Pre-injured Lungs Research Articles

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.

Exploring alveolar recruitability using positive end-expiratory pressure in mice overexpressing TGF-β1: a structure–function analysis

Pre-injured lungs are prone to injury progression in response to mechanical ventilation. Heterogeneous ventilation due to (micro)atelectases imparts injurious strains on open alveoli (known as volutrauma). Hence, recruitment of (micro)atelectases by positive end-expiratory pressure (PEEP) is necessary to interrupt this vicious circle of injury but needs to be balanced against acinar overdistension. In this study, the lung-protective potential of alveolar recruitment was investigated and balanced against overdistension in pre-injured lungs. Mice, treated with empty vector (AdCl) or adenoviral active TGF-β1 (AdTGF-β1) were subjected to lung mechanical measurements during descending PEEP ventilation from 12 to 0 cmH2O. At each PEEP level, recruitability tests consisting of two recruitment maneuvers followed by repetitive forced oscillation perturbations to determine tissue elastance (H) and damping (G) were performed. Finally, lungs were fixed by vascular perfusion at end-expiratory airway opening pressures (Pao) of 20, 10, 5 and 2 cmH2O after a recruitment maneuver, and processed for design-based stereology to quantify derecruitment and distension. H and G were significantly elevated in AdTGF-β1 compared to AdCl across PEEP levels. H was minimized at PEEP = 5–8 cmH2O and increased at lower and higher PEEP in both groups. These findings correlated with increasing septal wall folding (= derecruitment) and reduced density of alveolar number and surface area (= distension), respectively. In AdTGF-β1 exposed mice, 27% of alveoli remained derecruited at Pao = 20 cmH2O. A further decrease in Pao down to 2 cmH2O showed derecruitment of an additional 1.1 million alveoli (48%), which was linked with an increase in alveolar size heterogeneity at Pao = 2–5 cmH2O. In AdCl, decreased Pao resulted in septal folding with virtually no alveolar collapse. In essence, in healthy mice alveoli do not derecruit at low PEEP ventilation. The potential of alveolar recruitability in AdTGF-β1 exposed mice is high. H is optimized at PEEP 5–8 cmH2O. Lower PEEP folds and larger PEEP stretches septa which results in higher H and is more pronounced in AdTGF-β1 than in AdCl. The increased alveolar size heterogeneity at Pao = 5 cmH2O argues for the use of PEEP = 8 cmH2O for lung protective mechanical ventilation in this animal model.

Upregulation of alveolar fluid clearance is not sufficient for Na+,K+-ATPase β subunit-mediated gene therapy of LPS-induced acute lung injury in mice

Acute Lung Injury/Acute Respiratory Distress Syndrome (ALI/ARDS) is characterized by diffuse alveolar damage and significant edema accumulation, which is associated with impaired alveolar fluid clearance (AFC) and alveolar‐capillary barrier disruption, leading to acute respiratory failure. Our previous data showed that electroporation‐mediated gene delivery of the Na+, K+-ATPase β1 subunit not only increased AFC, but also restored alveolar barrier function through upregulation of tight junction proteins, leading to treatment of LPS‐induced ALI in mice. More importantly, our recent publication showed that gene delivery of MRCKα, the downstream effector of β1 subunit-mediated signaling towards upregulation of adhesive junctions and epithelial and endothelial barrier integrity, also provided therapeutic potential for ARDS treatment in vivo but without necessarily accelerating AFC, indicating that for ARDS treatment, improving alveolar capillary barrier function may be of more benefit than improving fluid clearance. In the present study, we investigated the therapeutical potential of β2 and β3 subunits, the other two β isoforms of Na+, K+-ATPase, for LPS‐induced ALI. We found that gene transfer of either the β1, β2, or β3 subunits significantly increased AFC compared to the basal level in naïve animals and each gave similar increased AFC to each other. However, unlike that of the β1 subunit, gene transfer of the β2 or β3 subunit into pre-injured animal lungs failed to show the beneficial effects of attenuated histological damage, neutrophil infiltration, overall lung edema, or increased lung permeability, indicating that β2 or β3 gene delivery could not treat LPS induced lung injury. Further, while β1 gene transfer increased levels of key tight junction proteins in the lungs of injured mice, that of either the β2 or β3 subunit had no effect on levels of tight junction proteins. Taken together, this strongly suggests that restoration of alveolar-capillary barrier function alone may be of equal or even more benefit than improving AFC for ALI/ARDS treatment.

