Acute lung injury: how to stabilize a broken lung

ANGPTL2 knockdown induces autophagy to relieve alveolar macrophage pyroptosis by reducing LILRB2-mediated inhibition of TREM2

Acute lung injury (ALI) is featured with a robust inflammatory response. Angiopoietin-like protein 2 (ANGPTL2), a pro-inflammatory protein, is complicated with various disorders. However, the role of ANGPTL2 in ALI remains to be further explored. The mice and MH-S cells were administrated with lipopolysaccharide (LPS) to evoke the lung injury in vivo and in vitro. The role and mechanism of ANGPTL was investigated by haematoxylin-eosin, measurement of wet/dry ratio, cell count, terminal deoxynucleotidyl transferase deoxyuridine triphosphate (dUTP) nick end labeling, reverse transcription quantitative polymerase chain reaction, immunofluorescence, enzyme-linked immunosorbent assay, detection of autophagic flux and western blot assays. The level of ANGPTL2 was upregulated in lung injury. Knockout of ANGPTL2 alleviated LPS-induced pathological symptoms, reduced pulmonary wet/dry weight ratio, the numbers of total cells and neutrophils in BALF, apoptosis rate and the release of pro-inflammatory mediators, and modulated polarization of alveolar macrophages in mice. Knockdown of ANGPTL2 downregulated the level of pyroptosis indicators, and elevated the level of autophagy in LPS-induced MH-S cells. Besides, downregulation of ANGPTL2 reversed the LPS-induced the expression of leukocyte immunoglobulin (Ig)-like receptor B2 (LILRB2) and triggering receptor expressed on myeloid cells 2 (TREM2), which was reversed by the overexpression of LILRB2. Importantly, knockdown of TREM2 reversed the levels of autophagy- and pyroptosis-involved proteins, and the contents of pro-inflammatory factors in LPS-induced MH-S cells transfected with si ANGPTL2, which was further inverted with the treatment of rapamycin. Therefore, ANGPTL2 silencing enhanced autophagy to alleviate alveolar macrophage pyroptosis via reducing LILRB2-mediated inhibition of TREM2.

The role of fatty acid metabolism in acute lung injury: a special focus on immunometabolism

Reputable evidence from multiple studies suggests that excessive and uncontrolled inflammation plays an indispensable role in mediating, amplifying, and protracting acute lung injury (ALI). Traditionally, immunity and energy metabolism are regarded as separate functions regulated by distinct mechanisms, but recently, more and more evidence show that immunity and energy metabolism exhibit a strong interaction which has given rise to an emerging field of immunometabolism. Mammalian lungs are organs with active fatty acid metabolism, however, during ALI, inflammation and oxidative stress lead to a series metabolic reprogramming such as impaired fatty acid oxidation, increased expression of proteins involved in fatty acid uptake and transport, enhanced synthesis of fatty acids, and accumulation of lipid droplets. In addition, obesity represents a significant risk factor for ALI/ARDS. Thus, we have further elucidated the mechanisms of obesity exacerbating ALI from the perspective of fatty acid metabolism. To sum up, this paper presents a systematical review of the relationship between extensive fatty acid metabolic pathways and acute lung injury and summarizes recent advances in understanding the involvement of fatty acid metabolism-related pathways in ALI. We hold an optimistic believe that targeting fatty acid metabolism pathway is a promising lung protection strategy, but the specific regulatory mechanisms are way too complex, necessitating further extensive and in-depth investigations in future studies.

Airway pressure release ventilation for lung protection in acute respiratory distress syndrome: an alternative way to recruit the lungs

PURPOSE OF REVIEW

Airway pressure release ventilation (APRV) is a modality of ventilation in which high inspiratory continuous positive airway pressure (CPAP) alternates with brief releases. In this review, we will discuss the rationale for APRV as a lung protective strategy and then provide a practical introduction to initiating APRV using the time-controlled adaptive ventilation (TCAV) method.

RECENT FINDINGS

APRV using the TCAV method uses an extended inspiratory time and brief expiratory release to first stabilize and then gradually recruit collapsed lung (over hours/days), by progressively 'ratcheting' open a small volume of collapsed tissue with each breath. The brief expiratory release acts as a 'brake' preventing newly recruited units from re-collapsing, reversing the main drivers of ventilator-induced lung injury (VILI). The precise timing of each release is based on analysis of expiratory flow and is set to achieve termination of expiratory flow at 75% of the peak expiratory flow. Optimization of the release time reflects the changes in elastance and, therefore, is personalized (i.e. conforms to individual patient pathophysiology), and adaptive (i.e. responds to changes in elastance over time).

SUMMARY

APRV using the TCAV method is a paradigm shift in protective lung ventilation, which primarily aims to stabilize the lung and gradually reopen collapsed tissue to achieve lung homogeneity eliminating the main mechanistic drivers of VILI.

CPT1A as a potential therapeutic target for lipopolysaccharide-induced acute lung injury in mice

Acute lung injury (ALI) remains a high mortality rate with dramatic lung inflammation and alveolar epithelial cell death. Although fatty acid β-oxidation (FAO) impairment has been implicated in the pathogenesis of ALI, whether Carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme for FAO, plays roles in lipopolysaccharide (LPS)-induced ALI remains unclear. Accordingly, we focused on exploring the effect of CPT1A in the context of ALI and the underlying mechanisms. We found that overexpression of CPT1A (AAV-CPT1A) effectively alleviated lung injury by reduction of lung wet-to-dry ratio, inflammatory cell infiltration, and protein levels in the BALF of ALI mice. Meanwhile, AAV-CPT1A significantly lessened histopathological changes and several cytokines' secretions. In contrast, blocking CPT1A with etomoxir augmented inflammatory responses and lung injury in ALI mice. Furthermore, we found that overexpression of CPT1A with lentivirus reduced the apoptosis rates of alveolar epithelial cells and the expression of apoptosis-related proteins induced by LPS in MLE12 cells, while etomoxir increased the apoptosis of MLE12 cells. Overexpression of CPT1A prevented the drop in bioenergetics, palmitate oxidation, and ATP levels. In conclusion, the results rendered CPT1A worthy of further development into a pharmaceutical drug for the treatment of ALI.

Time-Controlled Adaptive Ventilation (TCAV): a personalized strategy for lung protection

Acute respiratory distress syndrome (ARDS) alters the dynamics of lung inflation during mechanical ventilation. Repetitive alveolar collapse and expansion (RACE) predisposes the lung to ventilator-induced lung injury (VILI). Two broad approaches are currently used to minimize VILI: (1) low tidal volume (LVT) with low-moderate positive end-expiratory pressure (PEEP); and (2) open lung approach (OLA). The LVT approach attempts to protect already open lung tissue from overdistension, while simultaneously resting collapsed tissue by excluding it from the cycle of mechanical ventilation. By contrast, the OLA attempts to reinflate potentially recruitable lung, usually over a period of seconds to minutes using higher PEEP used to prevent progressive loss of end-expiratory lung volume (EELV) and RACE. However, even with these protective strategies, clinical studies have shown that ARDS-related mortality remains unacceptably high with a scarcity of effective interventions over the last two decades. One of the main limitations these varied interventions demonstrate to benefit is the observed clinical and pathologic heterogeneity in ARDS. We have developed an alternative ventilation strategy known as the Time Controlled Adaptive Ventilation (TCAV) method of applying the Airway Pressure Release Ventilation (APRV) mode, which takes advantage of the heterogeneous time- and pressure-dependent collapse and reopening of lung units. The TCAV method is a closed-loop system where the expiratory duration personalizes VT and EELV. Personalization of TCAV is informed and tuned with changes in respiratory system compliance (CRS) measured by the slope of the expiratory flow curve during passive exhalation. Two potentially beneficial features of TCAV are: (i) the expiratory duration is personalized to a given patient's lung physiology, which promotes alveolar stabilization by halting the progressive collapse of alveoli, thereby minimizing the time for the reopened lung to collapse again in the next expiration, and (ii) an extended inspiratory phase at a fixed inflation pressure after alveolar stabilization gradually reopens a small amount of tissue with each breath. Subsequently, densely collapsed regions are slowly ratcheted open over a period of hours, or even days. Thus, TCAV has the potential to minimize VILI, reducing ARDS-related morbidity and mortality.

