Air you breathe out is around 40 thousand ppm (and higher during exertion), and the air in the lungs isn't completely replaced every breath - I doubt there's mu

Air you breathe out is around 40 thousand ppm (and higher during exertion), and the air in the lungs isn't completely replaced every breath - I doubt there's much measurable difference at the actual alveoli at the levels we're talking about. You'll probably get more of a difference if you're breathing deeper and faster, or just got up to get a coffee or similar. And interestingly there are studies that show that breathing in air up to 3% co2 (30k ppm) "did not substantially impair either cognitive and motor performance" [0] [0] https://www.tandfonline.com/doi/epdf/10.1080/10803548.2007.11076705 https://www.tandfonline.com/doi/epdf/10.1080/10803548.2007.1...