By decrease I mean systematically, but 0,5% from the basic 21%. I am aware that the oxygen level is always the same, though the air pressure makes it a little bit more diluted on higher attitudes, and our kidneys, if my memory serves, start to produce more erythropoietin then, untill the level of erythrocytes in our blood system reaches the proper level to transport more oxygen molecules. But, I am curious, what effects would lower and lower level of oxygen force on our bodies, and by what percentage drop would we actually die?
Thank You.