OXFORD, UK—Despite obstructive sleep apnea’s association with hypertension, it has remained unclear whether treating apnea could lower blood pressure (BP). A randomized parallel trial now rigorously demonstrates the value of continuous positive airway pressure (CPAP) for lowering ambulatory daytime and nighttime BP in patients with severe sleep apnea, suggesting additional therapeutic benefits for these patients.[1]

“If you have symptoms of severe obstructive sleep apnea, CPAP can give a substantial reduction of vascular risk as well as a substantial quality-of-life improvement,” emphasized Robert J. O. Davies, DM, a Senior Lecturer at the Oxford Centre for Respiratory Medicine in Oxford, United Kingdom. The 3.3-mm Hg mean BP decrease induced with CPAP “reduces stroke risk by about 20%” and cardiac event risk by about 15%, he noted.

Although the mechanisms are not fully understood, raised BP in apnea patients may be related to their increased catecholamine levels. Despite obstructive sleep apnea’s link with obesity, a risk factor for hypertension, previous work has “shown that sleep apnea’s association was independent of weight,” Dr. Davies told PULMONARY REVIEWS.

Previous research suggested that CPAP lowered BP; however, these studies were criticized for being poorly controlled or using a control intervention significantly different from the mask-based CPAP treatment. To rule out the possible subjective impact of the CPAP apparatus, Dr. Davies and colleagues randomly assigned 118 men with obstructive sleep apnea to either therapeutic CPAP or CPAP at ineffective pressures for one month. All subjects initially had excessive subjective daytime sleepiness (Epworth scores of 9 or greater) and obstructive sleep apnea with more than 10 episodes per hour of greater than 4% oxygen desaturation.

As expected, therapeutic (but not subtherapeutic) CPAP significantly improved mean daytime sleepiness scores from 15.5 to 7.0. Notably, however, therapeutic CPAP also significantly reduced mean arterial ambulatory BP by 2.5 mm Hg (compared with an increase of 0.8 mm Hg in controls). Group differences in BP decrements remained significant even when comparisons were limited to overall systolic or diastolic pressures, or to mean pressures during sleep or wake periods. Drops in BP were proportional to baseline sleep apnea severity only among patients receiving therapeutic CPAP, with patients who initially suffered 33 or more dips in oxygen saturation per hour achieving the greatest decrements.

“If you take the patients who were on antihypertensive medications, you see the largest drop in mean BP with therapeutic CPAP,” Dr. Davies noted. This 7.9-mm Hg decrement “implies that the mechanisms causing hypertension in patients with untreated apnea may be antagonizing the efficacy of the BP-reducing drugs,” he remarked. Thus, “I think theirs is probably a subgroup of patients with difficult-to-control hypertension in whom treating sleep apnea appears to be of particular benefit,” he added.

—Mimi Zucker, PhD

Reference
1. Pepperell JCT, Ramdassingh-Dow S, Crosthwaite N, et al. Ambulatory blood pressure after therapeutic and subtherapeutic nasal continuous positive airway pressure for obstructive sleep apnoea: a randomised parallel trial. Lancet. 2002;359:204-210.

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