Assessment of clinical, laboratory and polysomnographic features in obstructive sleep apnea-overlap syndrome

Objective: Obstructive sleep apnea (OSAS) is a sleep disorder characterized by recurrent total or partial upper airway obstruction with no airflow through the mouth and nose despite respiratory effort during sleep. Overlap syndrome (OS) is a term used to describe the association between OSAS and lung diseases, such as chronic obstructive pulmonary disease (COPD), asthma, and interstitial lung disease (ILD). Chronic lung diseases can cause OSAS, which is difficult to control. When there is a problem in follow-up for both disease groups, other diseases should be investigated. In this study, we aimed to determine the frequency of OS in patients with OSAS and the clinical, laboratory, and polysomnographic characteristics of the patients and to determine the parameters necessary for the early diagnosis and treatment of these patients. Materials and Methods: Between March 2019 and August 2023, 1135 patients were diagnosed with OSAS by polysomnography (PSG) at the sleep center of Abant Izzet Baysal University Izzet Baysal Training and Research Hospital between March 2019 and August 2023. The independent variables were age, sex, smoking history, comorbidity, long-term oxygen therapy (USOT) use, ejection fraction (EF), systolic pulmonary artery pressure (sPAB), and hematocrit value. The dependent variables were recording time, effective sleep duration, non-REM N1 stage, N1 percentage, N2 stage, N2 percentage, N3 stage, N3 percentage, REM stage, REM percentage, obstructive apnea, central apnea, mixed apnea, hypopnea, apnea hypopnea index (AHI), mean saturation, minimum saturation, and pulse rate/min. Results: Of the 1135 patients, 115 had chronic lung diseases, and the OS rate was 10.1%. The most common association was asthma (75.7%), followed by COPD (21.7%), and the least common was ILD (2.6%). The mean age of all patients was 48.8 years, and the male-to-female ratio was 29.2%/70.8%. Patients with OS were older, more likely to be female, and more likely to smoke than those with isolated OSAS. Comorbidities and USOT use were higher in the OS group. PSG data showed that N3 and REM duration were significantly shorter in the OS group. There were no significant differences between the two groups in the number of obstructive apneas, central apneas, mixed apneas, hypopneas, AHI, and heart rate/min. The mean oxygen saturation was significantly lower in the OS group. sPAB, EF% and Hct values did not differ between the groups. The mean FEVs of patients with COPD were 58.3% and 19.6%, respectively, and the asthma-OS group had preserved pulmonary function. No significant differences were observed between the chronic lung disease and OSAS stages. Conclusion: Patients diagnosed with OSAS should be vigilant for OS if they are of advanced age, particularly females, have a history of smoking, have high comorbidities, and have a low mean oxygen saturation. In the presence of asthma or COPD accompanying OS, it should not be expected that respiratory function should not be severely impaired in these diseases. The shortened N3 and REM sleep stages observed in the PSG data may be a mechanism to compensate for these diseases.