air quality and thermal comfort. However, to improve indoor thermal comfort, the air renewal rate to be used, in general, will depend on the outdoor air temperature values. This article presents the modelling of indoor air quality and thermal comfort for occupants of a passive building subject to a climate with warm conditions. The ventilation and shading strategies implemented for the interior spaces are then considered, as well as the use of an underground space for storing cooled air. The indoor air quality is evaluated using the carbon dioxide concentration, and thermal comfort is evaluated using the Predicted Mean Vote index. The geometry of the passive building, with complex topology, is generated using a numerical model. The simulation is performed by Building Thermal Response software, considering the building’s geometry and materials, ventilation, and occupancy, among others. The building studied is a circular auditorium. The auditorium is divided into four semi-circular auditoriums and a central circular space, with vertical glazed windows and horizontal shading devices on its entire outer surface. Typical summer conditions existing in a Mediterranean-type environment were considered. In this work, two cases were simulated: in Case 1, the occupation is verified in the central space and the four semi-circular auditoriums and all spaces are considered as one; in Case 2, the occupation is verified only in each semi-circular auditorium and each one works independently. For both cases, three strategies were applied: A, without shading and geothermal devices; B, with a geothermal device and without a shading device; and C, with both shading and geothermal devices. The airflow rate contributes to improving indoor air quality throughout the day and thermal comfort for occupants, especially in the morning. The geothermal and shading devices improve the thermal comfort level, mainly in the afternoon.

Association Between Tidal Volume in Invasive Mechanical Ventilation and Mortality in Children With Extracorporeal Membrane Oxygenation.

Mechanical ventilation (MV) strategies in children on extracorporeal membrane oxygenation (ECMO) have not been studied much and the ventilatory parameters to avoid greater lung damage are still unclear. Our objective was to determine the relationship between conventional tidal volume (4-8 ml/kg, CTV) versus low tidal volume (<4 ml/kg, LTV) and mortality in children with MV at the beginning of ECMO. This was a retrospective cohort study that included 101 (10.9 months interquartile range [IQR]: 6.0-24.0) children. Children with LTV had greater odds of hospital mortality (adjusted odds ratio [aOR]: 2.45; 95% confidence interval [CI]: 1.05-5.71; p = 0.03) regardless of age, reason for ECMO, and disease severity, as well as a longer duration of MV after ECMO. We found no differences between the groups in other MV settings. The CTV group required fewer fibrobronchoscopies than patients with LTV (aOR: 0.38; 95% CI: 0.15-0.99; p = 0.04). We found that a tidal volume (VT) lower than 4 ml/kg at the onset of ECMO support in children with MV was associated with higher odds of mortality, longer post-decannulation ventilation, and a greater need for fibrobronchoscopies. Lung-protective bundles in patients with ECMO and MV should consider the VT to maintain plateau and driving pressure that avoid major lung injury caused by MV.

VENO-VENOUS EXTRACORPOREAL MEMBRANE OXYGENATION IMPROVES OUTCOMES IN TRAUMA PATIENTS SUFFERING RESPIRATORY FAILURE.

Veno-venous extracorporeal membrane oxygenation (VV ECMO) improves hypoxemia and carbon dioxide clearance in patients with severe respiratory derangements. A greater understanding of the potential benefits of VV ECMO in trauma patients could lead to broader adoption. We hypothesize that trauma patients who receive VV ECMO have improved mortality outcomes when compared to those receiving conventional ventilator management given the rapid stabilization VV ECMO promotes. We performed a single center, propensity score matched cohort study. All trauma patients from January 1, 2014, to October 30, 2023, who were placed on VV ECMO or who would have met institutional guidelines for VV ECMO but were managed with conventional ventilator strategies were matched 1:1. The primary outcome analysis was survival at hospital discharge. Significance was defined as p < 0.05. Eighty-one trauma VV ECMO patients and 128 patients who received conventional management met criteria for inclusion. After matching, VV ECMO and conventional treatment cohort characteristics were similar in age and MOI. Matched ISS, SI, lactate levels, and frequency of TBI were also similar. Finally, respiratory parameters including pre-intervention, pH, partial pressure of carbon dioxide (PaCO2), lactate levels, and oxygen saturation were similar between matched groups. VV ECMO patients had higher survival rates at discharge when compared to the matched conventional treatment group (70% v 41%, p < 0.001). Corresponding hazard ratio for VV ECMO use was 0.31 (95%CI 0.18-0.52; p < 0.001). The odds ratio of mortality in matched trauma patients who receive VV ECMO versus conventional treatment was 0.29 (95%CI 0.14-0.58; p < 0.001). VV ECMO may represent a safe, alternative treatment approach for appropriately screened trauma patients with acute respiratory failure, however further studies are warranted.

