ACUTE EFFECTS OF OZONE ON THE PULMONARY-FUNCTION OF EXERCISING SCHOOLCHILDREN FROM MEXICO-CITY

The acute effects of ozone (O-3) on the change in lung function before and after exercise was assessed in 22 boys and 18 girls from 7 1/2 to 11 yr of age tested up to eight times over a 1 1/2%-yr period outdoors (under a tarpaulin) at a school in Mexico City. Ozone and particulates were monitored at an adjacent government station, in the school yard, and under the tarp. Subjects were selected to oversample children with chronic respiratory symptoms, although children with active asthma under regular medication or FEV(1) < 80% predicted were excluded. Of the participants, 21 had chronic cough, chronic phlegm, or ever wheeze with colds or apart from colds. Children performed two cycles of treadmill exercise (15 min) and rest (15 min) for a total of 1 h of intermittent exercise. Most subjects attained the target minute ventilation of 35 L/min/m(2). Subjects exercised alternately during low ozone hours (8:00-10:00 A.M.) and during peak O-3 hours (12:00-2:00 P.M.), to assure a range of exposures. On 85% of exercise days, the maximum daily 1-h average for ambient O-3 exceeded the Mexican guideline of 110 parts per billion (ppb). O-3 exposure during the hour of exercise was divided into quintiles, and the response was adjusted for repeated measures, subject having a cold, and prior outdoor exercise. Ambient O-3 in the fifth quintile (mean = 229 ppb) was associated with a percentage change in FVC (-1.43% +/- 0.70), FEV(1) (-2.85% +/- 0.79), FEF(25-75)% (-6.32% +/- 1.87) and FEV(1)/FVC (-1.41% +/- 0.46). The decrements in lung function observed are comparable to those previously reported in children and young adults exercised in exposure chambers with acute but not chronic O-3 exposure. Thus, despite repeated exposure to high levels of O-3 exercising children from Mexico City responded acutely to an hour of exposure to O-3 at levels above 150 ppb.