'Dying In Sleep' Linked To Sleep Apnea

People who die in their sleep may stop breathing because they have lost too many brain cells, U.S. researchers recently reported.

Sleep apnea -- a condition in which people stop breathing for long stretches of time in their sleep -- may sometimes be caused by the destruction of cells in the brain stem, where autonomic functions such as breathing are controlled, they said.

Tests on rats showed that the loss of key brain stem cells that die off with age caused such disrupted sleep that the animals eventually stopped breathing completely.

The same thing may be happening in elderly people, said neurobiologist Jack Feldman of the University of California Los Angeles.

"We wanted to reveal the mechanism behind central sleep apnea, which most commonly affects people after age 65," Feldman said in a statement.

"Unlike obstructive sleep apnea, in which a person stops breathing when their airway collapses, central sleep apnea is triggered by something going awry in the brain's breathing center."

Writing in this week's issue of Nature Neuroscience, Feldman and colleagues said they deliberately killed brain cells in the pre-Boetzinger complex of the brains of rats -- a region believed to be the "command post" for breathing in mammals.

Then they monitored the rats' breathing.

"We were surprised to see that breathing completely stopped when the rat entered REM (rapid eye movement) sleep, forcing the rat to wake up in order to start breathing again," said Leanne McKay, who worked on the study.

"Over time, the breathing lapses increased in severity, spreading into non-REM sleep and eventually occurring when the rats were awake, as well."

Feldman believes the same thing could be happening in elderly people, especially those with degenerative diseases such as Parkinson's, which are marked by disturbed sleep.

"Our research suggests that the pre-Boetzinger complex contains a fixed number of neurons that we lose as we age," Feldman said.

"We speculate that our brains can compensate for up to a 60 percent loss of pre-Boetzinger cells, but the cumulative deficit of these brain cells eventually disrupts our breathing during sleep. There's no biological reason for the body to maintain these cells beyond the average lifespan, and so they do not replenish as we age," said Feldman.

"As we lose them, we grow more prone to central sleep apnea."

And weaker people may not be able to rouse themselves when this happens. They simply stop breathing.

Reference Source 89
August 9, 2005

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