Study Explains Sleep Apnea Link to Stroke

The U.S. researchers who linked higher risks of stroke to sleep apnea are finding the reasons why.

Dr. Vahid Mohsenin of the Yale University School of Medicine in New Haven, Conn., and colleagues say that untreated sleep apnea eventually harms the brain's ability to modulate blood pressure changes and prevent damage to itself.

In sleep apnea, the upper airway becomes blocked, hindering or stopping breathing -- causing blood oxygen levels to drop and blood pressure to rise. The person eventually awakens and begins breathing -- restoring normal blood oxygen and blood flow to the brain.

"After we found that sleep apnea is a risk factor for stroke and death, independent of other risk factors, we hypothesized that there must be something wrong with the regulation of blood flow to the brain," Mohsenin says in a statement.

The study, published in the Journal of Applied Physiology, compared a sleep apnea group to those without sleep apnea and found the group with apnea had lower cerebral blood flow velocity.

Those with apnea also took longer to recover from a drop in blood pressure and to normalize blood flow to the brain, the study said. These repeated surges and drops over time result in a reduction in the brain's ability to regulate its blood flow to meet its own metabolic needs, Mohsenin says.