Let me see if I can explain this. I asked my pulmonologist the same question. He said that my lungs process the air I receive normally so my pulse ox will stay in the normal range. The problem with my breathing is that my diaphragm is weak and therefore my lungs are having difficulty pumping. (Just in case you thought like I did that lungs are muscles, they are not. They are organs and the diaphragm is the muscle that pumps the lungs) Your pulse ox will remain in the normal range until your diaphragm basically stops working. This happened to me in ICU. My pulse ox was 96, but I was struggling to breathe. The nurses didn't realize what was happening and thought I was having a panic attack. They called my docs on-call partner who ordered Atavan (which should never be given to a patient with MG) Within 30 minutes my pulse ox dropped to 36 and I had to be intubated. So, long story short, with mg, your pulse ox will be fine until your diaphragm stops working and then it will drop very fast. Don't let anyone tell you that since your pulse ox is fine, your mg is fine. Hope this helps.