We conclude that TNF-alpha overexpression causes pathologic changes consistent with both emphysema and pulmonary fibrosis combined with a general lung inflammation, and consequently does not model any single human disease. Our study thus confirms the pleiotropic effects of TNF-alpha, which has been implicated in multiple inflammatory disorders, and underscores the necessity of using a wide range of investigative techniques to link gene expression and phenotype in animal models of disease.

Reopening the injured lung with deep inflation (DI) and positive end-expiratory pressure (PEEP) likely depends on the duration and severity of acute lung injury (ALI), key features of which include increased alveolar permeability and fibrin accumulation. We hypothesized that the response to DI and PEEP would worsen as ALI evolves and that this would correspond with increasing accumulation of alveolar fibrin. C57BL/6 mice were anesthetized and aspirated 75 microl of HCl (pH 1.8) or buffered normal saline. Subgroups were reanesthetized 4, 14, 24, and 48 h later. Following DI, tissue damping (G) and elastance (H) were measured periodically at PEEP of 1, 3, and 6 cmH(2)O, and air within the lung (thoracic gas volume) was quantified by microcomputed tomography. Following DI, G and H increased with time during progressive lung derecruitment, the latter confirmed by microcomputed tomography. The rise in H was greater in acid-injured mice than in controls (P < 0.05) and also increased from 4 to 48 h after acid aspiration, reflecting progressively worsening injury. The rise in H was reduced by PEEP, but this effect was significantly blunted by 48 h (P < 0.05), also confirmed by thoracic gas volume. Lung permeability and alveolar fibrin also increased over the 48-h study period, accompanied by increasing levels and transcription of the fibrinolysis inhibitor plasminogen activator inhibitor-1. Lung injury worsens progressively in mice during the 48 h following acid aspiration. This injury manifests as progressively increasing alveolar instability, likely due to surfactant dysfunction caused by increasing levels of alveolar protein and fibrin.

The role of gastroesophageal reflux and micro-aspiration as a trigger of airways hyperresponsiveness (AHR) in patients with asthma is controversial. The role of acid reflux and aspiration as a direct cause of AHR in normal subjects is also unclear. We speculated that aspiration of a weak acid with a pH (1.8) equivalent to the upper range of typical gastric contents would lead to AHR in naive mice. We further speculated that modest reductions in aspirate acidity to a level expected during gastric acid suppression therapy (pH 4.0) would impede aspiration-induced AHR. BALB/c female mice were briefly anesthetized with isoflurane and allowed to aspirate 75 microl of saline with HCl (pH 1.8, 4.0, or 7.4) or underwent sham aspiration. Mice were re-anesthetized 2 or 24 h later, underwent tracheostomy, and were coupled to a mechanical ventilator. Forced oscillations were used to periodically measure respiratory impedance (Zrs) following aerosol delivery of saline and increasing doses of methacholine to measure for AHR. Values for elastance (H), airways resistance (R(N)), and tissue damping (G) were derived from Zrs. Aspirate pH of 1.8 led to a significant overall increase in peak R(N), G, and H compared with pH 4.0 and 7.4 at 2 and 24 h. Differences between pH 7.4 and 4.0 were not significant. In mice aspirating pH 1.8 compared with controls, airway lavage fluid contained more neutrophils, higher protein, and demonstrated higher permeability. We conclude that acid aspiration triggers an acute AHR, driven principally by breakdown of epithelial barrier integrity within the airways.

In select cases where additional tissue may be needed, sampling with a 19-G EBUS needle following standard aspiration with a 22-G needle results in an increase in diagnostic yield.