Cryosleep

Suspended animation is the slowing or stopping of life processes by exogenous or endogenous means without termination. Breathing, heartbeat, and other involuntary functions may still occur, but they can only be detected by artificial means.

Tiny organisms (e.g. embryos up to eight cells) can be cryogenically preserved and revived. Some have been kept in suspended animation for as long as 13 years.

Placing astronauts in suspended animation has been proposed as one way for an individual to reach the end of an interstellar or intergalactic journey, avoiding the necessity for a gigantic generation ship; occasionally the two concepts have been combined, with generations of "caretakers" supervising a large population of frozen passengers.

Since the 1970s, induced hypothermia has been performed for some open-heart surgeries as an alternative to heart-lung machines. Hypothermia, however, provides only a limited amount of time in which to operate and there is a risk of tissue and brain damage for prolonged periods.

Lowering the temperature of a substance reduces chemical activity by the Arrhenius equation. This includes life processes such as metabolism.

In June 2005, scientists at the University of Pittsburgh's Safar Center for Resuscitation Research announced they had managed to place dogs in suspended animation and bring them back to life, most of them without brain damage, by draining the blood out of the dogs' bodies and injecting a low temperature solution into their circulatory systems, which in turn keeps the bodies alive in stasis. After three hours of being clinically dead, the dogs' blood was returned to their circulatory systems, and the animals were revived by delivering an electric shock to their hearts. The heart started pumping the blood around the body, and the dogs were brought back to life.

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