It's not entirely new concept, but most "freediving nerds" will probably find this interesting.
The Journal of the American Society of Anesthesiologists, Inc. - Anesthesiology Fulltext: Volume 108(4) April 2008 p 659-668 Inhaled Hydrogen Sulfide: A Rapidly Reversible Inhibitor of Cardiac and Metabolic Function in the Mouse.
Money quote:
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.
Bit hesitant to post it, but since it's only a matter of time someone discovers it, I guess I might as well...
The good news is that you should be able to spot cheaters pretty easily from the stink
