Researchers have for a long time identified the risks of heart-related illness with sleep apnea.
This is mentioned in many of these FAQ posts. The following is more specific information.
The following is an article about the 2005 study by Yale University School of Medicine, published in the New England Journal of Medicine concerning stroke:
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Quote:
Sleep Apnea Linked to Stroke Risk
10 November, 2005 02:35 GMT
'This is probably the best data available now showing that if you have obstructive sleep apnea, you have an increased risk for stroke or death.' Obstructive sleep apnea, which involves frequent stoppages of breathing caused by narrowing of the upper airways, can increase risks for stroke and death, according to groundbreaking research.
The study of nearly 700 people found a doubled risk of stroke in all those with sleep apnea, and a threefold increased risk in those with a severe case of the condition.
"We followed people with sleep apnea forward in time to see who had strokes or died, and found this increased risk," said lead researcher Dr. H. Klar Yaggi, an assistant professor of medicine at the Yale University School of Medicine. "What our study found is a new risk factor for the development of stroke."
His team published its findings in the Nov. 10 issue of the New England Journal of Medicine.
Chicken-or-Egg Question
Other studies looking at sleep apnea and stroke have been done, but they focused on the incidence of sleep apnea in people who had already suffered strokes, Yaggi explained.
Those studies found that "a high percentage of patients with stroke have sleep apnea," he said. But they didn't solve the chicken-or-egg question of whether sleep apnea helps trigger stroke, or whether stroke risk factors cause sleep apnea by affecting the brain's sleep center.
But in its three-year prospective study, Yaggi's team found that the presence of sleep apnea nearly doubled the risk of stroke or death, even after the researchers adjusted for other risk factors.
The finding closes a gap in knowledge about the relationship between sleep apnea and heart problems, said Dr. Virend K. Somers, a professor of medicine at the Mayo Clinic, who wrote an accompanying editorial.
"We know there is an association between obstructive sleep apnea and various kinds of heart disease -- hypertension, atrial fibrillation, stroke and heart failure," he said. "We've never been able to prove that sleep apnea causes these things, other than hypertension. The evidence has been mainly circumstantial, and that is especially true of people with stroke. This is probably the best data available now showing that if you have obstructive sleep apnea, you have an increased risk for stroke or death."
Missing Piece
But there is still one more missing piece to the puzzle, Yaggi said.
"The next research has to be on the impact of treating sleep apnea," he said. "The question that this study raises is whether primary or secondary prevention would be helpful in reducing the risk."
No such trials are now underway, said Dr. Carl E. Hunt, director of the National Center on Sleep Disorders Research at the National Heart, Lung, and Blood Institute (NHLBI), which helped finance Yaggi's trial.
NHLBI is funding two trials on the effectiveness of the current first-line medical treatment for sleep apnea, continuous positive airway pressure (CPAP), Hunt said, "but neither of these clinical trials addresses stroke as a primary outcome."
However, the newly reported trial "provides a very rational basis for undertaking long-term interventional trials," he said.
Weight Loss
Another paper in the same issue of the journal reported that CPAP did not help people with a variant of the condition called central sleep apnea. But Yaggi noted that this form has a different cause than obstructive sleep apnea.
"Central sleep apnea is much less common, and results from a problem with the brain's breathing center, so that there is a lack of drive to breathe," he said. "Obstructive sleep apnea, which is significantly more common, is a problem of the upper airway, which is all muscle. When people with obstructive sleep apnea are awake and alert, there is enough muscle to keep the airway open. During sleep, they lose tone. The airway becomes significantly relaxed and closes off. The result is what I call 'industrial-strength' snoring."
Daytime drowsiness is another sleep apnea side effect, Somers said. "Until now, physicians have worked against sleep apnea primarily to prevent daytime sleepiness," he said. "We still need to prove that it can prevent stroke, but we believe that treating sleep apnea is good for a patient's heart disease."
Weight loss is perhaps the most direct intervention in fighting sleep apnea, since the condition often is associated with obesity, Yaggi added. "Weight loss of 10 to 20 percent can significantly reduce sleep apnea," he said.
More information: Find out more on sleep apnea at the National Library of Medicine.
The following is from a June 2001 article on the reutershealth website:
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The following quote from this article is only one part of the article. Refer to the link for more information about sleep apnea.
Quote:
Serious Health Effects of Sleep Apnea
The effects of sleep apnea on major health conditions are currently under debate. Among the problems that have been associated with this sleep disorder are the following:
High blood pressure.
