Impact of mechanical ventilation on the pathophysiology of progressive acute lung injury

Extracellular vesicle release in an experimental ventilator-induced lung injury porcine model

Harmful effects of mechanical ventilation with large tidal volumes, volutrauma, may contribute much to diffuse acute lung injury. Extracellular vesicles have been noted in the context of vital organ injury. We hypothesized that extracellular vesicles from acutely injured lung can be found in both lung and blood. In a two-hit experimental porcine model, we tested if extracellular vesicles could be detected in bronchoalveolar lavage fluid and in plasma over a six-hour period of large tidal volume ventilation after surfactant depletion. After 2 hours of volutrauma, bronchoalveolar lavage fluid showed increased levels of extracellular vesicles containing nucleic acids (stained by SYTO 13) and those positive for both SYTO 13 and HMGB1. No such increase was detected in plasma at any timepoint during the six-hour experiments. This shows that nucleic acid-containing extracellular vesicles appear to be involved in progression of lung injury, possibly indicating cellular damage, but their potential to serve as diagnostic biomarkers of acute lung injury progression, based on plasma sampling, and in the very early phase, is not confirmed by these findings.

Dynamic driving pressure predicts ventilator-induced lung injury in mice with and without endotoxin-induced acute lung injury

Mechanical ventilation (MV) is a necessary lifesaving intervention for patients with acute respiratory distress syndrome (ARDS) but it can cause ventilator-induced lung injury (VILI), which contributes to the high ARDS mortality rate (∼40%). Bedside determination of optimally lung-protective ventilation settings is challenging because the evolution of VILI is not immediately reflected in clinically available, patient-level, data. The goal of this work was therefore to test ventilation waveform-derived parameters that represent the degree of ongoing VILI and can serve as targets for ventilator adjustments. VILI was generated at three different positive end-expiratory pressures in a murine inflammation-mediated (lipopolysaccharide, LPS) acute lung injury model and in initially healthy controls. LPS injury increased the expression of proinflammatory cytokines and caused widespread atelectasis, predisposing the lungs to VILI as measured in structure, mechanical function, and inflammation. Changes in lung function were used as response variables in an elastic net regression model that predicted VILI severity from tidal volume, dynamic driving pressure (PDDyn), mechanical power calculated by integration during inspiration or the entire respiratory cycle, and power calculated according to Gattinoni' s equation. Of these, PDDyn best predicted functional outcomes of injury using either data from the entire dataset or from 5-min time windows. The windowed data show higher predictive accuracy after an ∼1-h "run in" period and worse accuracy immediately following recruitment maneuvers. This analysis shows that low driving pressure is a computational biomarker associated with better experimental VILI outcomes and supports the use of driving pressure to guide ventilator adjustments to prevent VILI.NEW & NOTEWORTHY Elastic net regression analysis of ventilation waveforms recorded during mechanical ventilation of initially healthy and lung-injured mice shows that low driving pressure is a computational biomarker associated with better ventilator-induced lung injury (VILI) outcomes and supports the use of driving pressure to guide ventilator adjustments to prevent VILI.

The Development of Lung Tissue Engineering: From Biomaterials to Multicellular Systems

The challenge of the treatment of end-stage lung disease poses an urgent clinical demand for lung tissue engineering. Over the past few years, various lung tissue-engineered constructs are developed for lung tissue regeneration and respiratory pathology study. In this review, an overview of recent achievements in the field of lung tissue engineering is proposed. The introduction of lung structure and lung injury are stated briefly at first. After that, the lung tissue-engineered constructs are categorized into three types: acellular, monocellular, and multicellular systems. The different bioengineered constructs included in each system that can be applied to the reconstruction of the trachea, airway epithelium, alveoli, and even whole lung are described in detail, followed by the highlight of relevant representative research. Finally, the challenges and future directions of biomaterials, manufacturing technologies, and cells involved in lung tissue engineering are discussed. Overall, this review can provide referable ideas for the realization of functional lung regeneration and permanent lung substitution.

Identification of novel sub-phenotypes of severe ARDS requiring ECMO using latent class analysis

BACKGROUND

Sub-phenotyping of acute respiratory distress syndrome (ARDS) could be useful for evaluating the severity of ARDS or predicting its responsiveness to given therapeutic strategies, but no studies have yet investigated the heterogeneity of patients with severe ARDS requiring veno-venous extracorporeal membrane oxygenation (V-V ECMO).

METHODS

We conducted this retrospective multicenter observational study in adult patients with severe ARDS treated by V-V ECMO. We performed latent class analysis (LCA) for identifying sub-phenotypes of severe ARDS based on the radiological and clinical findings at the start of ECMO support. Multivariate Cox regression analysis was conducted to investigate the differences in mortality and association between the PEEP setting of ≥ 10 cmH2O and mortality by the sub-phenotypes.

RESULTS

We identified three sub-phenotypes from analysis of the data of a total of 544 patients with severe ARDS treated by V-V ECMO, as follows: Dry type (n = 185; 34%); Wet type (n = 169; 31%); and Fibrotic type (n = 190; 35%). The 90-days in-hospital mortality risk was higher in the patients with the Fibrotic type than in those with the Dry type (adjusted hazard ratio [95% confidence interval] 1.75 [1.10-2.79], p = 0.019) or the Wet type (1.50 [1.02-2.23], p = 0.042). The PEEP setting of ≥ 10 cmH2O during the first 3 days of ECMO decreased the 90-days in-hospital mortality risk only in patients with the Wet type, and not in those with the Dry or Fibrotic type. A significant interaction effect was observed between the Wet type and the PEEP setting of ≥ 10 cmH2O in relation to the 90-day in-hospital mortality (pinteraction = 0.036).

CONCLUSIONS

The three sub-phenotypes showed different mortality rates and different relationships between higher PEEP settings in the early phase of V-V ECMO and patient outcomes. Our data suggest that we may need to change our management approach to patients with severe ARDS during V-V ECMO according to their clinical sub-phenotype.

Low-volume ventilation of preinjured lungs degrades lung function via stress concentration and progressive alveolar collapse

Mechanical ventilation can cause ventilation-induced lung injury (VILI). The concept of stress concentrations suggests that surfactant dysfunction-induced microatelectases might impose injurious stresses on adjacent, open alveoli and function as germinal centers for injury propagation. The aim of the present study was to quantify the histopathological pattern of VILI progression and to test the hypothesis that injury progresses at the interface between microatelectases and ventilated lung parenchyma during low-positive end-expiratory pressure (PEEP) ventilation. Bleomycin was used to induce lung injury with microatelectases in rats. Lungs were then mechanically ventilated for up to 6 h at PEEP = 1 cmH2O and compared with bleomycin-treated group ventilated protectively with PEEP = 5 cmH2O to minimize microatelectases. Lung mechanics were measured during ventilation. Afterward, lungs were fixed at end-inspiration or end-expiration for design-based stereology. Before VILI, bleomycin challenge reduced the number of open alveoli [N(alvair,par)] by 29%. No differences between end-inspiration and end-expiration were observed. Collapsed alveoli clustered in areas with a radius of up to 56 µm. After PEEP = 5 cmH2O ventilation for 6 h, N(alvair,par) remained stable while PEEP = 1 cmH2O ventilation led to an additional loss of aerated alveoli by 26%, mainly due to collapse, with a small fraction partly edema filled. Alveolar loss strongly correlated to worsening of tissue elastance, quasistatic compliance, and inspiratory capacity. The radius of areas of collapsed alveoli increased to 94 µm, suggesting growth of the microatelectases. These data provide evidence that alveoli become unstable in neighborhood of microatelectases, which most likely occurs due to stress concentration-induced local vascular leak and surfactant dysfunction.NEW & NOTEWORTHY Low-volume mechanical ventilation in the presence of high surface tension-induced microatelectases leads to the degradation of lung mechanical function via the progressive loss of alveoli. Microatelectases grow at the interfaces of collapsed and open alveoli. Here, stress concentrations might cause injury and alveolar instability. Accumulation of small amounts of alveolar edema can be found in a fraction of partly collapsed alveoli but, in this model, alveolar flooding is not a major driver for degradation of lung mechanics.

