The dose-response relationship in older men exposed to ozone

Nine male subjects (56-71 years) were exposed to filtered air (FA) or 0.45 ppm O3 with inhaled dose altered by varying ventilation volume (VE = 25, 40, or 55 L/min (BTPS)) to evaluate pulmonary function dose-responses in older men. The subjects walked on a motor-driven treadmill and rested in alternating 20-min periods during the 2-h exposures. Functional residual capacity and maximal voluntary ventilation (MVV) were measured pre- and postexposure. Forced expiratory volume in 1 s (FEV1.0) and forced expiratory flow rate between 25% and 75% of vital capacity (FEF25-75%) were calculated from FVC. Residual volume (RV) was calculated from FRC. VE was measured during the last 4 min of each exercise period, and the electrocardiogram was monitored throughout each exposure. There were no significant changes in any measured parameter with FA exposure. All three O3 exposures induced small, statistically significant decrements in FVC and FEV1.0, but no significant changes in FEF25-75%. There were no significant differences among responses to the three O3 exposures. The decrements in measured pulmonary functions were smaller than typically observed in young males exposed to similar inhaled doses of O3. The data suggest possible saturation of the pulmonary response mechanism at a low degree of functional impairment in older men. Reflex-mediated impairment of inspiration, with concomitant reduction in all dependent pulmonary functions has been suggested as the mechanism of pulmonary dysfunction with O3 exposure in young adults. The results suggest that this reflex may be less active in older adults.