So you can see 17% oxygen

There won't be that much CO2 for a long time, even if we increase our carbon output. Currently it stands at around 0.04%, third to argon at a bit under 1%. Oxygen is just under 21%. Oxygen and nitrogen together make up over 99% of the atmosphere (at sea level). That's for dry air, otherwise water vapour is at around 1% and the others reduced to fit that in.

Unless you are blowing from an oxygen tank. You don't need to use your lungs.