We assessed chronic bronchitis as the combination of the symptoms of cough and mucus production in the morning during winter (defined as “CB”), which required positive answers to the following two binary-choice questions: 1) “In the winter, do you usually cough as soon as you wake up in the morning?” and 2) “In the winter, do you usually bring up mucus as soon as you wake up in the morning?” [23 (link)].
Childhood asthma at ages 1–16 years was defined if at least two of the following three criteria were fulfilled: doctor's diagnosis of asthma ever; wheezing in the past 12 months; and/or use of asthma medication during the past 12 months [24 (link)].
Current asthma was defined as a positive answer to doctor diagnosis of asthma, and at least one of the following: wheezing in the past 12 months; or use of asthma medication during the past 12 months.
Lung function was tested according to American Thoracic Society (ATS)/European Respiratory Society (ERS) spirometry criteria [25 (link)] using the Jaeger MasterScreen-IOS system (Carefusion Technologies, San Diego, CA, USA) and post-bronchodilator lung function was tested 15 min after the administration of 400 μg salbutamol. The highest values of pre- and post-forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were recorded [19 (link), 20 (link)]. Predicted values and z-scores of FEV1, FVC and FEV1/FVC ratios were calculated for each patient using equations from the Global Lung Function Initiative (GLI) [26 (link)] according to age, sex, height and ethnicity. The lower limit of normal (LLN) was defined as the bottom fifth percentile of the predicted value and calculated by GLI equations for every participant.
Fractional exhaled nitric oxide (FeNO) was measured using a chemiluminescence analyser (EcoMedics Exhalyzer, Duernten, Switzerland) according to the ATS/ERS guidelines [27 (link)].
Childhood asthma at ages 1–16 years was defined if at least two of the following three criteria were fulfilled: doctor's diagnosis of asthma ever; wheezing in the past 12 months; and/or use of asthma medication during the past 12 months [24 (link)].
Current asthma was defined as a positive answer to doctor diagnosis of asthma, and at least one of the following: wheezing in the past 12 months; or use of asthma medication during the past 12 months.
Lung function was tested according to American Thoracic Society (ATS)/European Respiratory Society (ERS) spirometry criteria [25 (link)] using the Jaeger MasterScreen-IOS system (Carefusion Technologies, San Diego, CA, USA) and post-bronchodilator lung function was tested 15 min after the administration of 400 μg salbutamol. The highest values of pre- and post-forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were recorded [19 (link), 20 (link)]. Predicted values and z-scores of FEV1, FVC and FEV1/FVC ratios were calculated for each patient using equations from the Global Lung Function Initiative (GLI) [26 (link)] according to age, sex, height and ethnicity. The lower limit of normal (LLN) was defined as the bottom fifth percentile of the predicted value and calculated by GLI equations for every participant.
Fractional exhaled nitric oxide (FeNO) was measured using a chemiluminescence analyser (EcoMedics Exhalyzer, Duernten, Switzerland) according to the ATS/ERS guidelines [27 (link)].
