A randomised clinical trial to evaluate the effects of continuous positive airway pressure (CPAP) on nocturnal beat to beat blood pressure and vascular function

INTERVENTION: Participants will be subjected to both active continuous positive airway pressure (CPAP) (their usual settings) and sham CPAP while undergoing polysomnography on two separate nights in a randomised order. Each night will be separated by at least one week, but no more than 6 weeks between visits. Participants will use their own clinically fitted mask (i.e. nasal mask, full face mask etc). Each sleep study will be for a duration of 8h. The sleep study will be conducted at The Centre for Sleep Science at The University of Western Australia. CONDITION: Obstructive sleep apnoea PRIMARY OUTCOME: Conduit artery function: Brachial and femoral artery flow mediated dilation (FMD) will be assessed according to best practice guidelines. A cuff is inflated (220mmHg) around the forearm and upper thigh for 5min to induce ischaemic conditions whilst high resolution ultrasound of the brachial and femoral artery are obtained pre‐post‐ artery occlusion. The FMD% increase in artery dilation is an indicator of artery function and independently predicts CV events. Intracranial cerebral blood velocity: Cerebral blood flow velocity (CBFv) is assessed by combining bilateral measures of middle (MCA) and posterior cerebral artery (PCA) flow velocities using non‐invasive transcranial Doppler (TCD) ultrasound. Blood flow to the brain will also be simultaneously collected using non‐invasive duplex ultrasound of the internal carotid artery and vertebral artery (VA). Cerebral vascular reactivity to carbon dioxide is assessed using breathing mixtures. Participants are asked to breathe the gas mixtures through a non‐re‐breathing three‐way breathing apparatus (i.e., mouthpiece, disposable spirometry filter, spirometer, hans rudolph three way valve) connected to each douglas bag through a sterilised respiratory bore tubing. Nocturnal beat to beat blood pressure measured by a Finapress device throughout the night. ; (Finometer Pro). SECONDARY OUTCOME: Urinary catecholamines INCLUSION CRITERIA: Participants will be individuals with obstructive sleep apnoea and who have been established on Continuous positive airway pressure (CPAP) therapy within the last three years. They will also need to be compliant with CPAP therapy (average nightly use > 4 hours per night at the last review). Only participants whose CPAP therapy has been shown to be effective (i.e., residual AHI <10/hr on CPAP machine download or polysomnographic assessment of control of OSA while using CPAP) will be included.