Full-lung simulations of mechanically ventilated lungs incorporating recruitment/derecruitment dynamics

This study developed and investigated a comprehensive multiscale computational model of a mechanically ventilated ARDS lung to elucidate the underlying mechanisms contributing to the development or prevention of VILI. This model is built upon a healthy lung model that incorporates realistic airway and alveolar geometry, tissue distensibility, and surfactant dynamics. Key features of the ARDS model include recruitment and derecruitment (RD) dynamics, alveolar tissue viscoelasticity, and surfactant deficiency. This model successfully reproduces realistic pressure-volume (PV) behavior, dynamic surface tension, and time-dependent descriptions of RD events as a function of the ventilation scenario. Simulations of Time-Controlled Adaptive Ventilation (TCAV) modes, with short and long durations of exhalation (T Low - and T Low +, respectively), reveal a higher incidence of RD for T Low + despite reduced surface tensions due to interfacial compression. This finding aligns with experimental evidence emphasizing the critical role of timing in protective ventilation strategies. Quantitative analysis of energy dissipation indicates that while alveolar recruitment contributes only a small fraction of total energy dissipation, its spatial concentration and brief duration may significantly contribute to VILI progression due to its focal nature and higher intensity. Leveraging the computational framework, the model may be extended to facilitate the development of personalized protective ventilation strategies to enhance patient outcomes. As such, this computational modeling approach offers valuable insights into the complex dynamics of VILI that may guide the optimization of ventilation strategies in ARDS management.

Protective effect of liriodendrin on IgG immune complex-induced acute lung injury via inhibiting SRC/STAT3/MAPK signaling pathway: a network pharmacology research

The primary objectives of this research were to investigate the protective effects of liriodendrin against IgG immune complex (IgG-IC)-induced acute lung injury (ALI) and to elucidate the underlying mechanisms. This study employed a mouse and cell model of IgG-IC-induced acute lung injury. Lung tissue was stained with hematoxylin-eosin to observe pathological alterations and arterial blood gas analysis was tested. Inflammatory cytokines, including interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α), were measured using ELISA. The mRNA expression of inflammatory cytokines was assessed via RT-qPCR. Molecular docking and enrichment analysis were combined to identify the most potential signaling pathways modulated by liriodendrin, which were then verified using western blot analysis in IgG-IC-induced ALI models. We identified 253 shared targets between liriodendrin and IgG-IC-induced acute lung injury from the database. Through network pharmacology, enrichment analysis, and molecular docking, SRC was determined to be the most closely associated target of liriodendrin in IgG-IC-induced ALI. Pretreatment with liriodendrin notably reduced the increased cytokine secretion of IL-1β, IL-6, and TNF-α. Histopathological analysis of lung tissue demonstrated a protective effect of liriodendrin on IgG-IC-induced acute lung injury in mice. Arterial blood gas analysis showed liriodendrin ameliorated acidosis and hypoxemia efficiently. Further studies revealed that liriodendrin pretreatment substantially attenuated the elevated phosphorylation levels of SRC's downstream components (JNK, P38, and STAT3), suggesting that liriodendrin may protect against IgG-IC-induced ALI via the SRC/STAT3/MAPK pathway. Our findings indicate that liriodendrin protects against IgG-IC-induced acute lung injury by inhibiting the SRC/STAT3/MAPK signaling pathway, suggesting that liriodendrin may serve as a potential treatment for acute lung injury caused by IgG-IC.

American Association for the Surgery of Trauma/American College of Surgeons Committee on Trauma clinical protocol for management of acute respiratory distress syndrome and severe hypoxemia

LEVEL OF EVIDENCE

Therapeutic/Care Management: Level V.

First Stabilize and then Gradually Recruit: A Paradigm Shift in Protective Mechanical Ventilation for Acute Lung Injury

Acute respiratory distress syndrome (ARDS) is associated with a heterogeneous pattern of injury throughout the lung parenchyma that alters regional alveolar opening and collapse time constants. Such heterogeneity leads to atelectasis and repetitive alveolar collapse and expansion (RACE). The net effect is a progressive loss of lung volume with secondary ventilator-induced lung injury (VILI). Previous concepts of ARDS pathophysiology envisioned a two-compartment system: a small amount of normally aerated lung tissue in the non-dependent regions (termed "baby lung"); and a collapsed and edematous tissue in dependent regions. Based on such compartmentalization, two protective ventilation strategies have been developed: (1) a "protective lung approach" (PLA), designed to reduce overdistension in the remaining aerated compartment using a low tidal volume; and (2) an "open lung approach" (OLA), which first attempts to open the collapsed lung tissue over a short time frame (seconds or minutes) with an initial recruitment maneuver, and then stabilize newly recruited tissue using titrated positive end-expiratory pressure (PEEP). A more recent understanding of ARDS pathophysiology identifies regional alveolar instability and collapse (i.e., hidden micro-atelectasis) in both lung compartments as a primary VILI mechanism. Based on this understanding, we propose an alternative strategy to ventilating the injured lung, which we term a "stabilize lung approach" (SLA). The SLA is designed to immediately stabilize the lung and reduce RACE while gradually reopening collapsed tissue over hours or days. At the core of SLA is time-controlled adaptive ventilation (TCAV), a method to adjust the parameters of the airway pressure release ventilation (APRV) modality. Since the acutely injured lung at any given airway pressure requires more time for alveolar recruitment and less time for alveolar collapse, SLA adjusts inspiratory and expiratory durations and inflation pressure levels. The TCAV method SLA reverses the open first and stabilize second OLA method by: (i) immediately stabilizing lung tissue using a very brief exhalation time (≤0.5 s), so that alveoli simply do not have sufficient time to collapse. The exhalation duration is personalized and adaptive to individual respiratory mechanical properties (i.e., elastic recoil); and (ii) gradually recruiting collapsed lung tissue using an inflate and brake ratchet combined with an extended inspiratory duration (4-6 s) method. Translational animal studies, clinical statistical analysis, and case reports support the use of TCAV as an efficacious lung protective strategy.

Developing an explainable machine learning model to predict the mechanical ventilation duration of patients with ARDS in intensive care units

BACKGROUND

Acute respiratory distress syndrome (ARDS) is common in intensive care units with high mortality rate and mechanical ventilation (MV) is the most important related treatment. Early prediction of MV duration has benefit for patients risk stratification and care strategies support.

OBJECTIVE

To develop an explainable model for predicting mechanical ventilation (MV) duration in patients with ARDS using the machine learning (ML) approach.

METHOD

The number of 1,148, 1,697, and 29 ARDS patients admitted to intensive care units (ICU) in the MIMIC-IV, eICU-CRD, and AmsterdamUMCdb databases were included in the study. Features at MV initiation from the MIMIC-IV dataset were used to train prediction models based on seven supervised machine learning algorithms. After 5-fold cross-validation for hyperparameters tuning, the hyperparameters- optimized model of different algorithms was tested by external datasets extracted from eICU-CRD and Amsterdamumcdb. Finally, three descriptive machine learning explanation methods were conducted for the model explanation.

RESULT

The XGBoosting model showed the most stable and accurate performance among two testing datasets (RMSE= 5.57 and 5.46 days in eICU-CRD and AmsterdamUMCdb) and was selected as the optimal model. The model explanation based on SHAP, LIME, and DALEX results showed a consistent result, vasopressor, PH, and SOFA score had the highest effect on MV duration prediction.

CONCLUSION

ML models with features at MV initiation can accurate predict MV duration in patients with ARDS in ICUs. Among seven algorithms, XGB models showed the best performance (RMSE= 5.57 and 5.46 in two external datasets). LIME, SHAP, and Breakdown methods showed good performance as AXI methods.

