I agree this is good to run to ground. But one thing to keep in mind is that I believe the oxygen that one exhales is about four percentage points lower than inhaled. That means on average in the lung the oxygen is about two percentage points lower, meaning the average carbon dioxide level is about 20,000 ppm. So I would be surprised to see big impacts based only on CO2 changing around 500 ppm because you can get bigger changes in the lung CO2 just by changing breathing rate slightly.
I agree this is good to run to ground. But one thing to keep in mind is that I believe the oxygen that one exhales is about four percentage points lower than inhaled. That means on average in the lung the oxygen is about two percentage points lower, meaning the average carbon dioxide level is about 20,000 ppm. So I would be surprised to see big impacts based only on CO2 changing around 500 ppm because you can get bigger changes in the lung CO2 just by changing breathing rate slightly.