Washington: Scientists have tried to unravel how some people who seemingly freeze to death, with no heart rate or respiration for extended periods, can be brought back to life with no long-term negative health consequences.
New findings from the lab of cell biologist Mark B. Roth, Fred Hutchinson Cancer Research Centre (FHCRC), may help explain the mechanics behind this widely documented phenomenon.
Roth and colleagues show that two widely divergent model organisms, yeast and nematodes, can survive hypothermia, or potentially lethal cold, if they are first put into a state of suspended animation by means of anoxia or extreme oxygen deprivation.
They found that under normal conditions, yeast and nematode embryos cannot survive extreme cold.
After 24 hours of exposure to temperatures just above freezing, 99 percent of the creatures die.
Conversely, if the organisms are first deprived of oxygen and thus enter a state of anoxia -- induced suspended animation, 66 percent of the yeast and 97 percent of the nematode embryos will survive the cold.
Once normal growth conditions are resumed -- upon rewarming and reintroduction of oxygen -- the organisms will reanimate and go on to live a normal lifespan.
A better understanding of the potentially beneficial, symbiotic relationship between low oxygen and low temperatures may one day lead to the development of improved techniques for extending the shelf life of human organs for transplantation, Roth said.
"We have found that extension of survival limits in the cold is possible if oxygen consumption is first diminished," he said. "Our experiments in yeast and nematodes suggest that organs may last longer outside the body if their oxygen consumption is first reduced before they are made cold."
Roth first got the idea to study the link between anoxia-induced suspended animation and hypothermia from documented cases in which humans have managed to make complete recoveries after apparently freezing to death.
Widely publicised cases include Canadian toddler Erica Nordby, who in the winter of 2001 wandered outside clad only in a diaper. Her heart had stopped beating for two hours and her body temperature had plummeted to 61 degrees Fahrenheit before she was discovered, rewarmed and resuscitated.
Another incident that made headlines was that of a Japanese man, Mitsutaka Uchikoshi, who in 2006 fell asleep on a snowy mountain and was found by rescuers 23 days later with a core body temperature of 71 degrees Fahrenheit. He, too, resuscitated and made a full recovery, said an FHCRC release.
"There are many examples in the scientific literature of humans who appear frozen to death. They have no heartbeat and are clinically dead. But they can be re-animated."
These findings will appear online in the July issue of Molecular Biology of the Cell.