Airway Pressure Release Ventilation for Acute Respiratory Failure Due to Coronavirus Disease 2019: A Systematic Review and Meta-Analysis

Objective: To explore the evidence surrounding the use of Airway Pressure Release Ventilation (APRV) in patients with coronavirus disease 2019 (COVID-19). Methods: A Systematic electronic search of PUBMED, EMBASE, and the WHO COVID-19 database. We also searched the grey literature via Google and preprint servers (medRxive and research square). Eligible studies included randomised controlled trials and observational studies comparing APRV to conventional mechanical ventilation (CMV) in adults with acute hypoxemic respiratory failure due to COVID-19 and reporting at least one of the following outcomes; in-hospital mortality, ventilator free days (VFDs), ICU length of stay (LOS), changes in gas exchange parameters, and barotrauma. Two authors independently screened and selected articles for inclusion and extracted data in a pre-specified form. Results: Of 181 articles screened, seven studies (one randomised controlled trial, two cohort studies, and four before-after studies) were included comprising 354 patients. APRV was initiated at a mean of 1.2-13 days after intubation. APRV wasn't associated with improved mortality compared to CMV (relative risk [RR], 1.20; 95% CI 0.70-2.05; I², 61%) neither better VFDs (ratio of means [RoM], 0.80; 95% CI, 0.52-1.24; I², 0%) nor ICU LOS (RoM, 1.10; 95% CI, 0.79-1.51; I², 57%). Compared to CMV, APRV was associated with a 33% increase in PaO₂/FiO₂ ratio (RoM, 1.33; 95% CI, 1.21-1.48; I², 29%) and a 9% decrease in PaCO₂ (RoM, 1.09; 95% CI, 1.02-1.15; I², 0%). There was no significant increased risk of barotrauma compared to CMV (RR, 1.55; 95% CI, 0.60-4.00; I², 0%). Conclusions: In adult patients with COVID-19 requiring mechanical ventilation, APRV is associated with improved gas exchange but not mortality nor VFDs when compared with CMV. The results were limited by high uncertainty given the low quality of the available studies and limited number of patients. Adequately powered and well-designed clinical trials to define the role of APRV in COVID-19 patients are still needed. Registration: PROSPERO; CRD42021291234.

The role of NLRP3 inflammasome in sepsis: A potential therapeutic target

Sepsis is the host immune imbalance following infection and leads to organ dysfunction, with highly complicated pathophysiology. To date, sepsis still lacks effective therapies with high mortality rates. Recently, numerous studies have highlighted the potential of NLRP3 inflammasome as a therapeutic target during sepsis. NLRP3 inflammasome is a protein complex that could induce the activation of caspase-1 and the following release of pro-inflammatory cytokines such as IL-1β and IL-18. It was demonstrated that NLRP3 inflammasome was involved in the development and progression of sepsis. In contrast, inhibition of NLRP3 inflammasome activation could mitigate the inflammatory response, protect organ function, and improve outcomes and mortality. This paper illustrated the activation pathways of the NLRP3 inflammasome and its possible molecular mechanisms in the pathophysiology of sepsis. Meanwhile, the beneficial effects of inhibiting NLRP3 activation in sepsis-related organ damage were also presented. In addition, the diverse role of NLRP3 inflammasome in bacterial clearance was addressed. Of note, several herbal extracts targeting NLRP3 inflammasome in the treatment of sepsis were emphasized. We hope that this paper could provide a basis for further drug research targeting NLRP3 inflammasome.

Heme oxygenase-1 ameliorates endotoxin-induced acute lung injury by modulating macrophage polarization via inhibiting TXNIP/NLRP3 inflammasome activation

Acute lung injury (ALI) remains a global public health issue without specific and effective treatment options available in the clinic. Alveolar macrophage polarization is involved in the initiation, development and progression of ALI; however, the underlying mechanism remains poorly understood. Heme oxygenase-1 (HO-1) acts as an antioxidant in pulmonary inflammation and has been demonstrated to be linked with the severity and prognosis of ALI. In this study, the therapeutic effects of HO-1 were examined, along with the mechanisms involved, mainly focusing on alveolar macrophage polarization. HO-1 depletion induced higher iNOS and CD86 (M1 phenotype) expression but was significantly decreased in Arg-1 and CD206 (M2 phenotype) expression in BALF alveolar macrophages after equivalent LPS stimulation. We also found that HO-1 deletion distinctly accelerated the expression of inflammasome-associated components NLRP3, ASC and caspase-1 in vivo and in vivo and in vitro. Moreover, on the basis of LPS for MH-S cells, levels of TXNIP, NLRP3, ASC and caspase-1 were increased and HO-1 depletion exacerbated these changes, whereas double depletion of HO-1 and TXNIP partially mitigated these elevations. Also, HO-1 knockdown induced more M1 phenotype and less M2 phenotype compared with LPS alone, whereas double silence of HO-1 and TXNIP partially changed the polarization state. Taken together, we demonstrated that HO-1 could modulate macrophage polarization via TXNIP/NLRP3 signaling pathway, which could be a potential therapeutic target for ALI treatment.

Mechanisms of pulmonary disease in F344 rats after workplace-relevant inhalation exposure to cross-linked water-soluble acrylic acid polymers

BACKGROUND

Recently in Japan, six workers at a chemical plant that manufactures resins developed interstitial lung diseases after being involved in loading and packing cross-linked water-soluble acrylic acid polymers (CWAAPs). The present study focused on assessing lung damage in rats caused by workplace-relevant inhalation exposure to CWAAP and investigated the molecular and cellular mechanisms involved in lung lesion development.

METHODS

Using a whole-body inhalation exposure system, male F344 rats were exposed once to 40 or 100 mg/m³ of CWAAP-A for 4 h or to 15 or 40 mg/m³ of CWAAP-A for 4 h per day once per week for 2 months (9 exposures). In a separate set of experiments, male F344 rats were administered 1 mg/kg CWAAP-A or CWAAP-B by intratracheal instillation once every 2 weeks for 2 months (5 doses). Lung tissues, mediastinal lymph nodes, and bronchoalveolar lavage fluid were collected and subjected to biological and histopathological analyses.

RESULTS

A single 4-h exposure to CWAAP-A caused alveolar injury, and repeated exposures resulted in regenerative changes in the alveolar epithelium with activation of TGFβ signaling. During the recovery period after the last exposure, some alveolar lesions were partially healed, but other lesions developed into alveolitis with fibrous thickening of the alveolar septum. Rats administered CWAAP-A by intratracheal instillation developed qualitatively similar pulmonary pathology as rats exposed to CWAAP-A by inhalation. At 2 weeks after intratracheal instillation, rats administered CWAAP-B appeared to have a slightly higher degree of lung lesions compared to rats administered CWAAP-A, however, there was no difference in pulmonary lesions in the CWAAP-A and CWAAP-B exposed rats examined 18 weeks after administration of these materials.

CONCLUSIONS

The present study reports our findings on the cellular and molecular mechanisms of pulmonary disease in rats after workplace-relevant inhalation exposure to CWAAP-A. This study also demonstrates that the lung pathogenesis of rats exposed to CWAAP-A by systemic inhalation was qualitatively similar to that of rats administered CWAAP-A by intratracheal instillation.

Therapeutic effects and mechanism of Atractylodis rhizoma in acute lung injury: Investigation based on an Integrated approach

Acute lung injury (ALI) is characterized by an excessive inflammatory response. Atractylodes lancea (Thunb.) DC. is a traditional chinese medicine with good anti-inflammatory activity that is commonly used clinically for the treatment of lung diseases in China; however, its mechanism of against ALI is unclear. We clarified the therapeutic effects of ethanol extract of Atractylodis rhizoma (EEAR) on lipopolysaccharide (LPS)-induced ALI by evaluation of hematoxylin-eosin (HE) stained sections, the lung wet/dry (W/D) ratio, and levels of inflammatory factors as indicators. We then characterized the chemical composition of EEAR by ultra-performance liquid chromatography and mass spectrometry (UPLC-MS) and screened the components and targets by network pharmacology to clarify the signaling pathways involved in the therapeutic effects of EEAR on ALI, and the results were validated by molecular docking simulation and Western blot (WB) analysis. Finally, we examined the metabolites in rat lung tissues by gas chromatography and mass spectrometry (GC-MS). The results showed that EEAR significantly reduced the W/D ratio, and tumor necrosis factor-α (TNF-α), interleukin-1 beta (IL-1β), interleukin-6 (IL-6) levels in the lungs of ALI model rats. Nineteen components of EEAR were identified and shown to act synergetically by regulating shared pathways such as the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT) signaling pathways. Ferulic acid, 4-methylumbelliferone, acetylatractylodinol, atractylenolide I, and atractylenolide III were predicted to bind well to PI3K, AKT and MAPK1, respectively, with binding energies < -5 kcal/mol, although only atractylenolide II bound with high affinity to MAPK1. EEAR significantly inhibited the phosphorylation of PI3K, AKT, p38, and ERK1/2, thus reducing protein expression. EEAR significantly modulated the expression of metabolites such as D-Galactose, D-Glucose, serine and D-Mannose. These metabolites were mainly concentrated in the galactose and amino acid metabolism pathways. In conclusion, EEAR alleviates ALI by inhibiting activation of the PI3K-AKT and MAPK signaling pathways and regulating galactose metabolism, providing a new direction for the development of drugs to treat ALI.

