Objectives and background: Nocturnal apnea and hypoxia are implicated in the pathogenesis of pulmonary and systemic hypertension in obstructive sleep apnea syndrome (OSAS). We have hypothesized that vasodilating factors including nitric oxide (NO) are affected by nocturnal apnea and hypoxia in patients with OSAS.
Method: We examined the serum level of NO production in 24 patients with OSAS (mean age 54.2+/-7.9 years) and 24 age-matched control subjects (53.4+/-8.1 years) and tested the effects of oxygen administration on the production of NO in the patients.
Results: The serum level of nitrite/nitrates (NO(x)), which are stable metabolites of NO, was lower in patients with OSAS than in control subjects. Administration of 1-2 l/min of oxygen during night increased the patients' NO(x) level from 35.6+/-7.3 to 57.8+/-11.6 microM. Compressed air administration did not affect the NO(x) level in the patients.
Conclusion: These results indicate that systemic NO production is impaired in OSAS patients, possibly due to nocturnal hypoxia.