Flow Limitation - can you explain?

[christian4870]

Hi,
can somebody explain what "flow limits" or "flow limitation" means in Sleepyhead? There is a value from 0 to 1?
What is better 0 or 1? Which value is this?
thank you and best regards
Christian

[ajack]

A flow limit is an obstruction, but not big enough or long enough to be called a Hypopnea. It can be treated by increasing your minimum pressure
https://www.youtube.com/watch?v=-gie2dhqP2c&t=90s

[christian4870]

Thanks, for sleepyhead does it mean 0 would be best?

[ajack]

yes, 0 is low and I think 0.5 is max. I don't think I've seen a 0.6? Although it goes to 1.
0-0.5 is the resscan software scale

[quiescence at last]

I have seen flow limitations on Resmed machines get real close to 1, the range is 0.0 to 1.0 with 0.0 being no obstruction and 1.0 being 100% or fully obstructed. If you were fully obstructed and this lasted over 10 seconds the machine would count an OA.

Sometimes you have a great score but a crappy sleep, and can see that you experience lots of flow limitations but little or no counted events.

Resmed adjusts pressure in many tiny increments almost constantly, and reacts to these flow limitations rather than waiting for them to lead to obstructive apneas or hypopneas.

QAL

[christian4870]

Resmed adjusts pressure in many tiny increments almost constantly, and reacts to these flow limitations rather than waiting for them to lead to obstructive apneas or hypopneas.
QAL

I use reaction "soft" in settings, so does this mean - cust in case - if i get a lot of flow Limitations or hypnoneas it would be possibly better to turn back to "standard" setting?

[Sleeprider]

The Airsense 10 does not change pressure on a breath by breath basis, but the fastest algorithm for flow limitation, (meaning the one that increases pressure the most following detection of FL) is reported to be the STANDARD algorithm, followed by the FOR HER setting and finally the SOFT.  I have not personally made any comparisons and this is simply based on Resmed claims.  The quote below from http://www.resmed.com/us/en/commercial-p...r-her.html also shows what flow limitation looks like on a flow graph. I also have not seen a comparison between For Her and Soft. In the figure below the For Her response first to FL while standard Autoset remains flat, however when subsequent FL events are detected the Autoset Standard rises much faster than For Her. So cumulative increase in pressure is fastest in standard Autoset, but For Her will rise on a single event.

The pioneering new algorithm used in the AirSense 10 AutoSet for Her works by increasing sensitivity to flow limitation and optimizing the response to these events. By responding to each flow-limited breath, the algorithm helps provide comfortable therapy for women.

[stanleydean]

Until I read this thread my flow limitation data has sort of flown under my radar, guess I was seeing it as one of the lesser important items. On a recent night, data posted below, my AHI was 0.11 and FLI was 0.87. This is not an unusual night, my FLI average for the past thirty days is 0.66. If the number in parentheses that pops up when you hover on a FL event represents seconds three of the events below were (10) three were (8) and two were (6). Now, does that mean that there were three events that, had they lasted another second, should have registered as H or OA events? If so, does that indicate slow response times? Will bumping the minimum pressure up from 8 to 9 likely help reduce the flow limitations?

If I zoom in on the flow rate waveform to see individual breaths the top of the waveform is consistently flat, is this normal or does it reflect flow limitation? I am sleeping well and all things considered I feel good during the day but would like to optimize my therapy. Any and all input is appreciated and thanks to all who make this forum what it is.




Stan

[Sleeprider]

A flat-topped or downward sloping inspiratory curve shows flow limitation. There are many potential reasons that this can occur, including restrictive lung conditions and upper airway obstruction. An increase in minimum EPAP pressure from 8-9 would address obstructive apnea, and would be the only tool you have with a CPAP. Since you are using auto BiPAP, the correct approach for flow limitation, would be an increase in minimum pressure support instead.

[robysue]

Until I read this thread my flow limitation data has sort of flown under my radar, guess I was seeing it as one of the lesser important items. On a recent night, data posted below, my AHI was 0.11 and FLI was 0.87. This is not an unusual night, my FLI average for the past thirty days is 0.66. If the number in parentheses that pops up when you hover on a FL event represents seconds three of the events below were (10) three were (8) and two were (6). Now, does that mean that there were three events that, had they lasted another second, should have registered as H or OA events? If so, does that indicate slow response times? Will bumping the minimum pressure up from 8 to 9 likely help reduce the flow limitations?

First I do use a DreamStation BiPAP Auto and I used a PR System One BiPAP Auto for years before I got the DS.  So I've looked at a lot of PR flow limitation data, both of my own and of others through the years.

The meanings of the numbers attached to the FL are NOT officially known.  In Encore Pro, the FL tick marks show up in both the Encore events chart and on the wave flow data.  But the SleepyHead numbers that are attached to the FL events appear nowhere in the PR data when you look at it in Encore Pro.  The Encore Pro FL Index = (Number of FL tickmarks)/(run time). So the SleepyHead numbers are not used to compute the FL Index in Encore.

And as far as I know there is nothing I or anybody else has found in the PR documentation that indicates the meaning of those numbers.  In my own data, the smallest FL number I've seen is 4 (and I don't see that very often) and the largest is at least 14 (but I don't see that very often).  The vast majority of my FL numbers are 8's and 10's with a few 6's and 12's sprinkled in.  And since my FL is typically in the 1.0-3.0 range, I see a fair number of FL flags each night.  

I've always assumed that the number associated with the FL was either an approximate length (in seconds) of the sequence of flow limited breathing or perhaps the number of flow limited breaths in a certain period of time. I've never dug deeply into trying to figure out which because most of the time when I zoom in, the flow rate data shows very little visible distortion in the inhalations as compared to the inhalations in much of my night time breathing.  In other words, it's not always clear to me why there was a FL flagged in the first place.

If I zoom in on the flow rate waveform to see individual breaths the top of the waveform is consistently flat, is this normal or does it reflect flow limitation?

Yep, that's one of the classic shapes of a flow limited inhalation.

I am sleeping well and all things considered I feel good during the day but would like to optimize my therapy. Any and all input is appreciated and thanks to all who make this forum what it is.

Given that your FL Index is less than 1.0 AND the fact that you are sleeping well and feeling good, I'd say you don't need to do further tweaking.  In other words, this falls into the category of "If it ain't broke, don't fix it."

In other words, I don't think tweaking your pressure setting to reduce your already extremely low FLI closer to 0 is going to accomplish anything.   The standard "fix" for FLs is more pressure (on CPAP/APAP) or more PS (BiPAP) or a higher IPAP (BiPAP), but, quite frankly, sometimes more pressure (or PS) doesn't actually reduce the number of FLs because not all flow limitations are directly the result of an airway in danger of collapsing.