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.

A natural sesquiterpene lactone isolinderalactone attenuates lipopolysaccharide-induced inflammatory response and acute lung injury through inhibition of NF-κB pathway and activation Nrf2 pathway in macrophages

Isolinderalactone is the main sesquiterpene lactone isolated from Lindera aggregata, a traditional Chinese medicine widely used to treat pain and inflammation. Although isolinderalactone has been demonstrated to possess anti-cancer effect, its anti-inflammatory activity and underlying mechanism has not been well characterized. Herein, isolinderalactone was able to significantly inhibit the production of NO and PGE2 by reducing the expressions of iNOS and COX2 in LPS-stimulated RAW264.7 macrophages and BMDMs, and decreased the mRNA levels of IL-1β, IL-6, and TNF-α in LPS-induced RAW264.7 cells. In vivo, isolinderalactone effectively alleviated LPS-induced acute lung injury (ALI), which manifested as reduction in pulmonary inflammatory infiltration, myeloperoxidase activity, and production of PGE2, IL-1β, IL-6, TNF-α, and malondialdehyde. Furthermore, isolinderalactone inhibited phosphorylation of IKKα/β, phosphorylation and degradation of IκBα, and nuclear translocation of NF-κB p65, thereby blocking NF-κB pro-inflammatory pathway. Meanwhile, isolinderalactone reduced the intracellular ROS through promoting the activation of Nrf2-HMOX1 antioxidant axis. By using drug affinity responsive target stability assay and molecular docking, isolinderalactone was found to covalently interact with IKKα/β and Keap1, which may contribute to its anti-inflammatory action. Additionally, a thiol donor β-mercaptoethanol significantly abolished isolinderalactone-mediated anti-inflammatory action in vitro, indicating the crucial role of the unsaturated lactone of isolinderalactone on its anti-inflammatory effects. Taken together, isolinderalactone protected against LPS-induced ALI in mice, which may be associated with its inhibition of NF-κB pathway and activation of Nrf2 signaling in macrophages.

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.

Effects of aggressive and conservative strategies for mechanical ventilation liberation

BACKGROUND

The optimal approach for transitioning from strict lung protective ventilation to support modes of ventilation when patients determine their own respiratory rate and tidal volume remains unclear. While aggressive liberation from lung protective settings could expedite extubation and prevent harm from prolonged ventilation and sedation, conservative liberation could prevent lung injury from spontaneous breathing.

RESEARCH QUESTION

Should physicians take a more aggressive or conservative approach to liberation?

METHODS

Retrospective cohort study of mechanically ventilated patients from the Medical Information Mart for Intensive Care IV database (MIMIC-IV version 1.0) estimating effects of incremental interventions modifying the propensity for liberation to be more aggressive or conservative relative to usual care, with adjustment for confounding via inverse probability weighting. Outcomes included in-hospital mortality, ventilator free days, and ICU free days. Analysis was performed on the entire cohort as well as subgroups differentiated by PaO2/FiO2 ratio, and SOFA.

RESULTS

7433 patients were included. Strategies multiplying the odds of a first liberation relative to usual care at each hour had a large impact on time to first liberation attempt (43 h under usual care, 24 h (0.95 CI = [23,25]) with an aggressive strategy doubling liberation odds, and 74 h (0.95 CI = [69,78]) under a conservative strategy halving liberation odds). In the full cohort, we estimated aggressive liberation increased ICU-free days by 0.9 days (0.95 CI = [0.8,1.0]) and ventilator free days by 0.82 days (0.95 CI = [0.67,0.97]), but had minimal effect on mortality (only a 0.3% (0.95 CI = [-0.2%,0.8%]) difference between minimum and maximum rates). With baseline SOFA≥ 12 (n = 1355), aggressive liberation moderately increased mortality (58.5% [0.95 CI = (55.7%,61.2%)]) compared with conservative liberation (55.1% [0.95 CI = (51.6%,58.6%)]).

INTERPRETATION

Aggressive liberation may improve ventilator free and ICU free days with little impact on mortality in patients with SOFA score < 12. Trials are needed.

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.

Mathematical modeling of pulmonary acinus structure: Verification of acinar shape effects on pathway structure using rat lungs

The pulmonary acinus is the gas exchange unit in the lung and has a very complex microstructure. The structure model is essential to understand the relationship between structural heterogeneity and mechanical phenomena at the acinus level with computational approaches. We propose an acinus structure model represented by a cluster of truncated octahedra in conical, double-conical, inverted conical, or chestnut-like conical confinement to accommodate recent experimental information of rodent acinar shapes. The basis of the model is the combined use of Voronoi and Delaunay tessellations and the optimization of the ductal tree assuming the number of alveoli and the mean path length as quantities related to gas exchange. Before applying the Voronoi tessellation, controlling the seed coordinates enables us to model acinus with arbitrary shapes. Depending on the acinar shape, the distribution of path length varies. The lengths are more widely spread for the cone acinus, with a bias toward higher values, while most of the lengths for the inverted cone acinus primarily take a similar value. Longer pathways have smaller tortuosity and more generations, and duct length per generation is almost constant irrespective of generation, which agrees well with available experimental data. The pathway structure of cone and chestnut-like cone acini is similar to the surface acini's features reported in experiments. According to space-filling requirements in the lung, other conical acini may also be acceptable. The mathematical acinus structure model with various conical shapes can be a platform for computational studies on regional differences in lung functions along the lung surface, underlying respiratory physiology and pathophysiology.

Monitoring Lung Injury Severity and Ventilation Intensity during Mechanical Ventilation

Acute respiratory distress syndrome (ARDS) is a severe form of respiratory failure burden by high hospital mortality. No specific pharmacologic treatment is currently available and its ventilatory management is a key strategy to allow reparative and regenerative lung tissue processes. Unfortunately, a poor management of mechanical ventilation can induce ventilation induced lung injury (VILI) caused by physical and biological forces which are at play. Different parameters have been described over the years to assess lung injury severity and facilitate optimization of mechanical ventilation. Indices of lung injury severity include variables related to gas exchange abnormalities, ventilatory setting and respiratory mechanics, ventilation intensity, and the presence of lung hyperinflation versus derecruitment. Recently, specific indexes have been proposed to quantify the stress and the strain released over time using more comprehensive algorithms of calculation such as the mechanical power, and the interaction between driving pressure (DP) and respiratory rate (RR) in the novel DP multiplied by four plus RR [(4 × DP) + RR] index. These new parameters introduce the concept of ventilation intensity as contributing factor of VILI. Ventilation intensity should be taken into account to optimize protective mechanical ventilation strategies, with the aim to reduce intensity to the lowest level required to maintain gas exchange to reduce the potential for VILI. This is further gaining relevance in the current era of phenotyping and enrichment strategies in ARDS.

Plasma and bronchoalveolar lavage fluid oxylipin levels in experimental porcine lung injury

Inflammatory signaling pathways involving eicosanoids and other regulatory lipid mediators are a subject of intensive study, and a role for these in acute lung injury is not yet well understood. We hypothesized that oxylipin release from lung injury could be detected in bronchoalveolar lavage fluid and in plasma. In a porcine model of surfactant depletion, ventilation with hyperinflation was assessed. Bronchoalveolar lavage and plasma samples were analyzed for 37 different fatty acid metabolites (oxylipins). Over time, hyperinflation altered concentrations of 4 oxylipins in plasma (TXB₂, PGE₂, 15-HETE and 11-HETE), and 9 oxylipins in bronchoalveolar lavage fluid (PGF_2α, PGE₂, PGD₂, 12,13-DiHOME, 11,12-DiHETrE, 13-HODE, 9-HODE, 15-HETE, 11-HETE). Acute lung injury caused by high tidal volume ventilation in this porcine model was associated with rapid changes in some elements of the oxylipin profile, detectable in lavage fluid, and plasma. These oxylipins may be relevant in the pathogenesis of acute lung injury by hyperinflation.

