So long story short had battery of tests and heart is fine. I purchased a very expensive medical grade oximeter- Nonin 3250 OTC. My o2 drops rapidly when I start walking with it on and it is supposed to be accurate enough to do this. I mean down to the 70s. Does seem to come back up rather quickly if I sit. However, if I use it to spot check during exercise, it is never low. Does this mean I would fail 6 minute walk test and be prescribed supplemental o2? Shpuld I trust the oximeter?I don't go to new pulmonologist until the end of next month.