The level of xanthine oxidoreductase (XOR) in plasma is associated with oxidative stress and inflammation. Obstructive Sleep Apnea (OSA) is characterized by repeated upper airway obstruction and apneas during sleep, leading to chronic intermittent hypoxemia. The specific role of XOR in OSA, its relationship with the severity of OSA, and the changes in XOR levels before and after CPAP treatment remain unclear. The study will enroll 80 patients from the First Affiliated Hospital of Nanjing Medical University, categorized by their Apnea-Hypopnea Index (AHI) into mild, moderate, and severe OSA groups. Participants will undergo baseline assessments including polysomnography (PSG) and measurements of XOR activity and biomarkers such as uric acid, endothelin-1 (ET-1), endothelial nitric oxide synthase (eNOS), and inflammatory markers. Eligible patients will receive CPAP treatment for 3 months, after which their XOR activity and biomarker levels will be re-evaluated to assess treatment efficacy.