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Sleep Apnea and Stroke
SUMMARY OF:
Association of Sleep-Disordered Breathing and the Occurrence of Stroke http://ajrccm.atsjournals.org/cgi/content/short/172/11/1447
Authors: Artz M, Young T, Finn L, Skatrud JB, Bradley TD.
Published in: American Journal of Respiratory and Critical Care Medicine; Year: 2005; Volume: 172; Pages: 1447-1451.
Many studies have evaluated the effect of sleep apnea on health. This was the first major study to look at the risk of developing a stroke in people with sleep-disordered breathing (that is, obstructive sleep apnea or OSA). It was performed jointly by a group of investigators in Madison, Wisconsin and our group in Toronto, Ontario and was published in 2005.
The aim of this study was to determine whether there was an association between OSA and stroke. Both the association of stroke with OSA at the start of the study, and the risk of having a stroke over the next 4 to 12 years after an initial sleep study were analysed. The study included 1475 state employees in Wisconsin, aged 30 to 60 years. All people who took part had an overnight sleep study to see if they had OSA or not.
Of the 1475 people (809 men and 666 women) who had sleep studies, 24% had OSA. The severity of OSA was classified using the apnea-hypopnea index (AHI) which is the number of apneas (complete stoppage of breathing) and hypopneas (partial stoppage of breathing) per hour of sleep. An AHI of less than 5 was considered normal. An AHI of 5-19 was classified as mild OSA; 20 or greater as moderate-to-severe OSA. Seven percent of the subjects had moderate-to-severe OSA.
There was a significant association between moderate-severe OSA and stroke at the beginning of the study. Even after adjustment for other known stroke risk factors (such as age, sex, smoking, body mass index, high blood pressure, diabetes, etc.), those with moderate-severe sleep apnea were 3.8 times more likely than those with no OSA to have had a stroke.
Of the original group of people, 1189 were followed over 4 to 12 years after the original sleep study. The great majority of those with OSA were not treated for it. At the end of each 4 year period, participants were interviewed to find out if they had had a new stroke. Not taking into account the possible effects of known risk factors for stroke, people with moderate-severe OSA were approximately 4.3 times more likely to have developed a new stroke than those without OSA. This association remained significant after adjusting for the presence of male sex and higher age which are known risk factors for stroke. After taking into account body mass index (BMI), as well as higher age and male sex, the risk of stroke remained approximately 3 times greater in those with moderate-severe OSA than in those without OSA, but that result was not statistically significant, likely due to the low number of strokes in this relatively young population.
To summarize, like other large population studies, this study showed a significant association between moderate-to-severe obstructive sleep apnea and stroke at the time of sleep apnea diagnosis, independent of other known risk factors. It also was the first study to report data for subjects that were followed over time after their sleep study, and strongly suggested, but did not prove, that those with untreated moderate-to-severe OSA have an increased risk of suffering a stroke over the next 4 to 12 years.
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