Overnight Effects of nCPAP with and without humidification on upper airway function.

INTERVENTION: Participants will be randomised to 3 consecutive nights (Monday, Wednesday and Friday) of CPAP for one night CPAP + (conventional heated humidification) for one night CPAP + (optimal level of humidity) for one night Outcome measures:(all measured pre and post each overnight study) Saccharine transit time Mucus physical properties Cytology via lavage Inflammatory mediators Upper airways symptom score CONDITION: Obstructive Sleep Apnea PRIMARY OUTCOME: Saccharine transit time SECONDARY OUTCOME: Cytology via lavage Inflammatory mediators Mucus physical properties Upper airways symptom score INCLUSION CRITERIA: Moderate to severe obstructive sleep panea > 15 AHI > 75% of events must be obstructiveExcessive daytime sleepiness (ESS > 10).