AimThe impact of OSA-COPD overlap syndrome (OVS) on sleep quality and cardiovascular outcomes has not been fully explored. We aimed to compare clinical and polysomnographic characteristics of OVSversusOSA patients, and to explore pathophysiological links between OVS and comorbidities.Study design and methodsThis cross-sectional analysis initially included data from 5600 patients with OSA and lung function in the European Sleep Apnoea Database (ESADA). Two subgroups of patients with OSA (n=1109) or OVS (n=509) were matched (2:1) based on sex, age, body mass index (BMI), and apnoea-hypopnea index (AHI) at baseline.ResultsAfter matching, OVS patients had more severe hypoxia, lower sleep efficiency and presented higher prevalence of arterial hypertension, ischemic heart disease and heart failure compared to OSA patients.OVS was associated with a significant decrease in sleep efficiency (β −3.0% (95%CI −4.7, −1.3) and in nocturnal mean SpO2(β −1.1% (95%CI −1.5, −0.7). Further analysis revealed that a decrease in FEV1and PaO2was related with a decrease in sleep efficiency and in mean nocturnal SpO2.A COPD diagnosis increased by 1.75 and 1.36 the odds of having heart failure (95%CI 1.15, 2.67) and systemic hypertension (95%CI 1.07, 1.73), respectively.Nocturnal hypoxia was strongly associated with comorbidities, interestingly, the mean nocturnal SpO2and T90 were associated with increase odds of systemic hypertension, diabetes, and heart failure but ODI was only related to hypertension and diabetes.ConclusionOVS patients presented with more sleep-related hypoxia, a reduced sleep quality and a higher risk for heart failure and hypertension.