Nanomedicines Targeting Respiratory Injuries for Pulmonary Disease Management

The respiratory system holds crucial importance in the biology of vertebrate animals. Injuries of the respiratory system caused by viral infections (e.g., by COVID‐19, MERS, and SARS) can lead to severe or lethal conditions. So far there are no effective treatments for respiratory injuries. This represents a highly unmet clinical need, e.g., during the current COVID‐19 pandemic. Nanomedicines have high potential in the treatment of respiratory injuries. In this review, the pathology and clinical treatments of major respiratory injuries, acute lung injury, and acute respiratory distress syndrome are briefly summarized. The review primarily focuses on nanomedicines based on liposomes, solid lipid nanoparticles, polymeric nanoparticles, and inorganic nanoparticles, which are tested in preclinical models for the treatment of respiratory injuries. These nanomedicines are utilized to deliver a variety of therapeutic agents, including corticosteroids, statins, and nucleic acids. Furthermore, nanomedicines are also investigated for other respiratory diseases including chronic obstructive pulmonary disease and asthma. The promising preclinical results of various nanoformulations from these studies suggest the potential of nanomedicines for future clinical management of respiratory viral infections and diseases.

Fengreqing Oral Liquid Exerts Anti-Inflammatory Effects by Promoting Apoptosis and Inhibiting PI3K/AKT and NF-κB Signaling Pathways

Fengreqing oral liquid (FOL), a Chinese patent drug frequently used in clinical practice in China, is effective in treating inflammatory diseases of the upper respiratory tract such as colds and flu. However, its anti-inflammatory effects and mechanisms remain to be elucidated. In this study, the anti-inflammatory effects of FOL and its mechanisms on PI3K/AKT and NF-κB signaling pathways in LPS-induced RAW264.7 cells were explored, as well as the regulatory effect of FOL on apoptosis. In addition, the potential of FOL for the treatment of acute lung injury was explored in LPS-induced ALI mice. The results showed that treatment with FOL significantly reduced the levels of interleukin 1β (IL-1β), interleukin 6 (IL-6), nitric oxide (NO), and tumor necrosis factor α (TNF-α) in the supernatant of LPS-induced RAW264.7 cells, and also significantly reduced the phosphorylated protein levels of PI3K and AKT in the PI3K/AKT signaling pathway and also protein levels of NF-κB p50, phosphorylated NF-κB p65, and IκBα in the NF-κB signaling pathway. In addition, the results showed that FOL induced apoptosis in LPS-induced RAW264.7 cells at the level of 80%–90%, and significantly increased the protein expression levels of the pro-apoptotic Bax and cleaved-caspase-3. In LPS-induced ALI mice, FOL administration showed inhibition of IL-1β, IL-6, and TNF-α in Bronchoalveolar lavage fluid (BALF) and decreased protein expression levels of PI3K, AKT, NF-κB p50, and NF-κB p65, and elevated protein expression levels of Bax and cleaved-caspase-3 significantly. These results suggest that FOL may exert anti-inflammatory effects by inhibiting the PI3K/AKT signaling pathway to promote apoptosis and leading to attenuated activation of the NF-κB signaling pathway.

Molecular hydrogen is a potential protective agent in the management of acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome, which is a more severe form of ALI, are life-threatening clinical syndromes observed in critically ill patients. Treatment methods to alleviate the pathogenesis of ALI have improved to a great extent at present. Although the efficacy of these therapies is limited, their relevance has increased remarkably with the ongoing pandemic caused by the novel coronavirus disease 2019 (COVID-19), which causes severe respiratory distress syndrome. Several studies have demonstrated the preventive and therapeutic effects of molecular hydrogen in the various diseases. The biological effects of molecular hydrogen mainly involve anti-inflammation, antioxidation, and autophagy and cell death modulation. This review focuses on the potential therapeutic effects of molecular hydrogen on ALI and its underlying mechanisms and aims to provide a theoretical basis for the clinical treatment of ALI and COVID-19.

Effects of the Prone Position on Regional Neutrophilic Lung Inflammation According to 18F-FDG Pet in an Experimental Ventilator-Induced Lung Injury Model

ABSTRACT

Ventilator-induced lung injury (VILI) can be life-threatening and it is important to prevent the development of VILI. It remains unclear whether the prone position affects neutrophilic inflammation in the lung regions in vivo, which plays a crucial role in the pathogenesis of VILI. This study aimed to assess the relationship between the use of the prone position and the development of VILI-associated regional neutrophilic lung inflammation. Regional neutrophilic lung inflammation and lung aeration during low tidal volume mechanical ventilation were assessed using in vivo 2-deoxy-2-[(18)F] fluoro-D-glucose (18F-FDG) positron emission tomography and computed tomography in acutely experimentally injured rabbit lungs (lung injury induced by lung lavage and excessive ventilation). Direct comparisons were made among three groups: control, supine, and prone positions. After approximately 7 h, tissue-normalized 18F-FDG uptake differed significantly between the supine and prone positions (SUP: 0.038 ± 0.014 vs. PP: 0.029 ± 0.008, P = 0.038), especially in the ventral region (SUP: 0.052 ± 0.013 vs. PP: 0.026 ± 0.007, P = 0.003). The use of the prone position reduced lung inhomogeneities, which was demonstrated by the correction of the disproportionate rate of voxel gas over the given lung region. The progression of neutrophilic inflammation was affected by the interaction between the total strain (for aeration) and the inhomogeneity. The prone position is effective in slowing down the progression of VILI-associated neutrophilic inflammation. Under low-tidal-volume ventilation, the main drivers of its effect may be homogenization of lung tissue and that of mechanical forces.

JFNE-A isolated from Jing-Fang n-butanol extract attenuates lipopolysaccharide-induced acute lung injury by inhibiting oxidative stress and the NF-κB signaling pathway via promotion of autophagy

BACKGROUND

Jing-Fang powder consists of Jingjie (Nepeta tenuifolia Benth, (Lamiaceae)). and Fangfeng (Saposhnikovia divaricata (Turcz.) Schischk, (Apiaceae)) Previous studies have revealed that the Jing-Fang powder n-butanol extract (JFNE) has anti-acute lung injury (ALI) and anti-inflammatory properties; however, the active ingredient and mechanism remain unknown.

PURPOSE

In the present study, we investigated the anti-inflammatory effect of a bioactive fraction obtained from JFNE(JFNE-A) on lipopolysaccharide (LPS)-induced ALI in mice and explored the underlying mechanism.

STUDY DESIGN

The anti-acute lung injury effect and mechanism of JFNE-A was investigated by prophylactic administration of JFNE-A in mice with LPS-induced acute lung injury.

METHODS

The expression levels of myeloperoxidase(MPO) in lung tissues of mice and interleukin(IL)-6, tumor necrosis factor(TNF)-α, IL-1β, IL-5, interferon (IFN)-γ, monocyte chemotactic protein (MCP)-1, macrophage colony stimulating factor (M-CSF), macrophage inflammatory protein (MIP)-1α, and MIP-1β in bronchi alveolar lavage fluid (BALF) were detected by reagent kit and the histological changes were examined by hematoxylin and eosin (H & E) for general histopathological conditions under a light microscope. In addition, the ultrastructure of the cells in lung tissues were observed and photographed under a transmission electron microscope. The expression levels of protein were detected via Western blotting and the mRNA expression of relative genes were determined of via reverse transcriptase polymerase chain reaction (RT-PCR). What's more, we also further clarified the potential targets of JFNE-A through network pharmacology analysis, which could be utilized in ALI treatment.

RESULTS

Our results showed that pretreatment with JFNE-A for 7 days significantly reduced the lung pathological injury score, alleviated pulmonary edema, and decreased the lung tissue MPO level. Mechanistically, JFNE-A dramatically downregulated the protein levels of IL-6, TNF-α, IL-1β, M-CSF, and IFN-γ in BALF and mRNA expression levels of IL-6, TNF-α, IL-1β, and IFN-γ in lung tissues. JFNE-A also significantly lowered the protein levels of iNOS and phosphorylated NF-κB (p65) and mRNA expression levels of iNOS, Rela, CHUK, and NF-κB1, and also elevated the protein expression levels of Nrf2, HO-1, and SOD1 and the mRNA expression levels of Nrf2, Hmox1, and Keap-1 in the lungs. Moreover, JFNE-A significantly decreased the protein expression of p62 and increased the ratio of LC3II/LC3I. It also upregulated the mRNA expression levels of Atg5 and Beclin-1, whereas it reduced the mRNA expression level of SQSTM1 and increased autophagosome structures.

