Like so many of us, this is such a complicated puzzle and there are so many factors contributing to how are bodies regulates blood oxygen. Why my dr's have all said there isn't much more we can do for you is because all my testing comes back pretty normal and I appear healthy. They say if my 02 numbers really are what I tell them they are you wouldn't be able to run 15 miles like you do. My DLCO was actually 120% of predicted. Also, my a-a gradient (for those who have done CPET you might know about this) is 4 at rest. Because chat gpt can explain it better than I can, here is what an a-a gradient of 4 means: A resting A–a O₂ gradient of 4 mm Hg (≈ 0.5 kPa) means that the partial pressure of oxygen in the alveoli (PAO₂) is only 4 mm Hg higher than the arterial PO₂ (PaO₂). That is very low—well below the usual upper-normal limit of ~10–15 mm Hg in healthy adults—and indicates exceptionally efficient gas exchange with no evidence of ventilation–perfusion mismatch, diffusion limitation, or shunt at rest.

My a-a gradient at peak exercise was also normal as well. However, my pao2 at peak exercise was at the low end of normal, so even though my a-a gradient was normal (meaning good gas exchange) I believe this is where some clues suggest that the issue may be entirely 'ventilation'. Which does makes sense, low tidal volumes at rest, you hit a flight of stairs at 5000 feet and wham, o2 drops to 83% and quickly recovers. The issue becomes, when I go for a run, and my breathing has picked up, why does my 02 fluctuate between 84 and 89.... the harder I run the lower it goes. But I can literally pace my o2 in my runs by knowing what my heart rate is.

Lastly, learning the science behind all these numbers and tests has been quite enjoyable.... unfortunately it comes at the expense or my health! 🙁