Background: There are few long-term studies of the effects of treatment on the natural course of asthma.
Objective: To investigate the longitudinal changes in airflow limitation and airway hyperresponsiveness (AHR) in asthma.
Methods: We recruited 81 outpatients (never smokers) with stable asthma from the Kyoto University Hospital. They were evaluated for pulmonary function and AHR, expressed by forced expiratory volume in 1 second (FEV1) and the provocation dose that caused a 20% fall in FEV1 (PD20-FEV1), respectively, at entry and every 6 months over 3 years. We used random effects models to estimate the slopes of these changes, and then evaluated the relationship between these changes and their predictive factors.
Results: Using random effects models, the percentage of the predicted FEV1 (%FEV1) declined significantly but slightly at a mean rate of 0.5%/year (P = 0.002; 95% confidence interval, 0.3 to 0.8). The mean decline rate of FEV1 was 34 mL/year. However, Log(PD20-FEV1) showed significant improvement at a mean rate of 0.088 cumulative units/year (P < 0.001; 95% confidence interval, 0.053 to 0.122). Multiple regression analysis showed that the baseline values of %FEV1 and Log(PD20-FEV1) were the most significant predictive factors for their subsequent changes, respectively.
Conclusions: In stable asthmatic patients treated according to international guidelines, airflow limitation progressed at a nearly normal rate over 3 years. However, AHR continued to improve despite its ceiling effects. Multiple regression analysis revealed a significant negative relationship between the initial values and the subsequent changes in airflow limitation and AHR, respectively.