Protective Effects of Atractylodis lancea Rhizoma on Lipopolysaccharide-Induced Acute Lung Injury via TLR4/NF-κB and Keap1/Nrf2 Signaling Pathways In Vitro and In Vivo

Acute lung injury (ALI) is a syndrome caused by an excessive inflammatory response characterized by intractable hypoxemia both inside and outside the lung, for which effective therapeutic drugs are lacking. Atractylodis rhizoma, a traditional Chinese medicine, has excellent anti-inflammatory and antiviral properties in addition to protecting the integrity of the cellular barrier. However, few studies of Atractylodis rhizoma for the treatment of ALI have been published, and its mechanism of action remains unclear. In the present study, the chemical composition of the ethanolic extract of Atractylodis rhizoma (EEAR) was initially clarified by high performance liquid chromatography (HPLC), after which it was studied in vivo using a lipopolysaccharide (LPS)-induced ALI rat model. Treatment with EEAR significantly reduced the lung wet/dry (W/D) ratio, neutrophil infiltration, and malondialdehyde (MDA) and myeloperoxidase (MPO) formation, and enhanced superoxide dismutase (SOD) and glutathione (GSH) depletion in rats with ALI, thereby improving lung barrier function and effectively reducing lung injury. In addition, EEAR significantly reduced histopathological changes, decreased the expression of inflammatory factors (such as tumor necrosis factor-α (TNF-α), interleukin-1 beta (IL-1β), inducible nitric oxide synthase (INOS), and cyclooxygenase-2 (COX-2)), and inhibited the activation of the NF-κB signaling pathway, thus reducing inflammation. In addition, EEAR was found to also reduce oxidative stress in ALI by upregulating the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream proteins heme oxygenase-1 (HO-1) and NADPH quinone acceptor oxidoreductase 1 (NQO-1). EEAR also reduced LPS-induced inflammatory factor expression in THP-1 cells in vitro by inhibition of the NF-κB signaling pathway, and reduced damage from lipopolysaccharide (LPS)-induced oxidative stress in THP-1 cells by promoting the expression of Nrf2 and its downstream targets HO-1 and NQO-1, the molecular mechanism of which was consistent with in vivo observations. Therefore, we conclude that EEAR attenuates oxidative stress and inflammatory responses via TLR4/NF-κB and Keap1/Nrf2 signaling pathways to alleviate LPS-induced ALI, suggesting that Atractylodis rhizoma is a potential drug candidate for the treatment of ALI.

Molecular Pathogenesis of Fibrosis, Thrombosis and Surfactant Dysfunction in the Lungs of Severe COVID-19 Patients

The global scope and scale of the SARS-CoV-2 pandemic led to huge amounts of important data from clinical observations and experimental analyses being collected, in particular, regarding the long-term impact of COVID-19 on lung tissue. Visible changes in lung tissue mainly relate to the destruction of the alveolar architecture, dense cellularity, and pulmonary fibrosis with myofibroblast proliferation and collagen deposition. These changes are the result of infection, mainly with virus variants from the first pandemic waves (Alpha to Delta). In addition, proper regulation of immune responses to pathogenic viral stimuli is critical for the control of and recovery from tissue/organ damage, including in the lungs. We can distinguish three main processes in the lungs during SARS-CoV-2 infection: damage or deficiency of the pulmonary surfactant, coagulation processes, and fibrosis. Understanding the molecular basis of these processes is extremely important in the context of elucidating all pathologies occurring after virus entry. In the present review, data on the abovementioned three biochemical processes that lead to pathological changes are gathered together and discussed. Systematization of the knowledge is necessary to explore the three key pathways in lung tissue after SARS-CoV-2 virus infection as a result of a prolonged and intense inflammatory process in the context of pulmonary fibrosis, hemostatic disorders, and disturbances in the structure and/or metabolism of the surfactant. Despite the fact that the new Omicron variant does not affect the lungs as much as the previous variants, we cannot ignore the fact that other new mutations and emerging variants will not cause serious damage to the lung tissue. In the future, this review will be helpful to stratify the risk of serious complications in patients, to improve COVID-19 treatment outcomes, and to select those who may develop complications before clinical manifestation.

Functional Extracellular Vesicles for Regenerative Medicine

The unique biological characteristics and promising clinical potential of extracellular vesicles (EVs) have galvanized EV applications for regenerative medicine. Recognized as important mediators of intercellular communication, naturally secreted EVs have the potential, as innate biotherapeutics, to promote tissue regeneration. Although EVs have emerged as novel therapeutic agents, challenges related to the clinical transition have led to further functionalization. In recent years, various engineering approaches such as preconditioning, drug loading, and surface modification have been developed to potentiate the therapeutic outcomes of EVs. Also, limitations of natural EVs have been addressed by the development of artificial EVs that offer advantages in terms of production yield and isolation methodologies. In this review, an updated overview of current techniques is provided for the functionalization of natural EVs and recent advances in artificial EVs, particularly in the scope of regenerative medicine.

The phytochemical constituents and protective effect of Fritillaria hupehensis on acute lung injury

Acute lung injury (ALI), a severe respiratory disorder, frequently develops into acute respiratory distress syndrome (ARDS) without timely treatment and scores highly in terms of morbidity and mortality rates. Fritillaria hupehensis is a famous traditional Chinese medicine with antitussive, expectorant and anti-asthmatic effect. Here, the effects of F. hupehensis extracts on lipopolysaccharide (LPS)-induced ALI mice were evaluated for the first time. We showed ethyl acetate fraction (EAF) significantly reduced the leukocytes and neutrophils of bronchoalveolar lavage fluid (BALF) and the lung index as well as pro-inflammatory cytokines (TNF-α and IL-6) of lung homogenates but increasing the anti-inflammatory cytokines (IL-4 and IL-10). Additionally, the alleviation of EAF treatment on lung injury was verified through histopathological observations. Subsequent phytochemical investigation on bioactive fraction led to isolation of 17 compounds including two new, in which compounds 2, 5 and 6 exhibited better anti-inflammatory effect on LPS-induced 16 human airway epithelial (16HBE) cells model by inhibiting the production of CRP and PCT. Furthermore, compound 2 suppressed the LPS-induced upregulation of proteins containing p-p65, COX-2, Caspase-1 and IL-18. In summary, F. hupehensis alleviating LPS-induced ALI in mice may be associated with the anti-inflammatory activity of steroidal alkaloids by suppressing the NF-κB-regulated pro-inflammatory proteins.

Unshrinking the baby lung to calm the VILI vortex

A hallmark of ARDS is progressive shrinking of the ‘baby lung,’ now referred to as the ventilator-induced lung injury (VILI) ‘vortex.’ Reducing the risk of the VILI vortex is the goal of current ventilation strategies; unfortunately, this goal has not been achieved nor has mortality been reduced. However, the temporal aspects of a mechanical breath have not been considered. A brief expiration prevents alveolar collapse, and an extended inspiration can recruit the atelectatic lung over hours. Time-controlled adaptive ventilation (TCAV) is a novel ventilator approach to achieve these goals, since it considers many of the temporal aspects of dynamic lung mechanics.

Time-Controlled Adaptive Ventilation Does Not Induce Hemodynamic Impairment in a Swine ARDS Model

Background

The current standard of care during severe acute respiratory distress syndrome (ARDS) is based on low tidal volume (VT) ventilation, at 6 mL/kg of predicted body weight. The time-controlled adaptive ventilation (TCAV) is an alternative strategy, based on specific settings of the airway pressure release ventilation (APRV) mode. Briefly, TCAV reduces lung injury, including: (1) an improvement in alveolar recruitment and homogeneity; (2) reduction in alveolar and alveolar duct micro-strain and stress-risers. TCAV can result in higher intra-thoracic pressures and thus impair hemodynamics resulting from heart-lung interactions. The objective of our study was to compare hemodynamics between TCAV and conventional protective ventilation in a porcine ARDS model.

Methods

In 10 pigs (63–73 kg), lung injury was induced by repeated bronchial saline lavages followed by 2 h of injurious ventilation. The animals were then randomized into two groups: (1) Conventional protective ventilation with a VT of 6 mL/kg and PEEP adjusted to a plateau pressure set between 28 and 30 cmH₂O; (2) TCAV group with P-high set between 27 and 29 cmH₂O, P-low at 0 cmH₂O, T-low adjusted to terminate at 75% of the expiratory flow peak, and T-high at 3–4 s, with I:E > 6:1.

