Mortality in obstructive sleep apnea syndrome (OSAS) and overlap syndrome (OS): The role of nocturnal hypoxemia and CPAP compliance

Background: Obstructive sleep apnea syndrome (OSAS) and chronic obstructive pulmonary disease (COPD) are two chronic diseases that afflict many individuals worldwide with negative effects on health that may overlap in Overlap Syndrome (OS). The aim of our study was to investigate the differences in mortality between OSAS alone and OS and the risk factors involved. Methods: The study was conducted on patients with OSAS or OS diagnosis that completed 15-year follow-up between 2005 and 2023. Of these, the clinical, functional, sleep and survival data were registered and analysed. Risk factors were found by regression analysis. Results: 501 patients (428 OSAS and 73 OS) were enrolled. Patients with OS had higher mortality than OSAS (p < 0,001). The morality risk factors for the overall population found were age >65 years (odds ratio (OR) = 10.69 (95%CI 3,85–29,69), p < 0,001) and low forced-expiratory volume in 1-s (FEV1) (OR = 10.18 (95%CI 2,32–44,68), p = 0,002). In patients with OSAS, age and nocturnal hypoxemia (NH) (OR = 2.41 (95%CI 1,07–5,41), p = 0,03) were risk factors, while adherence to nighttime positive airway pressure (PAP) reduced mortality (OR = 0,36 (95%CI 0,15–0,83), p = 0,017). Multivariate analysis confirmed age and FEV1 as risk factors in OS. Conversely, the risk factors for the overall population under 65 years were NH, which is confirmed in patients with OSAS alone (OR = 4,72 (95%CI 1,07–20,77), p = 0,04) in whom, on the other hand, PAP compliance reduced the mortality risk. Conclusions: The study suggests that NH is a risk factor for all-cause mortality in sleep disorders by excluding the age; conversely, nighttime PAP improves the survival.