Suspended animation is the slowing of life processes by external means without termination. Breathing, heartbeat, and other involuntary functions may still occur, but they can only be detected by artificial means. Extreme cold can be used to precipitate the slowing of an individual's functions; use of this process has led to the developing science of cryonics. Cryonics is another method of life preservation but it cryopreserves organisms using liquid nitrogen that will preserve the organism until reanimation. Laina Beasley was kept in suspended animation as a two-celled embryo for 13 years.
Placing astronauts in suspended animation has been proposed as one way for an individual to reach the end of an interplanetary or interstellar 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, hypothermia has been induced for some open-heart surgeries as an alternative to heart-lung machines. Hypothermia, however, only provides a limited amount of time in which to operate and there is a risk of tissue and brain damage for prolonged periods.
In June 2005 scientists at the University of Pittsburgh's Safar Center for Resuscitation Research announced they had managed to bring dogs 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 3 hours of being clinically dead, their blood was returned to their circulatory systems, and the dogs were revived by delivering an electric shock to their hearts. The heart started pumping the blood around the frozen body, and the dogs were brought back to life.
While most of the dogs were fine, a few of the revived dogs had severe nervous and movement coordination damage, causing them to be mentally disabled, and demonstrating behavior that was deemed "zombie" like. This has been pushed further by the media which named them "zombie dogs". There is concern that this technique, if used on humans could result in brain damage similar to those suffered by some of the dogs in the experiment. In extreme cases, doctors can now use induced hypothermia which reduces brain and heart activity to a minimum. This allows doctors to have more time to heal or diagnose a patient.
On 20 January 2006, doctors from the Massachusetts General Hospital in Boston announced they had placed pigs in suspended animation by a similar technique. The pigs were anaesthetised and a major blood loss was induced. After they lost about half their blood the remaining blood was replaced with a chilled saline solution. As the body temperature reached 10 °C (50 °F) the damaged blood vessel was repaired and the blood was returned. The method was tested 200 times with a 90 percent success rate.
An article in the 22 April 2005. issue of the scientific journal Science reports success towards inducing suspended animation-like hypothermia in mice. The findings are significant, as mice do not hibernate in nature. The laboratory of Mark B. Roth at the Fred Hutchinson Cancer Research Center in Seattle, Washington, placed the mice in a chamber containing 80 ppm hydrogen sulfide for a duration of 6 hours. The mice's core body temperature dropped to 13 degrees Celsius and metabolism, as assayed by carbon dioxide production and oxygen use, decreased 10-fold.
On 9 October 2006, the Massachusetts General Hospital in Boston announced they had been able to hibernate mice using the same method. Their heart rate was slowed down from 500 to 200 beats per minute, respiration fell from 120 to 25 breaths per minute and body temperature dropped to 30°C (natural: 39°C). After 2 hours of breathing air without hydrogen sulfide the mice returned to normal. Further studies are needed to see if the gas had poisonous effects on the brain.
There are many research projects currently investigating how to achieve "induced hibernation" in humans. This ability to hibernate humans would be useful for a number of reasons, such as saving the lives of seriously ill or injured people by temporarily putting them in a state of hibernation until treatment can be given. NASA is also casually interested in possibly putting astronauts in hibernation when going on very long space journeys, though they are not funding any research to this effect.
There are cases of accidental human hibernation. The most recent is the case of Mitsutaka Uchikoshi, a Japanese man who survived the cold for 24 days in 2006 without food or water when he fell into a hypothermic state similar to hibernation.