Pathophysiologic correlations in asbestos-induced airway disease in the guinea pig

To determine whether asbestos-induced changes in the structure of the walls of small airways might be associated with abnormalities of pulmonary function, guinea pigs were given 10 mg of amosite asbestos (test group) or saline (control group) by intratracheal instillation. Pulmonary function tests performed 6 months later revealed significant increases in FRC, RV, and TLC in the test group. Measurement of airway wall thickness showed that both membranous and respiratory bronchioles were significantly thickened in the test group; this group also had airways of smaller internal diameter than the controls. Analysis for lung collagen content as hydroxyproline showed a 50% increase in the asbestos exposed animals. There was, however, only minimal and very focal interstitial fibrosis (asbestosis) in the lung parenchyma. Analysis of fiber size indicated that the fibers obtained by digestion of the tissue or from the lavage fluid were significantly longer and wider than those in the original asbestos sample; however, the tissue contained considerably larger fibers than the lavage fluid. We conclude that: Asbestos can produce airway fibrosis and narrowing causing air trapping on pulmonary function examination; this process occurs in the absence of significant interstitial fibrosis of the parenchyma (asbestosis), implying that abnormalities of pulmonary function which are consistent with airflow obstruction in asbestos exposed animals can be caused by pathologic changes in the small airways alone; long asbestos fibers are preferentially retained in the lung, and the longest fibers appear to be in a compartment inaccessible to lavage, presumably, in this model, in airway walls. Enhanced penetration of long fibers into tissue may be one reason why long fibers are more pathogenic than short ones.