High tidal volume ventilation induces lung injury after hepatic ischemia-reperfusion

Ischemia-reperfusion not only damages the affected organ but also leads to remote organ injuries. Hepatic inflow interruption usually occurs during hepatic surgery. To investigate the influence of liver ischemia-reperfusion on lung injury and to determine the contribution of tidal volume settings on liver ischemia-reperfusion-induced lung injury, we studied anesthetized and mechanically ventilated rats in which the hepatic inflow was transiently interrupted twice for 15 min. Two tidal volumes, 6 ml/kg as a low tidal volume (IR-LT) and 24 ml/kg as a high tidal volume (IR-HT), were assessed after liver ischemia-reperfusion, as well as after a sham operation, 6 ml/kg (NC-LT) and 24 ml/kg (NC-HT). Both the IR-HT and IR-LT groups had a gradual decline in the systemic blood pressure and a significant increase in plasma TNF-alpha concentrations. Of the four groups, only the IR-HT group developed lung injury, as assessed by an increase in the lung wet-to-dry weight ratio, the presence of significant histopathological changes, such as perivascular edema and intravascular leukocyte aggregation, and an increase in the bronchoalveolar lavage fluid TNF-alpha concentration. Furthermore, only in the IR-HT group was airway pressure increased significantly during the 6-h reperfusion period. These findings suggest that liver ischemia-reperfusion caused systemic inflammation and that lung injury is triggered when high tidal volume ventilation follows liver ischemia-reperfusion.     

Very low tidal volume ventilation with associated hypercapnia--effects on lung injury in a model for acute respiratory distress syndrome

Background

Ventilation using low tidal volumes with permission of hypercapnia is recommended to protect the lung in acute respiratory distress syndrome. However, the most lung protective tidal volume in association with hypercapnia is unknown. The aim of this study was to assess the effects of different tidal volumes with associated hypercapnia on lung injury and gas exchange in a model for acute respiratory distress syndrome.

Methodology/Principal Findings

In this randomized controlled experiment sixty-four surfactant-depleted rabbits were exposed to 6 hours of mechanical ventilation with the following targets: Group 1: tidal volume = 8–10 ml/kg/PaCO₂ = 40 mm Hg; Group 2: tidal volume = 4–5 ml/kg/PaCO₂ = 80 mm Hg; Group 3: tidal volume = 3–4 ml/kg/PaCO₂ = 120 mm Hg; Group 4: tidal volume = 2–3 ml/kg/PaCO₂ = 160 mm Hg. Decreased wet-dry weight ratios of the lungs, lower histological lung injury scores and higher PaO₂ were found in all low tidal volume/hypercapnia groups (group 2, 3, 4) as compared to the group with conventional tidal volume/normocapnia (group 1). The reduction of the tidal volume below 4–5 ml/kg did not enhance lung protection. However, oxygenation and lung protection were maintained at extremely low tidal volumes in association with very severe hypercapnia and no adverse hemodynamic effects were observed with this strategy.

Conclusion

Ventilation with low tidal volumes and associated hypercapnia was lung protective. A tidal volume below 4–5 ml/kg/PaCO₂ 80 mm Hg with concomitant more severe hypercapnic acidosis did not increase lung protection in this surfactant deficiency model. However, even at extremely low tidal volumes in association with severe hypercapnia lung protection and oxygenation were maintained.     

Temperature affects lung fluid and recoil during high tidal ventilation at low resting volume

Effects of tidal volume (VT), end-expiratory pressure (EEP), and environmental temperature (Tenv) on elastic recoil force (Pel) and edema formation were examined in open-chest anesthetized rabbits. Sixty-two rabbits in four groups were ventilated for 3 h with VT of either 10 or 25 ml/kg body wt, EEP of 0 or 2 cmH2O, and Tenv of 18 or 35 degrees C. After ventilation, Pel at 80% of total lung capacity (P80) was significantly increased when ventilation was performed with the combination of large VT, 0 EEP, and low Tenv. This change was prevented by altering any one of the three conditions, e.g., small VT, positive EEP, or high Tenv. Similarly, elevation of minimum surface tension and reduction of surface activity index of lavages from excised lungs after ventilation were observed only when increased P80 was noted. Additionally, the increase of P80 was well correlated with increment of wet weight-to-dry weight ratio and degree of perivascular cuffing and alveolar edema formation of excised lungs. These results indicate that elevation of Pel after high tidal ventilation in open-chest animals in vivo was influenced by level of EEP and Tenv and that the degree of edema formation was closely related to the increase of Pel. The increased Pel is presumably primary and causes fluid accumulation.     

