New details, possible treatment in the link between heart disease and sleep apnea
People with obstructive sleep apnea are at significantly increased risk for cardiovascular disease. The relationship between the two conditions is complex, and the mechanisms by which they may trigger or exacerbate one another are not yet well understood.
But the fundamental connection between OSA and cardiovascular disease is strong. Studies indicated that obstructive sleep apnea is 2-3 times more prevalent among people with cardiovascular disease than those without. Research shows that the mortality rate for cardiovascular disease is higher among older adults who also have OSA. Sleep apnea is linked to several cardiovascular conditions, including high blood pressure, arrhythmia, heart disease, heart failure, and stroke.
Two common conditions
Cardiovascular disease is the leading cause of death among adults in the United States. Obstructive sleep apnea affects an estimated 25 million or more U.S. adults -- with the great majority of cases remaining undiagnosed and untreated. Deepening our understanding of the relationship between sleep apnea and cardiovascular disease is critical to public health.
How OSA may trigger heart disease
Recent research reveals new details in the relationship between heart disease and sleep apnea, and also points to a possible treatment for lowering cardiovascular risks for people with OSA. Scientists at Columbia University Medical Center found that statins -- a type of drug used to treat cholesterol -- may reverse the damage done to the cardiovascular system that appears to occur as a consequence of sleep apnea. The scientists also identified new information about the process by which obstructive sleep apnea may inflict cardiovascular damage.
According to the study, people with OSA exhibit abnormalities in a protein that helps to limit cellular inflammation. The dysfunction with this particular protein - -known as CD59 -- appears to leave people with obstructive sleep apnea more vulnerable to inflammation, which is regarded as a significant contributor to cardiovascular disease.
The study included 128 people, including 78 with a diagnosis of sleep apnea and 52 who did not meet the diagnostic criteria for OSA. Scientists analyzed blood samples from all participants, looking in particular at endothelial cells -- cells that line the interior walls of blood vessels. The protein CD59 is normally found in these cells, lining blood vessel walls. From within the cell lining, CD59 works to prevent the buildup of inflammatory proteins on the surface of cells.
Scientists found that among people with obstructive sleep apnea, CD59 levels were elevated compared to those without OSA. Researchers found something else, both surprising and significant. In people with sleep apnea, CD59 protein was found primarily within the interior section of blood vessel cells, rather than in the cells' lining, as would have been expected -- and was the case among people without sleep apnea.
At a greater distance from cell walls, the CD59 protein was less able to exert its protective effect against inflammation. The result? A greater build-up of inflammatory proteins on the cells of people with obstructive sleep apnea, researchers found.
Statins a solution?
Included in the study were a small number of subjects with OSA who were already being treated with statins. Among this sub-group of sleep apnea sufferers, researchers discovered that CD59 remained in place in the lining of cells, in a position to inhibit inflammation -- similar to people without OSA. Additional research found that in people with OSA, the inward migration of CD59 is influenced by cholesterol.
This finding is important, opening the possibility of statins' use as a therapy to prevent cardiovascular damage in people with obstructive sleep apnea. Further study needs to take place before we'll know whether statins can serve as a viable treatment to prevent or reverse the cardiovascular damage from OSA, but this is a promising lead. More broadly, this study also provides some much needed insight into the process by which obstructive sleep apnea affects cardiovascular health and function.
The disrupted breathing of OSA
Obstructive sleep apnea involves repeated interruptions to normal breathing during sleep. During sleep, the airway temporarily narrows or closes altogether, compromising or fully interrupting breath flow. These episodes of shallow or paused breathing can last a few seconds, or more than a minute. In cases of mild sleep apnea, breathing is interrupted between 5-15 times an hours. In cases of moderate to severe sleep apnea, breathing is interrupted 15-30 times an hour, or more.
People with OSA are at higher risk for cardiovascular disease as well as other serious medical conditions, including type 2 diabetes and depression. They are also at significantly greater risk for accident and injury, in large part because of the tiredness and fatigue that accompany this sleep disorder.
Undiagnosed and untreated
Why do so many cases of obstructive sleep apnea go undiagnosed? Often, people with sleep apnea aren't aware of their most obvious symptoms -- since they occur during sleep. Snoring and other sounds of disrupted breathing during sleep can be signs of sleep apnea. Bed partners are frequently the people who are aware of these symptoms, before the sleepers themselves. Even when people are aware they snore or breathe with difficulty during sleep, they too often don't address these issues with their physicians. And physicians themselves often don't make the topic of sleep -- and questions about sleep-disordered breathing -- a priority during physicals and check ups.
What's more, many people aren't aware of the symptoms of obstructive sleep apnea that exist in addition to snoring:
• Dry mouth or sore throat upon waking
• Headaches, especially in the morning
• Severe tiredness during the daytime
• Trouble with concentration
• Memory problems
• Mood issues, including depression, anxiety, and irritability
The regular presence of any of these symptoms, even in the absence of snoring, warrants conversation with a physician.
Treatment works for OSA
Sleep apnea can wreak havoc with nightly rest, undermining health and daily performance. The good news is that OSA can be treated effectively with a number of different therapies. CPAP -- continuous positive airway pressure -- therapy is highly effective in reducing or eliminating sleep apnea, and is generally the recommended treatment for more severe cases of OSA. Other forms of PAP, or positive airway pressure, are also used to treat OSA. Oral appliances -- devices worn inside the mouth during sleep -- can also significantly improve sleep apnea, and are increasingly recommended for mild and moderate sleep apnea, as well as for people who have difficulty using CPAP therapy.
Positional therapy -- switching sleeping position -- is the simplest form of sleep apnea treatment, and can be effective particularly in cases of mild OSA. Airway obstructions and disrupted breathing are more likely to occur when sleeping on one's back. Moving to a side-sleeping position can reduce the frequency of interrupted-breathing episodes, and may even resolve mild sleep apnea in some cases. Lifestyle modifications, including losing weight, also help to alleviate OSA.
We need to improve our diagnosis rates OSA, and get more people into treatment for sleep apnea and the other health complications that often accompany the disorder. This latest research provides some significant new insight into how sleep apnea works to undermine heart health -- and may indicate a new way to treat and protect people with sleep apnea against cardiovascular risks.
Michael J. Breus, PhD
The Sleep Doctor™