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(Chest. 1999;116:28S.)
© 1999 American College of Chest Physicians

A Murine Model of Volutrauma*

Potential Contribution of Inflammatory Cell Proteases to Lung Injury

T. Gronski, Jr., MD, FCCP; E. Lum, MD; J. Campbell and S. D. Shapiro, MD, FCCP

* From the Departments of Medicine and Cell Biology, Washington University School of Medicine, St. Louis, MO. Supported by ALA and the Barnes-Jewish Hospital Foundation.

Correspondence to: Theodore J. Gronski, Jr., MD, FCCP, Pulmonary and Critical Care Medicine, Barnes Jewish Hospital North, 216 S Kingshighway Blvd, St. Louis, MO 63110

Although mechanical ventilation is recognized as an invaluable method of support for patients with severe respiratory failure, recent attention has been drawn to the phenomenon of lung injury caused by positive pressure ventilation. Studies of the pathogenesis of "volutrauma" have focused largely on the mechanical sequelae of excessive or repetitive alveolar distention, eg, the "stretched pore" phenomenon or capillary stress fracture. Even early investigations into lung injury associated with mechanical ventilation, however, have identified inflammatory cell accumulation with increasing airway pressures. We have developed a closed-chest murine model of volutrauma to pursue the individual contributions of these two potential mechanisms of lung injury.

Six 8-week-old 129/Sv mice were ventilated at room air for 2 h with a mouse ventilator (Harvard Apparatus). Normal pH and PCO2 were maintained through manipulation of respiratory rate. Tidal volumes were adjusted to achieve target Paw. Increasing extravasation of Evans blue dye from plasma into BAL fluid was noted with increasing Paw, indicating an alteration in epithelial/endothelial permeability. Western analysis of BAL fluid from ventilated animals revealed increased amounts of the basement membrane components perlecan (heparan sulfate) and laminin (ß1 chain) when compared with nonventilated control mice.

Basement membrane components may be released into the alveolar lining fluid through repetitive mechanical injury or via inflammatory cell-driven proteolytic degradation. With respect to this latter possibility, a ninefold increase in intravascular neutrophils (per myeloperoxidase assay on whole lung homogenate samples) and an eightfold increase in accumulated intra-alveolar macrophages (per cell count on cytospin samples) were associated with increasing Paw. Casein and gelatin zymography of whole lung homogenate samples demonstrated increased expression of the metalloproteinases matrilysin, macrophage metalloelastase (MME), and (activated) 92-kd gelatinase and 72-kd gelatinase at higher Paw. Subsequent immunohistochemical analysis has confirmed the presence of matrilysin and MME in interstitial and alveolar macrophages in lung tissue samples obtained from animals ventilated at high Paw. Additionally, Western analysis of BAL fluid revealed induction of surfactant protein D, a recently identified stimulator of alveolar macrophage metalloproteinase production, after mechanical ventilation for 2 h.

We are now applying mice that we have generated by gene-targeting, including MME-, matrilysin-, 92-kd gelatinase-, and neutrophil elastase-deficient animals, in this model to determine the contribution of inflammatory cell proteinases to the lung injury observed at 2 h as well as their potential effect on mediating subsequent injury.




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