Tehran University of Medical Sciences Journal of Sleep Sciences 2476-2938 1 4 2017 04 09 143 147 EN Fariborz Rezaeetalab Department of Neurology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Hadi Asadpour Department of Psychiatry, School of Medicine, Sleep Clinic of Ebn-e-Sina Hospital AND Psychiatry and Behavioral Sciences Research Center, Mashhad University of Medical Sciences, Mashhad, Iran Mohammadreza Ahmadi Mousavi Department of Pulmonary and Sleep Medicine, School of Medicine AND Chronic Respiratory Disease Research Center, National Research Institute of Tuberculosis and Lung Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran Mitra Safa Department of Pulmonary and Sleep Medicine, School of Medicine AND Chronic Respiratory Disease Research Center, National Research Institute of Tuberculosis and Lung Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran Ali Panahi Department of Pulmonary and Sleep Medicine, School of Medicine AND Chronic Respiratory Disease Research Center, National Research Institute of Tuberculosis and Lung Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran Parisa Adimi Department of Pulmonary and Sleep Medicine, School of Medicine AND Chronic Respiratory Disease Research Center, National Research Institute of Tuberculosis and Lung Diseases, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2016 09 10 2016 12 10 Background and Objective: The main causes of nocturnal hypoxemia are pulmonary diseases or sleep related breathing disorders. In overlap syndrome, the co-existence of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA), blood oxygen alteration, and hypercapnia may be more severe. We aimed to study hypoxemia markers in OSA patients with or without COPD. Materials and Methods: This cross-sectional study evaluated clinical data and polysomnographic findings of 210 patients with apnea hypopnea index (AHI) > 5 among whom 35 patients had COPD. Results: A total of 210 patients with mean age of 57 years were enrolled in this study. 140 patients (66.7%) had severe OSA (AHI ≥ 30). At wake stage, the mean oxygen saturation (SpO2) was 89.7 ± 5.1 mmHg for those with severe apnea, 91.0 ± 5.7 mmHg for non-severe apnea patients (AHI < 30), 82.7 ± 10.1 mmHg for COPD patients with severe apneas, and 89.3 ± 7.5 mmHg for COPD patients with non-severe OSA (P < 0.0001). Mean pressure of carbon dioxide was 52.9 ± 7.6 mmHg for COPD patients with severe apneas, and 50.2 ± 10.1 mmHg among those with not-severe OSA (P < 0.0001). In average, blood SpO2 dropped to 68.0 ± 12.6 mmHg in severe OSA group, to 57.0 ± 13.6 mmHg in COPD patients with severe OSA (P < 0.0001). Conclusion: Hypoxemia is significantly prominent in overlap syndrome. The presence of diurnal hypoxemia and hypercapnia may predict nocturnal hypoxemia in these patients. https://jss.tums.ac.ir/index.php/jss/article/view/43 https://jss.tums.ac.ir/index.php/jss/article/download/43/50