Bronchodilator response of spirometry and lung volumes in healthy subjects

Bronchodilator response (BDR) testing is commonly used to assess any change of pulmonary function measurements after inhalation of beta agonists. A significant improvement is usually defined by the amount of improvement above the 95^th percentile in a general healthy population. Previous studies and guidelines report this to be an absolute increase of 200ml and 10-12% change in relation to baseline for FEV1 and FVC, as well as a 10% improvement compared to the predicted value. We analysed the BDR defined by the upper limit of change in healthy participants, defined by the 95^th percentile, using the Austrian general population LEAD cohort. All healthy 18-82 years old subjects with complete pre- and post-BD lung function testing were included. Health was defined as never-smoking, no history of respiratory disease and absence of respiratory symptoms. The 95^th percentile of change for FEV1 was 300ml and +8.7%, for FVC 220ml and +5.5%. Expressing the change in relation to the predicted value, the upper limit was +8.2% and +5.1% for FEV1 and FVC respectively. The lung volumes expectedly decreased after BD, setting the upper limit for RV at -370ml and -18.9%, as well as -4.8% for the RV/TLC ratio. For FRC the 95^th percentile was a decrease of -410ml and -11.7%, for TLC -430ml and -4.3%. We observed the largest changes in relation to baseline for the specific conductance (sGaw), placing the 95^th percentile for improvement at 1.26 kPa and +91.5%. We provide new estimates for cut-offs defining BDR for spirometry in healthy subjects. Additionally, we offer upper limits for change in lung volumes and sGaw. Future studies will have to investigate if these cut-offs correspond to clinically significant changes.