Stroke.
Heart attack.
Heart failure.
Pulmonary Hypertension.
Diabetes.
Kidney failure.
Researchers are intensively investigating why a problem in the upper airways is associated with these serious health events. Here are some findings:
Obesity, smoking, and alcohol abuse, known risk factors for hypertension and heart disease, are also associated with sleep apnea. These factors however, do not explain all cases of higher heart risks in people with sleep apnea. For example, among overweight people, those who have sleep apneas have a greater heart risk than those without them.
When breathing stops during apneas, carbon dioxide levels in the blood increase and oxygen levels drop. This effect may trigger a cascade of physical and chemical events that can then increase risk for these conditions.
Researchers have reported high levels of certain immune factors called tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6) in people with sleep apnea, particularly those who are obese. High levels of TNF-alpha and IL-6 produce a damaging inflammatory response, which can harm cells in the body, including those in the arteries. Elevated TNF-alpha was associated in one study with fatigue, shortness of breath, and a weak heart-pumping action.
At this time, however, evidence of a clear causal relationship with any of these health problems is still weak. Some studies have found no significant independent risk for heart disease from obstructive sleep apnea. The following are some discussions on the possible effects of apnea on specific health problems.
High Blood Pressure. A number of studies have found a strong association between sleep apnea and high blood pressure (hypertension). For example, a 2000 study followed patients for four years and reported that the greater the number of nightly apnea episodes they had in year one the more likely they were to develop hypertension by the fourth year. A weak but still higher than normal association with high blood pressure has even been observed in those who snore or have mild sleep apnea.
The relationship between sleep apnea and hypertension has been thought to be largely due to obesity, a risk factor common to both conditions. Recent and major studies, however, are suggesting a higher rate of hypertension in people with sleep apnea regardless of weight.
The following is one way that apnea may directly affect blood pressure, regardless of other risk factors:
Blood pressure fluctuates widely and suddenly in response to episodes of apnea and hypopnea.
Such fluctuations are possibly to due to a sudden surge in the sympathetic nervous system, which has also been associated with sleep apnea. (The sympathetic nervous system controls involuntary muscles, importantly those in the blood vessels and heart.)
Over time such fluctuations could possibly lead to permanent hypertension.
Stroke. Sleep apnea appears to increase the chance for a stroke independent of its association with high blood pressure (a known risk factor for stroke). Sleep apnea is also thought to be related to small strokes called transient ischemic attacks (TIAs). How sleep apnea increases these risks is under investigation. Some theories are as follows:
One 2000 study observed that blood becomes more viscous (stickier) in the morning in people with obstructive sleep apnea compared to people without the sleep disorder. Such "sticky" blood is more apt to form clots that can lead to stroke.
To support this, another 2000 study reported that stroke victims with sleep apnea tended to have higher levels of the blood protein fibrinogen than stroke victims without sleep apnea. Fibrinogen is a factor in blood that causes it to clot. Higher levels of fibrinogen have been linked to both stroke and heart attack risk.
A 1998 study reported that the carotid artery (the major artery to the brain) is in far greater danger of becoming sclerotic (hardening and narrowing) in people with obstructive sleep apnea than in the average person. People with both diabetes and sleep apnea are at particularly high risk for this effect.
One small 1998 study reported a drop in blood flow in the brain during episodes of obstructive hypopnea (slow and shallow breathing associated with snoring). This may also contribute to the risk of stroke. Such declines in blood flow did not appear to occur with obstructive or central apnea, however.
Coronary Artery Disease and Heart Attack. In one 2001 study, researchers observed that the higher the number of apneas and hypopneas a patient had, the higher his risk for heart attack. Many of the factors associated with stroke and sleep apnea (a risk for blood clots and narrowing of the arteries) may also increase the risk for heart attacks. Evidence suggests, however, that the effect of apneas on coronary artery disease and heart attack is not as significant as it is on heart failure and stroke.
Heart Failure. The evidence for an association between heart failure and sleep apnea is suggested by the following:
High blood pressure, which is associated with sleep apnea, is a major cause of later heart failure.
In addition, a 2001 study reported a higher number of apneas in patients with left ventricular hypertrophy. This is an overgrowth of the heart's left ventricle that impairs the heart's pumping action over time and is a major factor in many cases of heart failure. More research, however, is needed to verify these results.
