The principal objective is to evaluate the effect of CPAP treatment on blood pressure (BP) in normotensive patients with dipper circadian pattern with sleep apnea-hypopnea syndrome (SAHS). The secondary objectives are: i) To evaluate the prevalence of the different circadian patterns of BP in ambulatory blood pressure monitoring (ABPM) ii) To establish the relationship between CPAP compliance and BP response; iii) Identify which ABPM variables and biomarkers are related to BP response; iv) Evaluate changes in the biomarkers' profile with the CPAP treatment. Methodology: Open-label, parallel, prospective, randomized and controlled trial including normotensive patients diagnosed with severe SAHS without significant somnolence. 64 patients with dipper circadian pattern will be included and will be randomized to receive CPAP (32) or conservative treatment (32). ABPM and blood sample collection will be performed at the beginning of the study and at 3 months.