Ventilation strategies in cardiogenic shock: insights from the FRENSHOCK observational registry.

Despite scarce data, invasive mechanical ventilation(MV) is widely suggested as first-line ventilatory support incardiogenic shock(CS) patients. We assessed the real-life use of different ventilation strategies in CS and their influence on short and mid-term prognosis. FRENSHOCK was a prospective registry including 772 CS patients from 49 centers in France. Patients were categorized into three groups according to the ventilatory supports during hospitalization: no mechanical ventilation group (NV), non-invasive ventilation alone group (NIV), and invasive mechanical ventilation group (MV). We compared clinical characteristics, management, and occurrence of death and major adverse event (MAE) (death, heart transplantation or ventricular assist device) at 30days and 1year between the three groups. Seven hundred sixty-eight patients were included in this analysis. Mean age was 66years and 71% were men. Among them, 359 did not receive any ventilatory support (46.7%), 118 only NIV (15.4%), and 291 MV (37.9%). MV patients presented more severe CS with more skin mottling, higher lactate levels, and higher use ofvasoactive drugs and mechanical circulatory support. MV was associated with higher mortality and MAE at 30days (HR 1.41 [1.05-1.90] and 1.52 [1.16-1.99] vs NV). No difference in mortality (HR 0.79 [0.49-1.26]) or MAE (HR 0.83 [0.54-1.27]) was found between NIV patients and NV patients. Similar results were found at 1-year follow-up. Our study suggests that using NIV is safe in selected patients with less profound CS and no other MV indication. NCT02703038.

Evaluation of Ventilation Strategies to Mitigate Airborne Infection Risk in a Dental School: A Three-Dimensional CFD Analysis of Airflow Patterns and Ventilation Efficiency

Infection prevention and control is a crucial element in providing a safe environment for dental clinics and reducing airborne infections risks during dental procedures. In response to the prevailing COVID-19 situations, the clinical space in the dental school was operated with ventilation strategies, increasing air exchanges and incorporating supply and return air arrangement based on seating positions. This study evaluated airflow patterns to examine personal exposure to airborne infection risk under these strategies. The three-dimensional computational fluid dynamics technique using computational fluid dynamics (CFD) analysis was performed in 50 multi-units of the dental school of the university in Bangkok, Thailand. The results revealed substantial improvements in indoor ventilation. Improvement of airflow patterns and directions surpassed conventional design of the pre-existing building’s system and helped reduce airborne contaminant concentrations. The further discussion of occupant-based design in dental schools is needed to optimize ventilation systems and engineering controls concerning indoor airborne infections.

Indoor Environmental Quality in Portuguese Office Buildings: Influencing Factors and Impact of an Intervention Study

Office workers spend a considerable part of their day at the workplace, making it vital to ensure proper indoor environmental quality (IEQ) conditions in office buildings. This work aimed to identify significant factors influencing IEQ and assess the effectiveness of an environmental intervention program, which included the introduction of indoor plants, carbon dioxide (CO2) sensors, ventilation, and printer relocation (source control), in six modern office buildings in improving IEQ. Thirty office spaces in Porto, Portugal, were randomly divided into intervention and control groups. Indoor air quality, thermal comfort, illuminance, and noise were monitored before and after a 14-day intervention implementation. Occupancy, natural ventilation, floor type, and cleaning time significantly influenced IEQ levels. Biophilic interventions appeared to decrease volatile organic compound concentrations by 30%. Installing CO2 sensors and optimizing ventilation strategies in an office that mainly relies on natural ventilation effectively improved air renewal and resulted in a 28% decrease in CO2 levels. The implementation of a source control intervention led to a decrease in ultrafine particle and ozone concentrations by 14% and 85%, respectively. However, an unexpected increase in airborne particle levels was detected. Overall, for a sample of offices that presented acceptable IEQ levels, the intervention program had only minor or inconsistent impacts. Offices with declared IEQ problems are prime candidates for further research to fully understand the potential of environmental interventions.

