Yeast and worms can survive hypothermia if they are first subjected to extreme oxygen deprivation, a new study finds.
The results could explain a long-held mystery as to how humans can be brought back to life after "freezing to death," the scientists say.
The study uncovered a previously unknown ability of organisms to survive lethal cold by temporarily slowing the biological processes that maintain life.
"We have found that extension of survival limits in the cold is possible if oxygen consumption is first diminished," said researcher Mark B. Roth of Fred Hutchinson Cancer Research Center in Seattle, Wash.
One form of "forced hibernation," the behavior known as "suspended animation," literally involves the sudden halting of chemical reactions in the body due to the lack of oxygen. A 10-hour time lapse video of a garden worm embryo in the process of developing into a full-fledged baby worm showed a rapid process of cell division freeze to a stop upon the environment’s oxygen removal. That same cell division resumed unaffected two and a half hours after oxygen was restored.
When subjected to literally freezing temperatures, the embryos of yeast and garden worms do not live, researchers found. A full 99 percent of those in the experiment died after 24 hours of exposure to temperatures just above freezing.
But, when first deprived of oxygen in the manner described above, 66 percent of the yeast and 97 percent of the garden worms survived. Upon re-warming and reintroduction of oxygen, the "two widely divergent organisms" reanimated and showed normal life spans, said scientists in a statement.
Improved understanding of the connection between low oxygen and low temperature could lead the way to extending the shelf-life of human organs for transplantation, Roth said.
It could also explain what has been an unsolved mystery: reported instances of humans "brought back to life" after succumbing to hypothermia.
"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 reanimated," Roth said. "Similarly, the organisms in my lab can be put into a state of reversible suspended animation through oxygen deprivation and other means. They appear dead but are not."
Documented cases of humans successfully revived after spending hours or days without a pulse in extremely cold conditions first inspired Roth to study the relationship between human hypothermia and his own research in forced hibernation.
In the winter of 2001, the body temperature of Canadian toddler Erica Norby plunged to 61 degrees Fahrenheit (16 degrees Celsius) as she lay for hours in below-freezing weather after wandering outside wearing only a diaper. Apparently dead, she recovered completely after being re-warmed and resuscitated.
The same curious fate befell Japanese mountain climber Mitsutaka Uchikoshi in 2006, who was discovered with a core body temperature of 71 degrees F (22 degrees C) after 23 days after falling asleep on a snowy mountain.
"We wondered if what was happening with the organisms in my laboratory was also happening in people like the toddler and the Japanese mountain climber. Before they got cold did they somehow manage to decrease their oxygen consumption? Is that what protected them?" Roth said. "Our work in nematodes and yeast suggests that this may be the case, and it may bring us a step closer to understanding what happens to people who appear to freeze to death but can be reanimated."
Oxygen deprivation’s protective effect comes from the way it arrests biological processes before dangerous instabilities can develop. When reanimated, the processes continue where they left off, with no sign of disruption having occurred.
"When an organism is suspended its biological processes cannot do anything wrong," Roth said. "Under conditions of extreme cold, sometimes that is the correct thing to be doing; when you can't do it right, don't do it at all."
The ultimate goal of such research is to "buy time" for patients in physical shock, such as after heart attacks and severe blood loss, increasing their chances of survival by preserving them until they can reach medical care, researchers said in a statement. Other forms of forced hibernation include exposure to chemical agents like hydrogen sulfide.
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