Search Results (342)

Culverts are widely used to provide crossings over small rivers and can strongly influence flood hydraulics by controlling upstream water levels. During high flows, insufficient conveyance may cause pressurization and overtopping, with important implications for flood hazard assessment. Although computational fluid dynamics (CFD) is increasingly applied to investigate these complex hydraulic processes, systematic evaluations of its performance remain limited. This study addresses this gap by validating a three-dimensional CFD model against previously published laboratory experiments for culvert-only, weir-only and combined culvert–weir configurations under both steady (rising and receding discharge sequences) and unsteady flow conditions. Beyond benchmark validation, diagnostic analyses examined inlet region mesh resolution, inflow ramp history and turbulence closure, together with the associated outlet ventilation and attachment mechanisms. The model reproduced upstream water levels with mean absolute relative error (MARE) values ranging from 0.90% to 5.42% and captured the main stage–discharge relationships across the tested configurations. However, the experimentally observed transition from partially full to pressurized flow in the combined culvert–weir configuration was not reproduced consistently. The diagnostic analyses showed that inlet resolution influences entrance losses and post-submergence headwater, inflow history alters outlet attachment and ventilation and turbulence closure affects barrel filling and air-pocket morphology. The results indicate that CFD can reproduce water level and overtopping responses well when carefully configured, while regime transition prediction remains more uncertain because of its sensitivity to ventilation and discharge history effects. Full article

Background: Severe COPD–OSA overlap syndrome remains challenging to manage, and existing approaches rarely combine guideline-directed OSA therapy with sustained pulmonary rehabilitation, leaving patients vulnerable to recurrent acute exacerbations. Case Presentation: A 71-year-old male with severe overlap syndrome had been hospitalized three times for hypercapnic encephalopathy requiring invasive ventilation. Following admission in 2021, we implemented a four-year, three-stage closed-loop rehabilitation program combined with multimodal OSA management guided by the American Academy of Sleep Medicine (AASM) and 2023 GOLD recommendations. The program included personalized BiPAP titration, quarterly pressure adjustments, positional therapy, and targeted weight control. Management and Outcomes: Over four years of follow-up, this combined approach improved arterial blood gas values and exercise tolerance and markedly improved sleep-disordered breathing parameters, with no readmissions for respiratory failure. Conclusions: Guideline-conformant multimodal OSA therapy combined with staged closed-loop respiratory rehabilitation may offer an effective long-term strategy for severe overlap syndrome. However, as the findings of a single case report are hypothesis-generating, they require validation in larger prospective studies. Full article

Building Information Modeling (BIM)-enabled performance assessment workflows for rural constructions remain relatively unexplored. This is even more important for buildings implementing process-oriented systems, such as airflow networks. This study presents a BIM-integrated framework for the early-stage design and performance assessment of rural constructions, with application to solar barn dryers and their ventilation systems through reduced-order airflow-network modeling. The proposed workflow combines parametric BIM-based geometry generation with lumped-parameter fluid-dynamic modeling to evaluate the influence of airflow-network topology on pressure losses, airflow distribution, fan power demand, and energy consumption. Nine BIM-generated design alternatives and ten geometric parameter sets were investigated under equivalent operating conditions. The airflow system was represented as a pressure-driven network including solar air panels, ducts, collectors, fan chambers, ventilation channels, and drying cells, accounting for both localized and distributed pressure losses. Results show that airflow-network geometry significantly affects system performance. Configurations characterized by more compact and aerodynamically efficient layouts reduced cumulative pressure losses by approximately 10–20% compared with less optimized solutions. More efficient designs enable reductions in required airflow rates of ~22% and in fan power demand of up to ~40% (≈11–18 kW). The most efficient configurations also exhibited lower annual energy consumption while maintaining the minimum overpressure required for effective hay drying. The study demonstrates how BIM environments can support physics-informed comparative evaluation of alternative ventilation layouts during the early design stage, extending BIM applications toward performance-oriented design and digital management of agricultural building systems. The proposed methodology provides a computationally efficient design-support framework that may also apply to other controlled-environment agricultural infrastructures governed by airflow-network dynamics. Full article

