Lung Injury Caused by Ambient Levels of Ozone

Abstract

ABSTRACT

Exposures to low levels of 0₃ cause epithelial and interstitial injury in the proximal alveolar region. The sequential development of this lesion caused by a simulated ambient pattern of 0₃ was studied by exposing Fisher 344 rats to 0.06 ppm 0₃ overnight with an 8 hours daytime exposure having a slow increase to a peak of 0.25 ppm and then gradually decreasing back to 0.06 ppm. Separate control groups for each exposure period were kept in filtered air. Ozone exposed animals (12/group) were studied after 7 days, 21 days and 90 days exposure, respectively. In addition, twelve animals exposed for 90 days and then allowed to recover for 42 days in air were studied. Randomly selected proximal alveolar regions were isolated from embedded tissue, thin-sectioned for electron microscopy and submitted to a morphometric analysis. The early changes in 0₃ exposed animals included increases in the relative volumes in type II epithelium (61%), type I epithelium (16%), cellular interstitium (52%), non-cell interstitium (33%), and in alveolar macrophages (180%). The response showed a biphasic reaction with the early injury subsiding after 21 days of 0₃ exposure. The animals exposed for 90 days showed a 28% increase in relative volume of type I epithelium and a 42% increase in type II epithelium. A mild increase in interstitial volume could also still be detected at this time. During the 42 days recovery period the changes in relative volume of epithelial cells subsided; however, an enhanced number (39%) of type I cells with smaller average surface area (32%) persisted and did not show any trend back to normal. The relative volume of interstitial matrix remained slightly increased (12%) after recovery. These data indicate that with long exposures a chronic alveolar epithelial and interstitial reaction occurs and that these reactions can only be partially reversed 42 days after the exposure is terminated.