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Toronto (July 14, 2005) - In the first sleep study of its kind, the presence of central sleep apnea in people who have had a stroke was associated with underlying heart failure in those people who had no previous symptoms of a heart condition. The findings, published recently in The American Journal of Respiratory & Critical Care Medicine, suggest that the presence of central sleep apnea in stroke patients is the proverbial canary in the coalmine for detecting previously undiagnosed heart disease.
"This study strengthens the notion that sleep apnea is a risk factor or is associated with heart disease. It is just another piece in the puzzle that tells us that the two are linked," says the study's lead author Dr. Douglas Bradley, Director of the Sleep Research Laboratory at the Toronto Rehabilitation Institute. "None of the patients in the study had any symptoms of heart failure so they were not on proper therapy at the time researchers diagnosed them, which means we found something new."
Central sleep apnea (CSA) is a medical condition in which breathing ceases for a few seconds (sometimes for as long as two minutes, or more) during sleep. The body simply "forgets" to breath. It is a neurological phenomenon; no "mechanical" obstruction is involved, as is the case with obstructive sleep apnea. These episodes are believed to originate in the brainstem. During a CSA episode, a person may not breathe for an unusually long time, they then gradually start to inhale again in progressively larger breaths, which gradually decline until their breathing stops once more.
Recent studies have shown that CSA is common among patients who have had a stroke. In the patients studied, the impairments in their heart function probably caused their sleep and breathing disorder. "When you have a poorly functioning heart, it can cause this kind of sleep apnea. Now when we see it, we automatically think, does this patient have a failing heart?" adds Bradley.
Stroke continues to be the number one cause of disability in the industrialized world; people who have had a stroke are at high risk for subsequent strokes and death from stroke. Moreover, approximately one third of stroke patients subsequently die of heart disease. Although the patients studied did not have the typical symptoms of heart failure (shortness of breath when walking or doing exercise or swelling of the ankles), there was still a chance that they could die from their unhealthy hearts.
Dr. Bradley believes that it is worth treating these patients heart failure even though they do not have any symptoms in order to prevent a second stroke or a heart attack and possibly even to prevent death. "We now know that central sleep apnea is related to underlying heart failure and heart failure is a risk factor for another stroke. We can now give patients appropriate medication to treat their heart failure and hopefully prevent the onset of symptomatic heart failure, stroke or even death."
"This study is important because it tells us that there are many things we can do of a preventative nature that could help people who have suffered a stroke get back on their feet, stay on their feet and not get sick again," says Dr. Bradley.
Dr. Bradley and his colleagues have built on existing sleep apnea findings, advancing the use of sleep studies in stroke patient populations as a means of decreasing the degree of disability after a stroke.
"Now we have two pieces of evidence that the presence of obstructive or central sleep apnea is something that is significant for stroke patients. For example, we know that the presence of obstructive sleep apnea is related to the degree of their disability after their stroke and to the length of their hospitalization. The worse the sleep apnea, the worse their disability, the longer they stay in hospital," says Dr. Bradley. "No matter what kind of sleep apnea we are diagnosing, the presence of sleep apnea in stroke patients has more clinical implications that go well beyond a sleep breathing disorder."
The study found that men are five times more likely to experience central sleep apnea than women. Currently, it is not known why men suffer more from this kind of sleep apnea. "Central sleep apnea is far more prevalent in men than it is in women and men have a worse outcome from heart failure than women. We are just beginning to wonder if the two are linked that way but in terms of causation, we just do not know yet," says Dr. Bradley.
The study took place over one and a half years, involved 93 patients in Toronto Rehab's stroke rehabilitation unit and found central sleep apnea in 19 per cent of the patients studied. A grant from the Toronto Rehabilitation Institute's research department funded Dr. Bradley's study. Dr. Bradley is a Senior Scientist and the leader of Toronto Rehab's research team that investigates sleep and cardiopulmonary function. He also holds positions at the Toronto General Hospital/University Health Network, Mount Sinai Hospital and the University of Toronto.
The Toronto Rehabilitation Institute (Toronto Rehab) is at the forefront of one of the most important and emerging frontiers in health care today- rehabilitation science. As a fully affiliated teaching and research hospital of the University of Toronto, Toronto Rehab is Canada's largest provider of adult rehabilitation services, complex continuing care, and long-term care. Toronto Rehab is advancing rehabilitation knowledge and practice through research, education and patient care.
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