Results

Both lung elastance and PaO₂:FiO₂ were consistent with severe ARDS after 2 h of injurious mechanical ventilation. There was no significant difference in systemic arterial blood pressure, pulmonary blood pressure or cardiac output between Conventional protective ventilation and TCAV. Levels of total PEEP were significantly higher in the TCAV group (p < 0.05). Driving pressure and lung elastance were significantly lower in the TCAV group (p < 0.05).

Conclusion

No hemodynamic adverse events were observed in the TCAV group compared as to the standard protective ventilation group in this swine ARDS model, and TCAV appeared to be beneficial to the respiratory system.

Airway Pressure Release Ventilation With Time-Controlled Adaptive Ventilation (TCAV™) in COVID-19: A Community Hospital's Experience

Santa Cabrini Ospedale, a community hospital in Montreal, Canada, used the airway pressure release ventilation following a time-controlled adaptive ventilation (APRV-TCAV™) approach for several patients in the first wave of the coronavirus disease 2019 (COVID-19) outbreak in the spring of 2021. Based on favorable patient responses, it became the primary mode of invasive mechanical ventilation—from initiation through extubation—during the second and third waves of COVID-19. In this article, we describe our success with APRV-TCAV™ over more conventional modes and protocols and look at three cases that aptly demonstrate our experience. We then outline several risks with our approach and the lessons learned from our experience. While we generally saw improvement in patients’ clinical course with APRV-TCAV™, there are inherent risks with this approach that others must prepare for if they attempt to implement it in their practice.

Stabilization of the floating sternocostal segment of the chest with multiple bilateral fractures of the ribs and the manubrium of the sternum

Among patients with floating rib fractures without pneumo- and hemopneumothorax or after their elimination, the most severe disorders of ventilation and circulation occur in patients with multiple bilateral rib fractures and a fracture of the sternum manubrium with the formation of a floating sternocostal segment of the chest. At the same time, the suction aero- and hemodynamic function of the chest is disturbed, there is pressure on the heart and large vessels. As a result, the efficiency of external respiration progressively decreases, the respiratory muscles are exhausted, which requires an urgent transfer to artificial ventilation of the lungs. The article presents a clinical case of successful treatment of such a chest injury using the author’s technique (Patent No. 2621871 of the Russian Federation). The extrathoracic silicone reinforced splint has two horizontal branches that go around the mammary glands. The splint is attached to the floating sternocostal segment with ligatures passed behind the sternum and laterally – to stable sections of the ribs along the posterior axillary line on both sides. The tire reliably holds the sternocostal segment from paradoxical movements. The tire is removed after 3  weeks. By this time, fibrous calluses are formed in places of fractures of bones and cartilage, and the swelling of the chest wall subsides. Superficial bedsores in the places of fixation of the splint are epithelialized under the scab within 7–8 days. The patient was examined a year later, her condition was satisfactory, she had no complaints, there was no chest deformity. The technique is less traumatic, it is indicated for patients with polytrauma and in other cases. 

LTB4 Promotes Acute Lung Injury via Upregulating the PLCε-1/TLR4/NF-κB Pathway in One-Lung Ventilation

Background

Mechanical ventilation (MV) can provoke acute lung injury (ALI) by increasing inflammation activation and disrupting the barrier in lung tissues even causing death. However, the inflammation-related molecules and pathways in MV-induced ALI remain largely unknown. Hence, the purposes of this study are to examine the role and mechanism of a novel inflammation-related molecule, leukotriene B4 (LTB4), in ALI.

Methods

The functions of LTB4 in one-lung ventilation (OLV) model were detected by the loss-of-function experiments. H&E staining was used to examine the pathologic changes of lung tissues. Functionally, PLCε-1 knockdown and Toll-like receptor 4 (TLR4)/NF-κB pathway inhibitor were used to detect the regulatory effects of LTB4 on the phospholipase Cε (PLCε-1)/TLR4/nuclear factor-kappa B (NF-κB) pathway. The levels of genes and proteins were determined by RT-qPCR and western blotting assay. The levels of inflammation cytokines and chemokines were measured by ELISA.

Results

Here, we found LTA4H, leukotriene B (4) receptor 1 (BLT1), LTB4, and PLCε-1 upregulated in OLV rats and associated with inflammatory activation and lung permeability changes of lung tissues. Inhibition of LTB4 alleviated the OLV-induced ALI by inhibiting inflammatory activation and lung permeability changes of lung tissues. For mechanism analyses, LTB4 promoted OLV-induced ALI by activating the PLCε-1/TLR4/NF-κB pathway.

Conclusion

LTB4 induced ALI in OLV rats by activating the PLCε-1/TLR4/NF-κB pathway. Our findings might supply a new potential therapeutic for OLV-induced ALI.

Pulmonary Interstitial Matrix and Lung Fluid Balance From Normal to the Acutely Injured Lung

This review analyses the mechanisms by which lung fluid balance is strictly controlled in the air-blood barrier (ABB). Relatively large trans-endothelial and trans-epithelial Starling pressure gradients result in a minimal flow across the ABB thanks to low microvascular permeability aided by the macromolecular structure of the interstitial matrix. These edema safety factors are lost when the integrity of the interstitial matrix is damaged. The result is that small Starling pressure gradients, acting on a progressively expanding alveolar barrier with high permeability, generate a high transvascular flow that causes alveolar flooding in minutes. We modeled the trans-endothelial and trans-epithelial Starling pressure gradients under control conditions, as well as under increasing alveolar pressure (Palv) conditions of up to 25 cmH2O. We referred to the wet-to-dry weight (W/D) ratio, a specific index of lung water balance, to be correlated with the functional state of the interstitial structure. W/D averages ∼5 in control and might increase by up to ∼9 in severe edema, corresponding to ∼70% loss in the integrity of the native matrix. Factors buffering edemagenic conditions include: (i) an interstitial capacity for fluid accumulation located in the thick portion of ABB, (ii) the increase in interstitial pressure due to water binding by hyaluronan (the "safety factor" opposing the filtration gradient), and (iii) increased lymphatic flow. Inflammatory factors causing lung tissue damage include those of bacterial/viral and those of sterile nature. Production of reactive oxygen species (ROS) during hypoxia or hyperoxia, or excessive parenchymal stress/strain [lung overdistension caused by patient self-induced lung injury (P-SILI)] can all cause excessive inflammation. We discuss the heterogeneity of intrapulmonary distribution of W/D ratios. A W/D ∼6.5 has been identified as being critical for the transition to severe edema formation. Increasing Palv for W/D > 6.5, both trans-endothelial and trans-epithelial gradients favor filtration leading to alveolar flooding. Neither CT scan nor ultrasound can identify this initial level of lung fluid balance perturbation. A suggestion is put forward to identify a non-invasive tool to detect the earliest stages of perturbation of lung fluid balance before the condition becomes life-threatening.

The Role of Glucocorticoids in the Treatment of ARDS: A Multicenter Retrospective Study Based on the eICU Collaborative Research Database

Background: Acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure in patients in intensive care unit (ICU). The therapeutic value of glucocorticoids (GCs) in the prognosis of ARDS remains controversial. The aim of this research is studying the impacts of GCs treatment on ARDS patients in ICU. Methods: We retrospectively studied 2,167 ARDS patients whose data were collected from the public eICU Collaborative Research Database, among which 254 patients who received glucocorticoid (GCs) treatment were 1:1 matched by propensity matching analysis (PSM). The primary outcome was ICU mortality. Every oxygenation index (PaO2/FiO2) measurement before death or ICU discharge was recorded. A joint model (JM) which combined longitudinal sub-model (mixed-effect model) and time-to-event sub-model (Cox regression model) by trajectory functions of PaO2/FiO2 was conducted to determine the effects of GCs treatment on both ICU mortality and PaO2/FiO2 level and further PaO2/FiO2's effect on event status. The marginal structural cox model (MSCM) adjusted the overall PaO2/FiO2 of patients to further validate the results. Results: The result of the survival sub-model showed that GCs treatment was significantly associated with reduced ICU mortality in ARDS patients [HR (95% CI) = 0.642 (0.453, 0.912)], demonstrating that GCs treatment was a protective factor of ICU mortality. In the longitudinal sub-model, GCs treatment was not correlated to the PaO2/FiO2. After adjusted by the JM, the HR of GCs treatment was 0.602 while GCs was still not significantly related to PaO2/FiO2 level. The JM-induced association showed that higher PaO2/FiO2 was a significant protective factor of mortality in ARDS patients and the HR was 0.991 which demonstrated that one level increase of PaO2/FiO2 level decreased 0.9% risk of ICU mortality. MSCM results also show that GCs can improve the prognosis of patients. Conclusion: Rational use of GCs can reduce the ICU mortality of ARDS patients in ICU. In addition to the use of GCs treatment, clinicians should also focus on the shifting trend of PaO2/FiO2 level to provide better conditions for patients' survival.

