According to Roth, suspended animation occupies the end of a continuum of metabolic flexibility and occurs when "the degree to which an organism ‘burns' oxygen, and produces carbon dioxide drops to zero. The candle is not burning, so to speak.” In Roth's candle analogy, organisms are like candles in that our cells consume or "burn” oxygen and fuel to create carbon dioxide and water. In candles, this burning produces light, while in us, it produces energy. This process of consuming oxygen to produce energy is called metabolism.
Roth's finding that you can induce a state of suspended animation in mice by exposing them to low levels of hydrogen sulfide, coupled with the fact that this gas is present in our bodies in small amounts, suggests to him that this toxic gas may be the key to stopping metabolism on demand.
"It's quite profound the role sulfides play in our ability to control the degree to which we burn,” Roth says. "You could almost begin to think that the regulation of the ability to use oxygen is being dictated by the amount of sulfide present.” So the more H2S that is present, the less O2 gets burned, and the slower our metabolism will be.
Samuel Tisherman of the Safar Center for Resuscitation Research at the University of Pittsburgh explains why this is important: "There are many acute disease states that lead to limited oxygen supply to either specific organs or the entire organism.” This list includes two of the three leading causes of death in the United States: heart attack and stroke. If these patients could be quickly placed in a state of suspended animation, it could forestall the death of vital organs and tissues that normally occurs when oxygen demand exceeds its supply.
There is little evidence besides Roth's that hydrogen sulfide is capable of influencing metabolic rate in animals, and no evidence yet in humans. This line of research is in its infancy, as Roth likes to say. But if the gas does turn out to do the same in humans as it did for Roth's mice, the payoff would be nothing short of breathtaking.