Ozone dose–response effects of varied equivalent minute ventilation rates

Abstract

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 (FEV_1.0) 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 FEV_1.0 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 O₃ 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 FEV_1.0 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 ∼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 FEV_1.0 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 FEV_1.0 and SS responses is not body-size-dependent.