Coexistence of Obstructive Sleep Apnea and Chronic Obstructive Pulmonary Disease

Background: Obstructive sleep apnea (OSA) and chronic obstructive pulmonary disease (COPD) may lead to chronic alveolar hypoventilation. The coexistence of OSA and COPD has been termed the ‘overlap syndrome’. The aim of the study was to determine the relationship between the severity of COPD and the occurrence of chronic alveolar hypoventilation in patients with OSA and to evaluate the impact of chronic alveolar hypoventilation in patients with the overlap syndrome on the severity of breathing disorders during sleep. Material and methods: The study included 64 obese patients (BMI 40.0 ± 6.5 kg/m²) with OSA (AHI > 15; mean AHI 52 ± 22) coexisting with COPD. We analysed the results of polysomnography, spirometry and arterial blood gas analysis. Results: Chronic alveolar hypoventilation was present in 67% of the patients, including 60.5%, 85% and 100% of patients with moderate, severe and very severe COPD by spirometry, respectively. Patients with chronic alveolar hypoventilation had lower values of FVC (2.7 ± 0.8 l vs. 3.6 ± 0.9 l; p < 0.001), FEV₁ (1.7 ± 0.6 l vs. 2.2 ± 0.5 l; p < 0.001) and mean SaO₂ at the end of obstructive sleep apneas and hypopneas (75% ± 10% vs. 84% ± 5%; p < 0.001). Conclusions: Chronic alveolar hypoventilation is observed in the majority of obese patients with moderate to severe OSA and coexisting COPD, including moderate COPD. The occurrence of chronic alveolar hypoventilation in obese patients with OSA coexisting with COPD is associated with a marked arterial hypoxia during obstructive sleep apneic and hypopneic episodes.