Suspended disbelief in suspended animation

When ground squirrels, groundhogs and bears hibernate, their heart and respiration rates drop to help them survive. Now scientists are asking whether humans can pull the same trick.

Some researchers believe the ability to hibernate is buried in our genetic code, and they're searching for ways to turn it on occasionally.


The goal: to put seriously injured people into a form of suspended animation, or a hibernation-like state, to stave off the infections, brain damage and organ failure that often accompany severe bleeding.

"Suspended Animation - Fact or Fiction?" is one of the cutting-edge topics scientists have been discussing during the five-day Experimental Biology conference that runs through tomorrow at the Washington Convention Center.


"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.

But Ichinose said the hypothermic approach has its drawbacks. Cooling the blood cripples its clotting ability, which increases the risk of excessive bleeding. And there's a limit to how long human organs can withstand chilling.

"If you cannot repair whatever you have to in 45 minutes, the risk of organ damage is going to increase," he said.

Roth has published results showing that mice slowed their metabolism when placed in chambers whose air was mixed with hydrogen sulfide - the poisonous gas that gives a rotten egg its stench.

The rodents' breathing dropped from a normal 120 breaths per minute to fewer than 10 and their body temperatures fell from 98.6 degrees Fahrenheit to a chilly 51.8 degrees. But when resuscitated, they were unharmed.

His first results were published in Science in 2005. Follow-up work, which appeared last month in the journal Shock, confirmed those results.


Roth has founded a company, Ikaria Inc., which is raising money for research to establish whether hydrogen sulfide can be used safely to treat humans.

Some researchers are skeptical. They say that hydrogen sulfide may lower metabolism rates, but only because it nearly kills the mice exposed to it.

"It's metabolic poisoning," Flourant said.

But Roth says survival rates of mice and dogs in other studies indicate that there's more involved than producing a near-death experience.

"We don't plan to take patients and put bags over their heads," he said.

Ichinose and a colleague recently replicated Roth's work in mice as part of a search for a replacement or a supplement to the hypothermic techniques used in some cardiac surgeries.


"Conceptually, whatever you can do to reverse the metabolic rate, that could be potentially very useful," Ichinose said. But he added that it is likely to be years before hydrogen sulfide or any similar compound is used as a suspended animation drug on humans.

"To jump from mouse to humans takes a lot of studies," he said.