Clinical implementation of advanced respiratory monitoring with esophageal pressure and electrical impedance tomography: results from an international survey and focus group discussion

BackgroundPopularity of electrical impedance tomography (EIT) and esophageal pressure (Pes) monitoring in the ICU is increasing, but there is uncertainty regarding their bedside use within a personalized ventilation strategy. We aimed to gather insights about the current experiences and perceived role of these physiological monitoring techniques, and to identify barriers and facilitators/solutions for EIT and Pes implementation.MethodsQualitative study involving (1) a survey targeted at ICU clinicians with interest in advanced respiratory monitoring and (2) an expert focus group discussion. The survey was shared via international networks and personal communication. An in-person discussion session on barriers, facilitators/solutions for EIT implementation was organized with an international panel of EIT experts as part of a multi-day EIT meeting. Pes was not discussed in-person, but we found the focus group results relevant to Pes as well. This was confirmed by the survey results and four additional Pes experts that were consulted.ResultsWe received 138 survey responses, and 26 experts participated in the in-person discussion. Survey participants had diverse background [physicians (54%), respiratory therapists (19%), clinical researchers (15%), and nurses (6%)] with mostly > 10 year ICU experience. 84% of Pes users and 74% of EIT users rated themselves as competent to expert users. Techniques are currently primarily used during controlled ventilation for individualization of PEEP (EIT and Pes), and for monitoring lung mechanics and lung stress (Pes). EIT and Pes are considered relevant techniques to guide ventilation management and is helpful for educating clinicians; however, 57% of EIT users and 37% of Pes users agreed that further validation is needed. Lack of equipment/materials, evidence-based guidelines, clinical protocols, and/or the time-consuming nature of the measurements are main reasons hampering Pes and EIT application. Identified facilitators/solutions to improve implementation include international guidelines and collaborations between clinicians/researcher and manufacturers, structured courses for training and use, easy and user-friendly devices and standardized analysis pipelines.ConclusionsThis study revealed insights on the role and implementation of advanced respiratory monitoring with EIT and Pes. The identified barriers, facilitators and strategies can serve as input for further discussions to promote the development of EIT-guided or Pes-guided personalized ventilation strategies.

ESTRATÉGIAS DE CONFORTO AMBIENTAL PARA QUADRAS FECHADAS VOLTADAS A ESPORTES DE ALTO RENDIMENTO

Sports architecture, with its particularities, is essential to optimize the efficiency of environments, considering the specific needs of each sport. This article addresses environmental comfort strategies applied to indoor courts intended for high-performance sports, highlighting the importance of an architecturally planned environment to ensure the well-being of athletes and optimize their performance. The study focuses on thermal, visual, acoustic and ergonomic aspects, and analyzes how each of these factors influences sports performance. In addition, it explores the interaction between the body and the physical environment, proposing solutions that favor the creation of functional and comfortable spaces for sports practice and competitive events. The research, of a bibliographic and exploratory nature, brings together concepts of environmental psychology and athletic performance, in addition to highlighting the construction strategies of ventilation, lighting and acoustic control that can be applied to indoor courts with the aim of promoting human well-being. The work proposes solutions so that sports centers offer adequate conditions for sports practice, supporting the creation of environments that favor both the satisfaction and the enhancement of the performance of athletes. From this study, it is possible to define the importance of the preparation and competition environment in the performance of high-performance athletes, and architecture, linked to environmental comfort, is shown to be a tool for the development of these spaces, essential for success in national and international sports competitions.

CFD Simulation of Dynamic Temperature Variations Induced by Tunnel Ventilation in a Broiler House.

Maintaining the optimal microclimate in broiler houses is crucial for bird productivity, yet enabling efficient temperature control remains a significant challenge. This study developed and validated a computational fluid dynamics (CFD) model to predict temporal changes in indoor air temperature in response to variable ventilation operations in a commercial broiler house. The model accurately simulated air velocity and airflow distribution for different numbers of tunnel fans in operation, with air-velocity errors ranging from -0.22 to 0.32 m s-1. The predicted airflow rates through inlets and cooling pads showed good agreement with measured values with an accuracy of up to 108.1%. Additionally, the CFD model effectively predicted temperature dynamics, accounting for chicken heat production and ventilation effect. The model successfully predicted the longitudinal temperature gradients and their variations during ventilation cycles, validating its reliability through comparison with experimental data. This study also explored different variable inlet configurations to mitigate the temperature gradient. The variable inlet adjustment showed the potential to relieve the high temperatures but may reduce overall ventilation efficiency or intensify temperature gradients, which confirms the importance of optimising ventilation strategies. This CFD model provides a valuable tool for evaluating and improving ventilation systems and contributes to enhanced indoor microclimates and productivity in poultry houses.

