Ozone dose-response effects of varied equivalent minute ventilation rates

While it is well known that exercise minute ventilation (V(E)) results in greater pulmonary function and subjective symptoms (SS) responses upon exposure to a given ozone (O3) dose, the magnitude of V(E) increase to produce a significant forced expiratory volume in 1 s (FEV1.0) response compared to that observed at a lower exercise V(E) for the same O3 concentration and exposure time is unclear, especially in prolonged (i.e., >2 h) exposures. Further, in prolonged exposures, the relationship of body size to FEV1.0 response to a given O3 exposure dose has not been systematically examined. In the present study, 30 young adults were exposed on four occasions for 6 h (during a 6.6-h period) to constant 03 levels of zero (filtered air, FA) or 0.12 parts per million (ppm). At the latter concentration, exercise V(E) was varied in exposures to 17, 20, and 23 l min(-1) m(-2) of BSA, respectively, for each individual to achieve an equivalent ventilation rate, EVR). In the FA exposure, EVR was 23 l min(-1) m2. Percent changes in FEV1.0 for the three 0.12 ppm O3 exposures were significantly greater than that for FA, but did not differ significantly from each other. For the 6.6-h exposures, exercise EVR at or in excess of 17 l min(-1) m(-2), SS values were significantly greater than those observed for the FA protocol. Further, SS values at 6.6 h of exposure to 0.12 ppm O3 for the exercise EVR of 23 l min(-1) m(-2) protocol were significantly greater than for the 0.12 ppm O3 exercise EVR of 17 l min(-1) m(-2) protocol. To achieve a widened EVR, two 1-h exposures to 0.30 ppm O3 with continuous exercise (CE) at a level necessitating an EVR of 17 and approximately 34 l min(-1) m(-2), respectively, were completed by each subject. All postexposure pulmonary function and SS responses were significantly greater for the higher 1-h EVR protocol. In all exposures with significant O3-induced changes in FEV1.0 and SS, it was found that the smaller subjects who exercised at the lowest absolute V(E) had significantly smaller responses than did the larger subjects. These results strongly suggest that for the O3 concentrations and exposure durations used in this study, the effect of V(E) on O3-induced FEV1.0 and SS responses is not body-size-dependent.