Table 2

Multiple linear regression analysis for the association between postbronchodilator lung function and the smoking status in young patients with untreated intermittent adult-onset asthma

Postbronchodilator lung function, (continuous)Number of cigarettes per dayAdjusted R2
Never smoker1–10† ≥11
n=156n=55n=51
(Ref.)Partial regression coefficient (95% CI)Partial regression coefficient (95% CI)
FEV1 (% predicted)0 −6.72 (−12.0 to −1.41)* −7.76 (−13.7 to −1.81)* 0.032
FEV1/FVC ratio0 −0.032 (−0.062 to −0.001)* −0.040 (−0.079 to −0.001)* 0.170
FEF25–75 (% predicted)0 −9.77 (−17.2 to −2.38)* −10.4 (−18.7 to −2.15)* 0.045
Duration of smoking (years)
Never1–7 years†≥8 years
n=156n=49n=57
FEV1 (% predicted)0 −2.89 (−8.64 to 2.86) −11.1 (−16.6 to −5.63)** 0.054
FEV1/FVC ratio0 −0.012 (−0.049 to. 026) –0.049 (−0.080 to −0.017)** 0.186
FEF25–75 (% predicted)0 −6.49 (−14.6 to 1.61) −13.2 (−20.9 to −5.47)** 0.053
Cumulative consumption, pack-years
Never0<pack years≤4†>4 pack-years
n=156n=55n=51
FEV1 (% predicted)0 −5.29 (–10.6 to –0.005)* −9.91 (−15.9 to −3.97)** 0.039
FEV1/FVC ratio0 −0.021 (−0.052 to 0.001) −0.055 (–0.091 to −0.018)** 0.185
FEF25–75 (% predicted)0 −8.85 (−16.3 to −1.43)* −11.7 (−20.0 to −3.35)** 0.047

  • Each lung function parameter was separately analysed after adjustment for sex, age, disease duration (log transformed) and BMI.

  • Each partial regression coefficient shows the difference between mean values and those for never smokers after adjustment for sex, age, disease duration (log transformed) and BMI.

  • Results highlighted in bold indicate statistically significant findings.

  • *P<0.05 , **P<0.01  versus  never smoker.

  • †Current smokers were stratified on the basis of the median value for each smoking parameter.

  • BMI, body mass index; FEV1, forced expiratory volume in one second ; FVC, forced vital capacity ; FEF25–75, forced expiratory flow between 25 % and 75 % of the vital capacity .