Background/Objectives: Mechanical power (MP) quantifies the energy delivered to the respiratory system during ventilation and serves as a promising marker for ventilator-induced lung injury (VILI). According to its original definition by Gattinoni, MP reflects the energy transferred from the ventilator to the respiratory system under conditions of deep sedation, passive breathing, neuromuscular blockade, and volume-controlled ventilation. Its role in coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome (ARDS) remains under investigation. This systematic review aimed to synthesize the available evidence on the association between MP and VILI, complications related to mechanical ventilation (MV), and mortality in adult patients with COVID-19 undergoing invasive mechanical ventilation (IMV). Methods: A systematic review was conducted using PubMed-MEDLINE (Medical Literature Analysis and Retrieval System Online) for studies published in recent years, focusing on adult COVID-19 patients undergoing IMV. Inclusion criteria centered on studies reporting MP and its association with VILI, complications, or mortality. Ten studies met eligibility criteria after screening 356 retrieved articles. Results: Most included studies were retrospective and observational, encompassing critically ill COVID-19 patients. Elevated MP was correlated with more severe outcomes, including increased 28-day mortality, prolonged MV, and weaning failure. Franck et al. demonstrated strong correlations between MP and driving pressure, elastance, and positive end-expiratory pressure, emphasizing the importance of calculation methods. González-Castro et al. identified a threshold of 17 J/min, above which mortality risk increased. Stalla et al. highlighted that dynamic MP reductions during prone positioning were associated with survival. Registry-based analyses confirmed that both magnitude and cumulative exposure above 18 J/min increased intensive care unit mortality. Novel indices combining MP with oxygenation parameters improved prognostic accuracy. While absolute MP at initiation provided limited predictive value, temporal trends and individual components were strongly linked to VILI. Conclusions: Higher MP has been associated with adverse clinical outcomes in patients with COVID-19 receiving invasive mechanical ventilation, supporting its potential role as a prognostic indicator. Its dynamic assessment, thresholds, and integration with ventilatory strategies such as prone positioning enhance risk stratification and may guide individualized, lung-protective ventilation. Continuous monitoring and standardized calculation are recommended to optimize clinical decision-making. Full article

In the mining process of shallow-buried and close-distance coal seam groups in western China, the interconnected collapse fractures between the overlying goaf and the surface form large-area composite goafs, which aggravate surface air leakage and elevate oxygen levels within the goaf. This, in turn, leads to hazardous conditions such as CO over-limits and O₂ deficiency at the working face’s return air corner, which seriously threatens the respiratory health of underground operators and the safe production of mines. Taking the 104 working face of a coal mine in Shenfu-Dongsheng Mining Area as the engineering background, this paper comprehensively adopts SF₆ tracer gas test, fuzzy cluster analysis, and CFD numerical simulation methods to systematically study the distribution characteristics of three-dimensional air leakage channels in composite goafs and their influence mechanism on gas migration in goafs, and proposes a dynamic pressure equalization ventilation (PEV) regulation technology system. The research results show that a multi-dimensional three-dimensional air leakage channel of “surface-interlayer-own layer-roadway” exists in the research area, in which the surface fracture air leakage velocity is about 0.068 m/s, and the interlayer and internal goaf air leakage velocity is about 0.384 m/s. The atmospheric pressure difference between the working face and the surface is the main controlling factor inducing the O₂ deficiency disaster of the working face. Every 100 Pa change in atmospheric pressure difference causes an O₂ concentration fluctuation of about 0.30% at the return air corner, and the critical pressure difference for activating PEV is determined to be 300 Pa. Setting the PEV regulation point at the return air outlet of the working face and adopting the combined dynamic regulation system of fans and air windows can realize accurate pressure balance between the working face and the overlying composite goaf. Full article

