Nitric oxide metabolites and erythrocyte deformability in a group of subjects with obstructive sleep apnea syndrome.

Our aim was to evaluate nitric oxide metabolites (nitrite and nitrate), expressed as NOx, and erythrocyte deformability, expressed as elongation index, in a group of subjects with obstructive sleep apnea syndrome (OSAS). We enrolled 48 subjects (36 men and 12 women; mean age 50.3±14.68 yrs) with OSAS diagnosed after a 1-night cardiorespiratory sleep study. OSAS severity was assessed evaluating the apnea/hypopnea index (AHI) and subjects were subdivided in two subgroups: Low (L=AHI<30) and High (H=AHI>30). NOx was examined converting nitrate into nitrite with a nitrate reductase and then assessing nitrite with spectrophotometry after the addition of Griess reagent. The elongation index was obtained using the diffractometer Rheodyn SSD of Myrenne at shear stresses of 30 and 60 Pa and it was expressed as elongation index (EI). We found no difference in NOx among the entire group of OSAS subjects and normal controls, while we observed a NOx decrease in the H subgroup in comparison with L subgroup, but not in comparison with normal controls. We noted a significant decrease in EI at each shear stress in the entire group and also in the two subgroups in comparison with controls. The decrease in NO bioavailability and in erythrocyte deformability might contribute to explain the increased cardiovascular risk in OSAS subjects.