I have large nitrous tank, from which I fill about 10-20 liters into a balloon. As I have no oxygen, I need to hyperventilate based either on SpO2, or on the time past after the last inspiration, so I cannot maintain 50% steady nitrous flow. Yes, I can maintain even a pure nitrous flow for 10-20 seconds inhaling the balloon into lungs, exhaling it and inhaling again without taking air. I have calculated approximate nitrous concentration I take based on respiratory rate, balloon volume and time it takes me to use. My approximate calculations showed I use about 1 liter of nitrous when I am using it for recreational purposes and about twice this amount when "pushing the limits" (I am afraid of hypoxia and do not try to use larger amounts in shorter time). When in at full rest and being a small man, I use about 5 liters of air a minute, it looks my concentration is 20-40%. Due to unsteady flow of nitrous (inhaling once a half minute-minute), immediately after the inspiration the momentum concentration can reach 50%, I think.