Study objectives: To investigate the relationship between the severity of obstructive sleep apnea (OSA) and oxidative stress, which plays an important role in the pathogenesis of cardiovascular disease, and to elucidate the factors contributing to this relationship.
Design: Cross-sectional study.
Participants: A total of 128 consecutive subjects referred to the sleep laboratory of our hospital for screening or treatment of OSA.
Interventions: Not applicable.
Measurements: The severity of sleep-disordered breathing was evaluated by polysomnography. We measured urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as an in vivo parameter of oxidative stress. Known risk factors for oxidative stress (age, obesity, smoking, hyperlipidemia, hypertension, and diabetes mellitus) were also investigated.
Results: Seventy subjects had nonsevere OSA (an apnea-hypopnea index [AHI] < 30), and 58 subjects had severe OSA (AHI >or= 30). Urinary 8-OHdG excretion was significantly higher in the severe OSA group (p = 0.03). Furthermore, urinary 8-OHdG excretion was significantly correlated with parameters of sleep-disordered breathing, including AHI, the apnea index, the oxygen desaturation index (ODI), the duration of oxygen saturation < 90%, and the respiratory arousal index. However, only ODI was significantly correlated with urinary 8-OHdG excretion after adjustment for confounding factors that are considered to be related to oxidative stress.
Conclusions: The severity of OSA is independently associated with oxidative stress. Among various sleep-disordered breathing parameters, ODI is most closely related to oxidative stress.