Impact of bronchodilator responsiveness on lung age: implications for clinical practice from a cross-sectional study

Background This study aimed to evaluate the impact of bronchodilator responsiveness (BDR) on lung age (LA). Methods This cross-sectional study analyzed patients undergoing spirometry and bronchodilator responsiveness (BDR) tests at the First Affiliated Hospital of Guangzhou Medical University between January 2023 and December 2024. The LA value was calculated using a reference equation derived from a healthy Chinese non-smoking population. Changes in LA and lung function parameters before and after BDR were compared. Linear regression equation was conducted to evaluate the relationship between The difference between LA and age (DeltaLA) and lung function parameters. A random forest model was employed to identify predictors of LA improvement. Receiver operating characteristic (ROC) analysis was performed to evaluate the predictive performance of pre-BDR parameters for post-BDR forced expiratory volume in one second to forced vital capacity (FEV₁/FVC) ratio < 0.7. Results A total of 9,316 subjects were included in the study, with 7,452 assigned to the training set and 1,864 to the validation set. Following BDR, significant improvements were observed in LA, FEV₁, FVC, forced expiratory flow at 50% of FVC (FEF_50%), and forced expiratory flow at 75% of FVC (FEF_75%) (all P < 0.001). In the random forest model, the top predictors of LA improvement after BDR were pre-bronchodilator LA (pre-LA), age, and pre-bronchodilator FEF_50% (pre-FEF_50%). Internal validation results showed that the prediction model had an accuracy of 92.6%. DeltaLA was moderately to strongly negatively correlated with lung function parameters (r = -0.5 ~ -0.8, all P < 0.001). In the validation set, receiver operating characteristic (ROC) curve analysis showed that the ability of the difference between the upper limit of normal (ULN) for LA and LA (ULNLA) to predict FEV₁/FVC ratio < 0.7 after BDR was comparable to that of FEV₁ (AUC: 0.84 vs. 0.85). Conclusion LA significantly improves after BDR test. Clinicians and technicians should consider both clinical context and resource availability whether to report post-bronchodilator LA value.