A translational rat model for ex vivo lung perfusion of pre-injured lungs after brain death.

The process of brain death (BD) detrimentally affects donor lung quality. Ex vivo lung perfusion (EVLP) is a technique originally designed to evaluate marginal donor lungs. Nowadays, its potential as a treatment platform to repair damaged donor lungs is increasingly studied in experimental models. Rat models for EVLP have been described in literature before, yet the pathophysiology of BD was not included in these protocols and prolonged perfusion over 3 hours without anti-inflammatory additives was not achieved. We aimed to establish a model for prolonged EVLP of rat lungs from brain-dead donors, to provide a reliable platform for future experimental studies. Rat lungs were randomly assigned to one of four experimental groups (n = 7/group): 1) healthy, directly procured lungs, 2) lungs procured from rats subjected to 3 hours of BD and 1 hour cold storage (CS), 3) healthy, directly procured lungs subjected to 6 hours EVLP and 4), lungs procured from rats subjected to 3 hours of BD, 1 hour CS and 6 hours EVLP. Lungs from brain-dead rats showed deteriorated ventilation parameters and augmented lung damage when compared to healthy controls, in accordance with the pathophysiology of BD. Subsequent ex vivo perfusion for 6 hours was achieved, both for lungs of healthy donor rats as for pre-injured donor lungs from brain-dead rats. The worsened quality of lungs from brain-dead donors was evident during EVLP as well, as corroborated by deteriorated ventilation performance, increased lactate production and augmented inflammatory status during EVLP. In conclusion, we established a stable model for prolonged EVLP of pre-injured lungs from brain-dead donor rats. In this report we describe tips and pitfalls in the establishment of the rat EVLP model, to enhance reproducibility by other researchers.

Gene Delivery of MRCKα Repairs the Alveolar‐Capillary Barrier and Rescues the Experimental Lipopolysaccharide‐Induced Acute Lung Injury

Rationale Acute Respiratory Distress Syndrome (ARDS) is a devastating condition which is characterized by the pulmonary accumulation of protein-rich edema fluids and insufficient gas exchange, leading to acute hypoxemic respiratory failure. During ARDS, the net fluid clearance is undermined not only due to the impaired alveolar fluid clearance (AFC) which osmotically drives water following the ion gradient out of alveoli, but also the disrupted alveolar-capillary barrier. The previous data from our lab indicated that electroporation-mediated gene delivery of the β1 subunit of the Na+, K+-ATPase into mouse lungs treats LPS induced acute lung injury (ALI), showing significantly decreased lung edema, and improved overall outcome of lung injury. Overexpression of β1 increased AFC in healthy and injured murine lungs, and more importantly, gene delivery of β1 restored pulmonary barrier function, demonstrated by upregulated tight junction (TJ) proteins, and decreased lung permeability, total protein and cellularity in BAL fluid. MRCKα (CDC42 binding protein kinase alpha) was identified by our lab as an interacting partner of the β1 subunit through mass spectrometry. MRCKα is a Rho GTPase effector kinase, regulating diverse cell behaviors, including junction formation. Our previous in vitro data indicate that MRCKα mediated β1’s upregulation of TJ proteins and epithelial barrier integrity. Overexpression of MRCKα alone sufficiently increased the trans-epithelial electrical resistance (TEER) in cell culture. Thus, it is intriguing to investigate whether MRCKα has the therapeutic potential to treat LPS induced ALI by restoring pulmonary barrier function in vivo. This study tested whether electroporation-mediated gene transfer of MRCKα could upregulate TJ protein and barrier function and treat LPS induced ALI in mice. Methods ALI was induced by LPS intratracheal administration and 24 hours later, plasmids encoding MRCKα, β1- Na+, K+-ATPase, or nothing (control) were delivered individually or in combination to mouse lungs by oropharyngeal aspiration and electroporation. Two days after gene delivery, various endpoint assays were performed to evaluate lung edema, permeability, inflammation and histological injury. In addition, AFC was performed on mice with MRCKα overexpression to evaluate the fluid clearance. Results Gene transfer of MRCKα alone did not enhance AFC, but alone or in combination with β1- Na+, K+-ATPase attenuated LPS-increased Wet/Dry ratio, lung leakage, and BAL cellularity and protein concentration, restored TJ protein expression, and improved overall outcome of lung injury. Conclusions Gene delivery ofMRCKα repair alveolar capillary barrier integrity without promoting ion transport, and could benefit the pre-injured lungs by reducing pulmonary edema, restoring lung barrier function and reducing inflammation. Moreover, the data also suggest that improving barrier function alone may be of equal or even more benefit than improving alveolar fluid clearance in order to treat ALI/ARDS.

