Results We found a dose–response relation between smoking and lower levels of both the ratio of forced expiratory volume in one second to forced vital capacity (FEV 1/FVC) and the forced expiratory flow between 25 and 75 percent of FVC (FEF 25–75). Each pack per day of smoking was associated with a 3.2 percent reduction in FEF 25–75 for girls (P = 0.01) and a 3.5 percent reduction in FEF 25–75 for boys (P = 0.007). Whereas the FVC level was elevated in smokers, the rate of growth of FVC and FEV 1 was reduced. Among adolescents of the same sex, smoking five or more cigarettes a day, as compared with never smoking, was associated with 1.09 percent slower growth of FEV 1 per year in girls (95 percent confidence interval, 0.70 to 1.47 percent) and 0.20 percent slower growth in boys (95 percent confidence interval, -0.16 to 0.56 percent), and with 1.25 percent slower growth of FEF 25–75 per year in girls (95 percent confidence interval, 0.38 to 2. Icom Radio Serial Numbers. 13 percent) and 0.93 percent slower growth in boys (95 percent confidence interval, 0.21 to 1.65 percent). Whereas girls who did not smoke reached a plateau in lung function at 17 to 18 years of age, girls of the same age who smoked had a decline of FEV 1 and FEF 25–75. Figure 2 Mean Rates of Pulmonary-Function Growth According to Age, Sex, and Category of Smoking.

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