BehindTheMedspeak: Hydrogen sulfide (the smell of rotten eggs) slows metabolism — and might produce suspended animation

Just published in the April, 2008 issue of Anesthesiology is a paper describing how low doses of hydrogen sulfide — a major component of sewer or swamp gas — markedly reduced oxygen consumption, carbon dioxide production and heart rate in experimental mice, with the animals returning to normal within 30 minutes of being given normal air.

Here's the abstract of the paper.

Inhaled Hydrogen Sulfide: A Rapidly Reversible Inhibitor of Cardiac and Metabolic Function in the Mouse

Background: Breathing hydrogen sulfide (H2S) has been reported to induce a suspended animation-like state with hypothermia and a concomitant metabolic reduction in rodents. However, the impact of H2S breathing on cardiovascular function remains incompletely understood. In this study, the authors investigated the cardiovascular and metabolic effects of inhaled H2S in a murine model.

Methods: The impact of breathing H2S on cardiovascular function was examined using telemetry and echocardiography in awake mice. The effects of breathing H2S on carbon dioxide production and oxygen consumption were measured at room temperature and in a warmed environment.

Results: Breathing H2S at 80 parts per million by volume at 27°C ambient temperature for 6 h markedly reduced heart rate, core body temperature, respiratory rate, and physical activity, whereas blood pressure remained unchanged. Echocardiography demonstrated that H2S exposure decreased both heart rate and cardiac output but preserved stroke volume. Breathing H2S for 6 h at 35°C ambient temperature (to prevent hypothermia) decreased heart rate, physical activity, respiratory rate, and cardiac output without altering stroke volume or body temperature. H2S breathing seems to induce bradycardia by depressing sinus node activity. Breathing H2S for 30 min decreased whole body oxygen consumption and carbon dioxide production at either 27° or 35°C ambient temperature. Both parameters returned to baseline levels within 10 min after the cessation of H2S breathing.

Conclusions: Inhalation of H2S at either 27° or 35°C reversibly depresses cardiovascular function without changing blood pressure in mice. Breathing H2S also induces a rapidly reversible reduction of metabolic rate at either body temperature.

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An American Society of Anesthesiologists (ASA) press release on the work began, "Imagine a substance that could facilitate safe long-term space travel in 'suspended animation' without using resources such as oxygen or food in the space capsule, a substance to help with organ preservation during surgery, and one that offers an on-demand decrease in metabolism while preserving cardiovascular function, especially after major wounding on the battlefield."

Dr. Warren Zapol, chief of anesthesia and critical care at Massachusetts General Hospital, who led the study, said, "Our research showed that breathing low concentrations of H2S rapidly and reversibly depresses metabolism in mice, yet preserves cardiovascular function. These properties may be exploitable to protect organ function when supplies of oxygen are limited, such as during or after major trauma or during surgery."

He added, "Thus, the ability to induce a reversible hypometabolic state, avoiding the damaging effects of hypothermia, could be a valuable and novel field tool for treatment of severely injured patients."

You can read the article in its entirety here.