Changes in Dogs’ Lungs After Long-Term Exposure to Ozone

Abstract

Dogs were exposed to 1 to 3 ppm of ozone (O₃) 8 to 24 hours daily for 18 months. Macrophages appeared and increased with “dosage.” Fibrous elements were deposited rarely at the lowest dosage but increased with the concentration of O₃. Additional features were thickening of the terminal and respiratory bronchiolar walls at the higher concentrations and their infiltration by lymphocytes, plasma cells, and “fibroblasts” that formed peribronchiolar collars. Connective tissue obstructed alveolar openings into bronchioles and ducts and extended into alveolar walls. Thick bronchiolar walls reduced the caliber of small airways. Bronchiolar epithelial changes included an increase in the proportion of mucus-forming cells and squamous metaplasia of columnar and cuboidal cells with occasional islands of hyperplasia. Metabolic effects were reflected in ultrastructural alteration of preexisting, intracytoplasmic bodies. Together with nitrogen dioxide, O₃ may contribute to pulmonary disease in a susceptible population.