CONCLUSION

Overall, treatment with JFNE-A ameliorated LPS-induced ALI in mice by suppressing the NF-κB signaling pathways and promoting Nrf2 signaling pathways by accelerating autophagy.

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.

Prospective comparison of the effects of intraoperative goal-directed fluid therapy and restrictive fluid therapy on complications in thoracoscopic lobectomy

Objective

Restrictive fluid therapy is recommended in thoracoscopic lobectomy to reduce postoperative pulmonary complications, but it may contribute to hypovolemia. Goal-directed fluid therapy (GDFT) regulates fluid infusion to an amount required to avoid dehydration. We compared the effects of GDFT versus restrictive fluid therapy on postoperative complications after thoracoscopic lobectomy.

Methods

In total, 124 patients who underwent thoracoscopic lobectomy were randomized into the GDFT group (group G, n = 62) or restrictive fluid therapy group (group R, n = 62). The fluid volume and postoperative complications within 30 days of surgery were recorded.

Results

The total fluid volume in groups G and R was 1332 ± 364 and 1178 ± 278 mL, respectively. Group R received a smaller colloid fluid volume (523 ± 120 vs. 686 ± 180 mL), had a smaller urine output (448 ± 98 vs. 491 ± 101 mL), and received more norepinephrine (120 ± 66 vs. 4 ± 18 µg) than group G. However, there were no significant differences in postoperative pulmonary complications, acute kidney injury, length of hospital stay, or in-hospital mortality between the two groups.

Conclusion

Restrictive fluid therapy performs similarly to GDFT in thoracoscopic lobectomy but is a simpler fluid strategy than GDFT.

Trial registration: This study has been registered at the Chinese Clinical Trial Registry (ChiCTR2100051339) (http://www.chictr.org.cn/index.aspx).

Pathophysiology of Acute Respiratory Distress Syndrome and COVID-19 Lung Injury

The pathophysiology of acute respiratory distress syndrome (ARDS) is marked by inflammation-mediated disruptions in alveolar-capillary permeability, edema formation, reduced alveolar clearance and collapse/derecruitment, reduced compliance, increased pulmonary vascular resistance, and resulting gas exchange abnormalities due to shunting and ventilation-perfusion mismatch. Mechanical ventilation, especially in the setting of regional disease heterogeneity, can propagate ventilator-associated injury patterns including barotrauma/volutrauma and atelectrauma. Lung injury due to the novel coronavirus SARS-CoV-2 resembles other causes of ARDS, though its initial clinical characteristics may include more profound hypoxemia and loss of dyspnea perception with less radiologically-evident lung injury, a pattern not described previously in ARDS.

Influence of rosuvastatin treatment on cerebral inflammation and nitro-oxidative stress in experimental lung injury in pigs

BACKGROUND

Many patients with acute respiratory distress syndrome (ARDS) suffer from cognitive impairment after hospital discharge. Different mechanisms have been implicated as potential causes for this impairment, inter alia cerebral inflammation. A class of drugs with antioxidant and anti-inflammatory properties are β-HMG-CoA-reductase inhibitors ("statins"). We hypothesized that treatment with rosuvastatin attenuates cerebral cytokine mRNA expression and nitro-oxidative stress in an animal model of acute lung injury.

METHODS

After approval of the institutional and state animal care committee, we performed this prospective randomized controlled animal study in accordance with the international guidelines for the care and use of laboratory animals. Thirty-two healthy male pigs were randomized to one of four groups: lung injury by central venous injection of oleic acid (n = 8), statin treatment before and directly after lung injury (n = 8), statin treatment after lung injury (n = 8), or ventilation-only controls (n = 8). About 18 h after lung injury and standardized treatment, the animals were euthanised, and the brains and lungs were collected for further examinations. We determined histologic lung injury and cerebral and pulmonal cytokine and 3-nitrotyrosine production.

RESULTS

We found a significant increase in hippocampal IL-6 mRNA after lung injury (p < 0.05). Treatment with rosuvastatin before and after induction of lung injury led to a significant reduction of hippocampal IL-6 mRNA (p < 0.05). Cerebral 3-nitrotyrosine was significantly higher in lung-injured animals compared with all other groups (p < 0.05 vs. animals treated with rosuvastatin after lung injury induction; p < 0.001 vs. all other groups). 3-Nitrotyrosine was also increased in the lungs of the lung-injured pigs compared to all other groups (p < 0.05 each).

CONCLUSIONS

Our findings highlight cerebral cytokine production and nitro-oxidative stress within the first day after induction of lung injury. The treatment with rosuvastatin reduced IL-6 mRNA and 3-nitrotyrosine concentration in the brains of the animals. In earlier trials, statin treatment did not reduce mortality in ARDS patients but seemed to improve quality of life in ARDS survivors. Whether this is attributable to better cognitive function because of reduced nitro-oxidative stress and inflammation remains to be elucidated.

The pathogenic role of epithelial and endothelial cells in early-phase COVID-19 pneumonia: victims and partners in crime

Current understanding of the complex pathogenesis of COVID-19 interstitial pneumonia pathogenesis in the light of biopsies carried out in early/moderate phase and histology data obtained at postmortem analysis is discussed. In autopsies the most observed pattern is diffuse alveolar damage with alveolar-epithelial type-II cell hyperplasia, hyaline membranes, and frequent thromboembolic disease. However, these observations cannot explain some clinical, radiological and physiopathological features observed in SARS-CoV-2 interstitial pneumonia, including the occurrence of vascular enlargement on CT and preserved lung compliance in subjects even presenting with or developing respiratory failure. Histological investigation on early-phase pneumonia on perioperative samples and lung biopsies revealed peculiar morphological and morpho-phenotypical changes including hyper-expression of phosphorylated STAT3 and immune checkpoint molecules (PD-L1 and IDO) in alveolar-epithelial and endothelial cells. These features might explain in part these discrepancies.

Incidence of Fat Embolism Syndrome in Femur Fractures and Its Associated Risk Factors over Time-A Systematic Review

BACKGROUND

Fat embolism (FE) continues to be mentioned as a substantial complication following acute femur fractures. The aim of this systematic review was to test the hypotheses that the incidence of fat embolism syndrome (FES) has decreased since its description and that specific injury patterns predispose to its development.

MATERIALS AND METHODS

Data Sources: MEDLINE, Embase, PubMed, and Cochrane Central Register of Controlled Trials databases were searched for articles from 1 January 1960 to 31 December 2019.

STUDY SELECTION

Original articles that provide information on the rate of FES, associated femoral injury patterns, and therapeutic and diagnostic recommendations were included.

DATA EXTRACTION

Two authors independently extracted data using a predesigned form.

STATISTICS

Three different periods were separated based on the diagnostic and treatment changes: Group 1: 1 January 1960-12 December 1979, Group 2: 1 January 1980-1 December 1999, and Group 3: 1 January 2000-31 December 2019, chi-square test, χ² test for group comparisons of categorical variables, p-value < 0.05.

RESULTS

Fifteen articles were included (n = 3095 patients). The incidence of FES decreased over time (Group 1: 7.9%, Group 2: 4.8%, and Group 3: 1.7% (p < 0.001)). FES rate according to injury pattern: unilateral high-energy fractures (2.9%) had a significantly lower FES rate than pathological fractures (3.3%) and bilateral high-energy fractures (4.6%) (p < 0.001).

CONCLUSIONS

There has been a significant decrease in the incidence of FES over time. The injury pattern impacts the frequency of FES. The diagnostic and therapeutic approach to FES remains highly heterogenic to this day.

