RESPIRATORY RESPONSES TO REPEATED PROLONGED EXPOSURE TO 0.12-PPM OZONE

Repeated exposure to high concentrations of ozone results first in aug mentation (typically on the second day) and then attenuation of pulmon ary response in humans. To determine the effects of repeated prolonged low-concentration ozone exposure, we exposed 17 healthy nonsmoking ma le subjects to 0.12 ppm ozone for 6.6 h on 5 consecutive days. Subject s were also exposed once to filtered air. Volunteers exercised at a ve ntilation of similar to 39 L/min for 50 min of each hour during the ex posure. Spirometry, plethysmography, and symptom responses were obtain ed before, during, and after each exposure. Nasal lavage and aerosol b olus dispersion were obtained before and after exposure. Spirometry de creased and symptoms increased on the first day. Responses were less o n the second day compared with those on the first day, and they were a bsent compared with control values on the subsequent 3 days of ozone e xposure. Percent change in FEV(1) after ozone exposure compared with t hat after air exposure averaged -12.79, -8.73, -2.54, -0.6, +0.18% for Days 1 to 5 of ozone exposure, respectively. FEV(1) responses ranged from a zero to 34% decrease on Days 1 and 2. After each exposure, we d etermined the ratio of SRaw after inhaling a fixed dose of methacholin e to SRaw after inhaling saline aerosol, as an index of airway respons iveness. Airway responsiveness was significantly increased after each ozone exposure. The mean ratios were 2.22, 3.67, 4.55, 3.99, 3.24, and 3.74 for filtered air and ozone Days 1 to 5, respectively. Symptoms o f cough and pain on deep inspiration increased significantly on ozone Day 1 only. We conclude that repeated prolonged exposure to low levels of ozone results in progressive attenuation of symptom and spirometri c responses without an augmented response on Day 2. However, the incre ased airway responsiveness, although tending to return toward baseline values in some subjects, was not fully attenuated after 5 days.