Greenhouses in subtropical and tropical regions must be designed as agricultural engineering systems adapted to local climates, rather than simply replicating the “insulation” models of temperate areas. Under extreme climatic conditions such as persistent high temperatures, intense solar radiation, high humidity, heavy rainfall, and frequent extreme winds, greenhouses transform from enclosed insulation layers into selective climate filters, mitigating crop stress while maintaining close contact with the outdoor environment. This paper summarizes how these climate drivers are reshaping the use, structure, and control concepts of greenhouses, emphasizing that the performance of warm-zone greenhouses depends primarily on heat dissipation, humidity management, and biohazard control, rather than heating and insulation. In this review, we analyze the climatic boundary conditions that define warm-climate conservation cultivation, including long-term overheating risk, high UV radiation, vapor pressure deficit, and suppressed condensation tendency, as well as storm-induced uplift and dynamic loads. These constraints necessitate unique structural forms: tall, lightweight, well-ventilated building types with large roof and side openings, roof geometries that facilitate rainwater runoff, sophisticated drainage systems, and corrosion-resistant materials suitable for humid and coastal environments. Because insect netting significantly reduces ventilation, pest control and temperature regulation become co-design issues, requiring oversized vents, optimized airflow paths, and hybrid roof–mesh structures. Ventilation is considered the primary climate-control mechanism, supplemented by passive cooling measures such as shading and radiation/optical management (e.g., diffuse films and near-infrared-selective films). Active evaporative cooling is considered a conditional measure due to humidity limitations and disease risks. This paper also integrates the impacts on specific crops (fruits and vegetables, leafy greens, and orchids). It highlights emerging trends: typhoon-resistant and adaptive geometries, computational fluid dynamics (CFD)-based design, and sensor-rich IoT/digital twin control frameworks. These principles collectively establish a coherent design framework for achieving resilient, resource-efficient greenhouse production in warm climates. Full article

To overcome the limited dust control efficiency and backward dust diffusion tendency in fully mechanized excavation faces, this study pioneeringly proposes a wind-splitting dust control method based on a mechanical iris structure. This method actively splits and precisely allocates the airflow from the forced air duct outlet, achieving a synergistic effect between axial dust suppression and radial dust blocking. Through laboratory experiments and numerical simulations, the influences of the radial split ratio and the installation distance of the wind-splitting device on airflow and dust distribution were investigated. Results indicate that the proposed method significantly outperforms traditional ventilation. Optimal dust-control performance, considering both roadway-average concentration reduction and rear-area protection, was obtained at a radial split ratio of 0.6 and an installation distance of 24 m. Under these conditions, the axial-radial airflow and the exhaust negative pressure form a stable dust-blocking air curtain and a dust-controlling vortex in the front roadway, confining dust primarily within 6.4 m from the heading face. The average breathing zone dust concentration decreased to 22.62 mg/m³, and the roadway average dropped to 31.50 mg/m³, with a dust control efficiency of 77.56% and a significant reduction in rear dust concentrations. This offers effective ventilation optimization. Full article

Transient tachypnea of the newborn (TTN) is a common cause of neonatal respiratory distress, yet the role of aquaporins in its pathophysiology remains unclear. We aimed to evaluate serum aquaporin-1 and aquaporin-5 levels in neonates with TTN and their association with clinical characteristics and respiratory support parameters. This prospective study included 49 neonates (27 controls, 22 with TTN). Serum aquaporin-1 and aquaporin-5 levels were measured on the first day of life (T0) in both groups and repeated on day 3 (T3) in the TTN group using an enzyme-linked immunosorbent assay. Clinical data and respiratory support requirements were recorded. Group comparisons, correlation analyses, and multivariable regression were performed. Baseline aquaporin-1 levels were lower in the TTN group than in controls (p = 0.024) and decreased further at T3 (p = 0.004). Aquaporin-5 levels were similar at T0 and increased non-significantly at T3. Aquaporin-1 decline was greater in infants requiring prolonged oxygen therapy, noninvasive mechanical ventilation, or higher mean airway pressure, and was inversely correlated with ventilation duration and mean airway pressure at day 3. Aquaporin-5 levels were higher in infants requiring shorter respiratory support. Serum aquaporin-1 and aquaporin-5 levels show time-dependent changes during the early postnatal period and may be associated with clinical course and respiratory support requirements in TTN. Full article