The steady motion of microbubbles in bifurcating airways: Role of shear-thinning and surface tension

Mucous fluid is non-Newtonian secretions in the lower lung airways that accumulates when the alveolar-capillary membrane ruptures during acute respiratory distress syndrome. The mucus fluid has, therefore, different types of non-Newtonian properties like shear-thinning, viscoelasticity, and non-zero yield stress. In this paper, we numerically solved the steady Stokes equations along with arbitrary Eulerian-Lagrangian moving mesh techniques to study the microbubble propagation in a two-dimensional asymmetric bifurcating airway filled with non-Newtonian fluid where the fluid has shear-thinning behavior described by the power-law model. Numerical results show that both shear-thinning and surface tension characterized by the behavior index (n) and Capillary number (Ca), respectively, had a significant impact on microbubble flow patterns and the magnitude of the pressure gradient. At low values of both n and Ca, the microbubble leaves a thin film-thickness with the airway wall while a large and sharp peak of the pressure gradient near the thin bubble tip. Interestingly, increasing both n and Ca, leads to an increase in film thickness and a decrease in the pressure gradient magnitude in both the daughter airway walls. It is observed the magnitude of the pressure gradient is more sensitive to Ca compared to n. We concluded that shear-thinning and surface tension not only significantly impact the patterns of microbubble propagation but also the hydrodynamic stress magnitudes at the airway wall.

Experimental lung injury induces cerebral cytokine mRNA production in pigs

Background

Acute respiratory distress syndrome (ARDS) is an important disease with a high incidence among patients admitted to intensive care units. Over the last decades, the survival of critically ill patients has improved; however, cognitive deficits are among the long-term sequelae. We hypothesize that acute lung injury leads to upregulation of cerebral cytokine synthesis.

Methods

After approval of the institutional and animal care committee, 20 male pigs were randomized to one of three groups: (1) Lung injury by oleic acid injection (OAI), (2) ventilation only (CTR) or (3) untreated. We compared neuronal numbers, proportion of neurons with markers for apoptosis, activation state of Iba-1 stained microglia cells and cerebral mRNA levels of different cytokines between the groups 18 hours after onset of lung injury.

Results

We found an increase in hippocampal TNFalpha (p < 0.05) and IL-6 (p < 0.05) messenger RNA (mRNA) in the OAI compared to untreated group as well as higher hippocampal IL-6 mRNA compared to control (p < 0.05). IL-8 and IL-1beta mRNA showed no differences between the groups. We found histologic markers for beginning apoptosis in OAI compared to untreated (p < 0.05) and more active microglia cells in OAI and CTR compared to untreated (p < 0.001 each).

Conclusion

Hippocampal cytokine transcription increases within 18 hours after the induction of acute lung injury with histological evidence of neuronal damage. It remains to be elucidated if increased cytokine mRNA synthesis plays a role in the cognitive decline observed in survivors of ARDS.

Hidden Microatelectases Increase Vulnerability to Ventilation-Induced Lung Injury

Mechanical ventilation of lungs suffering from microatelectases may trigger the development of acute lung injury (ALI). Direct lung injury by bleomycin results in surfactant dysfunction and microatelectases at day 1 while tissue elastance and oxygenation remain normal. Computational simulations of alveolar micromechanics 1-day post-bleomycin predict persisting microatelectases throughout the respiratory cycle and increased alveolar strain during low positive end-expiratory pressure (PEEP) ventilation. As such, we hypothesize that mechanical ventilation in presence of microatelectases, which occur at low but not at higher PEEP, aggravates and unmasks ALI in the bleomycin injury model. Rats were randomized and challenged with bleomycin (B) or not (H = healthy). One day after bleomycin instillation the animals were ventilated for 3 h with PEEP 1 (PEEP1) or 5 cmH₂O (PEEP5) and a tidal volume of 10 ml/kg bodyweight. Tissue elastance was repetitively measured after a recruitment maneuver to investigate the degree of distal airspace instability. The right lung was subjected to bronchoalveolar lavage (BAL), the left lung was fixed for design-based stereology at light- and electron microscopic level. Prior to mechanical ventilation, lung tissue elastance did not differ. During mechanical ventilation tissue elastance increased in bleomycin-injured lungs ventilated with PEEP = 1 cmH₂O but remained stable in all other groups. Measurements at the conclusion of ventilation showed the largest time-dependent increase in tissue elastance after recruitment in B/PEEP1, indicating increased instability of distal airspaces. These lung mechanical findings correlated with BAL measurements including elevated BAL neutrophilic granulocytes as well as BAL protein and albumin in B/PEEP1. Moreover, the increased septal wall thickness and volume of peri-bronchiolar-vascular connective tissue in B/PEEP1 suggested aggravation of interstitial edema by ventilation in presence of microatelectases. At the electron microscopic level, the largest surface area of injured alveolar epithelial was observed in bleomycin-challenged lungs after PEEP = 1 cmH₂O ventilation. After bleomycin treatment cellular markers of endoplasmic reticulum stress (p-Perk and p-EIF-2α) were positive within the septal wall and ventilation with PEEP = 1 cmH₂O ventilation increased the surface area stained positively for p-EIF-2α. In conclusion, hidden microatelectases are linked with an increased pulmonary vulnerability for mechanical ventilation characterized by an aggravation of epithelial injury.

Sine ventilation in lung injury models: a new perspective for lung protective ventilation

Mechanical ventilation is associated with the risk of ventilator induced lung injury. For reducing lung injury in mechanically ventilated patients, the application of small tidal volumes and positive end-expiratory pressures has become clinical standard. Recently, an approach based on linear airway pressure decline and decelerated expiratory flow during expiration implied lung protective capacities. We assumed that ventilation with a smoothed, i.e. sinusoidal airway pressure profile may further improve ventilation efficiency and lung protection. We compared the effects of mechanical ventilation with sinusoidal airway pressure profile (SINE) regarding gas exchange, respiratory system compliance and histology to conventional volume and pressure controlled ventilation (VCV and PCV) and to VCV with flow-controlled expiration (FLEX) in two rat models of lung injury, tween induced surfactant depletion and high tidal volume mechanical ventilation. In both lung injury models ventilation with SINE showed more efficient CO₂ elimination and blood oxygenation, improved respiratory system compliance and resulted in lower alveolar wall thickness, compared to VCV, PCV and FLEX. Optimization of the airway pressure profile may provide a novel means of lung protective mechanical ventilation.

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.

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.

Surfactant Protein B Deficiency Induced High Surface Tension: Relationship between Alveolar Micromechanics, Alveolar Fluid Properties and Alveolar Epithelial Cell Injury

High surface tension at the alveolar air-liquid interface is a typical feature of acute and chronic lung injury. However, the manner in which high surface tension contributes to lung injury is not well understood. This study investigated the relationship between abnormal alveolar micromechanics, alveolar epithelial injury, intra-alveolar fluid properties and remodeling in the conditional surfactant protein B (SP-B) knockout mouse model. Measurements of pulmonary mechanics, broncho-alveolar lavage fluid (BAL), and design-based stereology were performed as a function of time of SP-B deficiency. After one day of SP-B deficiency the volume of alveolar fluid V(alvfluid,par) as well as BAL protein and albumin levels were normal while the surface area of injured alveolar epithelium S(AEinjure,sep) was significantly increased. Alveoli and alveolar surface area could be recruited by increasing the air inflation pressure. Quasi-static pressure-volume loops were characterized by an increased hysteresis while the inspiratory capacity was reduced. After 3 days, an increase in V(alvfluid,par) as well as BAL protein and albumin levels were linked with a failure of both alveolar recruitment and airway pressure-dependent redistribution of alveolar fluid. Over time, V(alvfluid,par) increased exponentially with S(AEinjure,sep). In conclusion, high surface tension induces alveolar epithelial injury prior to edema formation. After passing a threshold, epithelial injury results in vascular leakage and exponential accumulation of alveolar fluid critically hampering alveolar recruitability.

