Nov 282013

Most people with obstructive sleep apnea (OSA) have high blood pressure (hypertension), but treating OSA with continuous positive airway pressure (CPAP) has been shown to reduce blood pressure only minimally (by about 2.5 mm Hg). A randomized trial in the November 2013 Chest suggests that in people with severe drug-resistant hypertension with OSA, CPAP can bring down daytime systolic blood pressure significantly more.

Rodrigo P. Pedrosa, Geraldo Lorenzi-Filho and colleagues from the Heart Institute at the Universidade de São Paulo (Brazil) randomized 40 patients with severe drug-resistant hypertension (taking at least 3 drugs with confirmed adherence by pill counting, but still with systolic BP >145) and obstructive sleep apnea (>15 AHI on polysomnography) to receive either CPAP (added to medical therapy) or continued medical therapy only for six months. At study onset and after 6 months, participants wore a 24-hour ambulatory blood pressure monitoring device.

Virtually all those randomized to CPAP therapy used it about 6 hours per night on average. Authors report that no patients stopped using CPAP during the trial, and that only one patient used it less than 4 hours per night. There's no comment on how they achieved these unusually high adherence rates (only about half of all people with OSA wear their CPAP machines more than 4 hours per night).

Those who received 6 months of continuous positive airway pressure (CPAP) treatment saw their daytime ambulatory blood pressure fall by 6.5 (systolic) and 4.5 mm (diastolic), from ~148/85 to ~142/81, while those being treated with drugs alone saw increases of 3.1 (systolic) and 2.1 mm Hg (diastolic), from ~146/88 to ~149/90. However, blood pressure crept up at night in both groups, so nighttime and 24-hour-averaged pressures didn't differ significantly.

The observed daytime improvements with CPAP are about 70% the blood pressure reduction achieved by most blockbuster hypertension drugs (most drugs reduce systolic blood pressure by about 9 mm Hg in previously untreated people with hypertension). Although the benefits were moderate, an associated editorial by Malcolm Kohler and John Stradling argued that the blood pressure reductions produced by CPAP here could theoretically reduce strokes and heart attacks by 20-30% (based on previous cardiovascular risk reduction studies).

But in this study enrolling only 40 highly selected patients, without a true placebo control group, such improvements in real-world outcomes are purely hypothetical. "Whether this beneficial effect of CPAP on blood pressure can be achieved over several years and can ultimately result in reduced vascular morbidity and mortality in patients with OSA remains to be proven," wrote Drs. Kohler and Stradling.

Nevertheless, since as many as 80% of people with drug-resistant hypertension may have OSA, and obstructive sleep apnea should be considered as a contributory or causative diagnosis in all patients with resistant hypertension, they argue.

There's no comment either on the ethical considerations involved in not offering CPAP therapy to patients with moderate-to-severe obstructive sleep apnea who were at elevated risk for cardiovascular events.

Rodrigo P. Pedrosa et al. Effects of OSA Treatment on BP in Patients With Resistant Hypertension:A Randomized Trial. Chest. 2013;144(5):1487-1494. doi:10.1378/chest.13-0085

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CPAP for sleep apnea improved drug-resistant hypertension