The Role of Pulmonary Surfactants in the Treatment of Acute Respiratory Distress Syndrome in COVID-19

Lung alveolar type-II (AT-II) cells produce pulmonary surfactant (PS), consisting of proteins and lipids. The lipids in PS are primarily responsible for reducing the air-fluid surface tension inside the alveoli of the lungs and to prevent atelectasis. The proteins are of two types: hydrophilic and hydrophobic. Hydrophilic surfactants are primarily responsible for opsonisation, thereby protecting the lungs from microbial and environmental contaminants. Hydrophobic surfactants are primarily responsible for respiratory function. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) enters the lungs through ACE-2 receptors on lungs and replicates in AT-II cells leading to the etiology of Coronavirus disease - 2019 (COVID-19). The SARS-CoV-2 virus damages the AT-II cells and results in decreased production of PS. The clinical symptoms of acute respiratory distress syndrome (ARDS) in COVID-19 patients are like those of neonatal respiratory distress syndrome (NRDS). The PS treatment is first-line treatment option for NRDS and found to be well tolerated in ARDS patients with inconclusive efficacy. Over the past 70°years, a lot of research is underway to produce natural/synthetic PS and developing systems for delivering PS directly to the lungs, in addition to finding the association between PS levels and respiratory illnesses. In the present COVID-19 pandemic situation, the scientific community all over the world is searching for the effective therapeutic options to improve the clinical outcomes. With a strong scientific and evidence-based background on role of PS in lung homeostasis and infection, few clinical trials were initiated to evaluate the functions of PS in COVID-19. Here, we connect the data on PS with reference to pulmonary physiology and infection with its possible therapeutic benefit in COVID-19 patients.

STAT3-activated lncRNA XIST accelerates the inflammatory response and apoptosis of LPS-induced acute lung injury

Acute lung injury (ALI) is a severe lung respiratory failure characterized by high morbidity and mortality. Novel findings demonstrated the critical roles of long non‐coding RNA (lncRNA) in ALI. Here, we tried to investigate the roles and potential mechanism of lncRNA X‐inactive specific transcript (XIST) in ALI. Results illustrated that lncRNA XIST was up‐regulated in the lipopolysaccharide (LPS)‐induced ALI mice models and pulmonary endothelial cells. Biofunctional assays unveiled that knockdown of XIST repressed the inflammatory response and apoptosis in LPS‐induced endothelial cells. Mechanistically, XIST acted as the miR‐146a‐5p sponge to positively regulate STAT3. Moreover, STAT3 combined the promoter region of XIST to accelerate the transcription, constituting the positive feedback loop of XIST/miR‐146a‐5p/STAT3 in ALI. Collectively, these findings suggested that XIST knockdown attenuates the LPS‐induced ALI, providing a potential therapeutic target.

Time controlled adaptive ventilation™ as conservative treatment of destroyed lung: an alternative to lung transplantation

Background

Acute respiratory distress syndrome (ARDS) often requires controlled ventilation, yielding high mechanical power and possibly further injury. Veno-venous extracorporeal membrane oxygenation (VV-ECMO) can be used as a bridge to recovery, however, if this fails the end result is destroyed lung parenchyma. This condition is fatal and the only remaining alternative is lung transplantation. In the case study presented in this paper, lung transplantation was not an option given the critically ill state and the presence of HLA antibodies. Airway pressure release ventilation (APRV) may be valuable in ARDS, but APRV settings recommended in various patient and clinical studies are inconsistent. The Time Controlled Adaptive Ventilation (TCAV™) method is the most studied technique to set and adjust the APRV mode and uses an extended continuous positive airway pressure (CPAP) Phase in combination with a very brief Release Phase. In addition, the TCAV™ method settings are personalized and adaptive based on changes in lung pathophysiology. We used the TCAV™ method in a case of severe ARDS, which enabled us to open, stabilize and slowly heal the severely damaged lung parenchyma.

Case presentation

A 43-year-old woman presented with Staphylococcus Aureus necrotizing pneumonia. Progressive respiratory failure necessitated invasive mechanical ventilation and VV-ECMO. Mechanical ventilation (MV) was ultimately discontinued because lung protective settings resulted in trivial tidal volumes. She was referred to our academic transplant center for bilateral lung transplantation after the remaining infection had been cleared. We initiated the TCAV™ method in order to stabilize the lung parenchyma and to promote tissue recovery. This strategy was challenged by the presence of a large bronchopleural fistula, however, APRV enabled weaning from VV-ECMO and mechanical ventilation. After two months, following nearly complete surgical closure of the remaining bronchopleural fistulas, the patient was readmitted to ICU where she had early postoperative complications. Since other ventilation modes resulted in significant atelectasis and hypercapnia, APRV was restarted. The patient was then again weaned from MV.

Conclusions

The TCAV™ method can be useful to wean challenging patients with severe ARDS and might contribute to lung recovery. In this particular case, a lung transplantation was circumvented.

A role for bronchial epithelial autotaxin in ventilator-induced lung injury

Background

The pathophysiology of acute respiratory distress syndrome (ARDS) may eventually result in heterogeneous lung collapse and edema-flooded airways, predisposing the lung to progressive tissue damage known as ventilator-induced lung injury (VILI). Autotaxin (ATX; ENPP2), the enzyme largely responsible for extracellular lysophosphatidic acid (LPA) production, has been suggested to play a pathogenic role in, among others, pulmonary inflammation and fibrosis.

Methods

C57BL/6 mice were subjected to low and high tidal volume mechanical ventilation using a small animal ventilator: respiratory mechanics were evaluated, and plasma and bronchoalveolar lavage fluid (BALF) samples were obtained. Total protein concentration was determined, and lung histopathology was further performed

Results

Injurious ventilation resulted in increased BALF levels of ATX. Genetic deletion of ATX from bronchial epithelial cells attenuated VILI-induced pulmonary edema.

Conclusion

ATX participates in VILI pathogenesis.

Functional pathophysiology of SARS-CoV-2-induced acute lung injury and clinical implications

The worldwide pandemic caused by the SARS-CoV-2 virus has resulted in over 84,407,000 cases, with over 1,800,000 deaths when this paper was submitted, with comorbidities such as gender, race, age, body mass, diabetes, and hypertension greatly exacerbating mortality. This review will analyze the rapidly increasing knowledge of COVID-19-induced lung pathophysiology. Although controversial, the acute respiratory distress syndrome (ARDS) associated with COVID-19 (CARDS) seems to present as two distinct phenotypes: type L and type H. The "L" refers to low elastance, ventilation/perfusion ratio, lung weight, and recruitability, and the "H" refers to high pulmonary elastance, shunt, edema, and recruitability. However, the LUNG-SAFE (Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure) and ESICM (European Society of Intensive Care Medicine) Trials Groups have shown that ∼13% of the mechanically ventilated non-COVID-19 ARDS patients have the type-L phenotype. Other studies have shown that CARDS and ARDS respiratory mechanics overlap and that standard ventilation strategies apply to these patients. The mechanisms causing alterations in pulmonary perfusion could be caused by some combination of 1) renin-angiotensin system dysregulation, 2) thrombosis caused by loss of endothelial barrier, 3) endothelial dysfunction causing loss of hypoxic pulmonary vasoconstriction perfusion control, and 4) hyperperfusion of collapsed lung tissue that has been directly measured and supported by a computational model. A flowchart has been constructed highlighting the need for personalized and adaptive ventilation strategies, such as the time-controlled adaptive ventilation method, to set and adjust the airway pressure release ventilation mode, which recently was shown to be effective at improving oxygenation and reducing inspiratory fraction of oxygen, vasopressors, and sedation in patients with COVID-19.

