Barbara, you have asked the million dollar question … for which there is no good, right, or acceptable answer in all cases. So, this is a question that depends on clinical judgment.
I approach these patients with some simple tests:
1) Can the patient talk in full sentences? (If so, then I’m more comfortable. If they must breathe every other word or so, that’s not good lung function.
2) Can the patient climb a flight of stairs without stopping?
3) Can the patient walk 100 feet without stopping? (I realize that patients with terrible diabetic foot ulcers simply cannot walk, but you get the point.)
As far as pulmonary function tests, there is no number set in stone for FEV1 or FVC … or anything else. Basically, my rule of thumb is to depend on the pulmonologist. If he/she comes back with mild or even moderate obstructive lung disease, that is responsive to bronchodilator, then take the patient whenever the pulmonologist says that he/she is maximally treated.
If I were to put someone in the chamber with moderate COPD/Emphysema, I might consider bringing the chamber from pressure to surface a little slower than usual. If you have a 5 minute decompression, then make it 10 minutes. If the CT scan showed large blebs, then I might think about not treating the patient at all. In that case, you run the risk of the bleb enlarging or rupturing with repeated treatments.
I hope this helps, but my standard answer stands for this patient … “It depends.”