Sleep is critical to human health, but insufficient and disrupted sleep caused by sleep apnea are common and have a major impact on brain health. However, there is still much that is not known about how sleep apnea damages the brain and what can be done to fix this. The Brain Changes in Sleep Apnea Study will look at the brain health of people with severe sleep apnea both before and after 4 months of treatment with a CPAP machine. Pre- and post-CPAP treatment, 80 participants with severe sleep apnea will undergo cognitive testing, blood and urine tests, a pulse wave velocity test, and an MRI. Also pre- and post-CPAP treatment, participants will wear a blood pressure monitor for 24 hours, wear an accelerometer watch for 8 nights to track the duration and quality of their sleep, and wear a device for 1 night of sleep to assess their breathing and blood oxygen levels. It is expected that there will be improvements in participants' brain health after 4 months of CPAP treatment.

Between January 2018 and February 2022, the Brain Changes in Sleep Apnea Study will recruit 80 adults with newly diagnosed severe sleep apnea attending the sleep clinics at Sunnybrook Health Sciences Centre (n=40) or the University of Edinburgh (n=40). Participants will undergo home-based assessment with 3 wearable devices (24 hours of ambulatory blood pressure monitoring, 8 nights of actigraphy to assess sleep duration and fragmentation, and 1 night of finger-probe peripheral arterial tonometry and oximetry to assess cardiorespiratory physiology including sleep apnea), completion of a sleep and health questionnaire, 24-hour collection of urine for assessing sympathetic nervous system activity, blood banking for endothelial biomarkers, cognitive evaluation, pulse wave velocity test, and an MRI of the brain, at 2 time points: 1) after initial polysomnographic diagnosis of sleep apnea but before the initiation of CPAP, and 2) after 4 months of CPAP treatment.

Inclusion Criteria:

• Newly diagnosed sleep apnea not on CPAP or any other treatment for sleep apnea;
• Apnea hypopnea index >=15 on diagnostic polysomnogram;
• Oxygen desaturation index >=10 or O2 saturation in sleep <90% for >15 minutes on diagnostic polysomnogram;
• Subjectively sleepy;
• Planning on starting CPAP for sleep apnea.

Exclusion Criteria:

• Known history of stroke, transient ischemic attack, or other CNS disease;
• Unable to safely undergo MRI;
• Use of alpha-blocking agents;
• Persistent non-sinus arrhythmia;
• Severe pulmonary or cardiac diseases including COPD and CHF;
• Waking spO2<90%;
• History of panic disorder.

80 adults with newly diagnosed severe sleep apnea will be recruited from the sleep clinics at Sunnybrook Health Sciences Centre (n=40) or the University of Edinburgh (n=40).