Study objective: To assess the nocturnal changes in mechanosensitivity and chemosensitivity in hypertensive sleep apnea-hypopnea syndrome (SAHS) patients and in SAHS patients with isolated nocturnal hypertension. To value the continuous positive airway pressure (CPAP) effect on these parameters.

Design: Controlled cross-over longitudinal study. Settings: Madrid metropolitan area. Patients: Day-night sustained hypertensive and isolated nocturnal hypertensive patients with SAHS without previous treatment. At least 30 patients are needed.

Interventions: Patients will allocate in each treatment arm (CPAP vs. sham CPAP) during three months. Explorations will perform before and immediately after sleep at 0-, 3-, and 6-months of trial.

Measurements: 24-h urinary catecholamine, local vascular factors, angiotensin and aldosterone levels. Diaphragmatic tension-time index, metabolic rate, hypoxic withdrawal test, and ventilatory and inspiratory neural drive responses to progressive isocapnic hypoxia.

Inclusion Criteria:

• Recent diagnosis of sleep apnea-hypopnea syndrome with an apnea-hypopnea index (AHI) > 10 h-1
• No previous treatment for SAHS or hypertension
• Diagnosis by 24-h ambulatory monitoring of blood pressure (AMBP) of isolated nocturnal hypertension (nighttime blood pressure of ≥120 mm Hg systolic or 70 mm Hg diastolic and a daytime blood pressure <135/85 mm Hg) or day-night sustained hypertension (nighttime blood pressure of ≥120 mm Hg or 70 mm Hg diastolic and a daytime blood pressure of ≥135 mm Hg systolic).

Exclusion Criteria:

• Severe hypertension (> 180/120 mmHg).
• Previous diagnosis of secondary hypertension.
• Myocardial infarction or stroke in the last three months.
• Severe diurnal sleepiness (Epworth score > 15)
• Previous diagnosis of chronic obstructive pulmonary disease, asthma, bronchiectasis, lung cancer, restrictive lung disease, chest wall disease or thoracic surgery.
• Previous diagnosis or clinical evidence of heart disease, neuromuscular disease or thyroid dysfunction.
• Morbid obesity (BMI > 40 Kg/m2)
• Respiratory infection in the last two months.
• Treatment with theophylline or systemic corticosteroids in the last two years.
• Excessive alcohol intake (>40 g/day)
• Absence of social or familiar support.