Effects of CPAP on nitrate and norepinephrine levels in severe and mild-moderate sleep apnea

BACKGROUND: Reduced plasma nitrate (NO(x)) levels and increased urinary norepinephrine (U-NE) levels have been described in severe obstructive sleep apnea (OSA), and are reverted by continuous positive airway pressure (CPAP). The effect of CPAP on these biomarkers in mild-moderate OSA is not well understood. The aim of this study was to compare NO(x) and U-NE levels and blood pressure (BP) between male patients with mild-moderate and severe OSA and determine the impact of 1 month of CPAP therapy on these parameters. METHODS: We undertook a prospective study of 67 consecutive OSA patients (36 mild-moderate, 31 severe). Measurements of plasma NO(x) at 11 pm, 4 am and 7 am, 24-h U-NE and ambulatory BP were obtained at baseline and after 1 month of CPAP. RESULTS: At baseline, NO(x) levels showed a significant decrease during the night in both groups (p < 0.001). U-NE level and BP were significantly higher in the severe OSA group. After 1 month of CPAP, there was a significant increase in NO(x) levels and a reduction in U-NE level and BP only in patients with severe OSA. CONCLUSIONS: One month of CPAP results in significant improvements in NO(x) levels, 24-h U-NE level and BP in patients with severe OSA, but not in patients with mild-moderate OSA. TRIAL REGISTRATION: ClinicalTrials.gov: http://NCT01769807