Mathematical modelling to centre low tidal volumes following acute lung injury: A study with biologically variable ventilation

Background

With biologically variable ventilation [BVV – using a computer-controller to add breath-to-breath variability to respiratory frequency (f) and tidal volume (V_T)] gas exchange and respiratory mechanics were compared using the ARDSNet low V_T algorithm (Control) versus an approach using mathematical modelling to individually optimise V_T at the point of maximal compliance change on the convex portion of the inspiratory pressure-volume (P-V) curve (Experimental).

Methods

Pigs (n = 22) received pentothal/midazolam anaesthesia, oleic acid lung injury, then inspiratory P-V curve fitting to the four-parameter logistic Venegas equation F(P) = a + b[1 + e^-(P-c)/d]^-1 where: a = volume at lower asymptote, b = the vital capacity or the total change in volume between the lower and upper asymptotes, c = pressure at the inflection point and d = index related to linear compliance. Both groups received BVV with gas exchange and respiratory mechanics measured hourly for 5 hrs. Postmortem bronchoalveolar fluid was analysed for interleukin-8 (IL-8).

Results

All P-V curves fit the Venegas equation (R² > 0.995). Control V_T averaged 7.4 ± 0.4 mL/kg as compared to Experimental 9.5 ± 1.6 mL/kg (range 6.6 – 10.8 mL/kg; p < 0.05). Variable V_Ts were within the convex portion of the P-V curve. In such circumstances, Jensen''s inequality states "if F(P) is a convex function defined on an interval (r, s), and if P is a random variable taking values in (r, s), then the average or expected value (E) of F(P); E(F(P)) > F(E(P))." In both groups the inequality applied, since F(P) defines volume in the Venegas equation and (P) pressure and the range of V_Ts varied within the convex interval for individual P-V curves. Over 5 hrs, there were no significant differences between groups in minute ventilation, airway pressure, blood gases, haemodynamics, respiratory compliance or IL-8 concentrations.

Conclusion

No difference between groups is a consequence of BVV occurring on the convex interval for individualised Venegas P-V curves in all experiments irrespective of group. Jensen''s inequality provides theoretical proof of why a variable ventilatory approach is advantageous under these circumstances. When using BVV, with V_T centred by Venegas P-V curve analysis at the point of maximal compliance change, some leeway in low V_T settings beyond ARDSNet protocols may be possible in acute lung injury. This study also shows that in this model, the standard ARDSNet algorithm assures ventilation occurs on the convex portion of the P-V curve.     

High tidal volume mechanical ventilation with hyperoxia alters alveolar type II cell adhesion

Patients with acute respiratory distress syndrome undergoing mechanical ventilation may be exposed to both high levels of stretch and high levels of oxygen. We hypothesized that the combination of high stretch and hyperoxia promotes loss of epithelial adhesion and impairs epithelial repair mechanisms necessary for restoration of barrier function. We utilized a model of high tidal volume mechanical ventilation (25 ml/kg) with hyperoxia (50% O(2)) in rats to investigate alveolar type II (AT2) cell adhesion and focal adhesion signaling. AT2 cells isolated from rats exposed to hyperoxia and high tidal volume mechanical ventilation (MVHO) exhibited significantly decreased cell adhesion and reduction in phosphotyrosyl levels of focal adhesion kinase (FAK) and paxillin compared with control rats, rats exposed to hyperoxia without ventilation (HO), or rats ventilated with normoxia (MV). MV alone increased phosphorylation of p130(Cas). RhoA activation was increased by MV, HO, and the combination of MV and HO. Treatment of MVHO cells with keratinocyte growth factor (KGF) for 1 h upon isolation reduced RhoA activity and restored attachment to control levels. Attachment and migration of control AT2 cells was significantly decreased by constitutively active RhoA or a kinase inactive form of FAK (FRNK), whereas expression of dominant negative RhoA in cells from MVHO-treated rats restored cell adhesion. Mechanical ventilation with hyperoxia promotes changes in focal adhesion proteins and RhoA in AT2 cells that may be deleterious for cell adhesion and migration.     

