Individuals who experience moderate to severe sleep-disordered breathing are four times more likely to have a stroke during the next four years than those who do not suffer from the problem.
These findings were reported in the first issue of the December 2005 American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
T. Douglas Bradley, M.D., of the Toronto General Hospital/ University Health Network, Toronto, Canada, together with four associates, analyzed research results from 1,475 participants who were tested for sleep-disordered breathing at the University of Wisconsin General Clinical Research Center, Madison. Follow-up visits were conducted over the next 4, 8, and 12 years. Among the group, 21 individuals suffered a first-ever stroke at an average age of 53.
"Our longitudinal analysis provides the first prospective evidence that sleep-disordered breathing after adjustment for age and sex is related to significantly increased odds of suffering a stroke over the next 4 years," said Dr. Bradley. "Although our analysis cannot shed light on the pathway by which sleep-disordered breathing affects stroke risk, these novel findings add justification to considering the problem as a condition that either precedes or may contribute to the development of stroke."
Sleep-disordered breathing is one of a group of serious sleep disorders in which a sleeping person repeatedly stops breathing long enough to reduce the amount of oxygen in the blood and to increase the amount of carbon dioxide. Researchers categorize its severity by counting the "events" per hour that a person stops breathing for 10 seconds or more. Moderate to severe sleep disordered breathing is defined as 20 or more "events" per hour.
During the study and follow-up visits, participants underwent a laboratory sleep test (polysomnography), along with measurement of blood pressure and serum cholesterol levels, together with a check of other stroke risk factors such as body mass index.
Among the 1,475 participants, 76 percent (1,121) did not have sleep-disordered breathing (less than 5 "events" per hour), 17 percent (251) had a mild disorder (5 to 19 "events"), and 7 percent (103) had a moderate to severe problem.
Dr. Bradley noted that stroke is an important public health issue since it constitutes the commonest cause of long-term disability in the United States. It affects more than 1.1 million persons, with direct and indirect costs estimated at $56.8 billion for 2005.
In the future, Dr. Bradley believes that randomized clinical trials will be required to determine whether treatment for sleep-disordered breathing could either prevent stroke or improve its outcome.
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