VOA常速英语:Sleep Apnea Associated with Stroke

Snoring can be irritating or funny - depending on whether or not it's disturbing your sleep. But it can also be deadly, especially when someone suffers from sleep apnea, a condition where a person stops breathing for a while and then gasps for air.  Increasingly, evidence points to a relationship between sleep apnea and stroke. 

For many people, the sound of sleep is anything but silent. And for some of these people, snoring could be a sign of sleep apnea.

"Sleep apnea means that the airway, the upper airway cuts off at night," says Dr. David Gross, a pulmonary specialist at the National Rehabilitation Hospital of  Washington. "So the person, while he’s breathing normally in the day time, when he goes to sleep, the muscles get all relaxed and cut off and this can happen over and over again, 60 to 100 times an hour."

Doctors say most of the people who snore do not have sleep apnea, but most the people with sleep apnea snore. And increasingly, the condition is being recognized as a risk factor for stroke and heart attack.

"Whenever we run out of enough air to breathe, it sends alerting signals to our minds," says Dr. Michael Twery at the U.S. National Institutes of Health. "It raises the levels of stress hormones. It tells our heart to work harder."

So the heart is working harder than it should, every night.

"And it's constantly exposing us, night after night, to periods of insufficient oxygen where the level in our blood will actually decrease to levels that would be considered a medical emergency," Twery adds.

He likens the effect of sleep apnea to that of racing a car engine for prolonged periods of time. It wears the engine out prematurely. "Our heart becomes overworked and we become more vulnerable to heart attack."

And stroke. Twery oversaw a study of about 9,000 people who had sleep apnea, but did not have cardiovascular disease. The researchers followed them over a nine-year period. Then they analyzed the data.

"They found that men can experience up to a three-fold increased risk of stroke," says Twery, "and that risk seemed to be well correlated with the severity of their sleep apnea."

The next step in the research is to find out if people who have already had a stroke or heart attack can lessen their risk of having another one by using a machine like this while they sleep. It has a mask that is hooked up to a motor that delivers constant air into the throat and lungs, making it impossible to experience apnea.