Pathologic changes in the small airways of the guinea pig after amosite asbestos exposure.

To determine whether asbestos dust produces pathologic changes in the small airways, and to determine where the anatomic lesions of asbestosis commence, the authors examined lungs from guinea pigs exposed to 10 or 30 mg of amosite asbestos by intratracheal instillation and sacrificed 6 months later. Measurement of airway wall thickness revealed that membranous and respiratory bronchioles of all sizes in exposed animals were significantly thicker than those of controls. Amosite fibers were found embedded in the walls of bronchi and in membranous and respiratory bronchioles; where these fibers penetrated the airway walls, an interstitial inflammatory and fibrotic reaction (asbestosis) occurred. It is concluded that 1) amosite asbestos produces diffuse abnormalities throughout the noncartilagenous airways and possibly the cartilagenous airways as well; 2) this effect is independent of interstitial fibrosis of the parenchyma (classical asbestosis); 3) asbestosis, at least that induced by amosite, commences at any site in the parenchyma to which the asbestos fibers can gain access, either by deposition in alveoli and alveolar ducts or by direct passage of fibers through the walls of all types and sizes of small airways.