Computational Modeling of Primary Blast Lung Injury: Implications for Ventilator Management

Primary blast lung injury (PBLI) caused by exposure to high-intensity pressure waves is associated with parenchymal tissue injury and severe ventilation-perfusion mismatch. Although supportive ventilation is often required in patients with PBLI, maldistribution of gas flow in mechanically heterogeneous lungs may lead to further injury due to increased parenchymal strain and strain rate, which are difficult to predict in vivo. In this study, we developed a computational lung model with mechanical properties consistent with healthy and PBLI conditions. PBLI conditions were simulated with bilateral derecruitment and increased perihilar tissue stiffness. As a result of these tissue abnormalities, airway flow was heterogeneously distributed in the model under PBLI conditions, during both conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation. PBLI conditions resulted in over three-fold higher parenchymal strains compared to the healthy condition during CMV, with flow distributed according to regional tissue stiffness. During high-frequency oscillatory ventilation, flow distribution became increasingly heterogeneous and frequency-dependent. We conclude that the distribution and rate of parenchymal distension during mechanical ventilation depend on PBLI severity as well as ventilatory modality. These simulations may allow realistic assessment of the risks associated with ventilator-induced lung injury following PBLI, and facilitate the development of alternative lung-protective ventilation modalities.

Heterogeneous structure and surface tension effects on mechanical response in pulmonary acinus: A finite element analysis

BACKGROUND

The pulmonary acinus is a dead-end microstructure that consists of ducts and alveoli. High-resolution micro-CT imaging has recently provided detailed anatomical information of a complete in vivo acinus, but relating its mechanical response with its detailed acinar structure remains challenging. This study aimed to investigate the mechanical response of acinar tissue in a whole acinus for static inflation using computational approaches.

METHODS

We performed finite element analysis of a whole acinus for static inflation. The acinar structure model was generated based on micro-CT images of an intact acinus. A continuum mechanics model of the lung parenchyma was used for acinar tissue material model, and surface tension effects were explicitly included. An anisotropic mechanical field analysis based on a stretch tensor was combined with a curvature-based local structure analysis.

FINDINGS

The airspace of the acinus exhibited nonspherical deformation as a result of the anisotropic deformation of acinar tissue. A strain hotspot occurred at the ridge-shaped region caused by a rod-like deformation of acinar tissue on the ridge. The local structure becomes bowl-shaped for inflation and, without surface tension effects, the surface of the bowl-shaped region primarily experiences isotropic deformation. Surface tension effects suppressed the increase in airspace volume and inner surface area, while facilitating anisotropic deformation on the alveolar surface.

INTERPRETATION

In the lungs, the heterogeneous acinar structure and surface tension induce anisotropic deformation at the acinar and alveolar scales. Further research is needed on structural variation of acini, inter-acini connectivity, or dynamic behavior to understand multiscale lung mechanics.

Microarray profiling of lung long non-coding RNAs and mRNAs in lipopolysaccharide-induced acute lung injury mouse model

Long non-coding RNAs (lncRNAs) are involved in various biological processes as well as many respiratory diseases, while the role of lncRNAs in acute lung injury (ALI) remains unclear. The present study aimed to profile the expression of lung lncRNAs and mRNAs in lipopolysaccharide (LPS)-induced ALI mouse model. C57BL/6 mice were exposed to LPS or phosphate-buffered saline for 24 h, and lncRNAs and mRNAs were profiled by Arraystar mouse LncRNA Array V3.0. Bioinformatics analysis gene ontology including (GO) and pathway analysis and cell study in vitro was used to investigate potential mechanisms. Based on the microarray results, 2632 lncRNAs and 2352 mRNAs were differentially expressed between ALI and control mice. The microarray results were confirmed by the quantitative real-time PCR (qRT-PCR) results of ten randomized selected lncRNAs. GO analysis showed that the altered mRNAs were mainly related to the processes of immune system, immune response and defense response. Pathway analysis suggests that tumor necrosis factor (TNF) signaling pathway, NOD-like receptor pathway, and cytokine-cytokine receptor interaction may be involved in ALI. LncRNA-mRNA co-expression network analysis indicated that one individual lncRNA may interact with several mRNAs, and one individual mRNA may also interact with several lncRNAs. Small interfering RNA (siRNA) for ENSMUST00000170214.1, - ENSMUST00000016031.13 significantly inhibited LPS-induced TNF-α and interleukin (IL)-1β production in murine RAW264.7 macrophages. Our results found significant changes of lncRNAs and mRNAs in the lungs of LPS-induced ALI mouse model, and intervention targeting lncRNAs may attenuate LPS-induced inflammation, which may help to elucidate the role of lncRNAs in the pathogenesis and treatment of ALI.

Evaluation of ventilator on lung profile of piglets (Sus scrofa) in hypovolemic shock treated with hypervolemic crystalloid resuscitation

AIM

This study was conducted to assess the effect of ventilators on the lung profile of piglets in the hypovolemic shock before and after the excessive resuscitation of the crystalloid fluid.

MATERIALS AND METHODS

Five male piglets were used in this study as the models of shock, and there are four phases of treatment: Stabilization, shock of bleeding, normovolemic resuscitation, and hypervolemic resuscitation. The application of mechanical ventilation to patients who suspected of having lung injury may worsen the patient's conditions. The purpose of this study was to set the ventilator with the set of positive end-expiratory pressure (PEEP) of 5 cm H2O, thefraction of inspired oxygen (FiO2) of 0.5, and the inspiration: expiration (I: E) ratio of 1:2, which was applied from the stabilization phase. The shock induction was performed by removing the blood until the mean arterial pressure decreasing by 20% from the stabilization. The solution of NaCl 0.9% was used for the normovolemic and hypervolemic resuscitation. The parameter of observation consisted of extravascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI) on pulse contour cardiac output 2 and exhaled tidal volume (VTE), peak inspiratory pressure (PIP), and respiratory rate (RR) on ventilators.

RESULTS

EVLWI does not indicate pulmonary edema. A significant decrease in VTE without any significant alterations in EVLWI, PIP, and RR has indicated the shallow breathing in the shock condition. Therefore, the PVPI parameter cannot be used as a parameter for capillary permeability since its formulation does not reinforce the results of data in the shock condition. The set of the ventilator may prevent the increase of EVLWI, and the uses of ventilators do not worsen the patient's conditions during the crystalloid resuscitation.

CONCLUSION

The use of mechanical ventilator as the support does not worsen the hypovolemic condition and is safe to use as long as the lung profile is not indicated to have lung injury.

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.

Effect of lung recruitment and titrated positive end-expiratory pressure (PEEP) versus low PEEP on patients with moderate-severe acute respiratory distress syndrome: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Setting a positive end-expiratory pressure (PEEP) on patients with acute respiratory distress syndrome (ARDS) receiving mechanical ventilation has been an issue of great contention. Therefore, we aimed to determine effects of lung recruitment maneuver (RM) and titrated PEEP versus low PEEP on adult patients with moderate-severe ARDS.

METHODS

Data sources and study selection proceeded as follows: PubMed, Ovid, EBSCO, and Cochrane Library databases were searched from 2003 to May 2018. Original clinical randomized controlled trials which met the eligibility criteria were included. To compare the prognosis between the titrated PEEP and low PEEP groups on patients with moderate-severe ARDS (PaO2/FiO2 < 200 mmHg). Heterogeneity was quantified through the I2 statistic. Egger's test and funnel plots were used to assess publication bias.

RESULTS

No difference was found in 28-day mortality and ICU mortality (OR = 0.97, 95% CI (0.61-1.52), p = 0.88; OR = 1.14, 95% CI (0.91-1.43), p = 0.26, respectively). Only ventilator-free days, length of stay in the ICU, length of stay in hospital, and incidence of barotrauma could be systematically reviewed owing to bias and extensive heterogeneity.

CONCLUSION

No difference was observed in the RM between the titrated PEEP and the low PEEP in 28-day mortality and ICU mortality on patients with moderate-severe ARDS.

