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Toronto (Nov. 30, 2005) - People with a moderate to severe form of sleep-disordered breathing called obstructive sleep apnea are more likely to have a stroke, says a study published today in the American Journal of Respiratory and Critical Care Medicine.
"We found that for people with moderate to severe sleep apnea, the odds of having a stroke in the next four years were almost four times greater than if you did not have sleep apnea," says Dr. Douglas Bradley, a Senior Investigator at the Toronto Rehabilitation Institute who worked with a team of Canadian and U.S. researchers, including Drs. Michael Arzt and Terry Young.
The study, using data from 1,474 participants in the Wisconsin Sleep Cohort Study, is the first to show a "very significant link" between sleep apnea and stroke, independent of other known risk factors such as diabetes and high blood pressure, says Dr. Bradley. The study found no significant stroke risk for people with mild sleep apnea.
The new findings are important because stroke is one of the leading causes of death and long-term disability in North America.
Sleep apnea causes a person to stop breathing repeatedly during sleep because of recurrent collapse of the throat. It can be caused by weight gain and aging. In the study, participants were considered to have moderate to severe obstructive sleep apnea if they stopped breathing 20 times or more per hour during sleep.
In another part of the study involving 1,189 participants, the researchers provided "the first prospective evidence that sleep-disordered breathing precedes stroke and may contribute to the development of stroke."
How might sleep apnea increase stroke risk? Recurrent interruptions in nighttime breathing deprive the brain of oxygen and activate the sympathetic nervous system, causing acute increases in blood pressure and heart rate, explains Dr. Bradley, who is Director of Toronto Rehab's Sleep Research Laboratory.
He says it is important to raise public awareness of signs of sleep apnea. Loud habitual snoring is the most common one. Others include: restless sleep; waking with a headache in the morning; or excessive sleepiness at work, during social situations or while driving. People should report these symptoms to their doctor, says Dr. Bradley.
The most effective treatment for sleep apnea is continuous positive airway pressure or CPAP. This controls sleep apnea by forcing air through a tube and into a mask worn over the nose at night. Air pressure is transmitted through the nose and into the throat where it props the throat open thereby preventing apneas and snoring.
Since sleep apnea is a treatable condition, the big question is whether treating sleep apnea could play a role in preventing people from having a first or second stroke. As a first step, Dr. Bradley plans to study stroke patients at Toronto Rehab to find out if treating sleep apnea improves their mental and physical function. Randomized trials will be needed to determine whether treating sleep apnea can prevent stroke in the first place.
The study published today was supported by grants from: the National Institutes of Health; the Canadian Institutes of Health Research; the Medical Research Service of the Department of Veteran Affairs; German Research Foundation Research Fellowship; and a Canadian Institutes of Health Research Senior Scientist Award.
Dr. Bradley also holds positions at the Toronto General Hospital/University Health Network, Mount Sinai Hospital and the University of Toronto. He is the recipient of a Senior Scientist Award from the Canadian Institutes of Health Research.
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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