Extended high flow limits -- what process is going on?

[cathyf]

A couple of nights ago I had a night where I went from Queen of Flow Limits to Empress of Flow Limits!

[attachment=32747]

My typical flow limit line is very up-and-down jaggy, and we have had discussions of the mechanism, which is flow limits interrupted by arousals on the one hand, or apneas on the other. But I don't think I've ever seen a night like that, with multiple long periods of time where the FL line comes up off zero and stays off zero. And I don't think that I've ever seen anyone else ever post such a flow limit graph, either.

That's a median FL of 0.11!

Can anyone tell me what my machine was trying to tell me was going on?!?

Has anybody else seen this sort of data?

[SarcasticDave94]

I've not seen that FL detailed and with up and down movements of this sort. I'd typically tell others you need higher pressure or to advocate for a VAuto for more PS than the EPR 3 can give.

[cathyf]

I've not seen that FL detailed and with up and down movements of this sort. I'd typically tell others you need higher pressure or to advocate for a VAuto for more PS than the EPR 3 can give.

But the response is going to be "but why do you need that?"

I had only one "event" which was a classic sleep/wake junk anyway -- I was clearly awake in the flow rate curve before it, and it ended literally 1.8 seconds before I pressed the power button.

I had no significant desaturations.

The flow limits weren't causing much in the way of arousals -- my point about the long flow limits is that I seem to be sleeping quite peacefully through them!

The one thing that I see as a real problem is that I got only 31 minutes of deep sleep, with an awakening cutting off each time I got there. In that way that strange night wasn't different from normal nights -- for sleep stages here are my statistics:
Saturday / 30-dayAverage / Benchmark (for 58-yr-old women)
Awake: 8.5% / 12% / 12-24%
REM: 30.8% / 26% / 15-25%
Light: 54.1% / 55% / 40-60%
Deep: 6.6% / 7% / 8-16%

Given those numbers, it's hard to make an argument that I need pressure at all, let alone pressure support!

What I'm really trying to get a handle on is this -- are my very impressive and very unusual flow limits pathological? Or do I have unusual anatomy that I have successfully adapted to over a lifetime of breathing through my naturally-narrow airway?

Can someone explain how to use the other numbers (minute vent? tidal volume?) to tell me if an unusually small amount of air is moving through my airway most/all of the time? The obvious weakness of using the "event" model of apnea/hypopnea is that you have to spend a lot of your time at baseline for the reduction-from-baseline to be significant. If you are rarely moving enough air, then you don't have that baseline to depart from.

[kappa]

The flow peaks during periods of high flow limitation are clearly lower than during low FL, while tidal volume, respiration rate and minute ventilation are stable.

It could be that you have nasal congestion (or some other anatomical flow limiting factor) that is restricting air flow to varing degrees through the night. You're still getting the same amount of air, just at a lower peak rate, and with a flat peaked flow graph which hits ResMed's flow limitation calculation.

It might be informative to look at zoomed views of flow limited and non flow limited breaths.

[Geer1]

There are events (specifically RERAs) tied to flow limited/restricted breathing that these machines are not capable of flagging (with any sort of consistency anyways). Why do you need that? Because APAP does not appear to treat my flow limited breathing and I believe I still have a higher number of RERAs causing poor sleep quality, please send me for a titration study with bilevel and higher pressure support as indicated to confirm RERA presence on APAP and try to find settings that treat them.

The periods of higher flow limitation look like they might be rem (somewhat periodic nature and flow limitations are usually worse in rem).

You only have two paths forward. Talk a doctor into titration study (with bilevel/increased pressure support if indicated and making sure they will score and titrate against RERA's) or buy a vauto yourself. The use is indicated and probably helpful although you may have a tough time convincing doctors because many if not most don't try to treat flow limitations/RERAs (so try to find a doctor that will if you can).

Edit: I too would like to see examples but I am assuming they will be obvious sawtooth style flow limitations.

[SarcasticDave94]

Assuming correct base a VAuto request on chronic discomfort. Make the case based on that.