Commercial greenhouses are becoming significant, controllable, and weather-dependent electricity loads in regions pursuing controlled environment agriculture (CEA). Their electrical demands—such as supplemental lighting, heating, ventilation/cooling, irrigation pumps, and CO₂ enrichment—exhibit substantial intra-day flexibility. This flexibility stems from the fact that plant productivity depends on time-integrated agronomic variables (e.g., Daily Light Integral, accumulated thermal time, and mean vapor pressure deficit) rather than instantaneous environmental setpoints. However, existing studies have predominantly focused on greenhouse thermal modeling and energy conservation, while decision-making models that integrate crop physiological characteristics into day-ahead (DA) market bidding remain limited. To bridge this gap, this paper develops a scenario-based stochastic DA bidding framework for a load aggregator, representing multiple smart greenhouses in a wholesale electricity market. In the DA stage, the aggregator submits hourly demand–price bidding curves based on price-conditional schedules of heating and lighting demand while satisfying coupled thermal–photon balance constraints. Fifty representative scenarios generated from 2023 to 2024 historical price and weather data through cGAN-based scenario generation and K-means scenario reduction are used for stochastic bid construction and feasibility analysis. A separate 30-day historical dataset from January 2025 is used for benchmark comparison. The aggregator portfolio consists of 100 greenhouses divided into five LAI-based crop groups, with 20 greenhouses in each group. Relative to the 15–25 °C trapezoidal temperature baseline, which is adopted as the primary practical benchmark, the proposed strategy reduces the mean daily electricity procurement cost by 15.80%. A reduction of 18.89% is also observed relative to the rigid 20 °C thermostat case, which is retained as a capacity-intensive reference. These results represent simulation-based operating-cost comparisons under a common equipment configuration and do not include equipment capital costs. Full article

Early detection of acute lung injury (ALI) remains challenging, as conventional diagnostics rarely capture initial molecular changes. We therefore examined whether extracellular vesicles (EVs) in bronchoalveolar lavage fluid (BALF) can detect early regional injury and distinguish initial stress mechanisms in a porcine ALI model. Unilateral ALI was induced using Triton X-100, followed by six hours of mechanical ventilation with either fixed positive end-expiratory pressure (PEEP) at 5 cmH₂O or transpulmonary-pressure (TPP)-guided PEEP. Spatially separated BALF sampling allowed direct comparison between injured and contralateral mechanically stressed lungs. EV concentration and size distribution were quantified by nano-flow cytometry, while vesicular identity was confirmed by transmission electron microscopy and tetraspanin dot blot analyses. Furthermore, EV metrics were related to corresponding histologic injury scores. Across both PEEP strategies, EV concentration was markedly higher in both directly injured and contralateral mechanically stressed lungs compared with sham controls, indicating alveolar stress beyond the primary injury site. Median EV size differed significantly by injury type and correlated inversely with histologic injury, particularly with alveolar neutrophil infiltration. BALF-derived EV concentration and size may therefore provide complementary, spatially resolved molecular readouts of early ALI. Full article

Pressure losses in heating, ventilation, and air-conditioning (HVAC) duct elbows significantly increase fan power requirements and reduce overall system efficiency. This study presents a comprehensive computational fluid dynamics (CFD) investigation aimed at identifying effective strategies for reducing pressure losses in 90° HVAC duct elbows. The numerical methodology was first validated against published experimental measurements, demonstrating excellent agreement and providing confidence in the predictive capability of the CFD model. The validated model was then employed to evaluate the influence of duct geometry, inlet velocity, guide vane configuration, inter-vane spacing, perforated guide vanes, and duct material roughness on aerodynamic performance using the SST k–ω turbulence model. The results show that round elbows reduce pressure losses by approximately 50% compared with hydraulically equivalent rectangular elbows, highlighting the strong influence of duct geometry on flow separation. Among the flow-control strategies investigated, curved guide vanes produced the greatest improvement, with an optimized three-vane arrangement and a non-dimensional spacing of $\mathrm{s}/{\mathrm{D}}_{\mathrm{h}}\approx 0.15$ (corresponding to 150 mm for the specific geometry tested) reducing pressure losses by approximately 31% relative to the baseline elbow without guide vanes. In contrast, the investigated perforated guide vane provided only marginal improvement, indicating that its geometry requires further optimization to minimize blockage and mixing losses. The material roughness study showed that smooth, rigid duct materials produced only minor differences in pressure loss, whereas flexible ducts generated noticeably higher losses because of their increased surface roughness. These findings demonstrate that optimizing elbow geometry and guide vane design is considerably more effective than modifying duct material or using the investigated perforated vane configuration. The study provides practical design recommendations for improving the aerodynamic performance and energy efficiency of HVAC duct systems. Full article

