Decreased plasma levels of nitric oxide derivatives in obstructive sleep apnoea: response to CPAP therapy

Background-Reduced endothelium dependent vasodilation has been reported in patients with obstructive sleep apnoea (OSA) but direct measurements of the most potent naturally occurring vasodilator, nitric oxide (NO) or its deri vatives (nitrate and nitrite, NOx), have not yet been performed in these pa tients. Methods-In 21 patients with OSA of mean (SE) age 54 (2) years, body mass in dex (BMI) 30.9 (1.1) kg/m(2), and apnoea-hypopnoea index (AHI) 37 (4)/h, NO x levels were measured in peripheral venous blood samples by chemiluminesce nce. Blood samples were obtained before and after two nights of continuous positive airway pressure (CPAP) and after 5.5 (1.5) months of follow up. Th irteen age matched, healthy volunteers and 18 patients without OSA but with a similar spectrum of comorbidity served as controls (control groups 1 and 2). Results-Before CPAP NOx levels were 21.7 (1.5) muM in patients with OSA com pared with 42.6 (2.2) muM and 36.7 (1.7) muM in control groups 1 and 2, res pectively (p<0.01 for each comparison). NOx concentrations increased to 32. 1 (2.7) <mu>M after two nights of CPAP and remained constant at 32.9 (2.3) muM at follow up (p<0.01 compared with levels before CPAP). Conclusions-Plasma NOx levels are reduced in OSA and can be increased by sh ort and long term CPAP therapy. Although the precise mechanism underlying t his observation remains to be clarified, it may have important implications for the development of cardiovascular disease in patients with OSA and for the life saving effect of CPAP.