The Effects of Provent® on Obstructive Sleep Apnea During Continuous Positive Airway Pressure Therapy Withdrawal

Inclusion criteria: 1. Objectively confirmed obstructive sleep apnoea (at the time of original diagnosis) with an oxygen desaturation index (ODI, \>4% dips) of between 10 and 50/h and an ESS of \>10 (these thresholds will exclude subjects with borderline and very severe forms of OSA in whom there may be a disproportionate treatment effect). 2. Currently \>10/h oxygen desaturations (\>4% dips) during an ambulatory nocturnal pulse oximetry performed at the end of a 4-night period without CPAP. 3. Treated with NCPAP for more than 12 months, minimum compliance 4h per night. 4. Current ESS \< 10. 5. Written informed consent. Exclusion criteria: 1. Previous ventilatory failure (awake resting arterial oxygen saturation \<93% or arterial PCO2 \> 6kPa). 2. Unstable, untreated coronary or peripheral artery disease, severe arterial hypertension (\>180/110mmHg). 3. Previously diagnosed with Cheyne-Stokes breathing. 4. Current professional driver. 5. Any sleep related accident. 6. Age \<20 or \>75 years at trial entry. 7. History of chronic nasal obstruction. 8. Mental or physical disability precluding informed consent or compliance with the protocol . 9. Non-feasible trial follow-up (for example, distance from follow-up centre, physical inability).