Pulmonary function alterations in F344 rats following chronic ozone inhalation

The impact of a 20-mo exposure to ozone on the pulmonary function of rats was assessed by performing a single series of measurements after exposures were completed. Four to 10 male and female F344 rats per group were exposed 6 h/day, 5 days/wk for 20 mo to ozone at 0.12, 0.5, or 1.0 ppm, or to clean air as controls. One to 3 days after the last exposure, the rats were anesthetized using halothane, fitted with oral endotracheal and esophageal catheters, and measured using plethysmographic techniques. The significances of differences between mean values for control and treated rats were tested by multiple comparisons. The values and intersubject variability for over 30 measured and calculated parameters were similar to those reported previously for similarly aged rats. The only consistent exposure-related effect was a small reduction of residual volume measured during slow lung deflation. This trend was observed in most exposed groups, but was most significant in females at the 0.5 ppm level. Fibrosis and epithelial changes were observed in the terminal bronchiole-alveolar duct region in parallel studies of different rats from the same exposure groups. It was hypothesized that these changes stiffened airspace walls and acted to maintain the patency oi the air pathway to a lower than normal lung volume during deflation. Overall, the exposures had little impact on the integrated pulmonary function of the lung as measured in anesthetized rats.