Study shows how sleep apnea may cause stroke

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - A dangerous type of snoring known as sleep apnea can cause stroke by decreasing blood flow, raising blood pressure and harming the brain's ability to modulate these changes, researchers reported on Tuesday.

The study may help explain why people with sleep apnea are more likely to have strokes and to die in their sleep, the team led by Vahid Mohsenin of Yale University in Connecticut said.

An estimated 18 million Americans have sleep apnea, which is characterized by repeated episodes in which someone who is sleeping stops breathing.

"Three years ago we showed that patients with sleep apnea ... they die or have strokes three times more than people with a comparable age or risk factors without sleep apnea," Mohsenin said in a telephone interview.

"We asked the question of why they have a higher risk for stroke."

Writing in the Journal of Applied Physiology, Mohsenin and colleagues said they tested 48 middle-aged men and women, 22 of whom had sleep apnea but who were otherwise healthy. They checked blood pressure and used ultrasound to monitor blood flow in the brain.

They had the volunteers do a blood pressure test in which they squatted and then stood suddenly.

"We found that patients with sleep apnea had difficulty compensating for the change in blood pressure," Mohsenin said. "They actually had decreased blood flow to brain."