K Torén, B Bake, A-C Olin, G Engström, A Blomberg, J Vikgren, J Hedner, J Brandberg, H L Persson, C M Sköld, A Rosengren, G Bergström, C Janson

Data are lacking from general population studies on how to define changes in lung function after bronchodilation. This study aimed to analyze different measures of bronchodilator response of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC) and slow vital capacity (SVC). Data were derived from the Swedish Cardiopulmonary Bioimage Study (SCAPIS) Pilot study. This analysis comprised 1,050 participants aged 50-64 years from the general population. Participants were investigated using a questionnaire, and FEV1, FVC and SVC were recorded before and 15 minutes after inhalation of 400 µg of salbutamol. A bronchodilator response was defined as the relative change from baseline value expressed as the difference in units of percent predicted normal. Predictors of bronchodilator responses were assessed using multiple linear regression models. Airway obstruction was defined as FEV1/FVC ratio below lower limit of normal (LLN) before bronchodilation, and COPD was defined as an FEV1/FVC ratio below LLN after bronchodilation. Physician-diagnosed asthma was defined as an affirmative answer to "Have you ever had asthma diagnosed by a physician?". Asymptomatic never-smokers were defined as those not reporting physician-diagnosed asthma, physician-diagnosed COPD or emphysema, current wheeze or chronic bronchitis and being a lifelong never-smoker. Among all subjects, the greatest bronchodilator responses (FEV1, FVC and SVC) were found in subjects with asthma or COPD. The upper 95th percentile of bronchodilator responses in asymptomatic never-smokers was 8.7% for FEV1, 4.2% for FVC and 5.0% for SVC. The bronchodilator responses were similar between men and women. In a multiple linear regression model comprising all asymptomatic never-smokers, the bronchodilator response of FEV1 was significantly associated with airway obstruction and height. When the bronchodilator response in asymptomatic never-smokers is reported as the difference in units of predicted normal, significant reversibility of FEV1, FVC and SVC to bronchodilators is ~9%, 4% and 5%, respectively.