[Sleeprider]

The problem with sleep titration studies is that very few of them will actually target RERA, flow limits or other sources of arousal. They are mainly minions of insurance protocols that is only concerned with AHI and sometimes oxygen saturation. While such a titration is possible, I am waiting to see the member on Apnea Board that got anything other than what I described above. My first bilevel machine was purchased off a Craigslist listing, and I used the data and my experience to demonstrate improved efficacy and comfort with my doctor. I think you have equal chances of getting a bilevel prescription with or without the titration study, and focusing on persuading your doctor. I have not used a sleep specialist to manage my care since my first diagnostic sleep study in 2008, and I think your odds of getting good care, or being a participant in your care, go down if you do.

I see a listing in Marquette, MI for a Vauto at $450 if you are interested.

[Geer1]

Fair point Sleeprider but you may very well have to buy first bilevel out of pocket which not all people can afford to do which is why I always propose to try the medical/insurance route first. If they want to speed up the process and buy out of pocket then have at it.

Cathyf I just looked through your sleep study thread and I am guessing your first sleep study didn't have rem sleep (no events in rem) and your RDI was still raised in supine position. In your second study you had your worst AHI in rem and also high AHI in non supine nrem, all were hypopneas and it appears they didn't score RERA's.

It is very possible that APAP is only partially capable of treating your hypopnea/RERA based sleep apnea and leaving flow limitations and RERA's untreated.

[cathyf]

Fair point Sleeprider but you may very well have to buy first bilevel out of pocket which not all people can afford to do which is why I always propose to try the medical/insurance route first. If they want to speed up the process and buy out of pocket then have at it.

Cathyf I just looked through your sleep study thread and I am guessing your first sleep study didn't have rem sleep (no events in rem) and your RDI was still raised in supine position. In your second study you had your worst AHI in rem and also high AHI in non supine nrem, all were hypopneas and it appears they didn't score RERA's.

It is very possible that APAP is only partially capable of treating your hypopnea/RERA based sleep apnea and leaving flow limitations and RERA's untreated.

Ok, my first sleep study did show decent amounts of REM, with all but one of my hypopneas in one of the three REM segments. The other hypopnea and the cluster of RERAs was during the nine minutes that I was on my back.

As for what the studies showed, I'm pretty puzzled by the second study. Which showed massive clusters of hypopneas while I was on my back, but not a single apnea of either kind. And my first study in 2014 also showed almost all hypopneas. While my APAP shows clusters of OAs when I'm on my back, and very few hypopneas. It's like the standards are different!

This is a close-up of one of the shorter extended flow limits (I picked it because it fits is a 10-minute view.) My Fitbit thought I was in REM from 5:57 to 6:20, and it clearly saw the awake at 6:19:30. (And the FLs dropped off for a half minute, which means "awake" for me.)
[attachment=32768]

And for another perspective, here's that same 10-minute zoom, except that I made the Flow Rate graph very tall.
   

And the whole night with the flow rate very tall:
   
This is showing very long segments where the peak inspiratory flow is down at 10, but with the top at 15, that doesn't count as a hypopnea -- those have to be 50% not 30%.


And I have no idea what made Saturday night with a median flow limit of 0.11 different from last night with a median of 0.02. Same settings, same mask, didn't feel much different, but just much tamer flow limits.

I'm having a lot of trouble figuring out if I'm just a sleep apnea wannabe...

[cathyf]

As for buying a vauto out of pocket, that's a possibility. (There is a vauto in Cedar Rapids -- about 2 hours from me -- where the seller didn't even put a price up. Just "best offer gets it." So I might be able to get that for reasonable.)

But I'm back at trying to figure out what the machine is telling me. It's telling me that I have massive FLs, and it really wants to peg the pressure at 20, but even if I restrict the max pressure to 8 nothing much happens. Ok, I have massive flow limits -- so what? The sleep docs don't care about flow limits, and I don't think that my OSCAR charts are going to convince anyone that I should even be on a CPAP at all, forget about a vauto.