Hi marylpn!
Good questions.
When I was put on o2, the doctor warned me about having too high of a concentration of oxygen. That I were to remove the cannula when my o2 got back into the nineties. This cover most of the time that I am just sitting around surfing the net or watching TV.
Lately, though, my oxygen can plummet when standing, like making a meal. It gets even worse when I try to clean my apartment or exercise. I've had it as low as the mid 70's.
Recently I was upped in my dosage from a 2LPM flow to a 3LPM flow when I'm taking a casual walk (my choice for passive exercise). I usually get up to a 4/5LPM flow on the treadmill and elliptical trainer.
My night time flow is to remain at 2LPM, and the initial instruction to go off the o2 when my blood oxygen is above 90 still stands.
As for the trapped air, pursed lip breathing may help especially with a puffing of air at the very end.
The use of a spirometer ten times followed by intentional gentle coughing has gotten my lungs to clear and made my breathing easier.
Drinking water can thin the contents of the lungs and make coughing up mucus, and breathing, easier. The use of NAC, if available, may help. I was using it to help clear my lungs for years, it doesn't seem to help anymore.
Sorry for getting 'long winded'!
The Best!
Will