Mechanical ventilation-induced alterations of intracellular surfactant pool and blood\u2013gas barrier in healthy and pre-injured lungs

Mechanical ventilation triggers the manifestation of lung injury and pre-injured lungs are more susceptible. Ventilation-induced abnormalities of alveolar surfactant are involved in injury progression. The effects of mechanical ventilation on the surfactant system might be different in healthy compared to pre-injured lungs. In the present study, we investigated the effects of different positive end-expiratory pressure (PEEP) ventilations on the structure of the blood–gas barrier, the ultrastructure of alveolar epithelial type II (AE2) cells and the intracellular surfactant pool (= lamellar bodies, LB). Rats were randomized into bleomycin-pre-injured or healthy control groups. One day later, rats were either not ventilated, or ventilated with PEEP = 1 or 5 cmH2O and a tidal volume of 10 ml/kg bodyweight for 3 h. Left lungs were subjected to design-based stereology, right lungs to measurements of surfactant proteins (SP−) B and C expression. In pre-injured lungs without ventilation, the expression of SP-C was reduced by bleomycin; while, there were fewer and larger LB compared to healthy lungs. PEEP = 1 cmH2O ventilation of bleomycin-injured lungs was linked with the thickest blood–gas barrier due to increased septal interstitial volumes. In healthy lungs, increasing PEEP levels reduced mean AE2 cell size and volume of LB per AE2 cell; while in pre-injured lungs, volumes of AE2 cells and LB per cell remained stable across PEEPs. Instead, in pre-injured lungs, increasing PEEP levels increased the number and decreased the mean size of LB. In conclusion, mechanical ventilation-induced alterations in LB ultrastructure differ between healthy and pre-injured lungs. PEEP = 1 cmH2O but not PEEP = 5 cmH2O ventilation aggravated septal interstitial abnormalities after bleomycin challenge.

Ventilation following established ARDS: a preclinical model framework to improve predictive power

BackgroundDespite advances in understanding the pathophysiology of acute respiratory distress syndrome, effective pharmacological interventions have proven elusive. We believe this is a consequence of existing preclinical models being designed primarily...

Mechanical Ventilation Induces an Inflammatory Response in Preinjured Lungs in Late Phase of Sepsis

Mechanical ventilation (MV) may amplify the lung-specific inflammatory response in preinjured lungs by elevating cytokine release and augmenting damage to the alveolar integrity. In this study, we test the hypothesis that MV exerts different negative impacts on inflammatory response at different time points of postlung injury. Basic lung injury was induced by cecal ligation and puncture (CLP) surgery in rats. Physiological indexes including blood gases were monitored during MV and samples were assessed following each experiment. Low V T (tidal volume) MV caused a slight increase in cytokine release and tissue damage at day 1 and day 4 after sepsis induced lung injury, while cytokine release from the lungs in the two moderately ventilated V T groups was amplified. Interestingly, in the two groups where rats received low V T MV, we found that infiltration of inflammatory cells was only profound at day 4 after CLP. Marked elevation of protein leakage indicated a compromise in alveolar integrity in rats that received moderate V T MV at day 4 following CLP, correlating with architectural damage to the alveoli. Our study indicates that preinjured lungs are more sensitive to mechanical MV at later phases of sepsis, and this situation may be a result of differing immune status.

