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What exactly IS flow rate and flow limitation?
#1
What exactly IS flow rate and flow limitation?
I see these phrases thrown around alot, and see the results on my sleepyhead graphs, but I'm not exactly sure what they mean in terms of treatment and effectiveness of treatment (or lack thereof). I've never really understood what they are. 

Can someone explain them to me? What's good in a flow rate. What's bad to see. 


I got my leaks down by switching from nasal cushion to a nasal pillow (plus, they gave me a new machine too), but I'm still really tired, so something must be causing it. 

Thanks!
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#2
RE: What exactly IS flow rate and flow limitation?
Hi.  The flow rate is more about looking at how the waveform looks, whether it is at least close to the 'ideal' shape, and if the peak-to-valley is relatively constant and consistent in timing...the gap between.  When you look at the rise and fall on the other side of the apex, or when looking at the bottom (nadir), if it 'drags', these indicate flow limitations of some kind.  Ideally, the machine shows 'flow limitations' superimposed on the time scale, and that way we know that they are measured and noteworthy.  This is also why we look for 'clustering' off noted events because they very often mean that the person ain't sleepin' quite right, possibly by tucking their chins down toward their chests.

Flow limitations are indications that the airway is not fully open, not fully expanded, but is partly restricting the freest possible flow for the typical user of PAP.  And such limitations can be due to constrictions (swollen tissues, bent and partly closed tubes, as examples), or due to collapsed tissues that have lost their tone or that are being impinged upon by heavy muscles and adipose tissues around and over them.  Yeah, it's a complicated subject, our disorders, and they need sophisticated machines, drivers (software), and also sophisticated interpretations and learning to better deal with individual responses and differences.

You should get other replies, hopefully with something similar, perhaps with refined descriptions.
Serial Tapist
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#3
RE: What exactly IS flow rate and flow limitation?
The flow rate is the speed at which air is moving in/out of your body in ml/s. 

When you don't have any obstruction, a typical breath look like this :
   

But when there is an obstruction, you can't inhale as quickly so the inspiration is flattened like this :
   

To get the same amount of air in (the tidal volume), you inhalation needs to be longer and sometimes that's not enough to keep the tidal volume constant. 
A series of flow limitations can lead to a RERA, Hypoapnea or apnea.

Hope this help!
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#4
RE: What exactly IS flow rate and flow limitation?
(09-19-2019, 02:19 PM)alexp Wrote: The flow rate is the speed at which air is moving in/out of your body in ml/s. 

When you don't have any obstruction, a typical breath look like this :


But when there is an obstruction, you can't inhale as quickly so the inspiration is flattened like this :


To get the same amount of air in (the tidal volume), you inhalation needs to be longer and sometimes that's not enough to keep the tidal volume constant. 
A series of flow limitations can lead to a RERA, Hypoapnea or apnea.

Hope this help!

Very helpful - thanks! So, when the inspiration is flattened, that's flow limitation? I know that in my sleep study/titration, I had a ton of RERAs. Is a RERA just a shorter in duration apnea? My AHI is pretty much always under 2 with my treatment, but I'm always tired.
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#5
RE: What exactly IS flow rate and flow limitation?
(09-19-2019, 02:04 PM)mesenteria Wrote: Hi.  The flow rate is more about looking at how the waveform looks, whether it is at least close to the 'ideal' shape, and if the peak-to-valley is relatively constant and consistent in timing...the gap between.  When you look at the rise and fall on the other side of the apex, or when looking at the bottom (nadir), if it 'drags', these indicate flow limitations of some kind.  Ideally, the machine shows 'flow limitations' superimposed on the time scale, and that way we know that they are measured and noteworthy.  This is also why we look for 'clustering' off noted events because they very often mean that the person ain't sleepin' quite right, possibly by tucking their chins down toward their chests.

Flow limitations are indications that the airway is not fully open, not fully expanded, but is partly restricting the freest possible flow for the typical user of PAP.  And such limitations can be due to constrictions (swollen tissues, bent and partly closed tubes, as examples), or due to collapsed tissues that have lost their tone or that are being impinged upon by heavy muscles and adipose tissues around and over them.  Yeah, it's a complicated subject, our disorders, and they need sophisticated machines, drivers (software), and also sophisticated interpretations and learning to better deal with individual responses and differences.

You should get other replies, hopefully with something similar, perhaps with refined descriptions.

I know that my doctor told me that my throat was a grade 4 on some scale that I can't remember right now - very small opening. Would that lead to flow limitation and therefore, RERAs? Not sure there's anything I can do about that though, from what I've read :/
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#6
RE: What exactly IS flow rate and flow limitation?
If your airway's cross-section at any one place along it is narrow, then that's your 'bottleneck'.  If it happens to be where you begin to get pinched when chin-tucking, as an example, well now you're really in a world of hurt.  As I explained earlier, it may be that, it might be inflammation, it might be your tongue sagging and falling back if you're on your back,...who knows?   The idea is to reduce limiting factors to the extent possible, and that might be helped a lot by not sleeping on your back (supine sleeping), or not tucking your chin toward your chest, which unfortunately isn't entirely associated with just back-sleeping; it can happen on your side as well.  Just ask me.  

You may have what is known in the broader disorder literature is UARS, or 'upper airway resistance syndrome'.  I don't know much about it, but you are correct in that flow restrictions, or limitations, can cause RERAs, and they're bad because they adversely affect our sleep stage progression.  We need uninterrupted sleep for at least 90 minutes in order to get to the REM cycle, but the best sleep is several of those in succession.  Also, most of us do most of our dreaming, about 60% of it, in the last two hours of a seven-hour night.  Those last two hours, according to my sleep coach, are exceedingly important for overall health.  If you have the type of impediment that affects you all night long, then you might not be getting much of that golden sleep.
Serial Tapist
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#7
RE: What exactly IS flow rate and flow limitation?
hypopneas, flow limits, RERAs, and UARS are traditionally treated with pressure support from a BiLevel or to a limited degree with EPR from an AutoSet.

simply stated RERAs are a series of flow limitations ending with arousal. Arousals are bad.
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
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