In the near future more than 20% of the European population will be over 65 years old and the prevalence of obstructive sleep apnea (OSA) in this aged population is known to be higher than 50%. OSA is a risk factor for cognitive dysfunction in middle-aged subjects, but the relationship between cognitive impairment and sleep breathing disorders (SBD) in the elderly has scarcely been observed.

The aim of this study is to investigate cognitive performance in elderly OSA patients, the corresponding brain morphology changes and biological markers and their reversibility with continuous positive airway pressure (CPAP) treatment.

Patients: We will include consecutive patients with a diagnosis of severe OSA (AHI> 30) without significant comorbidities or excessive daytime sleepiness (Epworth ≤ 12). Patients will be randomized to CPAP treatment or conservative treatment.

Methodology: We will assess at baseline and after 3 months of treatment:

1. Neuroimaging by MRI
2. Neurocognitive function with an extensive neuropsychological battery assessing principally memory, attention and executive functions (Trail-making test A and B, Rey Auditory Verbal Learning Test, Digit span, Digit symbol),
3. Biological markers of inflammation and endothelial dysfunction.

Patients included in the study will be monitored and followed for three months. They will be examined at the time of inclusion, after two and six weeks and at the end (12 weeks) for clinical monitoring and the evaluation of adaptation to treatment and compliance.

Inclusion Criteria:

1. Men and women ≥ 65 years old.
2. Patients diagnosed with OSA with an apnea-hypopnea index per hour >30.
3. Patients with an Epworth Sleep Scale score ≤ 12 (without excessive daytime sleepiness).
4. Signed written informed consent.

Exclusion Criteria:

1. Patients with severe chronic diseases: cardiovascular or pulmonary, neurological (stroke, epilepsy, head injury...) or psychiatric.
2. Any current significant systemic illness or unstable medical condition that could lead to difficulty in complying with the protocol or may, in the opinion of the investigator, compromise the conclusions.
3. Mini Mental State Exam (MMSE) <24.
4. Any MRI exclusions - presence of aneurysm clips, pacemakers, mechanic heart valves, ear implants, metal fragments or foreign objects in the eyes, skin or body.
5. Previous CPAP treatment.
6. Psycho-physical inability to complete questionnaires. Inadequate visual and auditory acuity will be excluded.
7. Presence of any previously diagnosed sleep disorders: narcolepsy, insomnia, chronic sleep deprivation, REM behavior disorder and restless leg syndrome.
8. Patients with > 50% of central apneas or the presence of Cheyne-Stokes Respiration.
9. History of alcohol abuse or dependence.