Bill66 made this as a comment a few days ago. I think it is a topic worthy of further discussion. Clearly as COPD'ers we experience SOB with little or no provocation. I know I can walk from the bedroom to the bath in the morning with O2 in the low 90's and can hardly breath. Watching the oximeter, as my pulse reduces, O2 will increase as I use PLB. Thus, is the purpose of PLB in effect to expell CO2?