The aim of this prospective single-center study is to evaluate sympathetic nervous system directly measured by microneurography, 24-hour blood pressure, endothelial function, vascular compliance, quality of life and platelet adhesion in patients with sleep apnea syndrome (defined by a complaint of excessive daytime sleepiness, an Epworth sleepiness score>8[10], and an apnea/hypopnea index (AHI>15/h) before and after catheter-based radiofrequency ablation of renal nerve. If the selected patients are treated with CPAP, this therapy should be stable during the whole study time. Primary and secondary end-point will be measured before and 1, 3, 6 and 12 months after renal sympathetic denervation.

Inclusion criteria: We plan to include male or female subjects, age 18-80 with a diagnosis of medium-severe sleep apnea syndrome (defined by symptoms, a complaint of excessive daytime sleepiness, an Epworth sleepiness score >8, and an apnea / hypopnea index >15/h) and a resistant hypertension (systolic blood pressure >140 mmHg or >130 mmHg in patients with type II diabetes or chronic kidney disease, under treatment with three antihypertensive drugs including a diuretic).

If the selected patients are treated with CPAP, this therapy should be stable during the whole study time.

Every patient will be asked for a written informed consent.

Exclusion criteria: - Heart failure (normal ejection fractions on echocardiography and no clinical signs and symptoms of heart failure).

• Long acting nitrates, or PDE-5-Hemmer
• Alcohol or drug abuse,
• Malignancy (unless healed or remission > 5 years)
• Disease with systemic inflammation (e.g. rheumatoid arthritis, M. Crohn)
• Pulmonary Hypertension (PAP>50 mmHg)
• Pregnancy
• Anatomical contraindication to renal denervation
• Know allergy to contrast
• Participation in another study within the last month

patients with therapy-resistant arterial hypertension and sleep apnea syndrome