Distribution and reproducibility of spirometric response to ozone by gender and age

Subjects were healthy nonsmoking men (n = 146) and women (n = 94) 18-60 yr old. Initially, each subject was exposed for 1.5 h to 0.42 ppm O3. Forty-seven individuals were later reexposed twice, 1 wk to several months apart, to 0.4 ppm O3. Intermittent exercise utilized in all exposures was adjusted to produce an O3 dose of 560 ppm x l/m2 body surface area. The post-O3 percent change in forced-expiratory volume in 1 s (delta%FEV1) decrements of young (18-35 yr) and middle-aged (36-60 yr) men and women differed significantly (P < 0.05) from normal distribution with values skewed toward larger decrements in younger subjects. The mean delta%FEV1 rates were -16.3%, -16.6%, -11.6%, and -6.4%, respectively. The rate of decline with age was 2.5 times higher in young women compared with young men (P < 0.05). This pattern was reversed in the middle-age cohort. Our data support earlier reports of no significant difference in spirometric response to O3 between young men and women. The data also confirm that large FEV1 decrements after O3 exposure are mostly confined to younger individuals that also show much greater variance in response to repeated exposures than the middle-aged subjects. The majority of subjects remained in their initial category of O3 sensitivity on retesting after various time lapses. The r value (Spearman) between the first and second and first and third exposure response ranged from 0.544 to 850, depending on classification. However, the mean delta%FEV1 differed by as much as six percentage points between exposure days. The yearly loss of responsiveness (0.2% to 0.7%/year) with progressing age determined by cross-sectional analyses was substantially smaller.