Preexposure to low ozone concentrations does not diminish the pulmonary function response on exposure to higher ozone concentrations.

To determine whether persons repeatedly exposed to low ozone concentrations would demonstrate a diminished responsivity, as a result of adaptation or desensitization, when subsequently exposed to a higher ozone concentration, we performed the following study. Respiratory sensitivity (pulmonary function response) to 2 h of exposure to 0.42 or 0.50 ppm ozone (acute exposure) was determined 3 months before or 6 to 8 wk after the study. Twenty-one subjects (8 men, 13 women) were exposed for 2 h or 5 consecutive days to filtered air, 0.20, 0.20, 0.20, and 0.42 to 0.50 ppm ozone, respectively. There were no significant differences between the responses of men and women to ozone. Subjects were divided into a sensitive group (greater than 20% drop in FEV1) and a nonsensitive group (less than 10% drop in FEV1) on the basis of their responses to the acute exposure. Neither the overall group nor the nonsensitive group showed a significant response to 0.20 ppm. Sensitive subjects (n = 9) showed small but significant decreases in FEV1 on exposure to 0.20 ppm. The predominant finding was that the 3 days of preexposure to 0.20 ppm ozone had no effect on the response to 0.42 or 0.50 ppm ozone on the fourth day (when compared with the previous acute exposure to 0.42 or 0.50 ppm). We conclude that subjects repeatedly (3 times) exposed to a low (0.20 ppm) concentration of ozone do not demonstrate a pulmonary function adaptation or desensitization on a subsequent exposure to a higher (0.42 or 0.50 ppm) ozone concentration.