Effects of Continuous Positive Airway Pressure and Valsartan Treatments on Arterial Blood Pressure in OSAS Patients

Inclusion Criteria: * male/female over than 18 years old * patient with an obstructive sleep apnea (apnea-hypopnea index \> or equal to 15) * patient with weak or moderate hypertension (140 \<= SBP \< 180 mmHg and 90 \<= DBP \< 110 mmHg). Patient with antihypertensive monotherapy must stop their treatment and respect a washout period of at least 4 weeks before the screening visit. For patient treated by antialdosterone, the washout period will be of at least 8 weeks. * negative pregnancy test * ambulatory patient * patient who have signed the informed consent form * patient affiliated to social security Exclusion Criteria: * pregnant or nursing woman * woman who refuses to use contraceptive method * acute hepatic failure, biliary cirrhosis, cholestasis * clearance of Cockcroft \< 30 ml/min/1.73m2 * kaliemia \>= 5.5 mmol/l * acute hypertension (SBP\>= 180 mmHg and/or DBP \>= 110 mmHg) * acute daytime sleepiness (Epworth rating scale \> 15) * patient with a profession that is inconsistent with the continuous positive airway pressure (CPAP) treatment * known cardiovascular pathologies * contraindication to CPAP * allergy to Valsartan * patient treated with lithium * patient treated with drug(s) acting on arterial blood pressure * patient on tutelle or curatelle * patient kept in detention, major protected by the law, hospitalised person * patient currently participating in another clinical trial