The participants will sleep three nights at the sleep lab and undergo in their first night, Polysomnography (PSG). Then at random, some of them will do CPAP titration in the second night followed by HFNC titration in the third night. While others will do HFNC titration in the second night followed by CPAP titration in the third night

Continuous Positive Airway Pressure (CPAP) is a form of positive airway pressure ventilation in which a constant level of pressure greater than atmospheric pressure is continuously applied to the upper respiratory tract of an individual.

the Apnea/Hypopnea Index (AHI) is 5 events or less

Standard sleep architecture: sleep breathing disorder e.g. apnea, hypopnea, snoring Oxygenation : minimum oxygen saturation, duration of desaturation and number of desaturation Arousals : number and index

Comparison of High Flow Nasal Cannula device compared to the Continuous Positive Airway Pressure for a long term usage; being assessed in

1. How well did you accept the device yesterday?
2. How comfortable was the usage of the device?
3. Was the used mask comfortable? (1)not acceptable, (2)tolerable, (3)acceptable, (4)well received, (5)excellent
4. Did you face any difficulties breathing through your nose while using the device last night?
5. Did you have any of these symptoms while using the mask last night? Nasal dryness, Mouth dryness, Runny nose, Fear or anxiety, Congested nose
6. Did you feel any air leakage from the mask last night ?
7. Was it hard keeping the mask on while sleeping?
8. Are you prepared to use the CPAP machine as a therapy daily?

Refine the sleep structure with the usage of the device, the count of Apnea/Hypopnea index, number of arousals, number of desaturations