Background/Objectives: Retained airway secretions are a common complication of mechanical ventilation and a major contributor to ventilator-associated pneumonia. Airway Pressure Release Ventilation following a Time-Controlled Adaptive Ventilation protocol (APRV-TCAV) has been anecdotally observed to improve secretion clearance, but the mechanism is not well established. Because TCAV sets the release time (TLow) from each patient’s own expiratory flow decay, we hypothesized that the resulting expiratory-dominant flow profile would generate a net antegrade force on secretions. This bench study compared secretion movement between APRV-TCAV and conventional Volume-Control Continuous Mandatory Ventilation (VC-CMV), with and without an in-line oscillatory device. Methods: A critical care ventilator was connected to a 3 L test lung via a 7 mm endotracheal tube (ETT). Simulated mucus (1% guar gum) was instilled into the ETT, and secretion movement was measured under VC-CMV (positive end-expiratory pressure (PEEP) 5, 10, 15 cmH₂O) and APRV-TCAV (PHigh 20, 25, 30 cmH₂O; PLow 0 cmH₂O). Each condition was repeated with an in-line oscillatory device. Results: All VC-CMV settings produced retrograde secretion movement toward the test lung; all APRV-TCAV settings produced antegrade movement. The largest antegrade movement was observed at the widest PHigh-to-PLow differential. Adding the oscillatory device raised peak expiratory flow above peak inspiratory flow in every condition, yet abolished antegrade movement under APRV-TCAV. Conclusions: In this bench study, APRV-TCAV reversed the direction of secretion movement within the ETT, with larger antegrade movement at wider PHigh-to-PLow differentials. This suggests a potential mechanism by which the ventilator flow profile itself may influence secretion movement. The directional effect depended on the intact release-phase waveform and was abolished by in-line oscillatory therapy despite preserved peak flow asymmetry. Full article

Introduction: Permissive hypercapnia has become an integral component of lung-protective ventilation strategies during one-lung ventilation (OLV), particularly in thoracic surgery. Its potential immunomodulatory effects have attracted increasing interest; however, clinical evidence remains limited and inconsistent. The Aim: The primary objective was to evaluate the effects of permissive hypercapnia on inflammatory biomarkers in bronchoalveolar lavage fluid and serum during one-lung ventilation. The secondary objective was to assess the influence of different ventilation modes on these inflammatory responses. Methods: Forty patients undergoing elective lung surgery requiring OLV were prospectively enrolled and allocated to either a normocapnic (n = 20) or hypercapnic group (n = 20). BAL concentrations of TNF-α, IL-1β, IL-6, and IL-8 were measured before and after intervention. Serum IL-6, C-reactive protein (CRP), and leukocyte counts were also assessed. Outcome Measures: Primary outcome: Change in bronchoalveolar lavage (BAL) levels of preselected biomarkers for inflammation (TNF-α, IL-1β, IL-6, and IL-8) and in serum (IL-6, CRP, and WBC) between the normocapnic and hypercapnic groups during one-lung ventilation. Secondary outcome: Whether the inflammatory response differed according to the ventilation mode (pressure-controlled versus volume-controlled ventilation). Results: Baseline and post-intervention BAL concentrations of TNF-α, IL-1β, IL-6, and IL-8 were generally comparable between the hypercapnic and normocapnic groups. No significant differences were observed in post-intervention BAL concentrations of TNF-α, IL-1β, or IL-6 among the ventilated subgroups. However, post hoc analysis demonstrated significantly lower IL-8 concentrations in the hypercapnic-PC subgroup compared with the normocapnic-PC subgroup (p = 0.034). Within the normocapnic cohort, BAL IL-8 concentrations were significantly higher in the PC subgroup than in the VC subgroup (p = 0.012). In serum, postoperative IL-6 concentrations were significantly higher in the hypercapnic than in the normocapnic group (p = 0.003). Conclusions: Permissive hypercapnia was not associated with a reduction in BAL concentration of the pro-inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-8. However, postoperative serum IL-6 concentrations were significantly higher in patients exposed to hypercapnia. As the duration of surgery, one-lung ventilation, and mechanical ventilation was longer in the hypercapnic group, the observed increase in serum IL-6 cannot be attributed solely to hypercapnia. Further large-scale randomized studies are required to clarify the immunological effects of permissive hypercapnia during thoracic surgery. Full article

