Unless I'm missing it there isn't anything in the paper or the article about oxygen. The paper mentions facial alkalinization and indirect increase in dehydration. Limiting oxygen seems unlikely, CO2 build up however is a different story (and harder to actually measure).
Does a mask significantly limit your supply of oxygen?
For a healthy person at rest - your lung is only doing 5% of what it is capable of.
It would obviously take some extra work to breath around the mask.
But it also takes some extra work to breathe when you are walking or talking.
Unless I'm missing it there isn't anything in the paper or the article about oxygen. The paper mentions facial alkalinization and indirect increase in dehydration. Limiting oxygen seems unlikely, CO2 build up however is a different story (and harder to actually measure).