"There's something about being in the hibernation state that's very protective," said symposium panelist Hannah V. Carey, an expert on ground squirrels at the University of Wisconsin.
The panel of physicians and researchers planned to discuss yesterday how hibernating animals reach a state where their heart and respiration rates slow to a crawl, cutting their demand for oxygen-rich blood.
"Seventy or 80 years ago, if someone said 'suspended animation,' it would sound like science fiction. But with the research that's developed recently, it's beginning to seem more realistic," said Lisa Leon, a U.S. Army research physiologist who co-chaired the suspended animation symposium.
The Army is interested in being able to slow a soldier's metabolism to curb the effects of heatstroke, among other injuries, Leon said.
The heart rates of groundhogs and ground squirrels drop from 150 beats per minute to about seven - and their respiration slows to a point where they only draw breath once every three to four minutes, experts say. Fattened up for the winter, they also fast for up to seven months, but somehow avoid getting sick.
If humans could do that on cue, they would have more time to survive injuries that cause blood loss and damaged organs, experts say.
Blood delivers oxygen to the body's organs and tissues. When the blood supply is cut off - by damage from a gunshot, a car accident, or a stroke or heart attack - it can quickly destroy the organs that depend on it. Without oxygen, the brain begins to die after about six minutes.
"Your body constantly needs oxygen and everything is fine as long as supply meets demand, but if you can reduce that demand you can eliminate the problem," said Mark Roth, a cellular biologist at the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle.
Biologists have long known that the metabolism rates of fruit flies, zebra fish, yeast and roundworms slow down under stress.
But they were thrilled three years ago when German researchers reported in Nature that the Madagascan fat-tailed dwarf lemur hibernates in tree holes. The lemur was the first primate to demonstrate hibernation, reinforcing arguments that fellow primates, including humans, carry the same ability in their genes.
That might explain how a 29-year-old Swedish skier survived 80 minutes in a frozen river in 1999 after she fell through a crack in the ice. Her temperature had dropped to about 57 degrees Fahrenheit before she was flown to a hospital where her blood was extracted, warmed and recirculated.
Researchers say their goal is finding the internal mechanism that can trigger this hibernation-like response when needed. "We may have the genes, but we don't have the regulatory system set in just the right way," said Gregory Flourant, who studies the hibernation habits of groundhogs at Colorado State University.
In recent years, scientists in Boston and Pittsburgh have stopped the hearts of rats, pigs and dogs by draining their blood and pumping them with chilled preservation fluid. Then the scientists were able to resuscitate the animals - many apparently unharmed - by recycling warmed-up blood into their organs.
Physicians already use hypothermia to reduce metabolism. Heart surgeons, for instance, reduce a patient's temperature to about 64 degrees Fahrenheit when repairs to the aorta require stopping the body's entire circulatory system. The process is known as deep hypothermic circulatory arrest.
"It's a common technique, done all over the world," said Dr. Fumito Ichinose, a cardiac anesthesiologist at Massachusetts General Hospital in Boston. A heart-lung machine normally maintains circulation during most heart surgeries, he said. |
