Table 4

Determinants of baseline lung function and methacholine slope at the initial and final cross sectional phases and change in lung function and change in methacholine slope in the longitudinal survey: multiple regression analyses*

FVC β (95% CI)‡FEV1β (95% CI)FEF25–75% β (95% CI)
p%pFEV1/FVC β (95% CI)p%pMethacholine slope† β (95% CI)p
Initial phase
Hairdressing apprentices v office apprentices1.98 (−0.77 to 4.74)0.153.07 (0.43 to 5.71)0.020.64 (−0.57 to 1.86)0.304.81 (0.29 to 9.32)0.04−0.002 (−0.052 to 0.051)0.99
Atopy¶−2.01 (−3.38 to −0.63)0.0040.18 (0.12 to 0.24)<0.0001
Gender (female v male)0.07 (0 to 0.14)0.05
Final phase
Hairdressing apprentices v office apprentices2.21 (−0.29 to 4.71)0.081.93 (−0.50 to 4.35)0.12−0.13 (−0.31 to 1.06)0.83−1.58 (−6.03 to 2.87)0.480.029 (−0.022 to 0.081)0.99
Gender (female v male)0.08 (0 to 0.16)0.05
Current or ex-smokers v non-smokers−1.23 (−2.40 to −0.07)0.04
Δ (final − initial)**Δ (final − initial)Δ (final − initial)Δ (final − initial)Δ (final − initial)††
Initial phase: 239 hairdressing apprentices, 124 office apprentices; for methacholine slope 234 hairdressing apprentices and 116 office apprentices; final phase: 218 hairdressing apprentices, 138 office apprentices; for methacholine slope 204 hairdressing apprentices and 129 office apprentices.
Longitudinal survey: 119 hairdressing apprentices and 76 office apprentices; for change in methacholine challenge: 108 hairdressing apprentices and 67 office apprentices.
*Variables examined in the models are: group status (fixed variable), smoking status, atopy for the change in baseline lung function values and group status (fixed variable), gender, age, smoking status, atopy for the methacholine slope. Variables with no significant effect on any of the lung function parameters were deleted from the table: smoking status and age at the initial phase, age at the final phase, and gender and age in the longitudinal survey.
†Methacholine slope defined by the percent decline in FEV1 divided by the final cumulative dose of methacholine administered, expressed as log(slope+0.02).
‡Regression coefficients and 95% confidence interval.
§Baseline lung function parameters are expressed as percentage of the reference values established by Knudson and colleagues.8
¶Atopy defined by positive medical history of asthma or allergic rhinitis or medical history of atopic dermatitis. Information on this parameter was missing for 89 hairdressing apprentices and 61 office apprentices participating only in the final phase. Therefore, this parameter was not examined in the multiple regression models of the final phase.
**Δ: % predicted at the final phase − % predicted at the initial phase.
††Change in methacholine slope defined as log(slope+0.02) at the final phase − log(slope+0.02) at the initial phase.
Longitudinal survey
Hairdressing apprentices v office apprentices−1.92 (−4.06 to 0.22)0.08−2.56 (−4.91 to −0.21)0.03−0.57 (−1.73 to 0.59)0.33−5.21 (−9.62 to −0.81)0.020.06 (−0.01 to 0.13)0.08
Current or ex-smokers v non-smokers4.64 (0.31 to 8.96)0.04
Atopy−5.43 (−10.63 to −0.23)0.04−0.12 (−0.20 to −0.03)0.01