Continuous Positive Airway Pressure Treatment of Obstructive Sleep Apnea to Prevent Cardiovascular Disease

Inclusion Criteria: 1. Males and females, any race, and aged between 45 and 75 years 2. Evidence of established coronary or cerebrovascular disease as evident by: * Coronary artery disease * Previous MI (equal to or greater than 90 days prior to ApneaLinkTM assessment) * Stable angina or unstable angina (Clinical event equal to or greater than 30 days and confirmatory test equal to or greater than 7 days prior to ApneaLinkTM assessment) defined as either ≥70% diameter stenosis of at least one major epicardial artery segment, or ≥50% diameter stenosis of the left main coronary artery, or \>50% stenosis in at least two major epicardial arteries.; or positive stress test (ST depression equal to or greater than 2 mm or a positive nuclear perfusion scintigram) * Multi-vessel percutaneous angioplasty (PTCA) and/or stent equal to or greater than 90 days prior to ApneaLinkTM assessment * Multi-vessel coronary artery bypass surgery (CABG) \>1 year prior to ApneaLinkTM assessment * Cerebrovascular disease * Previous stroke (includes definite or presumed cerebral ischaemia/infarction and intracerebral but not subarachnoid haemorrhage) equal to or greater than 90 days prior to ApneaLinkTM assessment or minor disabling stroke with minimal residual neurological disability (modified Rankin Score of '0 = no symptoms' or '1 = No significant disability despite symptoms, able to carry out all usual duties and activities' within 7 days of stroke onset) ≥7 days prior to ApneaLinkTM assessment. * Previous transient ischaemic event (TIA) of the brain or retina (symptoms \<24 hours) but not of presumed vertebrobasilar system ischemia. The TIA diagnosis must be confirmed by a suitably qualified clinician (≥7 days but \<1year prior to ApneaLinkTM assessment) 3. Patients have moderate-severe OSA (equivalent to apnea plus hypopneas index \[AHI\] \>30 per hour of sleep) as determined by a ≥ 4% oxygen dip rate \> 12/ h on overnight testing using the ApneaLinkTM device and confirmed by the SAVE core lab in Adelaide upon receipt of the ApneaLinkTM data 4. Patients are able and willing to give appropriate informed consent Exclusion Criteria: Patients will be excluded from entry if ANY of the criteria listed below are met: 1. Any condition that in the opinion of the responsible physician or investigator makes the potential participant unsuitable for the study. For example, * co-morbid disease with severe disability or likelihood of death * significant memory, perceptual, or behavioural disorder * neurological deficit (e.g. limb paresis) preventing self administration of the CPAP mask * contraindication to CPAP use e.g. pneumothorax * residence sufficiently remote from the clinic to preclude follow-up clinic visits 2. Any planned coronary or carotid revascularisation procedure in the next 6 months 3. Severe respiratory disease defined as * severe chronic obstructive pulmonary disease (FEV1/FVC \< 70% and FEV1 \< 50% predicted), or * resting, awake SaO2 \< 90% by ApneaLinkTM device 4. New York Heart Association (NYHA) categories III-IV of heart failure 5. Other household member enrolled in SAVE trial or using CPAP 6. Prior use of CPAP treatment for OSA 7. Increased risk of a sleep-related accident and/or excessive daytime sleepiness, defined by any one of the following: * driver occupation (eg truck, taxi) * 'fall-asleep' accident or 'near miss' accident in previous 12 months * high (\> 15) score on the Epworth Sleepiness Scale 8. Severe nocturnal desaturation documented on the ApneaLinkTM device as \> 10% overnight recording time with arterial oxygen saturation of \< 80% 9. Cheyne-Stokes Respiration (CSResp) * CSResp identified on ApneaLinkTM nasal pressure recording by typical crescendo-decrescendo pattern of respiration with associated apneas and/or hypopneas in the absence of inspiratory flow limitation. * patients excluded if \> 50% of nasal pressure - defined apneas and hypopneas judged to be due to CSResp.