Ammonia aggravates stress-induced gastric mucosal oxidative injury through the cancellation of cytoprotective heat shock protein 70

The relationship between Helicobacter pylori colonization and the formation of stress-induced gastric mucosal injury remains unknown. Since ammonia (NH(3)) is known as one of the injurious factors in H. pylori-colonized gastric mucosa, the present study is designed to investigate the level of stress-induced gastric mucosal oxidative injury with or without intragastric NH(3) overloading. To apply emotional stress, the communication box paradigm was used in the mouse model. Mice (C57BL/6, male) were pretreated with distilled water (responder-H(2)O) or 0.01% NH(3) (responder-NH(3)) through a gastric tube once a day for a week. Emotional stress was then applied to the responder mice for 3 h per day for 3 d by watching and hearing the behavior of the sender mice subjected to electric shocks to the feet (2 mA, 10 s, 50 s interval). After the communication box protocol, the tissue MPO activity, the contents of TBA-reactive substances (TBARS), and the level of gastric mucosal HSP70 were examined. Responder-NH(3) mice developed more severe gastric lesions than the responder-H(2)O subjects. MPO activity and TBARS contents were enhanced significantly in the responder-NH(3) group compared with the responder-H(2)O subjects. Although the contents of HSP70 in the gastric mucosa increased in the responder-H(2)O group compared with the control-H(2)O animals, they were significantly attenuated in the responder-NH(3) mice. Excess intragastric NH(3) was able to enhance the formation of emotional stress-induced gastric mucosal lesions. This injury may be associated with the enhanced production of oxygen free radicals from accumulated neutrophils under the NH(3)-mediated cancellation of gastric mucosal cytoprotective HSP70.     

High tidal volume upregulates intrapulmonary cytokines in an in vivo mouse model of ventilator-induced lung injury.

Mechanical ventilation has been demonstrated to exacerbate lung injury, and a sufficiently high tidal volume can induce injury in otherwise healthy lungs. However, it remains controversial whether injurious ventilation per se, without preceding lung injury, can initiate cytokine-mediated pulmonary inflammation. To address this, we developed an in vivo mouse model of acute lung injury produced by high tidal volume (Vt) ventilation. Anesthetized C57BL6 mice were ventilated at high Vt (34.5 +/- 2.9 ml/kg, mean +/- SD) for a duration of 156 +/- 17 min until mean blood pressure fell below 45 mmHg (series 1); high Vt for 120 min (series 2); or low Vt (8.8 +/- 0.5 ml/kg) for 120 or 180 min (series 3). High Vt produced progressive lung injury with a decrease in respiratory system compliance, increase in protein concentration in lung lavage fluid, and lung pathology showing hyaline membrane formation. High-Vt ventilation was associated with increased TNF-alpha in lung lavage fluid at the early stage of injury (series 2) but not the later stage (series 1). In contrast, lavage fluid macrophage inflammatory protein-2 (MIP-2) was increased in all high-Vt animals. Lavage fluid from high-Vt animals contained bioactive TNF-alpha by WEHI bioassay. Low-Vt ventilation induced minimal changes in physiology and pathology with negligible TNF-alpha and MIP-2 proteins and TNF-alpha bioactivity. These results demonstrate that high-Vt ventilation in the absence of underlying injury induces intrapulmonary TNF-alpha and MIP-2 expression in mice. The apparently transient nature of TNF-alpha upregulation may help explain previous controversy regarding the involvement of cytokines in ventilator-induced lung injury.     

Enhanced protection against lipopolysaccharide‐induced acute lung injury by autologous transplantation of adipose‐derived stromal cells combined with low tidal volume ventilation in rats

Adipose‐derived stromal cells (ADSCs) showed excellent capacity in regeneration and tissue protection. Low tidal volume ventilation (LVT) strategy demonstrates a therapeutic benefit on the treatment of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). This study, therefore, aimed to undertaken determine whether the combined LVT and ADSCs treatment exerts additional protection against lipopolysaccharide (LPS)‐induced ALI in rats. The animals were randomized into seven groups: Group I (control), Group II (instillation of LPS at 10 mg/kg intratracheally), Group III (LPS+LVT 6 ml/kg), Group IV (LPS+intravenous autologous 5 × 10⁶ ADSCs which were pretreated with a scrambled small interfering RNA [siRNA] of keratinocyte growth factor [KGF] negative control), Group V (LPS+ADSCs which were pretreated with a scrambled siRNA of KGF, Group VI (LPS+LVT and ADSCs as in the Group IV), and Group VII (LPS+LVT and ADSCs as in the Group V). We found that levels of tumor necrosis factor‐α, transforming growth factor‐β1, and interleukin (IL)‐1β and IL‐6, the proinflammatory cytokines, were remarkably increased in LPS rats. Moreover, the expressions of ENaC, activity of Na, K‐ATPase, and alveolar fluid clearance (AFC) were obviously reduced by LPS‐induced ALI. The rats treated by ADSCs showed improved effects in all these changes of ALI and further enhanced by ADSCs combined with LVT treatment. Importantly, the treatment of ADSCs with siRNA‐mediated knockdown of KGF partially eliminated the therapeutic effects. In conclusion, combined treatment with ADSCs and LVT not only is superior to either ADSCs or LVT therapy alone in the prevention of ALI. Evidence of the beneficial effect may be partly due to improving AFC by paracrine or systemic production of KGF and anti‐inflammatory properties.     