Mechanical ventilation drives pneumococcal pneumonia into lung injury and sepsis in mice: protection by adrenomedullin.

IntroductionVentilator-induced lung injury (VILI) contributes to morbidity and mortality in acute respiratory distress syndrome (ARDS). Particularly pre-injured lungs are susceptible to VILI despite protective ventilation. In a previous study, the endogenous peptide adrenomedullin (AM) protected murine lungs from VILI. We hypothesized that mechanical ventilation (MV) contributes to lung injury and sepsis in pneumonia, and that AM may reduce lung injury and multiple organ failure in ventilated mice with pneumococcal pneumonia.MethodsWe analyzed in mice the impact of MV in established pneumonia on lung injury, inflammation, bacterial burden, hemodynamics and extrapulmonary organ injury, and assessed the therapeutic potential of AM by starting treatment at intubation.ResultsIn pneumococcal pneumonia, MV increased lung permeability, and worsened lung mechanics and oxygenation failure. MV dramatically increased lung and blood cytokines but not lung leukocyte counts in pneumonia. MV induced systemic leukocytopenia and liver, gut and kidney injury in mice with pneumonia. Lung and blood bacterial burden was not affected by MV pneumonia and MV increased lung AM expression, whereas receptor activity modifying protein (RAMP) 1–3 expression was increased in pneumonia and reduced by MV. Infusion of AM protected against MV-induced lung injury (66% reduction of pulmonary permeability p < 0.01; prevention of pulmonary restriction) and against VILI-induced liver and gut injury in pneumonia (91% reduction of AST levels p < 0.05, 96% reduction of alanine aminotransaminase (ALT) levels p < 0.05, abrogation of histopathological changes and parenchymal apoptosis in liver and gut).ConclusionsMV paved the way for the progression of pneumonia towards ARDS and sepsis by aggravating lung injury and systemic hyperinflammation leading to liver, kidney and gut injury. AM may be a promising therapeutic option to protect against development of lung injury, sepsis and extrapulmonary organ injury in mechanically ventilated individuals with severe pneumonia.

Aggravation of myocardial dysfunction by injurious mechanical ventilation in LPS-induced pneumonia in rats

BackgroundMechanical ventilation (MV) may cause ventilator-induced lung injury (VILI) and may thereby contribute to fatal multiple organ failure. We tested the hypothesis that injurious MV of lipopolysaccharide (LPS) pre-injured lungs induces myocardial inflammation and further dysfunction ex vivo, through calcium (Ca2+)-dependent mechanism.Materials and methodsN = 35 male anesthetized and paralyzed male Wistar rats were randomized to intratracheal instillation of 2 mg/kg LPS or nothing and subsequent MV with lung-protective settings (low tidal volume (Vt) of 6 mL/kg and 5 cmH2O positive end-expiratory pressure (PEEP)) or injurious ventilation (high Vt of 19 mL/kg and 1 cmH2O PEEP) for 4 hours. Myocardial function ex vivo was evaluated in a Langendorff setup and Ca2+ exposure. Key mediators were determined in lung and heart at the mRNA level.ResultsInstillation of LPS and high Vt MV impaired gas exchange and, particularly when combined, increased pulmonary wet/dry ratio; heat shock protein (HSP)70 mRNA expression also increased by the interaction between LPS and high Vt MV. For the heart, C-X-C motif ligand (CXCL)1 and Toll-like receptor (TLR)2 mRNA expression increased, and ventricular (LV) systolic pressure, LV developed pressure, LV +dP/dtmax and contractile responses to increasing Ca2+ exposure ex vivo decreased by LPS. High Vt ventilation aggravated the effects of LPS on myocardial inflammation and dysfunction but not on Ca2+ responses.ConclusionsInjurious MV by high Vt aggravates the effects of intratracheal instillation of LPS on myocardial dysfunction, possibly through enhancing myocardial inflammation via pulmonary release of HSP70 stimulating cardiac TLR2, not involving Ca2+ handling and sensitivity.