Reinforcement Learning to Optimize Ventilator Settings for Patients on Invasive Mechanical Ventilation: Retrospective Study.

One of the significant changes in intensive care medicine over the past 2 decades is the acknowledgment that improper mechanical ventilation settings substantially contribute to pulmonary injury in critically ill patients. Artificial intelligence (AI) solutions can optimize mechanical ventilation settings in intensive care units (ICUs) and improve patient outcomes. Specifically, machine learning algorithms can be trained on large datasets of patient information and mechanical ventilation settings. These algorithms can then predict patient responses to different ventilation strategies and suggest personalized ventilation settings for individual patients. In this study, we aimed to design and evaluate an AI solution that could tailor an optimal ventilator strategy for each critically ill patient who requires mechanical ventilation. We proposed a reinforcement learning-based AI solution using observational data from multiple ICUs in the United States. The primary outcome was hospital mortality. Secondary outcomes were the proportion of optimal oxygen saturation and the proportion of optimal mean arterial blood pressure. We trained our AI agent to recommend low, medium, and high levels of 3 ventilator settings-positive end-expiratory pressure, fraction of inspired oxygen, and ideal body weight-adjusted tidal volume-according to patients' health conditions. We defined a policy as rules guiding ventilator setting changes given specific clinical scenarios. Off-policy evaluation metrics were applied to evaluate the AI policy. We studied 21,595 and 5105 patients' ICU stays from the e-Intensive Care Unit Collaborative Research (eICU) and Medical Information Mart for Intensive Care IV (MIMIC-IV) databases, respectively. Using the learned AI policy, we estimated the hospital mortality rate (eICU 12.1%, SD 3.1%; MIMIC-IV 29.1%, SD 0.9%), the proportion of optimal oxygen saturation (eICU 58.7%, SD 4.7%; MIMIC-IV 49%, SD 1%), and the proportion of optimal mean arterial blood pressure (eICU 31.1%, SD 4.5%; MIMIC-IV 41.2%, SD 1%). Based on multiple quantitative and qualitative evaluation metrics, our proposed AI solution outperformed observed clinical practice. Our study found that customizing ventilation settings for individual patients led to lower estimated hospital mortality rates compared to actual rates. This highlights the potential effectiveness of using reinforcement learning methodology to develop AI models that analyze complex clinical data for optimizing treatment parameters. Additionally, our findings suggest the integration of this model into a clinical decision support system for refining ventilation settings, supporting the need for prospective validation trials.

Mechanical power is associated with cardiac output and pulmonary blood flow in an experimental acute respiratory distress syndrome in pigs.

Despite being essential in patients with acute respiratory distress syndrome (ARDS), mechanical ventilation (MV) may cause lung injury and hemodynamic instability. Mechanical power (MP) may describe the net injurious effects of MV, but whether it reflects the hemodynamic effects of MV is currently unclear. We hypothesized that MP is also associated with cardiac output (CO) and pulmonary blood flow (PBF). 24 anesthetized pigs with experimental acute lung injury were ventilated for 18h according to one of three strategies: 1) Open lung approach (OLA), 2) ARDS Network high-PEEP/FIO2 strategy (HighPEEP), or 3) low-PEEP/FIO2 strategy (LowPEEP). Total MP was assessed as the sum of energy dissipated to overcome airway resistance and energy temporarily stored in the elastic lung tissue per minute. The distribution of pulmonary perfusion was determined by positron emission tomography. Regional PBF and MP, assessed in three iso-gravitational regions of interest (ROI) with equal lung mass (ventral, middle, and dorsal ROI), were compared between groups. MP was higher in the LowPEEP than in the OLA group, while CO did not differ between groups. After 18h, regional PBF did not differ between groups. During LowPEEP, regional MP was higher in the ventral ROI compared to OLA and HighPEEP groups (2.5 ± 0.3 vs. 1.4 ± 0.4 and 1.6 ± 0.3J/min, respectively, P < 0.001 each), and higher in the middle ROI compared to the OLA group (2.5 ± 0.4 vs. 1.6 ± 0.5J/min, P = 0.04). MP in the dorsal ROI did not differ between groups (1.4 ± 0.9 vs. 1.4 ± 0.5 vs. 1.3 ± 0.8J/min, P = 0.916). Total MP was independently associated with CO [0.34 (0.09, 0.59), P = 0.020]. Regional MP was positively associated with PBF irrespective of the regions [0.52 (0.14, 0.76), P = 0.01; 0.49 (0.10, 0.74), P = 0.016; 0.64 (0.32, 0.83), P = 0.001 for ventral, middle, and dorsal ROI, respectively]. Subgroup analysis revealed a significant association of MP and CO only in the OLA group as well as a significant association between MP with regional PBF only in the HighPEEP group. In this model of acute lung injury in pigs ventilated with either open lung approach, high, or low PEEP tables recommended by the ARDS network, MP correlated positively with CO and regional PBF, whereby these clinically relevant lung-protective ventilation strategies influenced the associations.

