In this study we describe, through stereological methods, the lung morphology following inhalation exposure of guinea pigs to 21 mg/m3 cotton dust (CD) for 1 year. Various stereological parameters were determined on semithin histological sections, through a multistage sampling approach, to study the reaction of the whole lung, alveolar parenchyma, and bronchioles to CD inhalation. After 1 year of exposure, the lung volume was increased. Two distinct patterns of lung response were identified among the exposed animals. In type I responders, most of the morphometric parameters measured to describe the alveolar parenchymal reaction were within control value limits x ± 2 SD). In type II responders, the volume density (Vv) of the parenchymal zone was decreased, while the Vv, mean thickness, and absolute volume of the alveolar septa were increased. These changes caused the surface density (Sv) of alveolar epithelium to decrease, and an estimate of the percentage of alveolar septa remaining functional for gas exchange was also significantly lowered in these animals. In both types of responders, fifth to ninth orders of bronchioles had a raised wall to lumen ratio; the Vv and mean thickness of the bronchiolar epithelium were markedly increased, denoting hyperplastic changes. Thus, chronic exposure to cotton dust induced definite morphological changes on the peripheral conducting airways in most of the exposed animals, and induced pronounced changes at the alveolar level in 8 of 17 CD-exposed guinea pigs.
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