Wildly fluctuating O2 levels

I don’t know about blood rushing past too fast but a technician did tell me that alveoli can be damaged by things like smoking so that the walls are tougher and the o2 molecules have a harder time getting through.
It would be like punching your fist through drywall-thicker would be harder to punch through. Maybe the blood would have gone past by the time the o2 got through.
I don’t know if diseases like Covid or respiratory infections could damage alveoli, but it might be worth looking into.

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! 🙁

Wow. You know a lot more than I do about this. Thanks for the technical explanation; I’ll have to reread it to digest it all.
I’m sure this “adventure” also comes with a cost to your mental health, as mine did.
I even went for a consult at Mayo Clinic, where I was told I do not have restrictive lung disease.
So those numbers I saw remain a mystery. I’ve taken the approach of no longer checking at home as this was really messing me up emotionally.
I am active, exercising and weight training, so I just ignore it.
If you can do half marathons then that’s very encouraging.
You mention a ventilation issue-you mean your lungs just can’t take in enough air at exertion?
Would that have to do with big lungs, normal pipes? Or is there something about the way you’re breathing that a coach could help you with? Perhaps a holistic practitioner? Have you been checked for things like exercise induced asthma?
I find it interesting that your cpap use doesn’t help the o2 levels. I also have sleep apnea, and it does make a difference. I spend much less time below 90 or 88-just minutes as I recall.
Please let me know how your visit in Denver goes.
I wish you the best, and keep on running.

I’ve been dealing with is issue for the past several weeks now. I can sit with 3 liters of O2 with my O2 showing 98/99 and my HR AT 60. As soon as I get up and start walking my O2 drops into the mid 80’s and my HR goes up to the 90s and above 110.

I would get a better pulse oximeter. I bought one that you wear on your finger (not the Aura Ring but a cheaper one) and it is much more reliable. I can wear it over night and see what is going on while sleeping. It isn't good on a treadmill or any place where you are moving a lot. The first one I bought at Walgreens wasn't reliable so went back and bought a more expensive one but then decided to buy the kind you wear on your finger like a ring. Mine called an O2 Ring by Well (from Amazon) and was around $150 I think. Not cheap but was reassuring.

I may have discovered a fairly significant piece of what is going on with me. Between dissecting my CPET data and my CPAP data and then adding in one subtle symptom.

The PaC02 numbers for my elevation were slightly elevated... basically the amount of Co2 in my blood. I don't think this triggered too much of a concern because the standards for abnormal PaCo2 is really based on being at sea level and I am 5000 feet. Also, my PaCo2 levels went up and down relative to the states of the cpet they expect so it may not have triggered anything (alhtough my paco2 was higher than normal at rest, AT, and peak exercise).

2nd. LOoking at my cpap detailed data, my drops in 02 correlate specificly with shallow breathing (hypoventilation) that doesn't trigger any apnea or hypopnea events. So basically my cpap AHI's are less than 1 every night. But when you look at my cpap detailed data(you have to get an SD card and download the software) there is obviously dysfunciton breathing happening that the cpap can't fix. Bibap is what is required to control this.

3rd, and crucial to the whole story.... Co2 tolerance while awake actually awful. This is tested by performing the bolt test (look it up). Basically breathe out a normal breathe and see how long you can hold it. This tests your co2 tolerance. I found out I can hold it for about 10 seconds (my bolt score is 6-7). Considering my overall conditioning it should be like 30. This screams major co2 intolerance.

TL/DR: My paCo2 baseline levels are too high. High baseline Paco2 causes low baseline Pa02. Low baseline Pa02 at 5000 feet elevation means low baseline sp02 and big swings with exertion, sleep disorder breathing, etc.

Anyways, this is just a hypothesis at the moment. It is certainly possible that all of this data is actually an 'effect' of other issues rather than the 'cause' but this really aligns with my overall 02 patterns.

For example, if I take a few slow deep breaths before climbing stairs, my 02 doesn't drop. Yet, i still have air hunger. This is because even getting more air into my aveloi and fixing my desat issue, my chemoreseptors in my brain still sense the increase in paCo2 and create the need to breathe more. Which is why I always have an 02 spike after my o2 drops climbing a flight of stairs.

Me too

When you say hold your breath after breathing out, does it include while your breathing out?

No. Just take a few natural breaths in out in out in out and then hold your breath on that last out. Your bolt score is how long you can hold it before the first urge to breathe. it’s obviously not a clinical test, but typically it’s a pretty good indicator of how well you tolerate CO2. For perspective, my first urge to breathe is between four and six seconds and I can’t hold that exhale for more than 15 seconds total. And the crazy thing is, I can hold an inhale for over three minutes.

It’s weird! I breath out the third time and push timer. Then about 7 seconds later I want to breathe more air out! Then hold another 7 or 8 seconds! My lungs work weird i think