High tidal volume ventilation does not exacerbate acid-induced lung injury in infant rats

The impact of mechanical ventilation with high VT-low PEEP in infant rats with preinjured lungs is unknown. After tracheal instillation of saline or acid, two week old rats were ventilated with VT 7mL/kg and PEEP 5cm H2O or VT 21mL/kg and PEEP 1cm H2O for 4h. Airway resistance and the coefficient of tissue elastance, measured via low-frequency forced-oscillation technique, and quasi-static pressure-volume curves deteriorated less with high VT-low PEEP when compared with low VT-high PEEP. IL-6 concentration in bronchoalveolar lavage fluid (BALF) did not differ between all ventilated groups. Moreover, differences in BALF protein concentration and histological lung injury scores were independent of applied ventilation strategies. In contrast to experimental studies with adult rats, short-term mechanical ventilation with high VT-low PEEP is not deleterious when compared to low VT-high PEEP in both healthy and pre-injured infant rat lungs. Our results call for caution when extrapolating data from adult studies and highlight the need for age-specific animal models.

Intermedin Stabilized Endothelial Barrier Function and Attenuated Ventilator-induced Lung Injury in Mice

BackgroundEven protective ventilation may aggravate or induce lung failure, particularly in preinjured lungs. Thus, new adjuvant pharmacologic strategies are needed to minimize ventilator-induced lung injury (VILI). Intermedin/Adrenomedullin-2 (IMD) stabilized pulmonary endothelial barrier function in vitro. We hypothesized that IMD may attenuate VILI-associated lung permeability in vivo.Methodology/Principal FindingsHuman pulmonary microvascular endothelial cell (HPMVEC) monolayers were incubated with IMD, and transcellular electrical resistance was measured to quantify endothelial barrier function. Expression and localization of endogenous pulmonary IMD, and its receptor complexes composed of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs) 1–3 were analyzed by qRT-PCR and immunofluorescence in non ventilated mouse lungs and in lungs ventilated for 6 h. In untreated and IMD treated mice, lung permeability, pulmonary leukocyte recruitment and cytokine levels were assessed after mechanical ventilation. Further, the impact of IMD on pulmonary vasoconstriction was investigated in precision cut lung slices (PCLS) and in isolated perfused and ventilated mouse lungs. IMD stabilized endothelial barrier function in HPMVECs. Mechanical ventilation reduced the expression of RAMP3, but not of IMD, CRLR, and RAMP1 and 2. Mechanical ventilation induced lung hyperpermeability, which was ameliorated by IMD treatment. Oxygenation was not improved by IMD, which may be attributed to impaired hypoxic vasoconstriction due to IMD treatment. IMD had minor impact on pulmonary leukocyte recruitment and did not reduce cytokine levels in VILI.Conclusions/SignificanceIMD may possibly provide a new approach to attenuate VILI.

Ventilator-induced lung injury in severe pneumococcal pneumonia: protection by Adrenomedullin

Ventilator-induced lung injury (VILI) contributes to mortality in ARDS. Particularly preinjured lungs may be susceptible to VILI despite lung protective ventilation. We previously observed protection against VILI by therapeutic use of the endogenous peptide Adrenomedullin (AM) in addition to lung protective ventilation in mice. The current study analyzed the impact of mechanical ventilation (MV) on lung injury, pulmonary and systemic inflammation and bacterial burden in established pneumonia. Further, AM was used therapeutically to limit VILI in a clinically relevant murine model.