The POOR Get POORer: A Hypothesis for the Pathogenesis of Ventilator-induced Lung Injury

Protective ventilation strategies for the injured lung currently revolve around the use of low Vt, ostensibly to avoid volutrauma, together with positive end-expiratory pressure to increase the fraction of open lung and reduce atelectrauma. Protective ventilation is currently applied in a one-size-fits-all manner, and although this practical approach has reduced acute respiratory distress syndrome deaths, mortality is still high and improvements are at a standstill. Furthermore, how to minimize ventilator-induced lung injury (VILI) for any given lung remains controversial and poorly understood. Here we present a hypothesis of VILI pathogenesis that potentially serves as a basis upon which minimally injurious ventilation strategies might be developed. This hypothesis is based on evidence demonstrating that VILI begins in isolated lung regions manifesting a Permeability-Originated Obstruction Response (POOR) in which alveolar leak leads to surfactant dysfunction and increases local tissue stresses. VILI progresses topographically outward from these regions in a POOR-get-POORer fashion unless steps are taken to interrupt it. We propose that interrupting the POOR-get-POORer progression of lung injury relies on two principles: 1) open the lung to minimize the presence of heterogeneity-induced stress concentrators that are focused around the regions of atelectasis, and 2) ventilate in a patient-dependent manner that minimizes the number of lung units that close during each expiration so that they are not forced to rerecruit during the subsequent inspiration. These principles appear to be borne out in both patient and animal studies in which expiration is terminated before derecruitment of lung units has enough time to occur.

Alveolar Dynamics and Beyond - The Importance of Surfactant Protein C and Cholesterol in Lung Homeostasis and Fibrosis

Surfactant protein C (SP-C) is an important player in enhancing the interfacial adsorption of lung surfactant lipid films to the alveolar air-liquid interface. Doing so, surface tension drops down enough to stabilize alveoli and the lung, reducing the work of breathing. In addition, it has been shown that SP-C counteracts the deleterious effect of high amounts of cholesterol in the surfactant lipid films. On its side, cholesterol is a well-known modulator of the biophysical properties of biological membranes and it has been proven that it activates the inflammasome pathways in the lung. Even though the molecular mechanism is not known, there are evidences suggesting that these two molecules may interplay with each other in order to keep the proper function of the lung. This review focuses in the role of SP-C and cholesterol in the development of lung fibrosis and the potential pathways in which impairment of both molecules leads to aberrant lung repair, and therefore impaired alveolar dynamics. From molecular to cellular mechanisms to evidences in animal models and human diseases. The evidences revised here highlight a potential SP-C/cholesterol axis as target for the treatment of lung fibrosis.

Lung and chest wall mechanics in patients with acute respiratory distress syndrome, expiratory flow limitation, and airway closure

Tidal expiratory flow limitation (EFL), which may herald airway closure (AC), is a mechanism of loss of aeration in ARDS. In this prospective, short-term, two-center study, we measured static and dynamic chest wall (Est,cw and Edyn,cw) and lung (Est,L and Edyn,L) elastance with esophageal pressure, EFL, and AC at 5 cmH₂O positive end-expiratory pressure (PEEP) in intubated, sedated, and paralyzed ARDS patients. For EFL determination, we used the atmospheric method and a new device allowing comparison of tidal flow during expiration to PEEP and to atmosphere. AC was validated when airway opening pressure (AOP) assessed from volume-pressure curve was found greater than PEEP by at least 1 cmH₂O. EFL was defined whenever flow did not increase between exhalation to PEEP and to atmosphere over all or part of expiration. Elastance values were expressed as percentage of normal predicted values (%N). Among the 25 patients included, eight had EFL (32%) and 13 AOP (52%). Between patients with and without EFL Edyn,cw [median (1st to 3rd quartiles)] was 70 (16-127) and 102 (70-142) %N (P = 0.32) and Edyn,L338 (332-763) and 224 (160-275) %N (P < 0.001). The corresponding values for Est,cw and Est,L were 70 (56-88) and 85 (64-103) %N (P = 0.35) and 248 (206-348) and 170 (144-195) (P = 0.02), respectively. Dynamic E_L had an area receiver operating characteristic curve of 0.88 [95% confidence intervals 0.83-0.92] for EFL and 0.74[0.68-0.79] for AOP. Higher Edyn,L was accurate to predict EFL in ARDS patients; AC can occur independently of EFL, and both should be assessed concurrently in ARDS patients.NEW & NOTEWORTHY Expiratory flow limitation (EFL) and airway closure (AC) were observed in 32% and 52%, respectively, of 25 patients with ARDS investigated during mechanical ventilation in supine position with a positive end-expiratory pressure of 5 cmH₂O. The performance of dynamic lung elastance to detect expiratory flow limitation was good and better than that to detect airway closure. The vast majority of patients with EFL also had AC; however, AC can occur in the absence of EFL.

Mechanical Ventilation Lessons Learned From Alveolar Micromechanics

Morbidity and mortality associated with lung injury remains disappointingly unchanged over the last two decades, in part due to the current reliance on lung macro-parameters set on the ventilator instead of considering the micro-environment and the response of the alveoli and alveolar ducts to ventilator adjustments. The response of alveoli and alveolar ducts to mechanical ventilation modes cannot be predicted with current bedside methods of assessment including lung compliance, oxygenation, and pressure-volume curves. Alveolar tidal volumes (Vt) are less determined by the Vt set on the mechanical ventilator and more dependent on the number of recruited alveoli available to accommodate that Vt and their heterogeneous mechanical properties, such that high lung Vt can lead to a low alveolar Vt and low Vt can lead to high alveolar Vt. The degree of alveolar heterogeneity that exists cannot be predicted based on lung calculations that average the individual alveolar Vt and compliance. Finally, the importance of time in promoting alveolar stability, specifically the inspiratory and expiratory times set on the ventilator, are currently under-appreciated. In order to improve outcomes related to lung injury, the respiratory physiology of the individual patient, specifically at the level of the alveolus, must be targeted. With experimental data, this review highlights some of the known mechanical ventilation adjustments that are helpful or harmful at the level of the alveolus.

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

Acute respiratory distress syndrome (ARDS) causes a heterogeneous lung injury and remains a serious medical problem, with one of the only treatments being supportive care in the form of mechanical ventilation. It is very difficult, however, to mechanically ventilate the heterogeneously damaged lung without causing secondary ventilator-induced lung injury (VILI). The acutely injured lung becomes time and pressure dependent, meaning that it takes more time and pressure to open the lung, and it recollapses more quickly and at higher pressure. Current protective ventilation strategies, ARDSnet low tidal volume (LVt) and the open lung approach (OLA), have been unsuccessful at further reducing ARDS mortality. We postulate that this is because the LVt strategy is constrained to ventilating a lung with a heterogeneous mix of normal and focalized injured tissue, and the OLA, although designed to fully open and stabilize the lung, is often unsuccessful at doing so. In this review we analyzed the pathophysiology of ARDS that renders the lung susceptible to VILI. We also analyzed the alterations in alveolar and alveolar duct mechanics that occur in the acutely injured lung and discussed how these alterations are a key mechanism driving VILI. Our analysis suggests that the time component of each mechanical breath, at both inspiration and expiration, is critical to normalize alveolar mechanics and protect the lung from VILI. Animal studies and a meta-analysis have suggested that the time-controlled adaptive ventilation (TCAV) method, using the airway pressure release ventilation mode, eliminates the constraints of ventilating a lung with heterogeneous injury, since it is highly effective at opening and stabilizing the time- and pressure-dependent lung. In animal studies it has been shown that by “casting open” the acutely injured lung with TCAV we can (1) reestablish normal expiratory lung volume as assessed by direct observation of subpleural alveoli; (2) return normal parenchymal microanatomical structural support, known as alveolar interdependence and parenchymal tethering, as assessed by morphometric analysis of lung histology; (3) facilitate regeneration of normal surfactant function measured as increases in surfactant proteins A and B; and (4) significantly increase lung compliance, which reduces the pathologic impact of driving pressure and mechanical power at any given tidal volume.

Airway Pressure Release Ventilation: A Review of the Evidence, Theoretical Benefits, and Alternative Titration Strategies

Objective:

To review the theoretical benefits of airway pressure release ventilation (APRV), summarize the evidence for its use in clinical practice, and discuss different titration strategies.

Data Source:

Published randomized controlled trials in humans, observational human studies, animal studies, review articles, ventilator textbooks, and editorials.

Data Summary:

Airway pressure release ventilation optimizes alveolar recruitment, reduces airway pressures, allows for spontaneous breathing, and offers many hemodynamic benefits. Despite these physiologic advantages, there are inconsistent data to support the use of APRV over other modes of ventilation. There is considerable heterogeneity in the application of APRV among providers and a shortage of information describing initiation and titration strategies. To date, no direct comparison studies of APRV strategies have been performed. This review describes 2 common management approaches that bedside providers can use to optimally tailor APRV to their patients.

