Key to Suspended Animation? Sewer Gas
Researchers have discovered that exposure to hydrogen sulfide - the chemical that gives sewer gas and rotten eggs their putrid smell - can put mice in a state of suspended animation. If similar exposure could do the same for humans, it could open up whole new areas of medicine and experimental research.
"Hydrogen sulfide is the stinky gas that can kill workers who encounter it in sewers; but when administered 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 Massachusetts General Hospital. Zapol and his colleagues' study is published in the journal Anesthesiology.
For the mice in the study, even low doses of hydrogen sulfide caused their bodies to slow down. The animals' heart rates dropped by 50% within 10 minutes of exposure. Their consumption of oxygen and production of carbon dioxide dropped significantly, and their respiration rate and metabolism also decreased - they entered a "hypometabolic state."
However, their major organs continued to function. The strength of their heart beats remained the same, as did their blood pressure and blood oxygen levels, which implied that their vital organs weren't at risk for oxygen starvation or permanent damage.
Generally, when in a state of suspended animation, an animal's body temperature decreases. This was also the case for the mice in the study. But the researchers also wanted to find out if the decreased body temperature was the sole cause of decreased metabolism. They kept one group of mice in an environment of 98 degrees F, so that their body temperatures remained high. This group experienced all the same symptoms as the control group, suggesting that body temperature itself did not cause the decrease in metabolism.
All the mice remained in a state of suspended animation as long as they were exposed to the low level of hydrogen sulfide. After several hours, the researchers removed the gas. Within 30 minutes, the mice returned to normal.
The researchers don't know if humans would react the same way as the mice. Since hydrogen sulfide is toxic to large animals, the chemical might have to be administered intravenously to prevent lung toxicity.
If humans could be induced into a state of reversible suspended animation, the technique could help save time after a traumatic injury by reducing the body's oxygen requirements, allowing more time for them to reach the hospital.