Flow Limitations

[DariaVader]

It looks like Flow limitations are a 0 to 1 scale. Flow limitations that are less than 50% seem to be the dominating feature of the majority of my nights. My AHI is low with CPAP - even if I set the pressure to a constant 7 (a 1 night experiment) the AHI is low, but the flow limitations were constant and I felt almost like i had slept without my cpap. Last night I set the min pressure to 8 and knocked out all FL for the first half of the night, and greatly reduced for second half. going to leave it that way for a couple nights to see how it works out... the higher pressure caused my water retention level to raise again, but i slept so well.

I am still not really clear on how flow limitations become obstructions... Did not see a 1 on the FL when an OA was scored, for instance. Would welcome some insight on the entire subject

BTW - saw my sleep doc yesterday and finally got my whole sleep study report. Seems the majority of my AHI was H in the study (for which I barely slept, unfortunately and it was a home study so they cannot tell) I think that FL = H at a certain level???

[Shastzi]

I'd like to find out too!

[AshSF]

It looks like Flow limitations are a 0 to 1 scale. Flow limitations that are less than 50% seem to be the dominating feature of the majority of my nights. My AHI is low with CPAP - even if I set the pressure to a constant 7 (a 1 night experiment) the AHI is low, but the flow limitations were constant and I felt almost like i had slept without my cpap. Last night I set the min pressure to 8 and knocked out all FL for the first half of the night, and greatly reduced for second half. going to leave it that way for a couple nights to see how it works out... the higher pressure caused my water retention level to raise again, but i slept so well.

I am still not really clear on how flow limitations become obstructions... Did not see a 1 on the FL when an OA was scored, for instance. Would welcome some insight on the entire subject

BTW - saw my sleep doc yesterday and finally got my whole sleep study report. Seems the majority of my AHI was H in the study (for which I barely slept, unfortunately and it was a home study so they cannot tell) I think that FL = H at a certain level???

Conventional wisdom says there are multiple stages of your airway's compromise:
1) When your airflow rate starts decreasing, it shows as flow limitation.
2) it reduces further and typically causes a RERA in most individuals.
3) if RERA is not induced to correct the airway patency, it becomes a hypopnea.
4) If it collapses further, it will become an obstructive event.

You machine (S9) reports all of stage 1 and 2 as flow limitations. Why it doesn't show an FL of 1 before an O event is beyond my level of competence.

The potential reason why you feel like crap at pressure of 7cm is that you are having a bunch of RERAs which correct your airway patency thus avoiding H or O event (so keeping your AHI low). But these RERAs harm your sleep architecture by knocking you out of a deeper sleep stage to a shallower one. When this happens multiple times in the night, you end up spending more time in shallower sleep stages than deeper ones (SWS,REM). And then you don't feel rested in the morning.

You could potentially use your FL no. as a proxy for RERAs. You probably need very little extra pressure to subdue the FL no. after AHI is in treated zone - as you experienced with pushing the pressure to 8.

My 2 cents. I am sure more experienced members will chime in soon.

[MobileBasset]

The machine software does not evaluate and report events real time. It has the luxury of time to evaluate the flow data and then report events and adjust pressure. An H that graduates over time to an A will be reported as an A. If it doesn't graduate it will be reported as an H. Otherwise there would be artificially high indices.
However, I notice on my graphs that my A events do not generally develop gradually from what appears as an H. The flow shows an acute stoppage. YMMV

[Sleeprider]

This probably won't help you much, but I made the transition from APAP to BPAP earlier this year and that had a profound affect on RERA, and a slight affect on FL. With an APAP range of 11-14 the RERA index (event/hour) ranges from 1.5 to 3. Using BPAP with EPAP at 8.5, PS +4 (IPAP 12.5) on auto mode, RERA is typically less than 0.5. Like you, I don't know why, but occasionally switching machines for a week continues to confirm that. I accidentally changed my PS to 0-5 and RERA was again similar to APAP, so it's not the machine nor pressure alone, it is the pressure support. For me, flow limitation events correlate with RERA, so both rise or both fall. And in a final ironic twist, CA is inversely proportional to RERA for me, so with low RERA I tend to have higher AHI composed mainly of CA, but the total time in apnea does not increase or decrease.

Some things maybe don't need to be understood, we just do our best to pick what feels best. Your experiment shows you positively respond to a higher minimum pressure compared to a lower fixed pressure. That could be useful information.

[DariaVader]

yeah, it appears currently (2 nights at 8) that i need a higher pressure - probably 9 or 10 - for the minimum, however, the higher the pressure I use, the worse the symptom of water retention - presumably caused by the upswing in thoracic pressure caused by PAP. The remedy for that is BIPAP with a higher pressure support than I can get with APAP which was born out by the symptomatic relief obtained by moving EPR from 2 to 3. Now I wonder how long should I wait to switch, if I don't want the DME to reclaim my S9. I have a son who is waiting for results on a sleep study who will almost certainly need an APAP!

the S9 does not report RERA. It ticks me off that I got the machine that won't since the bulk of my issue is hypopnea and rera. Do the newer BIPAPs report it???

[DariaVader]

interestingly, my home study did not report RERA count either!!!

[PaytonA]

One thing to keep in mind when considering hypopneas is that not all hypopneas are obstructive. Some are centrals.

Best Regards,

PaytonA

[Sleeprider]

Respironics reports RERA in all data capable machines, so BiPAP yes. Resmed seems to have incorporated RERA into the Airsense 10 autosets, but I don't know about the Aircurve VPAP line.

[iSnore]

Respironics' BIPAP (DS760) also has the option of using an auto-adjusted range of Pressure Support, rather than just a fixed value.