Ventilator-Induced Inflammatory Response in Lipopolysaccharide-Exposed Rat Lung Is Mediated by Angiotensin-Converting Enzyme

Angiotensin-converting enzyme (ACE) mediates the ventilator-induced inflammatory response in healthy lungs via angiotensin II (Ang II). A rat model was used to examine the role of ACE and Ang II in the inflammatory response during mechanical ventilation of preinjured (ie, lipopolysaccharide [LPS]-exposed) lungs. When indicated, rats were pretreated with the ACE inhibitor captopril and/or intratracheal administration of LPS. The animals were ventilated for 4 hours with moderate pressure amplitudes. Nonventilated animals served as controls. ACE activity and levels of Ang II and inflammatory mediators (interleukin-6, Cytokine-induced Neutrophil Chemoattractant (CINC)-3, interleukin-1beta, and interleukin-10) were determined in bronchoalveolar lavage fluid (BALF). The localization of ACE and Ang II type 1 receptor in lung tissue was determined by immunohistochemistry. The role of the Ang II pathway was assessed by using its receptor antagonist Losartan. Mechanical ventilation of LPS-exposed animals increased ACE activity and levels of inflammatory mediators in BALF compared with ventilated nonexposed and LPS-exposed nonventilated animals. Blocking ACE by captopril attenuated the lung inflammatory response. Furthermore, increased ACE activity in BALF was accompanied by increased levels of Ang II and enhanced expression of its receptor on alveolar cells. Blocking the Ang II receptor attenuated the inflammatory mediator response to a larger extent than by blocking ACE. In conclusion, during mechanical ventilation ACE, via Ang II, mediates the inflammatory response of both healthy and preinjured lungs.

Simvastatin attenuates ventilator-induced lung injury in mice

IntroductionMechanical ventilation (MV) is a life saving intervention in acute respiratory failure without alternative. However, particularly in pre-injured lungs, even protective ventilation strategies may evoke ventilator-induced lung injury (VILI), which is characterized by pulmonary inflammation and vascular leakage. Adjuvant pharmacologic strategies in addition to lung protective ventilation to attenuate VILI are lacking. Simvastatin exhibited anti-inflammatory and endothelial barrier stabilizing properties in vitro and in vivo.MethodsMice were ventilated (12 ml/kg; six hours) and subjected to simvastatin (20 mg/kg) or sham treatment. Pulmonary microvascular leakage, oxygenation, pulmonary and systemic neutrophil and monocyte counts and cytokine release in lung and blood plasma were assessed. Further, lung tissue was analyzed by electron microscopy.ResultsMechanical ventilation induced VILI, displayed by increased pulmonary microvascular leakage and endothelial injury, pulmonary recruitment of neutrophils and Gr-1high monocytes, and by liberation of inflammatory cytokines in the lungs. Further, VILI associated systemic inflammation characterized by blood leukocytosis and elevated plasma cytokines was observed. Simvastatin treatment limited pulmonary endothelial injury, attenuated pulmonary hyperpermeability, prevented the recruitment of leukocytes to the lung, reduced pulmonary cytokine levels and improved oxygenation in mechanically ventilated mice.ConclusionsHigh-dose simvastatin attenuated VILI in mice by reducing MV-induced pulmonary inflammation and hyperpermeability.

