This study tests the hypotheses that a recruitment maneuver per se yields and/or intensifies lung mechanical stress. Recruitment maneuver was applied to a model of paraquat-induced acute lung injury (ALI) and to healthy rats with (ATEL) or without (CTRL) previous atelectasis. Recruitment was done by using 40-cmH(2)O continuous positive airway pressure for 40 s. Rats were, then, ventilated for 1 h at zero end-expiratory pressure (ZEEP) or positive end-expiratory pressure (PEEP; 5 cmH(2)O). Atelectasis was generated by inflating a sphygmomanometer around the thorax. Additional groups did not undergo recruitment but were ventilated for 1 h under ZEEP. Lung resistive and viscoelastic pressures and static elastance were computed before and immediately after recruitment, and at the end of 1 h of ventilation. Lungs were prepared for histology. Type III procollagen (PCIII) mRNA expression in lung tissue was analyzed by RT-PCR. Lung mechanics improved after recruitment in the CTRL and ALI groups. One hour of ventilation at ZEEP increased alveolar collapse, static elastance, and lung resistive and viscoelastic pressures. Alveolar collapse was similar in ATEL and ALI, and recruitment opened the alveoli in both groups. ALI showed higher PCIII expression than ATEL or CTRL groups. One hour of ventilation at ZEEP did not increase PCIII expression but augmented it significantly in the three groups when applied after recruitment. However, PEEP ventilation after recruitment avoided any increment in PCIII expression in all groups. In conclusion, recruitment followed by ZEEP was more deleterious in ALI than in mechanical ATEL, although ZEEP alone did not elevate PCIII expression. Ventilation with 5-cmH(2)O PEEP prevented derecruitment and aborted the increase in PCIII expression.

The aim of this study was to test the hypothesis that bone marrow mononuclear cell (BMDMC) therapy led an improvement in lung mechanics and histology in endotoxin-induced lung injury. Twenty-four C57BL/6 mice were randomly divided into four groups (n = 6 each). In the acute lung injury (ALI) group, Escherichia coli lipopolysaccharide (LPS) was instilled intratracheally (40 μg, IT), and control (C) mice received saline (0.05 ml, IT). One hour after the administration of saline or LPS, BMDMC (2 × 10(7) cells) was intravenously injected. At day 28, animals were anesthetized and lung mechanics [static elastance (E(st)), resistive (ΔP(1)), and viscoelastic (ΔP(2)) pressures] and histology (light and electron microscopy) were analyzed. Immunogold electron microscopy was used to evaluate if multinucleate cells were type II epithelial cells. BMDMC therapy prevented endotoxin-induced lung inflammation, alveolar collapse, and interstitial edema. In addition, BMDMC administration led to epithelial and endothelial repair with multinucleated type II pneumocytes. These histological changes yielded a reduction in lung E(st), ΔP(1), and ΔP(2) compared to ALI. In the present experimental ALI model, the administration of BMDMC yielded a reduction in the inflammatory process and a repair of epithelium and endothelium, reducing the amount of alveolar collapse, thus leading to an improvement in lung mechanics.

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The time course of lung mechanics, histology, and inflammatory and fibrogenic mediators are analysed after intratracheal instillation (IT) of bone marrow-derived cells (BMDC) in a model of silicosis. C57BL/6 mice were randomly divided into SIL (silica, 20mg IT) and control (CTRL) groups (saline IT). At day 15, mice received saline or BMDC (2 x 10(6)cells) IT. The biodistribution of technetium-99m BMDC was higher in lungs compared with other organs. At days 30 and 60, lung mechanics, the area of granulomatous nodules, and mRNA expression of IL-1beta and TGF-beta were higher in SIL than CTRL animals. BMDC minimized changes in lung mechanics, the area of granulomatous nodules, and total cell infiltration at day 30, but these effects were no longer observed at day 60. Conversely, BMDC avoided the expression of IL-1beta at days 30 and 60 and TGF-beta only at day 30. In conclusion, BMDC therapy improved lung mechanics and histology, but this beneficial effect was not maintained in the course of injury.

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