 Up to 50 patients will be recruited from an OSA population, aged over 18. Participants will consist of male and female patients diagnosed with moderatesevere OSA Apnea Hypopnea Index AHI greater than or equal to 15 per hour. Eligible participants, according to the protocol approved by the Northern X Region Ethics Committee, providing written informed consent will be enrolled into the study. Patients will be enrolled sequentially according to the randomisation list. Patients will be randomised to CPAP or SPAP. 