Conclusion:

Airway pressure release ventilation remains a form of mechanical ventilation primarily used for refractory hypoxemia. It offers unique physiological advantages over other ventilatory modes, and providers must be familiar with different titration methods. Given its inconsistent outcome data and heterogeneous use in practice, future trials should directly compare APRV strategies to determine the optimal management approach.

Acute lung injury in patients with COVID-19 infection

During the 2020 Spring Festival in China, the outbreak of a novel coronavirus, named COVID-19 by WHO, brought on a worldwide panic. According to the clinical data of infected patients, radiologic evidence of lung edema is common and deserves clinical attention. Lung edema is a manifestation of acute lung injury (ALI) and may progress to hypoxemia and potentially acute respiratory distress syndrome (ARDS). Patients diagnosed with ARDS have poorer prognosis and potentially higher mortality. Although no effective treatment is formally approved for COVID-19 infection, support of ventilation with oxygen therapy and sometimes mechanical ventilation is often required. Treatment with systemic and/or local glucocorticoids might be helpful to alleviate the pulmonary inflammation and edema, which may decrease the development and/or consequences of ARDS. In this article, we focus on the lung edema and ALI of patients with this widely transmitted COVID-19 infection in order to provide clinical indications and potential therapeutic targets for clinicians and researchers.

Microphysiological systems modeling acute respiratory distress syndrome that capture mechanical force-induced injury-inflammation-repair

Complex in vitro models of the tissue microenvironment, termed microphysiological systems, have enormous potential to transform the process of discovering drugs and disease mechanisms. Such a paradigm shift is urgently needed in acute respiratory distress syndrome (ARDS), an acute lung condition with no successful therapies and a 40% mortality rate. Here, we consider how microphysiological systems could improve understanding of biological mechanisms driving ARDS and ultimately improve the success of therapies in clinical trials. We first discuss how microphysiological systems could explain the biological mechanisms underlying the segregation of ARDS patients into two clinically distinct phenotypes. Then, we contend that ARDS-mimetic microphysiological systems should recapitulate three critical aspects of the distal airway microenvironment, namely, mechanical force, inflammation, and fibrosis, and we review models that incorporate each of these aspects. Finally, we recognize the substantial challenges associated with combining inflammation, fibrosis, and/or mechanical force in microphysiological systems. Nevertheless, complex in vitro models are a novel paradigm for studying ARDS, and they could ultimately improve patient care.

Time-controlled adaptive ventilation (TCAV) accelerates simulated mucus clearance via increased expiratory flow rate

Background

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in intensive care units. Distal airway mucus clearance has been shown to reduce VAP incidence. Studies suggest that mucus clearance is enhanced when the rate of expiratory flow is greater than inspiratory flow. The time-controlled adaptive ventilation (TCAV) protocol using the airway pressure release ventilation (APRV) mode has a significantly increased expiratory relative to inspiratory flow rate, as compared with the Acute Respiratory Distress Syndrome Network (ARDSnet) protocol using the conventional ventilation mode of volume assist control (VAC). We hypothesized the TCAV protocol would be superior to the ARDSnet protocol at clearing mucus by a mechanism of net flow in the expiratory direction.

Methods

Preserved pig lungs fitted with an endotracheal tube (ETT) were used as a model to study the effect of multiple combinations of peak inspiratory (I_PF) and peak expiratory flow rate (E_PF) on simulated mucus movement within the ETT. Mechanical ventilation was randomized into 6 groups (n = 10 runs/group): group 1—TCAV protocol settings with an end-expiratory pressure (P_Low) of 0 cmH₂O and P_High 25 cmH₂O, group 2—modified TCAV protocol with increased P_Low 5 cmH₂O and P_High 25 cmH₂O, group 3—modified TCAV with P_Low 10 cmH₂O and P_High 25 cmH₂O, group 4—ARDSnet protocol using low tidal volume (LTV) and PEEP 0 cmH₂O, group 5—ARDSnet protocol using LTV and PEEP 10 cmH₂O, and group 6—ARDSnet protocol using LTV and PEEP 20 cmH₂O. PEEP of ARDSnet is analogous to P_Low of TCAV. Proximal (towards the ventilator) mucus movement distance was recorded after 1 min of ventilation in each group.

Results

The TCAV protocol groups 1, 2, and 3 generated significantly greater peak expiratory flow (E_PF 51.3 L/min, 46.8 L/min, 36.8 L/min, respectively) as compared to the ARDSnet protocol groups 4, 5, and 6 (32.9 L/min, 23.5 L/min, and 23.2 L/min, respectively) (p < 0.001). The TCAV groups also demonstrated the greatest proximal mucus movement (7.95 cm/min, 5.8 cm/min, 1.9 cm/min) (p < 0.01). All ARDSnet protocol groups (4–6) had zero proximal mucus movement (0 cm/min).

Conclusions

The TCAV protocol groups promoted the greatest proximal movement of simulated mucus as compared to the ARDSnet protocol groups in this excised lung model. The TCAV protocol settings resulted in the highest E_PF and the greatest proximal movement of mucus. Increasing P_Low reduced proximal mucus movement. We speculate that proximal mucus movement is driven by E_PF when E_PF is greater than I_PF, creating a net force in the proximal direction.

Airway pressure release ventilation during acute hypoxemic respiratory failure: a systematic review and meta-analysis of randomized controlled trials

Background

Airway pressure release ventilation (APRV) has been considered a tempting mode of ventilation during acute respiratory failure within the concept of open lung ventilation. We performed a systematic review and meta-analysis to verify whether adult patients with hypoxemic respiratory failure have a higher number of ventilator-free days at day 28 when ventilated in APRV compared to conventional ventilation strategy. Secondary outcomes were difference in PaO₂/FiO₂ at day 3, ICU length of stay (LOS), ICU and hospital mortality, mean arterial pressure (MAP), risk of barotrauma and level of sedation. We searched MEDLINE, Scopus and Cochrane Central Register of Controlled Trials database until December 2018.

Results

We considered five RCTs for the analysis enrolling a total of 330 patients. For ventilatory-free day at day 28, the overall mean difference (MD) between APRV and conventional ventilation was 6.04 days (95%CI 2.12, 9.96, p = 0.003; I² = 65%, p = 0.02). Patients treated with APRV had a lower ICU LOS than patients treated with conventional ventilation (MD 3.94 days [95%CI 1.44, 6.45, p = 0.002; I² = 37%, p = 0.19]) and a lower hospital mortality (RD 0.16 [95%CI 0.02, 0.29, p = 0.03; I² = 0, p = 0.5]). PaO₂/FiO₂ at day 3 was not different between the two groups (MD 40.48 mmHg [95%CI − 25.78, 106.73, p = 0.23; I² = 92%, p < 0.001]). MAP was significantly higher during APRV (MD 5 mmHg [95%CI 1.43, 8.58, p = 0.006; I² = 0%, p = 0.92]). Then, there was no difference regarding the onset of pneumothorax under the two ventilation strategies (RR 1.94 [95%CI 0.54, 6.94, p = 0.31; I² = 0%, p = 0.74]). ICU mortality and sedation level were not included into quantitative analysis.

Conclusion

This study showed a higher number of ventilator-free days at 28 day and a lower hospital mortality in acute hypoxemic patients treated with APRV than conventional ventilation, without any negative hemodynamic impact or higher risk of barotrauma. However, these results need to be interpreted with caution because of the low-quality evidence supporting them and the moderate heterogeneity found. Other well-designed RCTs need to be conducted to confirm our findings.

High-Mobility Group Box 1 (HMGB1) and Autophagy in Acute Lung Injury (ALI): A Review

Acute lung injury (ALI) is a life-threatening clinical syndrome in critically ill patients. The identification of novel biological markers for the early diagnosis of ALI and the development of more effective treatments are topics of current research. High mobility group box-1 protein (HMGB1) is a late inflammatory mediator associated with sepsis, malignancy, and immune disease. Levels of HMGB1 may reflect the severity of inflammation and tissue damage, indicating a potential role for HMGB1 as a prognostic biomarker in ALI, and a potential target for blocking inflammatory pathways. Several studies have shown that HMGB1 regulates autophagy. Autophagy, or type II programmed cell death, is an essential biological process that maintains cellular homeostasis. Studies have shown that HMGB1 and autophagy are involved in the pathogenesis of many lung diseases including ALI but the specific mechanisms underlying this association remain to be determined. This review aims to provide an update on the current status of the role of HMBG1 and autophagy in ALI.