SpO2 Drops Not Correlated with Apneas

[SunMesa]

I've been monitoring SpO2 for a number of months now, since before any sleep tests or PAP therapy.

I had seen my doctor complaining about tinnitus, which always got worse when I was additionally suffering from symptoms associated with OSA (daytime fatigue/somnolence, mental fog, etc). The doctor sent me first to an audiologist for a hearing test. It was the audiologist who commented, almost in passing, that low blood oxygen can cause (or exacerbate existing) tinnitus! That's when I began monitoring SpO2 with a Wellue O2Ring.

It revealed that my SpO2 was dropping significantly (to 83-88%) for extended periods, almost always at night, but very occasionally also during the daytime.

A subsequent Snap Diagnostics sleep test indicated mild-to-moderate OSA, and I eventually started APAP therapy. Now, using OSCAR, I import the O2Ring data so I can see it alongside the various levels/events data from the AirSense 10 APAP unit.

As I've noted in a previous thread, my OSA's disappeared completely with APAP, beginning with the first night, and have never reappeared. Unfortunately, they were replaced by (generally somewhat fewer) central apneas, which remain persistent after 12 nights now. I gather this is not uncommon, at least initially (treatment-emergent CSA's).

The SpO2 levels improved substantially with APAP at first, but lately have become erratic again, often looking the same as pre-APAP.

But what I find baffling is that these SpO2 drops have no time correlation at all with either CSA or hypopnea events! E.g., the nearest CSA/hypopnea event may be separated by an hour or more from a low SpO2 interval. Conversely, my SpO2 levels are commonly in completely acceptable ranges (93-95%) during time intervals that contain apneas.

For those on the forum who are also monitoring their SpO2 along with the standard OSCAR parameters, have you experienced anything similar? Intuition certainly suggests that low SpO2 should be concurrent with, or follow very soon after, an apnea or hypopnea event, unless the SpO2 drops have some other proximate cause altogether. Thanks for any feedback!

[G. Szabo]

My oxygen saturation is strongly correlated with OAs and Hs; and even with small irregularities in my breathing (flow rate disturbances).  Sometimes there are a few seconds delay, which might depend on the sincronisations of the time axis of the two devices.   

Have you tried to correlate your oxygen saturation with your flow limitation distribution?

[SunMesa]

Here are what seem to be relevant OSCAR plots from the vicinity of the two dramatic SpO2 drops from last night. The first is a drop from 94% to 87% over the course of  ~3 min, the second a drop from 94% to 85% over the course of ~1.3 min. I have the SpO2 intervals of interest highlighted in yellow:

       

I included the flow limit plots, though I must confess I'm not sure exactly what flow limit signifies.

The first SpO2 drop seems to have some possible clues in the ~30 sec preceding it: odd glitches in flow rate, leak rate climbing then dropping to zero, significant fluctuations in tidal volume and respiration rate, as well as some physical movement. But definitely no apneas or hypopneas anywhere nearby.

The second SpO2 drop is more dramatic and quicker, and doesn't have any obvious immediately preceding incidents or events associated with it, certainly no apneas.

[cdplatt]

My O2 desaturations also track very closely with my OA and Hypopnea events.  When they don't, it's because the time on my Airsense 10 is not in sync with my Wellue ring.  The only time it was off by an hour was when I neglected to update the time on my Airsense for daylight savings time.

Have you checked to ensure your Airsense 10 has the correct time set? If you notice that the time isn't in sync, correct the time on your Airsense in the clinical menu.  If you know you started your ring and the Airsense at about the same time, you can change the start time in a Wellue/Viatom binary data file by changing the time in the binary file name.  That will allow you to sync with an Airsense recording that had an incorrect start time.  Even though the time in the two files won't be correct, you will at least be able to correlate events.  Purge the O2 data for the day you're concerned about.  Change the binary file name and then reimport the file.

Example:  Change 20240803232730 to 20240803235930

[G. Szabo]

The first SpO2 drop seems to have some possible clues in the ~30 sec preceding it: odd glitches in flow rate ...

The second SpO2 drop is more dramatic and quicker, and doesn't have any obvious immediately preceding ... 

Before your second saturation drop, there are flow rate disturbances and flow limits (this latter is a more sensitive indicator than the OSs and Hs). These (and the disturbances in your first plot) are enough for my saturation to drop from 96% to 90%.

One of our members uses the following trick to "check"  or mentally correct the synchronization: He shakes the ring by shaking his wrist and simultaneously withholds his breath or takes some quick breaths to generate an easily recognizable pattern on the time axes of both the flow rate and the ring.

[SunMesa]

@cdplatt:
I had considered that, and have verified by various methods (e.g., movement and pulse rate jumps in the O2Ring correlated with shutting off the AirSense 10 to go to the bathroom) that the two devices are in close time synchronization, certainly within ~1 min.

@G.Szabo
Do you know the physical mechanism by which SpO2 would dramatically drop in this circumstance, absent an actual apnea or hypopnea? And, what is flow limit actually telling you? Thanks for any insight.

[G. Szabo]

 what is flow limit actually telling you? 

From Wikipedia: "Flow Limitation (FL)—Partial closure of the upper airway, which impedes the flow of air into the lungs." 
The answer is self-explanatory: you do not need complete obstruction to have reduced oxygen intake. 

[SunMesa]

Ah, I see. So, in practical terms, flow limitation is just a milder form of hypopnea. Indeed, according to the Wiki (which I obviously should have consulted earlier): Hypopnea = 50% to 80% reduction in airflow for >= 10 seconds, and Flow Limitation = <50% reduction in airflow for >= 10 seconds.

But that certainly isn't helping me make sense of the data. If flow limitation is sufficient to induce those kind of drops in my SpO2, why don't hypopneas, or even full-blown apneas, have that effect? I should think they would be even worse.

[G. Szabo]

Your case does not align with my experience and the trends I am familiar with. 
Are you sure that your oxide sensor is not loose? Try to secure it with some tape and move it to a thicker finger.

[SunMesa]

The O2Ring is on my left index finger, and quite snug... just short of constrictive. The data from it showed good correlation with the equivalent sensor used during the Snap Diagnostics sleep test I took back in May.

It really is puzzling, and does suggest something other than just breathing issues (or at least those that can be addressed with APAP) is affecting my SpO2. An echocardiogram last week showed borderline mild pulmonary hypertension and slightly elevated right atrial pressure, results that my doctor didn't seem particularly concerned about. He is equally puzzled about the uncorrelated SpO2 and apnea data. Getting a chest CT scan later today.

Did not use the APAP last night... SpO2 levels were mildly improved, but still over an hour below 90%, with ~half-dozen brief excursions down to 86%.