Influence of obstructive sleep apnoea on circadian blood pressure profile

A high prevalence of systemic hypertension in obstructive sleep apnoea (OSA) has been described but data on circadian blood pressure (BP) profile are limited and give inconsistent results. The present study examines 24-h BP in 106 patients referred because of loud snoring or excessive daytime sleepiness in combination with snoring. Patients were classified as OSA (n = 62) or habitual snorers (HS) (n = 44). Respiratory disturbance index (RDI) in OSA was 47 + 24 vs. 2 +/- 2 in HS. Mean age and body mass index in OSA was significantly higher. BP was measured non-invasively at 15-min intervals during a 24-h period. Daytime and night-time BP was higher in OSA compared to HS. BP night/day ratio in OSA was 0.92 +/- 0.07 vs. 0.86 + 0.06 in HS (P < 0.05). To investigate the influence of variables other than breathing abnormalities during sleep on our results we compared BP profiles of 25 OSA and 25 HS matched for sex, age and body weight. Again differences in daytime and night-time BP and BP night/day ratio were significant. Using a value of at least 10% fall in nocturnal BP to describe a regular BP profile (dipper) 68% of OSA were classified as non-dippers vs. 24% of HS. Influence of short-term (2-4 days) nCPAP therapy on circadian BP profile was investigated in 34 patients with OSA. Systolic and diastolic nocturnal (but not daytime) BP was significantly reduced. The percentage of non-dippers was 79% before and 50% after treatment. In conclusion results of this study indicate a causal link between OSA and abnormal circadian BP profile.