I bought a pulse oxygen sensor after seeing the meme yesterday showing your O2 levels plummet from using a mask for 20 minutes.
I am 45 and have well taken care of asthma, test done while sitting on couch watch tv, in an air conditioned room set at 75 F.
I was 98% O2 when I started the test… my level dropped to 96% almost immediately. I noticed after about 18 minutes I started feeling like I needed to take deeper breaths I was at 95% at 20 minutes at 25 minutes it was down to 94%… I then coughed involuntarily clear my lungs a bit and O2 shot back up tp 98% almost immediately. Back down to 96% after a few more minutes. When to took the mask off my O2 level went back to 98% almost immediately.
My conclusion is that it makes it harder to get in air, but not extremely so. The results might be worse for people who aren’t strong enough to take the deeper breaths required.