For the first time, scientists have solid evidence that heartbeats and breathing can become synchronized.

Scientists have investigated patterns between heartbeats, brain waves and other body signals for years. Discovering any such links could help spot early warning signs of illness.

But heartbeats and breathing normally have very different rhythms. The heart typically beats at 60 to 70 times per minute, while the breath rate is about one-fifth that.

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Prior studies had detected signs that breathing and heartbeat could synch up, but only in small groups of a dozen or so volunteers.

Computational and theoretical physicist Jan Kantelhardt at Martin Luther University in Halle, Germany, and his colleagues now have concrete proof for this synchronization.

The researchers observed 112 healthy subjects of varying ages, both men and women, during a variety of stages of sleep.

Healthy sleep normally goes through cycles one to two hours long, usually starting with light sleep, followed by deep sleep, then REM sleep when most vividly recalled dreams occur, and then back to light sleep.

Kantelhardt and his colleagues found that breathing and heartbeats synchronized more than twice as much during light and deep sleep than when people were awake.

On the other hand, breathing and heartbeat synchronization during REM sleep was suppressed by roughly a factor of three compared to wakefulness.

This suggests the high brain activity during REM sleep generates "noise" in the nervous system that upsets breathing and heartbeat synchronization, the scientists explained.

Further studies into links between heartbeat and breathing or blood pressure could help develop better diagnostics for patients with heart problems, Kantelhardt told LiveScience.

The researchers, whose synchronization work will be reported in the Feb. 2 issue of the journal Physical Review Letters, are currently investigating heart-attack patients.

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