Alveolar Micromechanics in Bleomycin-induced Lung Injury

Lung injury results in intratidal alveolar recruitment and derecruitment and alveolar collapse, creating stress concentrators that increase strain and aggravate injury. In this work, we sought to describe alveolar micromechanics during mechanical ventilation in bleomycin-induced lung injury and surfactant replacement therapy. Structure and function were assessed in rats 1 day and 3 days after intratracheal bleomycin instillation and after surfactant replacement therapy. Pulmonary system mechanics were measured during ventilation with positive end-expiratory pressures (PEEPs) between 1 and 10 cm H2O, followed by perfusion fixation at end-expiratory pressure at airway opening (Pao) values of 1, 5, 10, and 20 cm H2O for quantitative analyses of lung structure. Lung structure and function were used to parameterize a physiologically based, multicompartment computational model of alveolar micromechanics. In healthy controls, the numbers of open alveoli remained stable in a range of Pao = 1-20 cm H2O, whereas bleomycin-challenged lungs demonstrated progressive alveolar derecruitment with Pao < 10 cm H2O. At Day 3, ∼40% of the alveoli remained closed at high Pao, and alveolar size heterogeneity increased. Simulations of injured lungs predicted that alveolar recruitment pressures were much greater than the derecruitment pressures, so that minimal intratidal recruitment and derecruitment occurred during mechanical ventilation with a tidal volume of 10 ml/kg body weight over a range of PEEPs. However, the simulations also predicted a dramatic increase in alveolar strain with injury that we attribute to alveolar interdependence. These findings suggest that in progressive lung injury, alveolar collapse with increased distension of patent (open) alveoli dominates alveolar micromechanics. PEEP and surfactant substitution reduce alveolar collapse and dynamic strain but increase static strain.

The micromechanics of lung alveoli: structure and function of surfactant and tissue components

The mammalian lung´s structural design is optimized to serve its main function: gas exchange. It takes place in the alveolar region (parenchyma) where air and blood are brought in close proximity over a large surface. Air reaches the alveolar lumen via a conducting airway tree. Blood flows in a capillary network embedded in inter-alveolar septa. The barrier between air and blood consists of a continuous alveolar epithelium (a mosaic of type I and type II alveolar epithelial cells), a continuous capillary endothelium and the connective tissue layer in-between. By virtue of its respiratory movements, the lung has to withstand mechanical challenges throughout life. Alveoli must be protected from over-distension as well as from collapse by inherent stabilizing factors. The mechanical stability of the parenchyma is ensured by two components: a connective tissue fiber network and the surfactant system. The connective tissue fibers form a continuous tensegrity (tension + integrity) backbone consisting of axial, peripheral and septal fibers. Surfactant (surface active agent) is the secretory product of type II alveolar epithelial cells and covers the alveolar epithelium as a biophysically active thin and continuous film. Here, we briefly review the structural components relevant for gas exchange. Then we describe our current understanding of how these components function under normal conditions and how lung injury results in dysfunction of alveolar micromechanics finally leading to lung fibrosis.

Preemptive Mechanical Ventilation Based on Dynamic Physiology in the Alveolar Microenvironment: Novel Considerations of Time-Dependent Properties of the Respiratory System

The acute respiratory distress syndrome (ARDS) remains a serious clinical problem with the current treatment being supportive in the form of mechanical ventilation. However, mechanical ventilation can be a double-edged sword; if set properly, it can significantly reduce ARDS associated mortality but if set improperly it can have unintended consequences causing a secondary ventilator induced lung injury (VILI). The hallmark of ARDS pathology is a heterogeneous lung injury, which predisposes the lung to a secondary VILI. The current standard of care approach is to wait until ARDS is well established and then apply a low tidal volume (LVt) strategy to avoid over-distending the remaining normal lung. However, even with the use of LVt strategy, the mortality of ARDS remains unacceptably high at ~40%. In this review, we analyze the lung pathophysiology associated with ARDS that renders the lung highly vulnerable to a secondary VILI. The current standard of care LVt strategy is critiqued as well as new strategies used in combination with LVt to protect the lung. Using the current understanding of alveolar mechanics (i.e. the dynamic change in alveolar size and shape with tidal ventilation) we provide a rationale for why the current protective ventilation strategies have not further reduced ARDS mortality. New strategies of protective ventilation based on dynamic physiology in the micro-environment (i.e. alveoli and alveolar ducts) are discussed. Current evidence suggests that alveolar inflation and deflation is viscoelastic in nature, with a fast and slow phase in both alveolar recruitment and collapse. Using this knowledge, a ventilation strategy with a prolonged time at inspiration would recruit alveoli and a brief release time at expiration would prevent alveolar collapse, converting heterogeneous to homogeneous lung inflation significantly reducing ARDS incidence and mortality.

High Tidal Volume Induces Mitochondria Damage and Releases Mitochondrial DNA to Aggravate the Ventilator-Induced Lung Injury

Objective

This study aimed to determine whether high tidal volume (HTV) induce mitochondria damage and mitophagy, contributing to the release of mitochondrial DNA (mtDNA). Another aim of the present study was to investigate the role and mechanism of mtDNA in ventilator-induced lung injury (VILI) in rats.

Methods

Rats were tracheotomized and allowed to breathe spontaneously or mechanically ventilated for 4 h. After that, lung injury was assessed. Inhibition of toll-like receptor 9 (TLR9), named ODN2088, was used to determine the involvement of TLR9/myeloid differentiation factor 88 (MyD88)/nuclear factor-κB (NF-κB) signaling pathway in VILI. The mitochondrial damage and release of mtDNA were assessed. Pharmacological inhibition of mtDNA (chloroquine) was used to determine whether mtDNA trigger inflammation via TLR9 in VILI. EDU-labeled mtDNA deriving from mitophagy was assessed by immunofluorescence. The role of mitophagy in VILI was shown by administration of antimycin A and cyclosporine A.

Main results

Rats subjected to HTV showed more severe pulmonary edema and inflammation than the other rats. The decreased expression of TLR9, MyD88, and NF-κB were observed following the use of ODN2088. Mechanical ventilation (MV) with HTV damaged mitochondria which resulted in dysfunctional ATP synthesis, accumulation of reactive oxygen species, and loss of mitochondrial membrane potential. Moreover, the results of distribution of fluorescence in rats upon HTV stimulation indicated that mtDNA cleavage was associated with mitophagy. The expression levels of mitophagy related genes (LC3B-II/LC3B-I, PINK1, Parkin, and mitofusin 1) in animals ventilated with HTV were significantly upregulated. Administration of antimycin A aggregated the histological changes and inflammation after MV, but these effects were attenuated when administered in the presence of cyclosporine A.

Conclusion

MV with HTV induces mitochondrial damage and mitophagy, contributing to the release of mtDNA, which may be induced VILI in rat via TLR9/MyD88/NF-κB signaling pathway.

Acute lung injury: how to stabilize a broken lung

The pathophysiology of acute respiratory distress syndrome (ARDS) results in heterogeneous lung collapse, edema-flooded airways and unstable alveoli. These pathologic alterations in alveolar mechanics (i.e. dynamic change in alveolar size and shape with each breath) predispose the lung to secondary ventilator-induced lung injury (VILI). It is our viewpoint that the acutely injured lung can be recruited and stabilized with a mechanical breath until it heals, much like casting a broken bone until it mends. If the lung can be "casted" with a mechanical breath, VILI could be prevented and ARDS incidence significantly reduced.

Excessive Extracellular ATP Desensitizes P2Y2 and P2X4 ATP Receptors Provoking Surfactant Impairment Ending in Ventilation-Induced Lung Injury

Stretching the alveolar epithelial type I (AT I) cells controls the intercellular signaling for the exocytosis of surfactant by the AT II cells through the extracellular release of adenosine triphosphate (ATP) (purinergic signaling). Extracellular ATP is cleared by extracellular ATPases, maintaining its homeostasis and enabling the lung to adapt the exocytosis of surfactant to the demand. Vigorous deformation of the AT I cells by high mechanical power ventilation causes a massive release of extracellular ATP beyond the clearance capacity of the extracellular ATPases. When extracellular ATP reaches levels >100 μM, the ATP receptors of the AT II cells become desensitized and surfactant impairment is initiated. The resulting alteration in viscoelastic properties and in alveolar opening and collapse time-constants leads to alveolar collapse and the redistribution of inspired air from the alveoli to the alveolar ducts, which become pathologically dilated. The collapsed alveoli connected to these dilated alveolar ducts are subject to a massive strain, exacerbating the ATP release. After reaching concentrations >300 μM extracellular ATP acts as a danger-associated molecular pattern, causing capillary leakage, alveolar space edema, and further deactivation of surfactant by serum proteins. Decreasing the tidal volume to 6 mL/kg or less at this stage cannot prevent further lung injury.