Real-time detection of pneumothorax using electrical impedance tomography*

Pneumothorax is a frequent complication during mechanical ventilation. Electrical impedance tomography (EIT) is a noninvasive tool that allows real-time imaging of regional ventilation. The purpose of this study was to 1) identify characteristic changes in the EIT signals associated with pneumothoraces; 2) develop and fine-tune an algorithm for their automatic detection; and 3) prospectively evaluate this algorithm for its sensitivity and specificity in detecting pneumothoraces in real time. Prospective controlled laboratory animal investigation. Experimental Pulmonology Laboratory of the University of São Paulo. Thirty-nine anesthetized mechanically ventilated supine pigs (31.0 +/- 3.2 kg, mean +/- SD). In a first group of 18 animals monitored by EIT, we either injected progressive amounts of air (from 20 to 500 mL) through chest tubes or applied large positive end-expiratory pressure (PEEP) increments to simulate extreme lung overdistension. This first data set was used to calibrate an EIT-based pneumothorax detection algorithm. Subsequently, we evaluated the real-time performance of the detection algorithm in 21 additional animals (with normal or preinjured lungs), submitted to multiple ventilatory interventions or traumatic punctures of the lung. Primary EIT relative images were acquired online (50 images/sec) and processed according to a few imaging-analysis routines running automatically and in parallel. Pneumothoraces as small as 20 mL could be detected with a sensitivity of 100% and specificity 95% and could be easily distinguished from parenchymal overdistension induced by PEEP or recruiting maneuvers. Their location was correctly identified in all cases, with a total delay of only three respiratory cycles. We created an EIT-based algorithm capable of detecting early signs of pneumothoraces in high-risk situations, which also identifies its location. It requires that the pneumothorax occurs or enlarges at least minimally during the monitoring period. Such detection was operator-free and in quasi real-time, opening opportunities for improving patient safety during mechanical ventilation.

Perflubron dosing affects ventilator-induced lung injury in rats with previous lung injury*

Randomized controlled trials of partial liquid ventilation in acute respiratory distress syndrome have been negative. Reasons for this failure may reside in the use of too large doses of perfluorocarbon. The objective was to evaluate whether various doses of perflubron affect ventilation-induced injury in edematous lungs in different ways. Prospective, controlled animal study. Research laboratory of a university. Male Wistar rats weighing 300+/-20 g. Separate groups of rats were injected with alpha-naphtylthiourea to produce mild permeability pulmonary edema. They were then given 0, 7 (low), 13 (moderate), or 20 mL/kg (near functional residual capacity) perflubron doses and mechanically ventilated with a large (33 mL/kg) tidal volume for 15 mins. 125I-albumin distribution space was used to assess lung microvascular permeability. Quasi-static respiratory system pressure-volume curves were analyzed. Administration of low and moderate perflubron doses significantly improved respiratory mechanics and reduced the ventilator-induced permeability alterations to the level observed in rats that were not ventilated. By contrast, a perflubron dose that was near functional residual capacity increased end-inspiratory plateau pressure and aggravated the permeability alterations due to high tidal volume ventilation. Near functional residual capacity but not low perflubron dose worsens ventilation-induced lung injury of preinjured lungs. This may provide some explanation for the negative results of the recent clinical trials, and it stresses the importance of the amount of perflubron used for partial liquid ventilation.

Mechanical Ventilation Affects Lung Function and Cytokine Production in an Experimental Model of Endotoxemia

Mechanical ventilation using tidal volumes around 10 ml/kg and zero positive end-expiratory pressure is still commonly used in anesthesia. This strategy has been shown to aggravate lung injury and inflammation in preinjured lungs but not in healthy lungs. In this study, the authors investigated whether this strategy would result in lung injury during transient endotoxemia in the lungs of healthy animals. Volume-controlled ventilation with a tidal volume of 10 ml/kg and zero positive end-expiratory pressure was applied in two groups of anesthetized-paralyzed rabbits receiving either intravenous injection of 5 mug/kg Escherichia coli lipopolysaccharide (n = 10) or saline (n = 10) 2 h after the start of mechanical ventilation. The third group consisted of 10 spontaneously breathing anesthetized animals receiving lipopolysaccharide. Anesthesia was then continued for 4 h in the three groups while the ventilatory modes were maintained unchanged. Lung injury was studied using blood gases, respiratory physiologic variables, analysis of the bronchoalveolar lavage cell counts, and cytokine concentrations and lung pathologic examination. Significant histologic lung alterations, hypoxemia, and altered lung mechanics were observed in rabbits treated with mechanical ventilation and intravenous lipopolysaccharide but not in the mechanically ventilated animals injected with saline or in spontaneously breathing animals treated with lipopolysaccharide. Endotoxemic ventilated animals also had significantly more lung inflammation as assessed by the alveolar concentration of neutrophils, and the concentrations of the chemokines interleukin 8 and growth-related oncogen alpha. These results showed that positive-pressure mechanical ventilation using a tidal volume of 10 ml/kg and zero positive end-expiratory pressure was harmful in the setting of endotoxemia, suggesting that the use of this ventilator strategy in the operating room may predispose to lung injury when endotoxemia occurs.

