This study is designed to determine the effectiveness of two different CPAP devices. One a standard CPAP which has the ability to store comprehensive compliance and efficacy data and the second a auto adjusting CPAP which uses the energy spectrum analysis of flow signals to automatically adjust CPAP pressure and improve sleep variables.

All patients with suspected obstructive sleep apnea presenting at the Auckland Hospital Sleep Laboratory and referred for either a split-night or full night diagnostic study, will be offered participation in the study and will be recruited. From these patients, a total of 20 patients that are diagnosed with clinical obstructive sleep apnea syndrome, based on diagnostic polysomnography, will undergo titration with the HC254 Auto CPAP. An additional 20 patients will undergo titration with the HC244 CPAP.

The sleep physiologist evaluating the patient clinically will approach patients for participation in this study during their sleep laboratory visit. Consenting patients will undergo either an initial full night diagnostic polysomnography or a split night study as determined by the physician based on clinical requirements. Patients diagnosed with obstructive sleep apnea (AHI > 15/hr) during this diagnostic component will then undergo one of the following:

• Treatment with the HC254 Auto CPAP during the second half of the study.
• Treatment with the HC244 CPAP during the second half of the study.

The sleep physiologist will then determine final CPAP prescriptions for all patients based on the patient's response to CPAP therapy.

5 subjects who have completed the HC254 arm of the study will be brought back to the sleep lab for an additional PSG or partial PSG while on CPAP pressure set to 90th percentile pressure determined on the diagnostic night.

Inclusions criteria:

• AHI > 15 on the diagnostic night or portion of the split night study.
• ≥18yrs of age

Exclusion criteria:

• Significant Central Apnea
• CHF
• Co-existing obesity related hypoventilation
• Inability to give informed consent
• Patient intolerance to CPAP
• Anatomical or physiological conditions making CPAP therapy inappropriate.
• Less than 3 hours in the titration period
• Under Land Transport New Zealand (LTNZ) investigation