Obstructive Sleep Apnea and the Metabolic Syndrome

Jamie C.M. Lam; Mary S.M. Ip

Disclosures

Expert Rev Resp Med. 2009;3(2):177-186. 

In This Article

OSA and Hypertension

Blood pressure elevation and hypertension may be considered as a continuum, and this probably also applies to the effect of OSA on blood pressure. Epidemiologic- and clinic-based studies in both adults and children have consistently shown that blood pressure level and the risk of hypertension increased with increasing AHI levels after correction for confounders such as obesity, age and gender.[49,50,51,52,53,54,55] An AHI of greater than 15 was associated with elevation of 3.6 mmHg and 1.8 mmHg for systolic and diastolic blood pressure, respectively, with an odds ratio for hypertension of 1.8.[49] Another population study showed that each additional apneic event per hour of sleep was associated with increases of 0.1 and 0.04 mmHg in systolic and diastolic blood pressure, respectively.[52] Prospective longitudinal follow-up over 4 years confirmed increased risks of developing hypertension that were dependent on the degree of elevation of AHI at baseline.[50]

A number of randomized, controlled trials of nasal CPAP treatment in OSA have demonstrated a reduction in arterial blood pressure, although results of meta-analyses did not uniformly confirm a positive effect,[56,57,58,59,60,61,62,63] probably due to differences in subject characteristics of various studies. Reductions in both systolic and diastolic blood pressure have been reported, and the magnitude of decrease in mean arterial blood pressure ranged from 2.5 to 10 mmHg. Most of the subjects in the randomized, controlled studies were normotensive, which probably limited the extent of any blood pressure-lowering effect, while those with hypertension on drug treatment seemed to have a more prominent blood pressure response in spite of the potential masking effect of antihypertensive medications.[57,58] Although cross-sectional studies showed a dose-dependent effect of OSA on blood pressure, which includes mild elevation of AHI, interventional studies that found a blood pressure-lowering effect mostly involved subjects with moderate-to-severe OSA in terms of AHI and hypersomnolence. One meta-analysis of placebo-controlled, randomized trials confirmed greater treatment-related reductions in ambulatory mean blood pressure among patients with more severe OSA and better effective nocturnal use of CPAP device.[61] Blood pressure response in mild OSA has not been as frequently explored, and one randomized, controlled study that investigated subjects with an AHI of less than 15 failed to show any decrease in blood pressure with CPAP treatment.[64] Subjects who do not suffer from sleepiness may also behave differently, as two randomized interventional trials did not reveal any decrease in blood pressure, despite treatment of severe OSA,[65,66] although another study of mildly sleepy subjects did show a positive effect.[60] The implications of sleepiness as a phenotypic marker of propensity to hypertension and other metabolic dysfunction due to OSA remains to be explored further.[67]

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