Remember all those SF movies where it takes suspended animation to travel to a distant planet or galaxy? Ripley, the buff female protagonist in the film Aliens, spends 57 years in “hypersleep” — without aging — before being rescued. The Defense Advanced Research Projects Agency (DARPA) is now funding research that may one day bring humans to a zombie-like form of hibernation. The motivation, however, is not so much space travel as emergency trauma care for wounded soldiers on the battlefield.

Actual hibernation occurs when an animal such as a squirrel goes into a state of suspended animation: heart rate, metabolism and body temperatures drop significantly. When a mammal is in hibernation, its body temperature is usually only 2-4ºC above freezing (as opposed to perhaps 38ºC), oxygen consumption is 2% of normal rates, and heart rate decreases by a factor of one hundred.

DARPA is committing $9.9 million to the Texas A&M Institute for Preclinical Studies (TIPS) to research how hydrogen sulfide can block the body’s ability to use oxygen and induce a state of suspended animation. Because they have a cardiovascular system similar to humans, TIPS researchers Theresa Fossum and Matthew Miller think they can accurately predict human results from trials with anesthetized pigs. Using swine, the researchers are testing various compounds — some containing hydrogen sulfide — to find one that can safely keep the hemorrhaging animals “as close to death as possible.” Here’s a video on the TIPS research:

As reported by Popular Science, nearly half of soldiers killed in action die of severe blood loss after being wounded by gunshots or IEDs. When emergency trauma care is administered during that first “golden hour,” soldiers’ odds of survival are relatively good, but after that their odds begin to drop quickly. That’s why TIPS researchers are looking for a way to send the human body into a state of suspended animation, essentially “shutting down” the heart and brain until proper care can be administered.

To understand the mechanics of hibernation, researchers have turned to squirrels. During the winter months, squirrels go through an amazing metamorphosis: their 300 beat-per-minute heart rate slows to a mere two to ten beats, their oxygen consumption drops to one-fiftieth of normal, and their body temperatures fall essentially to zero. And yet they emerge from hibernation no worse for wear.

One Stanford University project (also funded by DARPA) tried using a pancreatic enzyme found in both species to put humans into a state of squirrel-like hibernation, and another used hydrogen sulfide to stop wounds from bleeding by stopping heart function in rats and worms. Stanford’s Craig Heller discovered how squirrels and other hibernators manage to regulate their core body temperatures, even as they become zombie-like. Those trials lead to an examination of the human temperature-control system, which led to a specialized glove-like device, built for the military.

Cheng Chi Lee, an associate professor of biochemistry and molecular biology at the University of Texas Medical School at Houston, discovered that the 5-prime adenosine monophosphate (5’-AMP) molecule can induce a short hibernation-like state in mammals (such as humans) that don’t normally hibernate. He’s now trying to find ways to maintain that state long enough to perform major, live-saving surgeries.

Turning pigs into “zombies” could mean the difference between life and death for wounded soldiers on the battlefield.

According to the Cybercast News Service, when an animal hibernates, its cells are deprived of the oxygen it receives during its waking hours. The cells can better endure this low-oxygen state when the animal reaches a state of hypothermia and its metabolism slows. Similarly, a heart attack or stroke starves organs of oxygen. According to Dr. Lee, physicians have long been using cooling procedures to help human cells survive these conditions.

“If you follow the ambulance services now in response to heart attack — the first response when you reach a heart attack patient is to bring the body temperature down as quickly as possible while the patient is being transported to the hospital,” says Lee. “If you cool the body temperature down, then you expand the window of preventing ischemia [oxygen-shortage] damage. It’s really simple, because if the cell is cooled, it needs less oxygen.”

Lee said the same principle applies to organ transplants. When the organ donor and recipient live in different parts of the country, the organ is preserved in an ice cooler or other refrigeration system during transport.

More recently, a US-Chinese team of researchers has identified differences in expression levels between proteins and messenger RNA (mRNA) between hibernating and non-hibernating arctic squirrels, suggesting “substantial post-transcriptional regulation of proteins during torpor-arousal cycles of hibernation.”

The study, published in a recent issue of the ProteoMonitor, asserts that hibernation “involves complex mechanisms of metabolic reprogramming and tissue protection.” Previous studies looked primarily into changes at the mRNA level. The newly published study identifies “significant differences” in mRNA levels in hibernating and non-hibernating ground squirrels — the transcripts of mRNA “are protected while translation is inhibited during torpor. Therefore protein variety and abundance can be very different from corresponding gene expression at the mRNA level, and differential protein expression may more directly reflect regulatory changes related to hibernation.”

A form of squirrel-like hypersleep-hibernation would help solve a great many of the problems involved in sending humans interstellar distances. And metabolic and genetic research is zeroing in on what makes squirrels tick. But more immediately, turning pigs into “zombies” could mean the difference between life and death for wounded soldiers on the battlefield.