a comparison of nocturnal hypoxia markers in apnea patients with chronic obstructive pulmonary disease and without it: a cross-sectional study

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 ob-structive sleep apnea (osa), blood oxygen alteration, and hypercapnia may be more severe. we aimed to study hypox-emia 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 se-vere 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.