Effect of tidal volume and PEEP in ethchlorvynol-induced asymmetric lung injury.

We examined the effects of positive end-expiratory pressure (PEEP) and tidal volume on the distribution of ventilation and perfusion in a canine model of asymmetric lung injury. Unilateral right lung edema was established in 10 animals by use of a selective infusion of ethchlorvynol. Five animals were tested in the supine position (horizontal asymmetry) and five in the right decubitus position (vertical asymmetry). Raising PEEP from 5 to 12 cmH2O improved oxygenation despite a redistribution of blood flow toward the damage lung and a consistent decrease in total respiratory system compliance. This improvement paralleled a redistribution of tidal ventilation to the injured lung. This was effected primarily by a fall in the compliance of the noninjured lung due to hyperinflation. The effects of higher tidal volume were additive to those of PEEP. We propose that the major effect of PEEP in inhomogeneous lung injury is to restore tidal ventilation to a population of alveoli recruitable only at high airway pressures.     

呼吸机相关肺损伤模型建构的最佳潮气量

目的:应用大潮气量机械通气探讨制作兔的呼吸机相关肺损伤模型的最佳潮气量。方法:根据黄金分割法原理,采用三种不同潮气量68mL/kg、60mL/kg和45mL/kg各持续通气1分钟造成兔的急性肺损伤,取0h,12h,24h,48h四个时间点进行观察,观察兔存活情况,计算各时间点肺湿/干重比观察肺水肿严重程度及变化,组织病理学切片观察各时间点肺组织形态学改变。结果:1、潮气量68mL/kg组、60mL/kg组和45mL/kg组兔48h存活率分别为58.33%(7/12)、91.67%(11/12)和100%(12/12);与正常对照组相比,三组肺湿/干重比在0小时无明显变化,12小时明显增高,在24小时时达峰值,48小时后降低。3、镜下观察机械通气后不同时间肺组织均有不同程度形态学改变,68mL/kg组肺组织形态学改变非常明显,60mL/kg组肺组织形态学改变明显,45mL/kg组肺组织形态学改变不明显。结论:大潮气量通气成功建立兔的呼吸机相关肺损伤实验动物模型,潮气量指标为60mL/kg。     

Fructose-1,6-bisphosphatase aggravates oxidative stress-induced apoptosis in asthma by suppressing the Nrf2 pathway

Asthma is a chronic airway disease that causes excessive inflammation, oxidative stress, mucus production and bronchial epithelial cell apoptosis. Fructose-1,6-bisphosphatase (Fbp1) is one of the rate-limiting enzymes in gluconeogenesis and plays a critical role in several cancers. However, its role in inflammatory diseases, such as asthma, is unclear. Here, we examined the expression, function and mechanism of action of Fbp1 in asthma. Gene Expression Omnibus (GEO) data sets revealed that Fbp1 was overexpressed in a murine model of asthma and in interleukin (IL)-4- or IL-13-stimulated bronchial epithelial cells. We confirmed the findings in an animal model as well as Beas-2B and 16HBE cells. In vitro investigations revealed that silencing of Fbp1 reduced apoptosis and the proportion of cells in the G2/M phase, whereas overexpression led to increases. Fbp1 knock-down inhibited oxidative stress by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, whereas Fbp1 overexpression aggravated oxidative stress by suppressingthe Nrf2 pathway. Moreover, the Nrf2 pathway inhibitor ML385 reversed the changes caused by Fbp1 inhibition in Beas-2B and 16HBE cells. Collectively, our data indicate that Fbp1 aggravates oxidative stress-induced apoptosis by suppressing Nrf2 signalling, substantiating its potential as a novel therapeutic target in asthma.     

