8-Isoprostane, a marker of oxidative stress, is increased in exhaled breath condensate of patients with obstructive sleep apnea after night and is reduced by continuous positive airway pressure therapy

Study objectives: Obstructive sleep apnea (OSA) is characterized by recurrent apnea during sleep that may compromise oxidative balance. Oxidative stress is increased in the blood and in the airways of OSA patients. Design: The aim of this study was to investigate whether oxidative stress is determined by nocturnal apneas and could be reduced by CPAP therapy, and whether there is a relation between local and systemic oxidative stress in these patients. Patients and methods: Eighteen patients with OSA (13 men; mean [+/-SD] age, 48 +/- 3 years) and 12 healthy age-matched and weight-matched subjects (8 men; mean age, 46 7 years) were recruited. 8-Isoprostane was measured in exhaled breath condensate and blood by a specific enzyme immunoassay. Measurements and results: Higher concentrations of 8-isoprostane were found in the morning exhaled condensate (9.5 +/- 1.9 pg/mL) and plasma (9.7 +/- 1.5 pg/mL) of OSA patients compared to healthy obese subjects (6.7 +/- 0.2 and 7.1 +/- 0.3 pg/mL, respectively; p < 0.0001). Elevated mean concentrations of exhaled 8-isoprostane were observed in the OSA patients at 8:00 AM (9.5 1.9 pg/mL) but not at 8:00 Pm (7.6 < 0.8 pg/mL; p < 0.0005), and a significant reduction was seen after continuous positive airway pressure (CPAP) therapy (7.7 +/- 0.9 pg/mL; before treatment, 9.6 +/- 1.7 pg/mL; p < 0.005). A positive correlation was found between morning exhaled 8-isoprostane levels and the apnea-hypopnea index (r = 0.8; p < 0.0001), and 8-isoorostane levels and neck circumference (r = 0.6; p < 0.0001). Conclusions: These findings suggest that systemic and local oxidative stress are increased in OSA patients, and that they are higher after nocturnal apnea and reduced by CPAP therapy.