“Lowered arterial oxygen” – that means lowered oxygen in the bloodstream, doesn’t it? Surely, that’s very unlikely from a mask; bodily homoeostasis would simply increase the breathing rate to compensate, or the urge to tear the mask off would become unbearable. That, or we’d have people fainting in winter from wearing scarves.
“If you take a barrel of sewage and add a spoonful of wine, you get sewage.
If you take a barrel of wine and add a spoonful of sewage, you get sewage.”
There’s a lot of it about.