A simplified parametrised model for lung microstructures capable of mimicking realistic geometrical and mechanical properties

The respiratory zone of mammalian lungs contains several millions of so-called alveoli. The geometrical and mechanical properties of this microstructure are crucial for respiration and influence the macroscopic behaviour of the entire organ in health and disease. Hence, if computational models are sought to gain more insight into lung behaviour, predict lung states in certain scenarios or suggest better treatment options in early stages of respiratory dysfunction, an adequate representation of this microstructure is essential. However, investigating the real alveolar architecture requires complex medical-imaging methods and would be computationally extremely expensive. Even worse, there is currently no way of obtaining the real patient-specific microstructure in vivo. Hence, we present a fast and easy to compute parametrised model of lung microstructures based on tetrakaidecahedra which can represent both geometrical and mechanical properties of the parenchyma. We show that gas transport pathways and stress and strain distributions are comparable to real alveolar microstructures and even capable of capturing variations present in biology. The created parametrised lung microstructure models can be utilized in finite element simulations to study, e.g., alveolar flow phenomena, particle deposition, or alveolar stresses and strains during mechanical ventilation. Due to the simpler geometry of the parametrised microgeometries compared to imaging-based microstructures, remarkable savings in CPU time can be achieved. We show that our model requires a minimum of 10% of the computational time for computing the same strain state in structural mechanics simulations compared to imaging-based alveolar microstructures.

Physiology in Medicine: Understanding dynamic alveolar physiology to minimize ventilator-induced lung injury

Acute respiratory distress syndrome (ARDS) remains a serious clinical problem with the main treatment being supportive in the form of mechanical ventilation. However, mechanical ventilation can be a double-edged sword: if set improperly, it can exacerbate the tissue damage caused by ARDS; this is known as ventilator-induced lung injury (VILI). To minimize VILI, we must understand the pathophysiologic mechanisms of tissue damage at the alveolar level. In this Physiology in Medicine paper, the dynamic physiology of alveolar inflation and deflation during mechanical ventilation will be reviewed. In addition, the pathophysiologic mechanisms of VILI will be reviewed, and this knowledge will be used to suggest an optimal mechanical breath profile (MBP: all airway pressures, volumes, flows, rates, and the duration that they are applied at both inspiration and expiration) necessary to minimize VILI. Our review suggests that the current protective ventilation strategy, known as the "open lung strategy," would be the optimal lung-protective approach. However, the viscoelastic behavior of dynamic alveolar inflation and deflation has not yet been incorporated into protective mechanical ventilation strategies. Using our knowledge of dynamic alveolar mechanics (i.e., the dynamic change in alveolar and alveolar duct size and shape during tidal ventilation) to modify the MBP so as to minimize VILI will reduce the morbidity and mortality associated with ARDS.

Purinergic signalling links mechanical breath profile and alveolar mechanics with the pro-inflammatory innate immune response causing ventilation-induced lung injury

Severe pulmonary infection or vigorous cyclic deformation of the alveolar epithelial type I (AT I) cells by mechanical ventilation leads to massive extracellular ATP release. High levels of extracellular ATP saturate the ATP hydrolysis enzymes CD39 and CD73 resulting in persistent high ATP levels despite the conversion to adenosine. Above a certain level, extracellular ATP molecules act as danger-associated molecular patterns (DAMPs) and activate the pro-inflammatory response of the innate immunity through purinergic receptors on the surface of the immune cells. This results in lung tissue inflammation, capillary leakage, interstitial and alveolar oedema and lung injury reducing the production of surfactant by the damaged AT II cells and deactivating the surfactant function by the concomitant extravasated serum proteins through capillary leakage followed by a substantial increase in alveolar surface tension and alveolar collapse. The resulting inhomogeneous ventilation of the lungs is an important mechanism in the development of ventilation-induced lung injury. The high levels of extracellular ATP and the upregulation of ecto-enzymes and soluble enzymes that hydrolyse ATP to adenosine (CD39 and CD73) increase the extracellular adenosine levels that inhibit the innate and adaptive immune responses rendering the host susceptible to infection by invading microorganisms. Moreover, high levels of extracellular adenosine increase the expression, the production and the activation of pro-fibrotic proteins (such as TGF-β, α-SMA, etc.) followed by the establishment of lung fibrosis.

The role of high airway pressure and dynamic strain on ventilator-induced lung injury in a heterogeneous acute lung injury model

BACKGROUND

Acute respiratory distress syndrome causes a heterogeneous lung injury with normal and acutely injured lung tissue in the same lung. Improperly adjusted mechanical ventilation can exacerbate ARDS causing a secondary ventilator-induced lung injury (VILI). We hypothesized that a peak airway pressure of 40 cmH₂O (static strain) alone would not cause additional injury in either the normal or acutely injured lung tissue unless combined with high tidal volume (dynamic strain).

METHODS

Pigs were anesthetized, and heterogeneous acute lung injury (ALI) was created by Tween instillation via a bronchoscope to both diaphragmatic lung lobes. Tissue in all other lobes was normal. Airway pressure release ventilation was used to precisely regulate time and pressure at both inspiration and expiration. Animals were separated into two groups: (1) over-distension + high dynamic strain (OD + H_DS, n = 6) and (2) over-distension + low dynamic strain (OD + L_DS, n = 6). OD was caused by setting the inspiratory pressure at 40 cmH₂O and dynamic strain was modified by changing the expiratory duration, which varied the tidal volume. Animals were ventilated for 6 h recording hemodynamics, lung function, and inflammatory mediators followed by an extensive necropsy.

RESULTS

In normal tissue (N_T), OD + L_DS caused minimal histologic damage and a significant reduction in BALF total protein (p < 0.05) and MMP-9 activity (p < 0.05), as compared with OD + H_DS. In acutely injured tissue (ALI_T), OD + L_DS resulted in reduced histologic injury and pulmonary edema (p < 0.05), as compared with OD + H_DS.

CONCLUSIONS

Both N_T and ALI_T are resistant to VILI caused by OD alone, but when combined with a H_DS, significant tissue injury develops.

CGRP 8-37 enhances lipopolysaccharide-induced acute lung injury and regulating aquaporin 1 and 5 expressions in rats

Calcitonin gene-related peptide (CGRP) has been shown to play important roles in biological functions. However, there is very little evidence on the value of CGRP in lipopolysaccharide (LPS)-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Therefore, this study aimed to investigate the role of CGRP in LPS-induced ALI in rats. In the experiment, Sprague-Dawley (SD) rats were randomized into control, an antagonist of α-calcitonin gene-related peptide receptor (CGRP8-37), LPS groups, and CGRP8-37 + LPS groups. ALI model was prepared through retrograde injection of LPS (10 mg/kg). At 6 and 12 h, bronchoalveolar lavage was performed and used to assess total cell count and levels of tumor necrosis factor-α, interleukin-1β, -6, and -10 by enzyme-linked immunosorbent assay (ELISA). Lung tissue was collected for assessing wet-to-dry (W/D) ratio, hematoxylin and eosin staining. Aquaporin (AQP)-1 and -5 expressions in lung tissues were detected by quantitative PCR and Western blot. The results showed that histological injury, total cell count, and W/D ratio significantly reduced in LPS group after 6 h. The levels of inflammatory cytokines in CGRP8-37 + LPS-treated rats were higher than that in LPS-treated rats (all, P < 0.001). Real-time RT-PCR analysis showed that levels of AQP-1 in rats from CGRP8-37 + LPS group was lower than that in LPS-treated rats (P = 0.005 and P < 0.001). Western blotting analysis showed that AQP-1 protein levels at 6 h significantly decreased in CGRP8-37 + LPS rats. Together, our data suggest that CGRP antagonists, CGRP8-37 could enhance ALI induced by LPS in the rat model, and regulate the expression levels of AQP-1 and AQP-5 by affecting inflammatory cytokines. Thereby, regulating endogenous CGRP may be a potential treatment for ALI/ARDS.