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 O-3. Forty-seven individuals were later reexposed twice, 1 wk to several months apart, to 0.4 ppm O-3. Intermittent exercise utilized in all exposures was adjusted to produce an O-3 dose of 560 ppm x l/m(2) body surface area. The post-O-3 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 Δ%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 O-3 between young men and women. The data also confirm that large FEV1 decrements after O-3 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 O-3 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.