High tidal volume ventilation induces NOS2 and impairs cAMP- dependent air space fluid clearance

Tidal volume reduction during mechanical ventilation reduces mortality in patients with acute lung injury and the acute respiratory distress syndrome. To determine the mechanisms underlying the protective effect of low tidal volume ventilation, we studied the time course and reversibility of ventilator-induced changes in permeability and distal air space edema fluid clearance in a rat model of ventilator-induced lung injury. Anesthetized rats were ventilated with a high tidal volume (30 ml/kg) or with a high tidal volume followed by ventilation with a low tidal volume of 6 ml/kg. Endothelial and epithelial protein permeability were significantly increased after high tidal volume ventilation but returned to baseline levels when tidal volume was reduced. The basal distal air space fluid clearance (AFC) rate decreased by 43% (P < 0.05) after 1 h of high tidal volume but returned to the preventilation rate 2 h after tidal volume was reduced. Not all of the effects of high tidal volume ventilation were reversible. The cAMP-dependent AFC rate after 1 h of 30 ml/kg ventilation was significantly reduced and was not restored when tidal volume was reduced. High tidal volume ventilation also increased lung inducible nitric oxide synthase (NOS2) expression and air space total nitrite at 3 h. Inhibition of NOS2 activity preserved cAMP-dependent AFC. Because air space edema fluid inactivates surfactant and reduces ventilated lung volume, the reduction of cAMP-dependent AFC by reactive nitrogen species may be an important mechanism of clinical ventilator-associated lung injury.     

Melatonin protects mice with intermittent hypoxia from oxidative stress-induced pancreatic injury

Sleep and Biological Rhythms - One of the most important mechanisms linking obstructive sleep apnea (OSA) to insulin resistance and type 2 diabetes involves oxidative stress. We examined whether...     

Enhancement of the endotoxin recognition pathway by ventilation with a large tidal volume in rabbits

Ventilation with a small tidal volume (V(t)) is associated with better clinical outcomes than with a large V(t), particularly in critical settings, including acute lung injury. To determine whether V(t) influences the lipopolysaccaharide (LPS) recognition pathway, we studied CD14 expression in rabbit lungs and the release of TNF-alpha by cultured alveolar macrophages after 240 min of ventilation with a large (20 ml/kg) vs. a small (5 ml/kg) V(t). We also applied small or large V(t) to lungs instilled with 50 microg/kg of LPS. The alveolar macrophages collected after large V(t) ventilation revealed a 20-fold increase in LPS-induced TNF-alpha release compared with those collected after small V(t) ventilation, whereas TNF-alpha was undetectable without LPS stimulation. In animals ventilated with a large V(t), the expression of CD14 mRNA in whole lung homogenates and the expression of CD14 protein on alveolar macrophages, assessed by immunohistochemistry, were both significantly increased in the absence of LPS stimulation. A large V(t) applied to LPS-instilled lungs increased the pulmonary albumin permeability and TNF-alpha release into the plasma. These results suggest that mechanical stress caused by a large V(t) sensitizes the lungs to endotoxin, a phenomenon that may occur partially via the upregulation of CD14.     

Alterations to surfactant precede physiological deterioration during high tidal volume ventilation

Lung injury due to mechanical ventilation is associated with an impairment of endogenous surfactant. It is unknown whether this impairment is a consequence of or an active contributor to the development and progression of lung injury. To investigate this issue, the present study addressed three questions: Do alterations to surfactant precede physiological lung dysfunction during mechanical ventilation? Which components are responsible for surfactant's biophysical dysfunction? Does exogenous surfactant supplementation offer a physiological benefit in ventilation-induced lung injury? Adult rats were exposed to either a low-stretch [tidal volume (Vt) = 8 ml/kg, positive end-expiratory pressure (PEEP) = 5 cmH2O, respiratory rate (RR) = 54-56 breaths/min (bpm), fractional inspired oxygen (Fi(O2)) = 1.0] or high-stretch (Vt = 30 ml/kg, PEEP = 0 cmH2O, RR = 14-16 bpm, Fi(O2) = 1.0) ventilation strategy and monitored for either 1 or 2 h. Subsequently, animals were lavaged and the composition and function of surfactant was analyzed. Separate groups of animals received exogenous surfactant after 1 h of high-stretch ventilation and were monitored for an additional 2 h. High stretch induced a significant decrease in blood oxygenation after 2 h of ventilation. Alterations in surfactant pool sizes and activity were observed at 1 h of high-stretch ventilation and progressed over time. The functional impairment of surfactant appeared to be caused by alterations to the hydrophobic components of surfactant. Exogenous surfactant treatment after a period of high-stretch ventilation mitigated subsequent physiological lung dysfunction. Together, these results suggest that alterations of surfactant are a consequence of the ventilation strategy that impair the biophysical activity of this material and thereby contribute directly to lung dysfunction over time.