I have BTM, and i am on 24/7 oxygen therapy. FYI, I had massive pulmonary emboli a few years ago which probably damaged my lungs (although pulmonary function tests were normal). So pls keep in mind that my problems could be from damage caused by the PE's. About 18 months after the pe's, I had a sleep study done and my O2 sats were below 84 while I slept. Started on O2 at night only, but within 6 months was on O2 constantly. What is interesting is that during even mild exertion, my O2 sats stay 98-100, but my heart rate goes up (I know, your HR is supposed to go up with exercise, but mine goes way up just by walking across a room.). Doc (who does not believe BTM can cause symptom) says I have signs of Right Heart Stress (pre-congestive heart failure) and mild PHT. The O2 is to keep any additional strain off my heart rather than keeping my O2 sats up, Per doc this is all from PE's, but doesn't make sense as lung study was normal. Personally, I think the BTM is responsible, whether because that is what caused the PE's or because BTM is the primary culprit. Interestingly, even on Oxygen therapy, (and turning up the flow rate) I get short of breath with mild exertion---just as I always have. Seems to me my blood doesn't carry enough O2, which would make BTM the culprit. I have also noticed that my blood pressure fluctuates--sometimes a lot. It's always been low or normal, but sometimes now the systolic will go up as high as 165-170, even when I'm resting, while the diastolic can stay normal or is also sometimes be a little elevated.