Human pulmonary responses with 30-minute time intervals of exercise and rest when exposed for 8 hours to 0.12 ppm ozone via square-wave and acute triangular profiles.

Hazucha et al. (1992) compared pulmonary function responses during 8-h square-wave exposures to FA and to 0.12 ppm O3, as well as to an acute triangular exposure to a mean O3 concentration of 0.12 ppm. With 30 min of moderate exercise each hour during 8 h of continuous exposure, significantly greater pulmonary function responses were observed between 5 h and 7 h when O3 was varied in an acute triangular configuration from 0.00 ppm to 0.24 ppm over the first 4 h and back to 0.00 ppm during the last 4 h than when O3 concentration was maintained constant at 0.12 ppm throughout. These investigators employed equal periods of 30 min of exercise, in which mean VE was approximately 40 L/min, and 30 min of rest, with pulmonary function measurements taken at the end of each hour. This procedure (i.e., taking measurements at the end of each hour) could attenuate the full effect that would be observed very soon after exercise cessation, and permit some recovery to occur. Accordingly, in the present study, the primary objective was to determine what effect observations of pulmonary responses assessed immediately following repeated 30 min exercise bouts, as well as those at the end of each hour (following approximately 30 min rest) during 8-h square-wave exposures to FA and to 0.12 ppm O3, as well as to an acute triangular exposure to a mean O3 concentration of 0.12 ppm. During the last 4 h of the 8-h, 0.12-ppm square-wave exposure, the 30-min mean increases in FEV1.0 responses were consistently greater at the end of the first half hour immediately following exercise (-1.22%) than at the end of the second half-hour following 30 min of rest (+0.01%). Further, even though O3 concentration was steadily decreasing from 0.24 ppm to 0 ppm during the last 4 h of the triangular exposure, similar increases in FEV1.0 decrement (-1.38%) immediately after each 30 min exercise bout, and small recovery at the end of each 30 min rest (+0.56%) were observed. Symptom scores in both exposures during the last 4 h also showed this effect.