Scientists have unlocked the secret of suspended animation, a state of "undeath" where the body's metabolism shuts down but all major organs continue to function. Hydrogen sulfide, also known as sewer gas, may be the miracle substance that finally allows humans to stay alive in a frozen, non-aging state. In science fiction, of course, suspended animation is used by astronauts to travel across great distances in space by putting their bodies into suspend mode. Suspended animation could also be induced in dramatically injured people to prevent them from dying while being rushed to the hospital. What's truly amazing is how simple it turns out to be.

According to a release about the study, which will be published in the April issue of the journal Anaethesiology, the researchers are convinced that they've hit on something that's very close to the scifi idea of suspended animation.

"Hydrogen sulfide is the stinky gas that can kill workers who encounter it in sewers; but when adminstered to mice in small, controlled doses, within minutes it produces what appears to be totally reversible metabolic suppression," says Warren Zapol, MD, chief of Anesthesia and Critical Care at MGH and senior author of the Anesthesiology study. "This is as close to instant suspended animation as you can get, and the preservation of cardiac contraction, blood pressure and organ perfusion is remarkable."

The researchers measured factors such as heart rate, blood pressure, body temperature, respiration and physical activity in normal mice exposed to low-dose (80 ppm) hydrogen sulfide for several hours. They analyzed cardiac function with electrocardiograms and echocardiography and measured blood gas levels. While some mice were studied at room temperature, others were kept in a warm environment - about 98º F - to prevent their body temperatures from dropping.

In all the mice, metabolic measurements such as consumption of oxygen and production of carbon dioxide dropped in as little as 10 minutes after they began inhaling hydrogen sulfide, remained low as long as the gas was administered, and returned to normal within 30 minutes of the resumption of a normal air supply. The animals' heart rate dropped nearly 50 percent during hydrogen sulfide adminstration, but there was no significant change in blood pressure or the strength of the heart beat. While respiration rate also decreased, there were no changes in blood oxygen levels, suggesting that vital organs were not at risk of oxygen starvation.

The mice kept at room temperature had the same drop in body temperature seen in earlier studies, but those in the warm environment maintained normal body temperatures. The same metabolic and cardiovascular changes were seen in both groups, indicating that they did not depend on the reduced body temperature, and analyzing the timing of those changes showed that metabolic reduction actually began before body temperature dropped.

"Producing a reversible hypometabolic state could allow organ function to be preserved when oxygen supply is limited, such as after a traumatic injury," says Gian Paolo Volpato, MD, MGH Anesthesiology research fellow and lead author of the study. "We don't know yet if these results will be transferable to humans, so our next step will be to study the use of hydrogen sulfide in larger mammals."

If this turns out to work in humans, it's obvious that keeping people alive "when oxygen supply is limited" could apply to space travel as much as to post-traumatic injury situations.

Sewer-gas induced suspended animation is rapid and reversible [Eurekalert]