TIME COURSE OF RESPONSE TO OZONE EXPOSURE IN HEALTHY ADULT FEMALES

Abstract

Ozone exposure causes acute decrements in pulmonary function, increases airway responsiveness, and changes the breathing pattern. We examined these responses in 19 ozone-responsive (D FEV1 > 5%) young females exposed to both air and 0.35 ppm ozone. The randomized 75-min exposures included two 30-min exercise periods at V E 40 L/min. Responses were measured before, during, and after exposure and at 18 and 42 h postexposure. FVC, FEV1, and FIV0.5 decreased (p < .01) immediately postexposure by 13.2%, 19.9%, and 20.8%, respectively, and the airway responsiveness was significantly increased. Raw increased (p < .05), while TGV remained essentially unchanged. At 18 h postexposure, the airways were still hyperresponsive and FEV1 and FIV0.5 were still 5% below the preexposure levels. There were no residual effects in any of the variables at 42 h postexposure. During exercise in ozone the tidal volume was decreased (-14%) and respiratory frequency increased (+15%). The changes in airway responsiveness were not related to changes in spirometric measurements. We found no significant differences between postair and postozone mouth occlusion pressure (Pm0.1) and the hypercapnic response to CO2 rebreathing. We conclude that ozone induced typical acute changes in airway responsiveness and that ventilatory (exercise), spirometric (inspiratory and expiratory), and plethysmographic pulmonary function may show some residual effects for up to 18 h after exposure. The ozoneinduced alteration in breathing pattern during exercise does not appear to be related to a change in ventilatory drive.