Anti-Chlamydophila immunoglobulin prevalence in sarcoidosis and usual interstitial pneumoniae.

Sarcoidosis and usual interstitial pneumoniae (UIP) are diseases of unknown aetiology affecting the lower respiratory tract. Although there are a number of studies investigating the causal role of these disorders, no micro-organism could be identified as the causal agent. The high incidence of Chlamydophila pneumoniae infections associated with lung injury encouraged the present investigations to screen patients with sarcoidosis and with UIP for their Chlamydophila-specific immune response. Thirty-nine patients with sarcoidosis, 26 patients with UIP and 34 controls were tested for the prevalence of Chlamydophila-specific antibodies in bronchoalveolar lavage fluids (BALF) and sera. Samples were tested for the presence of antibodies in a genus-specific test for Chlamydophila-lipopolysaccharide (LPS) and in a species-specific test for C. pneumoniae. This study revealed a significantly higher prevalence of Chlamydophila LPS-specific immunoglobulin (Ig)-G in the BALF of sarcoidosis patients (36.8%) compared to controls (8.8%) and patients with UIP (12.0%). Similar findings were observed in sera. The prevalence of C. pneumoniae-specific antibodies in BALF was significantly higher in sarcoidosis patients for IgG and IgA (IgG: 74.4%; IgA: 46.2%) and in UIP for IgG (IgG: 50.0%; IgA: 11.5%) compared to controls (IgG: 14.7%; IgA: 14.7%). The elevated prevalence of Chlamydophila-specific antibodies in sarcoidosis patients might implicate Chlamydophila as a causal agent. However, considering the high prevalence of Chlamydophila antibodies in the healthy population, the data presented might reflect Chlamydophila co-infections in pre-injured lungs seen in these patients.

Activation of human macrophages by mechanical ventilation in vitro.

Positive-pressure mechanical ventilation supports gas exchange in patients with respiratory failure but is also responsible for significant lung injury. In this study, we have developed an in vitro model in which isolated lung cells can be submitted to a prolonged cyclic pressure-stretching strain resembling that of conventional mechanical ventilation. In this model, cells cultured on a Silastic membrane were elongated up to 7% of their initial diameter, corresponding to a 12% increase in cell surface. The lung macrophage was identified as the main cellular source for critical inflammatory mediators such as tumor necrosis factor-alpha, the chemokines interleukin (IL)-8 and -6, and matrix metalloproteinase-9 in this model system of mechanical ventilation. These mediators were measured in supernatants from ventilated alveolar macrophages, monocyte-derived macrophages, and promonocytic THP-1 cells. Nuclear factor-kappaB was found to be activated in ventilated macrophages. Synergistic proinflammatory effects of mechanical stress and molecules such as bacterial endotoxin were observed, suggesting that mechanical ventilation might be particularly deleterious in preinjured or infected lungs. Dexamethasone prevented IL-8 and tumor necrosis factor-alpha secretion in ventilated macrophages. Mechanical ventilation induced low levels of IL-8 secretion by alveolar type II-like cells. Other lung cell types such as endothelial cells, bronchial cells, and fibroblasts failed to produce IL-8 in response to a prolonged cyclic pressure-stretching load. This model is of particular value for exploring physical stress-induced signaling pathways, as well as for testing the effects of novel ventilatory strategies or adjunctive substances aimed at modulating cell activation induced by mechanical ventilation.