Central sleep apnea is particularly linked with heart failure. In any case, obstructive sleep apnea can affect breathing functions in a way that may be particularly harmful for patients with existing congestive heart failure. A 1999 study, in fact, indicated that sleep apnea is associated with poorer survival in patients with heart failure.
Effects on Diabetes. Researchers have also observed an association between diabetes and sleep apnea. Again, obesity may be the common factor, but there is also some evidence that sleep apnea is associated with abnormalities in insulin regulation independent of other conditions.
Effects on the Lung. Obstructive sleep apnea can play a role in the development of pulmonary hypertension, a serious but uncommon condition in which pressure rises in the blood vessels in the lungs.
The following is a link to a topic in our Interesting Links forum, a compilation of other journal sources about the risks associated with the Cardio and Vascular Effects of OSA. This was compiled by our moderator Vicki, a compilation of selected peer reviewed journal articles highlighting research from 2005.
Click here for link to Interesting Links topic
The following is an article on irregular heart rhythm linked with sleep disorders, specifically Atrial fibrillation (AF)
This is a July 2004 article from the website of americanheart.org.
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Quote:
Journal Report
07/12/2004
Irregular heart rhythm linked with sleep disorder
DALLAS, July 13 – People with an irregular heart rhythm are more likely to have sleep apnea than other cardiology patients, according to a report in today’s rapid access issue of Circulation: Journal of the American Heart Association.
Atrial fibrillation (AF) is a heart rhythm abnormality in which the heart’s two upper chambers (the atria) quiver instead of beating effectively, which can cause blood to pool and clot. A blood clot that leaves the heart and lodges in a brain artery can cause a stroke.
Obstructive sleep apnea contributes to heart attack and stroke risks. It is characterized by repeated interruption of breathing during sleep. The prevalence of sleep apnea is directly related to body mass index. As obesity increases, so does the incidence of sleep apnea.
AF and obstructive sleep apnea share associations with other common diseases and risk factors such as male gender, hypertension, congestive heart failure and coronary artery disease, but the prevalence of sleep apnea among AF patients is unknown, said senior author Virend K. Somers, M.D., Ph.D., professor of medicine in the Division of Cardiovascular Diseases at the Mayo Clinic, Rochester, MN.
“Because sleep apnea is significantly underdiagnosed and treatment may lower the risk of recurrent AF, determining its prevalence in patients with AF can be very important,” he said.
A group of 151 AF patients and 312 general cardiology patients answered a questionnaire regarding snoring, daytime sleepiness, body mass index, and hypertension to identify risk of sleep apnea. Almost half (49 percent) of the AF patients were identified as high risk for sleep apnea compared with about a third (32 percent) of general cardiology patients.
Patients with AF were twice as likely to have sleep apnea (2.19 odds ratio).
“Atrial fibrillation is predicted to affect more than 5 million people by the year 2050. The coinciding epidemics of obesity and AF underscore the clinical importance of these results,” said Apoor S. Gami, M.D., instructor in medicine in the Division of Cardiovascular Diseases at the Mayo Clinic, and lead author of the study.
Another novel observation was that the association of obstructive sleep apnea with AF was greater than the association of sleep apnea with its traditional risk factors such as body mass index, neck circumference and hypertension, Gami said.
The study also suggests that it is not only the common diseases associated with both conditions that may lead to AF, but there may be a unique interaction between the pathophysiologies of sleep apnea and AF.
When sleep apnea interrupts breathing, oxygen in the blood drops while carbon dioxide increases. The sympathetic nervous system (the flight-or-fight response) is activated. Also, the forceful breathing efforts through the obstructed airway may result in dramatic pressure shifts across the cardiac chambers. These reactions, if untreated over time, may predispose to AF.
While sleep apnea is ideally diagnosed by being observed overnight in a sleep lab, researchers say the questionnaire was able to very reliably predict who did or did not have sleep apnea.
Researchers suggest that the presence of obstructive sleep apnea be considered in all AF patients and screening might be warranted in AF patients who are also obese or have hypertension.
Co-authors are Gregg S. Pressman, M.D.; Sean M. Caples, M.D.; Ravi Kanagala, M.D.; Joseph J. Gard; Diane E. Davison, R.N., M.A.; Joseph F. Malouf, M.D.; Naser M. Ammash, M.D.; and Paul A. Friedman, M.D.
The study was partly funded by the National Institutes of Health.