Sleep apnea may prove to be a treatable cause of high blood pressure, according to research released today that suggests wearing a special breathing mask at night may protect apnea patients from the hypertension.
Most people think of obstructive sleep apnea as a snoring disorder. Although many sufferers snore, apnea is characterized by short episodes in which the patient's upper airway narrows or closes, reducing the flow of oxygen to the body and brain. Those episodes, which can number hundreds in a night, not only disrupt nighttime sleep but may reduce daytime alertness and over time stress the body. For the past 15 to 20 years, doctors have thought that these episodes send blood pressure upward and put patients at risk of heart attack and stroke.
Doctors most often treat sleep apnea by having their patients use devices that employ a technique called continuous positive airway pressure, or CPAP, which delivers mild air pressure through a nasal mask, to keep their airways open throughout sleep.
Two studies released today in JAMA suggest that CPAP may reduce the risk of hypertension among apnea patients.
Dr. Ferran Barbe and his colleagues at the Institut de Biomedia Recerca in Lleida, Spain, studied the effects of CPAP treatment on hypertension and risk of heart attack and stroke among 723 apnea sufferers who didn't have daytime sleepiness. They divided the patients into two groups, one that wore CPAP masks while sleeping and an observation-only group. In the course of more than two years, patients who used CPAP machines at least 4 hours a night did better, but the study didn't show a statistically significant reduction in cardiovascular problems.
However, a related study in the same issue found a stronger benefit. Dr. Jose M. Marin, a respiratory specialist, led an observational study that followed 1,889 patients without hypertension who underwent evaluations for abnormal nighttime breathing at a sleep center in Zaragoza, Spain. They subsequently came in for annual blood pressure checks.
With more than 12 years of follow-up, Marin's study suggested that apnea patients who used a CPAP didn't develop hypertension as much as patients with untreated OSA, those who refused treatment or those who don't wear a CPAP as prescribed. The greater the adherence to prescribed nightly CPAP use, the more protective the treatment.
Dr. Virend Somers, a sleep apnea and heart disease researcher at the Mayo Clinic in Rochester, Minn., cautioned that the results of the two studies are suggestive "but not definitive that CPAP is protective of the cardiovascular system."
He said the conclusion that better adherence to CPAP use is protective also "has to be taken with a pinch of salt – because the fact that someone uses CPAP more frequently and more conscientiously may mean they do other things, maybe take their medicines or do other things we don't measure that will improve their cardiovascular risk," said Somers, a professor of cardiovascular diseases.
Barbe's finding that those patients who adhered to therapy had a decreased incidence of hypertension" is in my opinion quite powerful and supports the relationship found in the Marin study," said Dr. James Rowley, medical director of the Sleep Disorders Center at the Detroit Receiving Hospital in Detroit and faculty member at Wayne State University. "The Marin study in particular was a more 'real-world' study and had a longer follow-up period so is in my opinion strongly supports the statement that OSA is associated with increased risk of hypertension."
The two studies provide more evidence for the benefits of CPAP therapy in reducing hypertension and its potential in preventing it among people with obstructive sleep apnea, Drs. Vishesh Kapur and Edward Weaver, both of the University of Washington in Seattle, wrote in an accompanying editorial.
Studies Taken Together Suggest Prevention Benefit
"Treatment may not only reduce blood pressure (although modestly on average), but if confirmed by future studies, also may prevent hypertension in at-risk patients. Thus, OSA deserves attention in patients with or at risk of developing hypertension as a potentially treatable cause of hypertension as well as other clinically important outcomes."
However, they said additional clinical trials were needed to determine the amount of CPAP therapy necessary to achieve a beneficial effect, and to evaluate other sleep apnea treatments.
Because so many apnea patients complain that they cannot tolerate wearing a mask throughout the night, Somers said that industry is "trying to develop new ways of delivering positive airway pressure that are more tolerable." He said the idea is for the machines to deliver constant air flow throughout the night, increasing the pressure when it's needed. That way, the treatment "will be primarily instituted" when breathing is blocked, "and when you're breathing quietly and happily, you don't need it."
The sleep apnea pipeline includes new technology being developed to address some of the neurologic issues that underlie disrupted breathing to reduce apnea episodes. One approach now being tested involves stimulating nerves that control how the body keeps the airways open, Somers said.
Rowley said that for now, none of the other treatments used for OSA, including surgery, some oral appliances that reposition the jaw, CPAP masks, or even devices in the pipeline "have been studied for long-term outcomes of OSA, particularly cardiovascular disease. Most of the data is short-term and relates to subjective symptoms such as sleepiness and quality of life."