Circulating Carbon Monoxide Level Is Elevated After Sleep in Patients With Obstructive Sleep Apnea

BackgroundPatients with obstructive sleep apnea (OSA) have an increased risk of cardiovascular morbidity. This study aimed to determine circulating carbon monoxide (CO) levels, which have been suggested to be a marker of cardiovascular risk in patients with OSA.MethodsVenous blood samples were obtained from 35 patients with OSA and 17 age-matched, healthy control subjects before and after polysomnography. Concentrations of venous CO and serum heme oxygenase (HO)-1 were determined by gas chromatography and enzyme-linked immunosorbent assay, respectively.ResultsCirculating CO levels in OSA patients were significantly increased in the morning, but not in the evening. The change in CO level, which was defined as a gap between the presleep and postsleep CO levels, correlated with apnea-hypopnea index and hypoxia duration as a percentage of total sleep time. No difference was found in serum HO-1 levels between OSA patients and control subjects. Treatment with continuous positive airway pressure (CPAP) resulted in normalization of the postsleep CO level.ConclusionsThe postsleep circulating CO level is helpful for assessing the clinical severity of OSA. Moreover, treatment of OSA with CPAP can potentially reduce the risk of the disease associated cardiovascular events.