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 O-3 with inhaled dose altered by varying ventilation volume (V-E = 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 (FEV(1.0)) 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. V-E 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 O-3 exposures induced small, statistically significant decrements in FVC and FEV(1.0), but no significant changes in FEF25-75%. There were no significant differences among responses to the three O-3 exposures. The decrements in measured pulmonary functions were smaller than typically observed in young males exposed to similar inhaled doses of O-3. 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 O-3 exposure in young adults. The results suggest that this reflex may be less active in older adults.