Obstructive sleep apnoea as a cause of nocturnal nondipping blood pressure: recent evidence regarding clinical importance and underlying mechanisms.

Obstructive sleep apnoea (OSA) is highly prevalent, with recent general population studies indicating that up to 50% of males and 23% of females have moderate or severe sleep disordered breathing (SDB) based on an apnoea–hypopnoea index (AHI) of >15 events·h [1, 2]. OSA is recognised as an independent risk factor for systemic hypertension [3] and a nondipping nocturnal blood pressure profile is particularly likely in patients with OSA [4], even in the absence of significant hypertension. Furthermore, hypertension is increasingly recognised as an important predictor of prevalent OSA and appears to be more predictive than excessive day-time sleepiness in some settings [5]. However, recent evidence also indicates that only moderate–severe OSA (AHI >20 events·h) constitutes a significant independent risk for hypertension [2] and cluster analysis of sleep clinic populations indicates that particular population subtypes are especially associated with hypertension [6].