 MAIN CRITERIA OF EVALUATION AND STATISTICAL ANALYSIS Normalized data during the experiment will be calculated according to baseline data. Changes in blood flow parameters reflected the vascular reactivity and correlations will be calculated with nonparametric tests Friedman and Wilcoxon tests for paired comparisons using the SPSS 12.0 software. Comparison of OSA group and healthy subjects group will be done using non parametric test Mann Whitney and Chi 2 test. A two-tailed approach test will determine significance, which is set as p0.05. 