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.
Experiments
Temperature-induced
Lowering the temperature of a substance reduces chemical activity by the Arrhenius equation. This includes life processes such as metabolism.
Hypothermic Range
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.
On 20 January 2006, doctors from the Massachusetts General Hospital in Boston announced they had placed pigs in suspended animation with a similar technique. The pigs were anaesthetized and major blood loss was induced, along with simulated - via scalpel - severe injuries (e.g. a punctured aorta as might happen in a car accident or shooting). After the pigs 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 vessels were repaired and the blood was returned.The method was tested 200 times with a 90% success rate.
From May 2014, a team of surgeons from UPMC Presbyterian Hospital in Pittsburgh plan to try the above method in gunshot victims (or those suffering from similar traumatic injuries). The trials will be done on ten such severely wounded patients and compared with ten others in similar situation but who had no access to the above method. They currently refer to the procedure as Emergency Preservation and Resuscitation for Cardiac Arrest from trauma.
Cryogenic range
This concept is speculative as well as frequently misunderstood. Human beings are unable to survive suspended animation at cryogenic (extremely cold) temperatures naturally due to damage from ice formation. The limits of current technology are also insufficient to prevent loss of cellular viability. Cryonics operates under a fundamentally distinct paradigm from suspended animation in that it depends on future technology as part of its premise for working.
Suspended animation is distinct from cryonics because it does not require this "benefit of the doubt" concerning future technology. It is something that immediately and demonstrably works. The medical use of suspended animation will still require optimism that diseases can be cured.
— Brian Wowk
In order to achieve suspended animation, a reliable method to prevent damage to cells would be needed. Vitrification can achieve this in the laboratory only for small amounts of tissue due to cooling and other physical limits combined with cryoprotectant toxicity.There is also only limited evidence that it is possible in principle, because only very small organisms can be vitrified or frozen safely. Research on Caenorhabditis elegans has shown that memories can be recovered, and such organisms can survive vitrification with around 100% success rates.
Chemically induced
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 core body temperature of the mice dropped to 13 degrees Celsius and metabolism, as assayed by carbon dioxide production and oxygen use, decreased 10-fold.They also induced hypoxia on nematode embryos and zebrafish embryos, placing them in suspended animation for hours, and then re-animating them simply by returning the oxygen to the embryos.
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 damaging effects on the brain, considering the effect of hydrogen sulfide on the body is similar to hydrogen cyanide; it does not slow the metabolic rate but rather inhibits the transfer of energy within the cell via ATP.
Experiments on sedated sheep and partially ventilated anesthetized pigs have been unsuccessful, suggesting that application to large mammals may not be feasible. In any case, long term suspended animation has not been attempted.
Human hibernation
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.
Actual and anecdotal cases of suspected human hibernation or states similar to hibernation exist in the literature:
Anna Bågenholm, a Swedish radiologist who survived 40 minutes under ice in a frozen lake in state of cardiac arrest and survived with no brain damage in 1999.
Mitsutaka Uchikoshi, a Japanese man who survived the cold for 24 days in 2006 without food or water when he fell into a state similar to hibernation
Paulie Hynek, who, at age 2, survived several hours of hypothermia-induced cardiac arrest and whose body temperature reached 64 °F (18 °C)
John Smith, a 14-year-old boy who survived 15 minutes under ice in a frozen lake before paramedics arrived to pull him onto dry land and saved him.
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