Statistical analysis of natural and mechanical ventilation performance in improving indoor air quality, thermal comfort, and perceived air quality in a healthcare facility

Ventilation strategies in healthcare facilities are mainly directed towards mechanical systems. Due to patients’ preferences or the necessity of terminal reheat/recool, Air Handler Units are often turned off or windows are opened when mechanical systems are active. This leads to poor IAQ, nosocomial infections, and energy loss. Besides, ventilation systems are not typically intended to optimize user satisfaction. Using field measurements in 140 spaces, survey studies, and statistical analysis, this study compares ventilation strategies in providing IAQ, thermal comfort, and Perceived Air Quality as an indicator of user satisfaction. 315 samples were collected for air velocity, air temperature, relative humidity, PAQ, odor intensity, and VOC concentrations. Lowest to highest pollutant concentrations were observed respectively in mechanical ventilation with two open windows, mechanical ventilation with one open window, natural ventilation with two open windows, mechanical ventilation with closed windows, natural ventilation with one open window, and nonventilated spaces. There was no evidence of an effect of ventilation strategies on environmental parameters and user satisfaction. Users’ thermal comfort and air quality satisfaction were not guaranteed even when ventilation rate, pollutant concentrations, and environmental parameters were within the permissible range. Findings support the efficient performance of natural ventilation in providing acceptable air quality.

Can the infection risk in elevators be negligible? A comparative study of airborne infection probability in elevators and conference rooms

People in crowded and poorly ventilated elevators are at risk of respiratory infection. However, due to the short duration of the elevator ride, the transmission of respiratory diseases in elevators does not get enough attention. To evaluate the infection risk, this study investigated the airborne transmission of respiratory diseases in the hospital elevator by comparison to the conference room. A validated computational fluid dynamics (CFD) model was adopted to simulate airflow, temperature and tracer gas dispersion in the elevator and conference room. We used Wells-Riley model to evaluate the infection probability of the susceptible persons. In addition, the influences of source patient posture and ventilation strategy on the transmission of tracer gas were analyzed. The results showed that the infection probability in the elevator with 5 min (average 2.70%) was higher than that in the conference room with 50 min (average 1.77%). The effects of source patient posture and ventilation strategy on the infection probability in the elevator were more significant than those in the conference room. Local air circulation could gather the tracer gas inside a confined space in the elevator and led to a high infection probability. The infection risk of respiratory diseases in the elevator was non-negligible.

A multimodal characterization of cardiopulmonary resuscitation-associated lung edema

BackgroundCardiopulmonary resuscitation-associated lung edema (CRALE) is a phenomenon that has been recently reported in both experimental and out-of-hospital cardiac arrest patients.We aimed to explore the respiratory and cardiovascular pathophysiology of CRALE in an experimental model of cardiac arrest undergoing prolonged manual and mechanical chest compression (CC). Oxygen delivery achieved during mechanical or manual CC were also investigated as a secondary aim, to describe CRALE evolution under different hemodynamic supports generated during CPR.MethodsVentricular fibrillation (VF) was induced and left untreated for 5 min prior to begin cardiopulmonary resuscitation (CPR), including CC, ventilation with oxygen, epinephrine administration and defibrillation. Continuous mechanical and manual CC was performed alternating one of the two strategies every 5 min for a total of 25 min. Unsynchronized mechanical ventilation was resumed simultaneously to CC. A lung computed tomography (CT) was performed at baseline and 1 h after return of spontaneous circulation (ROSC) in surviving animals. Partitioned respiratory mechanics, gas exchange, hemodynamics, and oxygen delivery were evaluated during the experimental study at different timepoints. Lung histopathology was performed.ResultsAfter 25 min of CPR, a marked decrease of the respiratory system compliance with reduced oxygenation and CO2 elimination were observed in all animals. The worsening of the respiratory system compliance was driven by a significant decrease in lung compliance. The presence of CRALE was confirmed by an increased lung weight and a reduced lung aeration at the lung CT, together with a high lung wet-to-dry ratio and reduced airspace at histology. The average change in esophageal pressure during the 25-min CPR highly correlated with the severity of CRALE, i.e., lung weight increase.ConclusionsIn this porcine model of cardiac arrest followed by a 25-min interval of CPR with mechanical and manual CC, CRALE was consistently present and was characterized by lung inhomogeneity with alveolar tissue and hemorrhage replacing alveolar airspace. Despite mechanical CPR is associated with a more severe CRALE, the higher cardiac output generated by the mechanical compression ultimately accounted for a greater oxygen delivery. Whether specific ventilation strategies might prevent CRALE while preserving hemodynamics remains to be proved.

