Time course of response to ozone exposure in healthy adult females

Ozone exposure causes acute decrements in pulmonary function, increases air way responsiveness, and changes the breathing pattern. We examined these re sponses in 19 ozone-responsive(Delta FEV1 > 5%) young females exposed to bo th air and 0.35 ppm ozone. The randomized 75-min exposures included two 30- min exercise periods at V-E approximate to 40 L/min. Responses were measure d before, during and after exposure and at 18 and 42 h postexposure. FVC, F EV1, 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 unchang ed. At 78 h postexposure, the airways were still hyperresponsive and FEV1 a nd FIV0.5 were still 5% below the preexposure levels. There were no residua l effects in any of the variables at 42 h postexposure. During exercise in ozone the tidal Volume was decreased (-14%) and respiratory frequency incre ased (+15%). The changes in airway responsiveness were not related to chang es in spirometric measurements. We found no significant differences between postair and postozone mouth occlusion pressure (Pm-0.1) and the hypercapni c response to CO2 rebreathing. We conclude that ozone induced typical acute changes in airway responsiveness and that ventilatory (exercise), spiromet ric (inspiratory and expiratory), and plethysmographic pulmonary function m ay show some residual effects for up to 18 h after exposure. The ozone-indu ced alteration in breathing pattern during exercise does not appear to be r elated to a change in ventilatory drive.