The hidden burden of overlap syndrome: Sleep quality and functional impairment in chronic obstructive pulmonary...

Chronic Obstructive Pulmonary Disease (COPD) is associated with reduced functional capacity and a high prevalence of sleep-related disturbances. However, the relationship between sleep-related disturbances and functional capacity remains incompletely understood.

To investigate the associations between COPD severity, sleep quality, nocturnal respiratory disturbances, and functional capacity assessed by the 6-min walk test (6MWT).

Eighty clinically stable patients with COPD underwent spirometry, home sleep monitoring, Pittsburgh Sleep Quality Index (PSQI), and 6MWT. Correlation and multiple linear regression analyses were performed.

Patients with more severe disease exhibited higher apnea-hypopnea index values, lower mean SpO₂, and longer periods with SpO₂<90% (p = 0.001). Poorer sleep quality, higher apnea-hypopnea index, and greater nocturnal hypoxaemia were associated with shorter 6MWT distance. In multiple regression analyses, FEV₁ and dyspnoea (mMRC) were the strongest predictors of functional capacity, while PSQI score, apnea-hypopnea index, and time spent with SpO₂<90% remained independently associated with walking distance.

Increasing COPD severity was associated with poorer sleep quality, greater nocturnal oxygen desaturation, and lower functional capacity. Sleep-related variables were independently associated with 6MWT performance, suggesting that sleep assessment may provide complementary information in the evaluation of patients with COPD.