Background/Objectives: Positive end-expiratory pressure (PEEP) increases end-expiratory lung volume through the addition of PEEP-induced lung volume (PEEPVol), potentially affecting respiratory mechanics and energy load. However, its physiological impact in patients without lung injury remains poorly characterized. We hypothesized that PEEPVol would be closely associated with respiratory system loading beyond conventional respiratory mechanics variables. Methods: We conducted a secondary analysis of a prospective physiological study including 16 deeply sedated, mechanically ventilated adults without lung disease. A standardized incremental PEEP titration (0–16 cmH₂O, steps of 4 cmH₂O) was performed under volume-controlled ventilation. At each step, respiratory mechanics were assessed, including static compliance (Cstat), driving pressure, plateau pressure, and mechanical power. PEEPVol was estimated as PEEP × Cstat, and strain indices were derived relative to predicted functional residual capacity. Linear mixed-effects models evaluated changes across PEEP levels, and associations were initially explored using Spearman correlation and linear regression. To account for repeated measurements within subjects, confirmatory linear mixed-effects regression models were subsequently performed using patients as a random intercept. Results: Incremental PEEP significantly increased PEEPVol, plateau pressure, mechanical power, and both static and global strain (all p < 0.001), while changes in compliance and driving pressure were minimal and not clinically meaningful. PEEPVol showed moderate-to-strong correlations with plateau pressure (ρ = 0.68) and mechanical power (ρ = 0.76) and explained 43% and 56% of their variance, respectively (all p < 0.001);these associations remained significant in additional linear mixed-effects regression analyses accounting for within-subject correlation. PEEPVol also correlated strongly with static strain (ρ = 0.93) and global strain (ρ = 0.83); however, because static strain is calculated as PEEPVol/FRCt, this association is mathematically expected rather than an independent physiological finding and is reported here only for completeness. Notably, 11.1% of measurements exceeded Pplat > 30 cmH₂O and 61.9% exceeded MP ≥ 17 J/min, even at moderate PEEP levels. Conclusions: In patients without lung injury, PEEP-induced increases in lung volume are strongly associated with higher mechanical load and strain, despite minimal changes in compliance or driving pressure. PEEPVol may represent a promising physiological surrogate of static lung deformation and energy transfer, whose potential to improve bedside detection of occult overdistension warrants validation against direct imaging or physiological measurements in larger prospective studies. Full article

Cervical spinal cord injury directly impacts the phrenic motor neuron pool, resulting in impaired ventilation and diaphragm muscle dysfunction. Previously, we demonstrated that hyperbaric oxygen (HBO) therapy, delivered during the acute phase following SCI, can attenuate diaphragm dysfunction. However, despite the demonstrated efficacy of HBO to improve muscle function, the molecular signaling pathways regulating this effect remain unclear. These experiments test the hypothesis that the protective effects of HBO therapy are associated with upregulation of the endogenous antioxidants SOD1, SOD2 and GPX1. Adult male Sprague-Dawley rats underwent a lateral spinal contusion injury at C4 followed by 10 consecutive days of HBO (3 ATA, 100% O₂, 1 h/day). Room air-treated spinal intact and injured rats were placed in a non-pressurized chamber for equal durations. To prevent the HBO-induced increase in antioxidant expression, antisense oligonucleotides directed towards each gene of interest were administered by intraperitoneal injection daily immediately following completion of HBO exposure (10 mg/kg/day). Saline was used as both the vehicle and placebo. Our results reveal that prevention of the HBO-induced upregulation of SOD1, SOD2 and GPX1 reduces diaphragm-specific force production compared to the control, injured HBO-treated rats. This effect occurred concomitantly with increased gene expression of the inflammatory cytokines IL-6, IL-1β and TNF-α and altered redox balance in the diaphragm. Thus, these data provide evidence that the HBO-induced increase in SOD1, SOD2 and GPX1 antioxidant expression contributes, at least in part, to the therapeutic effect of HBO to preserve diaphragm function following cervical spinal cord injury. Full article