Trying to determine lowest effective ASV settings

[Gideon]

In that case you would see UA events.

[Utah Desert Rat]

In that case you would see UA events.

Thanks for answering SonOf's question, I was beginning to wonder about that myself since I just had my third straight night of 0.00 AHI. 
Even if the machine was misreporting events, I'll settle for that placebo effect! ;-)

[SarcasticDave94]

A zero AHI is good if/when it happens, and better if you're well rested and comfortable for it. It sounds like this what you've got going on.

[Sleeprider]

The Aircurve 10 ASV assumes any failure to achieve spontaneous trigger to IPAP or an "apnea" is central and will use up to the maximum pressure support allowed by settings to facilitate or cause a breath. If that does not happen because the pressure support is too low or there is obstruction, the system flags a UA (unknown apnea) and increases EPAP pressure based on the algorithm that assumes any untreated apnea is obstructive. The ASV can be undermined by setting the maximum pressure support too low.

[SonofBiPAPuser]

Thank you for the answers! I appreciate it.

[Utah Desert Rat]

The ASV can be undermined by setting the maximum pressure support too low.

But if I’m reading you right, it still flags events, yes? If true, then my zero AHI is a real number.

My central sleep apnea is related to medication. My sleep doc described it as a “signalling” failure, i.e. my brain is not telling me to breathe when my O2 is low due to the hypopneas. Apparently it doesn’t take much pressure at all to goose my “signalling” software and get it going again.

One thing I’ve noticed: my SpO2 level during the day seems generally higher than it used to be. I’ve been spot-checking it a few times daily, and it runs around 97-98%, where it used to be around 95% before I started CPAP therapy. This has been quite a ride.

[Sleeprider]

My central sleep apnea is related to medication. My sleep doc described it as a “signalling” failure, i.e. my brain is not telling me to breathe when my O2 is low due to the hypopneas. Apparently it doesn’t take much pressure at all to goose my “signalling” software and get it going again.

This is interesting, and somewhat incomplete.  The signaling failure is when you do not respond to hypercapnia, when CO2 rises. Respiratory drive is generally less a function of hypoxia, but it does seem to go hand-in-hand with hypercapnia.  I completely agree that a machine triggering IPAP can cause many individuals to spontaneously take a full breath, even when pressure support is not set high enough to fully overcome the complete absence of spontaneous effort.  Good observation, but respiratory drive arises from changes in blood chemistry from CO2 as received by the medullary chemoreceptors and carotid bodies, but is mediated by a hypoxic response in the carotid bodies. The longer more technical story is here, although the important takeaway is you're breathing fine, even if it is not entirely the ASV driving it. https://www.sciencedirect.com/topics/med...moreceptor

[Utah Desert Rat]

Thank you for that in-depth explanation, I actually understood most of it -- from a sort of 50,000 foot height! ;-)

The "O2 is low due to the hypopneas" part of my post I mostly pulled out of a hat when I couldn't remember exactly what my sleep doc had said. Now I've had a chance to think about it, what he talked about had to do with vagal signalling. I looked around and found this on Wikipedia which, together with your explanation, is beginning to pull it all together for me nicely:

The feedback from the carotid body is sent to the cardiorespiratory centers in the medulla oblongata via the afferent branches of the glossopharyngeal nerve. The efferent fibres of the aortic body chemoreceptors are relayed by the vagus nerve. These centers, in turn, regulate breathing and blood pressure, with hypoxia causing an increase in ventilation.

I bought a recording oximeter that should be arriving today (thanks to CZOscar and his excellent review of the Wellue 02 ring). Hopefully that will shed a little more light on this weird response!

[Sleeprider]

Technical issues on respiratory drive aside, you seem to be doing extremely well with low pressures. How do you feel?

[Utah Desert Rat]

Technical issues on respiratory drive aside, you seem to be doing extremely well with low pressures. How do you feel?

In a word, Wow! I haven't had this much energy in well over a decade -- and it lasts all day. I never was a "morning person", but now I don't bite my husband's head off if he tries to speak to me before 10 a.m.! 

Even though it still takes me 30-40 minutes to get over the machine and fall asleep, I sleep much more deeply most nights and wake up actually refreshed. Interestingly, I used to get quite a few dyspnea spells during the day, now I almost never do (and we live at 3,000ft elevation!) It's almost as if my breathing software just needed a "reboot"! 

Of course I know it's not a "durable" fix, but I'm grateful I was fortunate enough to find the right mask (no thanks to my DME, which I'm dumping for AeroFlow Sleep) and help to get my machine settings to a comfortable level so I can settle down with the therapy long term. 

I've been taking opioids for severe refractory RLS/PLMD for something over 4 decades, I'm surprised it took as long as it did for the opioids to finally affect my breathing this badly. I was gratified to discover that ASV machines are just the ticket for my type of sleep apnea: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4106939/

Thanks to everyone in the community for all the info and support!