Background: A predominant feature of asthma is an accelerated rate of decline in forced expiratory volume in 1 s (FEV1), but data on the variability and factors associated with this change in patients with controlled asthma are largely unknown. Methods: 140 patients with controlled asthma were enrolled based on the Global Initiative for Asthma guidelines. We examined the data of a prospective analysis of the association between asthma control and change in FEV1 over time. Results: A 3-year follow-up assessment was completed in 128 patients. The mean rate of change in FEV1 was a decline of 22.2 mL yr-1, with significant variation in the levels of change. The between patient standard deviation for the rate of decline was 34.1 mL yr-1. We next classified the subjects of less than the 25th percentile as rapid decliners, and greater than the 25th percentile as non-rapid decliners. The decrease in the Asthma Control Test score over a 3-year period was higher for rapid decliners than that for non-rapid decliners (p < 0.001). The rapid decliner was more likely to be older, to have higher levels of FeNO, and to have had severe exacerbations during the study. Patients with severe exacerbations had a greater annual decline in FEV1 compared to patients with no exacerbations (-13.6 vs. -53.2 mL yr-1, p < 0.0001). Conclusions: Among patients with controlled asthma at baseline, the rate of change in FEV1 is highly variable. Severe exacerbations are strongly associated with a rapid loss of lung function.
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