Sleep-disordered breathing (SDB) briefly means cessation of breathing during sleep at least 5 times per hour. SDB is a common disorder affecting 9 to 24% of the middle-aged and overall 4% of the middle-aged male population suffers from the Obstructive sleep apnoea syndrome (OSA) i.e. SDB with associated daytime sleepiness. Several major epidemiological studies have shown that SDB is not only an independent risk factor for hypertension but it is also strongly associated with heart failure and stroke. The mechanism for the linkage between SDB and cardiovascular consequences is not fully determined. Vascular endothelial growth factor (VEGF) is a soluble 34-46 kD angiogenic heparin-binding glycoprotein. This cytokine regulates multiple endothelial cell functions including vascular permeability and vascular tone and some data suggest that it may contribute to the atherosclerotic process. Recent studies have shown increased plasma and serum concentrations of VEGF in patients with OSA and there were correlations between VEGF concentrations and the severity of OSA, as indexed by the minimum oxygen saturation level and the frequency of the upper airway obstruction per hour of sleep. A recent non-randomised study with a small sample size has shown a significant decrease in VEGF concentrations in patients in whom nocturnal hypoxia improved after 1 year of nasal continuous positive airway pressure (CPAP) therapy.

Despite robust evidence showing improvement of symptoms, cognitive function and quality of life in OSA patients treated with nasal CPAP, there are nevertheless conflicting data whether CPAP can reduce daytime blood pressure (BP) in patients with OSA. Two randomized placebo controlled studies have shown reduction of 24-hr systolic and diastolic BP in OSA patients after 1 month of nasal CPAP therapy while other investigators have shown no such benefit.

This randomized, sham-placebo controlled study aims to assess 1) the effect of nasal CPAP over a period of 3 months on 24 hr BP; and 2) whether any change in BP and plasma VEGF is related to the baseline severity of OSA and CPAP compliance.