3eaw - How Different Ventilation System’s Designs Affected Their Applications in Healthcare Facilities: A Comprehensive Review

Effective indoor ventilation systems are crucial in reducing airborne viruses in healthcare facilities which include significant sections such as OR, isolation room and emergency department. Infection control through indoor ventilation system can be done by manipulating the concentration of infectious particles to reduce airborne infections. This review article highlighted different types of indoor ventilation strategies including mechanical ventilation system, natural ventilation system and hybrid ventilation system that have been integrated into different healthcare facilities. The overview, advantages, and limitations of each strategy were discussed in detail. The utilization of mechanical was deemed more suitable for better air quality control, while a vertical (ceiling-mounted) airflow ventilation system was found to promote higher air cleanliness in the desired zone in healthcare facilities. However, many ventilation systems face limitations when attempting to maintain both thermal comfort, indoor air quality, and energy efficiency simultaneously. The findings of this review are useful for the researchers who design appropriate ventilation strategies in healthcare facilities to ensure good indoor air quality meanwhile reduce the risk of disease dissemination.

Night cooling by hybrid supply ventilation – analytical predictions of airflow rates and the ‘hybrid ventilation triangles’

Overheating in buildings can be mitigated during periods of excessively warm weather through the application of a night purge ventilation strategy. Building on the mathematical model of Waterson and Hunt (2024), we investigate the emerging field of hybrid ventilation – specifically the rates of airflow achieved by the simultaneous combination of ‘stack-driven’ natural displacement ventilation and a mechanical supply. Whilst the focus of Waterson and Hunt (2024) was specifically on predicting the time taken to complete a purge, herein we focus on airflow rates and in doing so elucidate the somewhat counter intuitive role that the mechanical supply has on the natural ventilation flow rates. Our results challenge the perception that a hybrid approach must be superior to both solely natural and mechanical strategies. Focusing on the variation in airflow rates during a hybrid purge, our model reveals: (i) a hybrid purge offers an improvement over a solely mechanical purge only during one of the two distinct flow regimes identified; and (ii) the manner in which the stack-driven and mechanical components combine is highly nuanced and cannot be predicted by the linear superposition of the constituent stack-driven and mechanical contributions.

Effectiveness of natural ventilation in controlling the smoke spread within a refuge floor of a high-rise building

Refuge floors in high-rise buildings ensure a haven for occupants to stay in an emergencyprimarily during a fire breakout. Provisions for natural ventilation of the refuge floor are mandatory in all fire codes as they help release smoke and heat build-up. However, the effectiveness of such provisions has been questioned in many studies. This research employs large eddy simulations based three-dimensional computational fluid dynamics modelling on a real-world high-rise building to investigate the efficacy of natural ventilation in a refuge floor during a fire. Consequently, the performance was assessed by evaluating the temporal and spatial distributions of temperature, visibility, smoke and carbon monoxide concentration. Emphasis was placed on determining the adequacy of window placement and openings. Analysis was started with a code-compliant window configuration. Subsequently the window size and the layout were iteratively modified using simulation results. Seasonal wind variations were also considered. Results showed that a well-engineered natural ventilation strategy can considerably improve the refuge floor habitability. Simulations also revealed limitations of natural ventilation under certain wind conditions, necessitating a backup mechanical system. This also underlined that combining fire analysis with cutting-edge modelling allows tailored natural ventilation for refuge floors, maximising safe occupancy during fires.