Continuous positive airway pressure therapy and cardiovascular outcomes in obstructive sleep apnoea syndrome: where are we now?

Obstructive sleep apnoea syndrome (OSA) is highly prevalent with recent epidemiological reports indicating prevalence for moderate or severe sleep disordered breathing (SDB) of up to 50% in the general male population, although the prevalence of a clinically significant syndrome is considerably less (1,2). Cardiovascular co-morbidity is also common among patients with OSA, and many reports have indicated an independent relationship between OSA and various cardiovascular diseases, especially systemic hypertension (3). The mechanisms of this relationship are complex, but likely include sympathetic excitation, systemic inflammation, and endothelial dysfunction (4). Several long-term observational studies have reported beneficial effects of continuous positive airway pressure therapy (CPAP) on cardiovascular morbidity and mortality (5-8), but these reports have typically suffered from the major methodological limitation that successful CPAP therapy was compared to CPAP non-compliance, which clearly indicates the likelihood of patient selection bias. Short-term randomized placebo-controlled studies of CPAP therapy have indicated significant reductions in blood pressure levels both in hypertensive and non-hypertensive patients (9-11), but until recently there has been a dearth of long-term randomized placebo controlled trials of CPAP effects on cardiovascular morbidity and mortality