Chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) are common diseases that strongly impact the quality and length of life. Their coexistence is determined by overlap syndrome (OS). This systematic review aims to define the significance of these comorbidities according to the current state of knowledge. For this systematic review, we searched PubMed, Scopus, and Cochrane for studies published between 2018 and 26 October 2022, to find original, observational, human studies published in English, where the diagnosis of COPD was according to the Global Initiative for Obstructive Lung Disease guidelines and the diagnosis of OSA was based on polysomnography. The quality of studies was assessed using the Newcastle–Ottawa quality assessment tool for cohort and case–control studies, as well as its modification for cross-sectional studies. Of the 1548 records identified, 38 were eligible and included in this systematic review. The included studies covered a total population of 27,064 participants. This paper summarizes the most important, up-to-date information regarding OS, including the prevalence, meaning of age/gender/body mass index, polysomnography findings, pulmonary function, comorbidities, predicting OSA among COPD patients, and treatment of this syndrome.

Review question / Objective: To provide the essential findings in the field of overlap syndrome of chronic obstructive pulmonary disease and obstructive sleep apnea, including prevalence, possible predictors, association with clinical outcomes, and severity compared to both chronic obstructive pulmonary disease and obstructive sleep apnea patients. Condition being studied: OSA is characterized by complete cessation (apnea) or significant decrease (hy-popnea) in airflow during sleep and recurrent episodes of upper airway collapse cause it during sleep leading to nocturnal oxyhemoglobin desaturations and arousals from rest. The recurrent arousals which occur in OSA lead to neurocognitive consequences, daytime sleepiness, and reduced quality of life. Because of apneas and hypopneas, patients are experiencing hypoxemia and hypercapnia, which result in increasing levels of catecholamine, oxidative stress, and low-grade inflammation that lead to the appearance of cardio-metabolic consequences of OSA. COPD is a chronic inflammatory lung disease defined by persistent, usually pro-gressive AFL (airflow limitation). Changes in lung mechanics lead to the main clini-cal manifestations of dyspnea, cough, and chronic expectoration. Furthermore, patients with COPD often suffer from anxiety and depression also, the risk of OSA and insomnia is higher than those hospitalized for other reasons. Although COPD is twice as rare as asthma but is the cause of death eight times more often.