Methods:

Men and women were recruited from a single-center Sleep Clinic. Subjects were excluded for previous CPAP therapy, respiratory failure, medications affecting blood pressure (BP), sleepiness when driving, professional driving, and contraindication to magnetic resonance imaging. Detailed medical history and records were examined to exclude a history of CVD or hypertension. A fasting venous glucose sample was taken to exclude DM. Data were collected from March 2007 to August 2008. All patients underwent attended overnight inpatient polysomnography and had moderate to severe OSA, defined as apnea-hypopnea index (AHI) ≥15 events/hour. Subjects were randomized in double-blinded fashion, placebo-controlled, in a crossover trial to examine effects of CPAP therapy on arterial stiffness and endothelial function. Patients were randomly assigned to 12 weeks of CPAP or sham therapy, achieved by setting the CPAP flow to the lowest possible setting and adding a flow-restricting connector and extra holes to the circuit, allowing air to escape. Arterial stiffness was measured by calculating the augmentation index (Alx) from radial artery pressure waveforms. Carotid-femoral (aortic) pulse wave velocity (PWV) was measured using a micromanometer by sequential acquisition of carotid and femoral pressure waveforms gated to the R-wave of a simultaneously recorded electrocardiogram. Cardiovascular magnetic resonance was used to determine aortic distensibility (AoD).