Low O2 Levels During Sleep with Low AHI

[cmpman1974]

Wellue makes a great SPO2 and pulse monitor that is called O Ring.  You can use it in Oscar.  Lanky Lefty has a video on it.  I use Sleep SQ because I find it easier with a Chromebook.

In my opinion, none of these are truly accurate, but they give a general baseline.   I proved that to myself after trying a few products.  They are FAR from medical grade.  Better than nothing though, but don't base anything important on them.

[StuartC]

Is it possible to have acceptable AHI numbers using a CPAP/BiPAP, but still drop O2 levels on an oximeter to bad levels during sleep? 

Going back to your original question, yes, you can.  It happened to me.

Responding to you most recent reply, I have a background that includes some instrumentation so I consider  three parameters that are relevant -  resolution, repeatability and accuracy. 

• The resolution of the O2ring is stated as 1, which means, for example, everything that it determines to be in the range 94.50% to 95.49999...% is recorded as 95%.  Put differently, a 1% drop is recorded as such.  It should mean that a 10% drop is similarly recorded as such.  Comparing my ring to the oximeter used in sleep studies, the ring's performance was pretty close and quite acceptable for what I needed. 
  
• Repeatability means that whatever value it reads for a particular SpO2 level, it will always read that same level at different times at night and on different nights. My SpO2 drops were extremely consistently linked to REM, and they were equally indicated by my ring and the sleep study oximeter.  I have developed a good opinion of the ring's repeatability. 
  
• Accuracy is the least important of these, it is always questionable without calibration.  Is it really 90%, or is it 89%, 91? or something more different than that.  There were some differences between my ring and the sleep study ring, especially below 85%, but it is more important for me to know that it has dropped by an amount in the rage of 10% than to know precise values.  Overall, I find the ring helpful.
  

My oxygen desaturations were caused by drops in minute vent, which were caused by drops in respiratory rate (from 15+ to 10 and below) that were not compensated for by tidal volume.  Apparently that is unusual, I certainly have not seem anyone else who exhibits that behaviour.  I have not been able to see many charts of yours that have helped me understand what is going on for you.  Personally, I have found that the charts I look at regularly are Flow, SpO2, Pressure, respiratory rate, tidal volume and minute vent.

I use iVAPS but I use it as "adaptive ST".  I do fine with EPAP = 5, PS = 5 in NREM, but need to increase PS to 7 during REM, when Mv drops.  If I increase PS when Mv is "normal", I suppress respiratory rate, causing the backup rate to take over.  So I set my target Mv about 15% below my spontaneous Mv achieved when PS min applied.  For me, that means my target Mv is 5.3 when my MV should be, and is typically, 6.2.  I have explained it in more detail in https://www.apneaboard.com/forums/Thread...#pid462207 .

Are you aware of this calculator? https://ivapscalculator.resmed.com/

I set Ti Max at 30 / Background Backup Rate (BBR).  Since my TPR is 15,  BBR is 10 and so my Ti Max is 3.0 s.  It is possibly a bit long, except as I fall asleep with RR of about 10, but I don't seem to need it shorter.

I was told Rise Time could be increased, even to its max value of 900 ms, "for comfort" providing I do not have COPD / an obstructive lung condition.  I don't particularly believe "for comfort" statements but it is closest to Easy-Breathe, where my rise time was almost 1.5 s and my spontaneous trigger (i.e mandatory backup not active) increased when I increased Rise Time, so I kept that setting.  You do need Ti min to be longer than Rise Time, so mine is set to 1.0 s.