Sleep Apnea Tied to Silent Strokes

Sleep apnea is a disorder characterized by abnormal pauses in breathing during sleep. It is already known that sleep apnea increases risk of stroke. Two studies are going to be presented Wednesday at the Stroke Conference in New Orleans. One of these studies discovered a link between sleep apnea and silent strokes, which cause tissue death in the brain without symptoms. The other study shows that rapid memory loss before a stroke increases the chances that the stroke will be fatal.

Stroke affects 795,000 Americans annually, according to the association.

Dr. Jessica Kepplinger, a fellow at the University of Technology in Dresden, Germany, and her colleagues evaluated 56 stroke victims. They already knew that silent strokes were linked to an increased risk of strokes. However, "there are barely any studies that have investigated the relationship between sleep apnea and the so-called clinically silent strokes," she said. They examined this relationship by first gaving patients in-hospital testing for apnea. Kepplinger said: "We found an overall high frequency of sleep apnea, 91 percent, in our study population of acute stroke patients, which underlines the importance of this stroke risk factor". The team also performed brain-imaging studies. The brain scans provided evidence that those with sleep apnea were more likely to have silent strokes. Having more than five episodes a night was linked with having silent strokes. The higher the severity of the apnea, the more likely these silent strokes were found on brain imaging.

The more severe the apnea, the less favorable the outcome when the patient was discharged.

The average age of the patients was 67 years old. Just over half of them were women. The study found an association between sleep apnea and stroke, but it did not prove a cause-and-effect relationship.

The second study was done by Qianyi Wang, a graduate student at the Harvard University School of Public Health, and colleagues. They evaluated nearly 12,000 men and women, all  above age 50, in the U.S. Health and Retirement Study.

All were stroke-free at the start. The men and women were given memory tests every two years for up to 10 years.

1,820 strokes were reported over time. The rest of the participants were stroke-free for the entire follow-up period.

The research studied the memory declines over time. Those who later survived a stroke "had memory decline that is nearly twice as fast as stroke-free individuals, even before their stroke," Wang said.

M. Maria Glymour, an assistant professor of society, human development and health at Harvard and a study co-author, said: "For people who do not survive stroke, this difference is even more striking. Prior to stroke, people who later died shortly after stroke were declining three times as fast as the stroke-free. Our study is the first national picture of how long-term memory changes before and after the occurrence of a stroke compared to individuals who have not had a stroke".

Funding for the study was provided by the U.S. National Institute on Aging and the American Heart Association.

Dr. Ralph Sacco, chair of neurology at the University of Miami Miller School of Medicine and past president of the American Heart Association, reviewed the findings and said that they both provide some valuable information.aid Dr.

Dr. Sacco said: "It's been mainly in smaller studies that sleep apnea has been shown to be a risk factor for stroke." He also noted that the new research goes further by linking sleep apnea with the milder "silent" strokes.

"There are many reasons to treat sleep apnea, including reducing the risk for clinical and now silent stroke," Dr. Sacco said. He said that the memory-loss study tells us that those who have the worst memory loss may have a greater death rate when they have the stroke, and that those with more  memory loss in the study may also have had more risk factors for stroke. He said he believed the message was that taking care of brain health may help us in several ways. "What is good for our memory may also be good for surviving a stroke," he concluded.

The data and conclusions of these studies should be viewed as preliminary until they are published in a peer-reviewed journal.