Obstructive sleep apnoea accelerates FEV₁ decline in asthmatic patients

Background: Although the prevalence of both obstructive sleep apnoea (OSA) and asthma are both increasing, little is known about the impact of OSA on the natural history of lung function in asthmatic patients. Methods: A total of 466 patients from our sleep laboratory were retrospectively enrolled. Of them, 77 patients (16.5%) had asthma with regular follow-up for more than 5 years. Their clinical characteristics, pulmonary function, emergency room visits, and results of polysomnography results were analysed. Results: The patients were divided into three groups according to the severity of the apnoea-hypopnea index (AHI). The decline in FEV₁ among asthma patients with severe OSA (AHI > 30/h) was 72.4 ± 61.7 ml/year (N = 34), as compared to 41.9 ± 45.3 ml/year (N = 33, P = 0.020) in those with mild to moderate OSA (5 < AHI ≤ 30) and 24.3 ± 27.5 ml/year (N = 10, P = 0.016) in those without OSA (AHI ≤ 5). For those patients with severe OSA, the decline of FEV₁ significantly decreased after continuous positive airway pressure (CPAP) treatment. After multivariate stepwise linear regression analysis, only AHI was remained independent factor for the decline of FEV₁ decline. Conclusions: Asthmatic patients with OSA had substantially greater declines in FEV₁ than those without OSA. Moreover, CPAP treatment alleviated the decline of FEV₁ in asthma patients with severe OSA.