SpO2 Drops Not Correlated with Apneas

[G. Szabo]

... SpO2 levels were mildly improved, but still over an hour below 90%, with ~half-dozen brief excursions down to 86%.

It is concerning, indeed

[BigWing]

I have been monitoring my SPO2 with a Wellue SleepU - and my sleep rotation with SomnoPose - for several months now. I spend an hour or more every morning synchronising all the data to within a second or two (using my sniffing and wrist twisting clapperboard) and studying everything. 

I do not see a good correlation between apneas or hypopneas with oxygen (either drops or general levels). 

I do not see any correlation between AHI and ODI. 

I do not see a good correlation between oxygen level and flow limitation. 

I think I see more correlation between CA's and oxygen drops, to be honest.

I too wonder what is really affecting oxygen most of the time. I often see very obvious periods where SPO2 is at a different level and which start and end at an arousal (as seen by a brief change in the Flow Rate waveform, a spike in the oximeter's Movement waveform and a step in SomnoPose's Orientation and Inclination signals). Perhaps caused by a slight change in chin tucking?

[Crimson Nape]

For the SpO₂ to display a drop at the apnea event, the sensor would have to be in the lungs.  The drop time offset is dependent on how far away the sensor is from your vital organs, your pulse, and any arterial restrictions.
- Red

[SunMesa]

Perhaps caused by a slight change in chin tucking?

I'm pretty certain chin tucking is not a factor in my case, but I have wondered about possible positional effects on O2 levels or even the O2 sensor itself. I've tried constricting my arm upstream of my O2Ring-ed finger, but it doesn't seem to have any noticeable effect on the SpO2 values. But maybe over a longer period of time of, say, sleeping on the arm with the sensor?

[SunMesa]

For the SpO2 to display a drop at the apnea event, the sensor would have to be in the lungs.  The drop time offset is dependent on how far away the sensor is from your vital organs, your pulse, and any arterial restrictions.

That's a good point, there has to be at least some delay. But from a cursory review of online sources, the round trip time for blood to go from the heart to the extremities and back is generally estimated as ~1 min or less. A delay of 1+ hr between oxygen deprivation and a response at the sensor seems hard to fathom.

[ArcherNeedsSleep]

My SpO2 drops never seemed to correlate with events, either, and I was spending more than half of each night in the 80's!  I "technically" don't even have sleep apnea based on my sleep study, and my AHI was always below 1, so there was clearly another reason for the drops.  (I don't have any lung or heart issues, so there was no known cause other than altitude.)

The changes in my SpO2 actually appeared to correlate more with sleep phase.  I seemed to drop into the 80s in deep sleep and REM, but be ok in lighter sleep stages.  Although I haven't found any studies that address the topic, I suspect that there are some physiological changes going on in the different stages that could impact the body's' effectiveness at absorbing O2 or its drive to breath in a new air supply regularly.

I'm not sure if this analysis applies to your situation, but it's something to consider if you can't line your SpO2 drops up with apnea events.

I still don't have a true explanation, but the folks on this board convinced me to request supplemental oxygen from my doc, and life is now 1000% better.

[SunMesa]

ArcherNeedsSleep, thanks for your very intriguing reply.

I haven't had a full polysomnogram, but I'm now scheduled for one (soonest available was 27 Aug). As such I can't really say what phase of sleep I'm in when these happen, although they seem to happen somewhat toward either end of the overall sleep interval, rather than the middle.

When I read your post, by coincidence I was literally in the process of drafting a message to my primary care physician to inquire about trying supplemental oxygen instead of the PAP device, more for immediate mitigation than for a long-term solution.

I'm very concerned about chronically low SpO2 causing permanent damage, including to the brain, and am not comfortable waiting for the effects of PAP therapy to 'kick in', possibly months down the road, if ever. I'd frankly say I'm already experiencing negative cognitive effects, and if supplemental O2 is potentially effective (even if only palliative), I'd definitely try it, hoping to get at least some degree of short-term control. The status quo feels like complete helplessness.

[BigWing]

I still don't have a true explanation, but the folks on this board convinced me to request supplemental oxygen from my doc, and life is now 1000% better.

That's good to hear.

I've just had another good look back in my charts, and I haven't yet found an OA  (or Flow Limitation) which seems to affect SpO2. Here's a typical example (with CPAP & Oximeter sync'd to within 1 second), and you can see no drop in SpO2 after the OA. The H's are a slightly different story though....

The first H seen here also seems to have no effect on SpO2, as I find in roughly half of H's.

The second H does coincide with an SpO2 drop, but I think this is more to do with the general stopping/starting/reduction of breathing. The ResMed 10 sometimes flags part of that as an H, as seen here, but often doesn't. 

Hence I say that there seems little correlation between SpO2 drops and OA's or H's. 

[Crimson Nape]

Maybe I'm not reading this correctly, but it appears that as your flow rate volume diminishes, so does your SpO₂ level too.
- Red

[BigWing]

Maybe I'm not reading this correctly, but it appears that as your flow rate volume diminishes, so does your SpO₂ level too.
- Red

I thought that's what I was saying? The SpO2 falls when breathing amplitude falls - not just when there are OA's or H's.