The medical community disagrees over whether continuous positive airway pressure (CPAP) helps patients with obstructive sleep apnea and improves their cardiovascular health in the long run. While CPAP addresses symptoms such as daytime sleepiness, clinicians are divided over the device’s utility with secondary burdens such as high blood pressure.
Apnea: A silent problem
An estimated 24 percent of middle-aged men and 9 percent of middle-aged women have sleep apnea. Moderate-to-severe obstructive sleep apnea occurs in approximately 9 percent of men and 4 percent of women in that age range (N Engl J Med 2014;370:2276-2285). Although risks for sleep apnea increase with age, it’s possible for someone to develop sleep apnea at any time and family history increases risks.
The exact number of people with chronic obstructive sleep apnea is hard to pin down. Diagnosis relies on patients approaching their doctor with obvious symptoms.
“There are a lot of people out there with sleep apnea who are not presenting and we do not know whether or not we should be going out looking for them, like we do hypertension, where it’s a silent thing,” states John R. Stradling, MD, of Churchill Hospital in the United Kingdom.
According to the National Heart, Lung, and Blood Institute, about half of patients with sleep apnea also have high blood pressure, hypertension and other risk factors for stroke and heart failure. However, sleep apnea itself has not been shown to increase risks for cardiovascular diseases.
Stradling is one of the physicians who is dubious of CPAP’s ability to become the next major treatment for blood pressure and sleep apnea, mostly because patients have difficulty maintaining the treatment long enough to alleviate the major symptom of sleepiness. Decreases in blood pressure have been seen using CPAP, but the effect may be minor compared with antihypertensive drugs. Most patients find the device cumbersome and difficult to use while taking tablet medications is easy.
If blood pressure control is the name of the game, he says, tablets are the way to go. He notes that some studies show positive blood pressure effects using CPAP when drugs aren’t working, but “that is a very specific subgroup: patients who have resistant hypertension as defined by three drugs that aren’t working.”
CPAP appears to have more benefit the longer patients use it. With as little as three to four hours a night, patients can see up to a 2 mm Hg reduction, although that varies (N Engl J Med 2014;370:2276-2285). While this seems positive, no firm data exist to confirm that CPAP lowers elevated blood pressure enough to reduce strokes or heart attacks, nor is cardiovascular risk fully understood in these patients. What physicians can do is estimate what those relative reductions would do to risk in patients who were hypertensive.
“At night, your blood pressure goes up and down like a yo-yo with sleep apnea, which is different from ordinary, what would be called essential, hypertension where it’s up but it’s fairly stably up,” says Stradling. “You could argue that that’s bad for the cardiovascular system, that going up and down like a yo-yo, and there’s some evidence that it could be, but there’s also some evidence that that kind of blood pressure going up and down is good for the cardiovascular system because it’s keeping it flexible.”
He notes that the sympathetic activity that accompanies apneic episodes—part of what creates this yo-yo effect—elevates blood pressure in a way that doesn’t persist. It may be particularly high in the morning, but, he says, “By the following evening, the blood pressure is much harder to demonstrate was raised. It’s almost a short-term carry-over effect.”
However, “We’ve certainly shown that if you stop somebody’s CPAP for a couple of weeks, that the blood pressure goes up really quite quickly.”
Which is part of the rub. What part of CPAP use is helpful to patients and their blood pressure? Are there other markers that could be used to determine if this is helping patients in the long term?
Stradling and colleagues study how taking away CPAP for a period affects cardiovascular comorbidities and vascular reactivity in the eye to see if that can offer some answers. Other researchers look at how endothelial function may change in these patients. “There’s a lot we don’t understand about whether sleep apnea is harmful to all parts of the cardiovascular system equally [or] does it harm some or maybe it helps others. We’re a long way off from understanding.”
Daniel J. Gottlieb, MD, MPH, of Veterans Affairs Boston Healthcare System, believes that the association between hypertension and sleep apnea is strong enough that treating sleep apnea should improve outcomes. “Hypertension is such a powerful predictor of, and presumed cause of, incident cardiovascular disease,” Gottlieb says. “It seems like a potential mediator, this relationship between sleep apnea and cardiovascular disease.”
Gottlieb argues that CPAP is helpful, but admits that when it’s a cumbersome treatment, patients aren’t going to be inclined to use it. He and his colleagues tried using oxygen, but didn’t see the hoped-for effect on blood pressure.
And he’s determined that by changing blood pressure through CPAP or some other device, physicians can tip the scales on a patient’s risks for stroke or heart attack. “For treatment of sleep apnea, we do not have as yet clinical trials demonstrating a reduction in cardiovascular risks. At least not randomized clinical trials,” he says.
In some nonrandomized trials, he notes, risks for heart attack, stroke or death appeared to decrease when patients were treated for sleep apnea using CPAP and blood pressure was reduced. “What those studies have shown is that generally a two- to threefold increased risk of heart attack, stroke or death in patients with untreated severe sleep apnea but no excess risk in those whose sleep apnea is treated. I think that we can get a better effect on blood pressure with a combination [of CPAP and tablets] than with pharmacotherapy alone, or certainly CPAP alone.”
He aims to find an approach that reduces blood pressure like CPAP does without the cumbersome gear and treats other aspects of apnea as well. “I am interested in looking at those people who have more severe sleep apnea who are not tolerant of CPAP, the ones who have the most hypoxemia [who] might still benefit from supplemental oxygen. I haven’t completely given up on oxygen in all cases.”
Stradling and Gottlieb agree on one thing: More work is needed to determine what makes CPAP work and whether or not it helps patients in the long term.