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Definition of Flow Limitation and Flow Limit
#1
Definition of Flow Limitation and Flow Limit
Our CPAP machines measure these values and we can read them on the application software and  I assume I know what they mean but I could be wrong.

Please would someone give a definite definition of these also what could be considered low or high values and  the ramifications of these readings?

Thanks
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#2
RE: Definition of Flow Limitation and Flow Limit
I meant  Flow Limit and Tidal Flow
Sorry for my confusion there.
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#3
RE: Definition of Flow Limitation and Flow Limit
Resmed defines a flow limitation as: This refers to any event that limits the flow of air into your body, due to a blockage or collapse of your upper airway. That's a pretty useless definition in my view. https://www.resmed.com/au/en/consumer/su...aries.html

They also provide a pretty picture here: https://www.resmed.com/au/en/healthcare-...ology.html

There is a more useful definition, together with a detailed technical discussion here: https://www.sciencedirect.com/science/ar...1105003744 Flow limitation occurs when increased esophageal pressure is not accompanied by a flow increase. Flow limitation depends on the interaction between the negative pleural pressure, which tends to collapse the upper airway, and upper airway muscle activity, which helps to keep the airway open. Flow limitation represents the physiological basis of the UARS also known as respiratory effort-related arousal (RERA). Its main characteristic is a flattening of the inspiratory flow shape which can be measured noninvasively by nasal prongs at diagnosis or by a pneumotachograph during continuous positive airway pressure (CPAP) titration. There are a number of other papers linked from the same page.

From our own glossary in the wiki we have: Flattening Index - A number that indicates the amount of airflow limitation caused by partial closure of the upper airway. 0.3 indicates an open airway, 0.15 is mildly obstructed, 0.1 is severely limited airflow, and 0.0 reflects a totally closed airway. Flattening Index is used to identify a condition known as Upper Airway Resistance Syndrome (UARS), and is continuously recorded in some diagnostic sleep studies and CPAP titration studies.

Flow Limitation - Partial closure of the upper airway, which impedes the flow of air into the lungs.


Hope this helps.
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#4
RE: Definition of Flow Limitation and Flow Limit
Thanks DeepBreathing.
One other question , probably obvious but to be sure -

With the Flow Limit chart are the numbers on the Y axis ( 0.00 to 1.00) is that the "Flattening Index" as per your reply.

Big Grin
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#5
RE: Definition of Flow Limitation and Flow Limit
Yes, though I think the indices are inverted - a low flattening index (0.1) more-or-less corresponds with a high flow limit number (1.0). I've done a fair bit of searching and it appears there is no one universally accepted quantification of flow limits. Oscar just uses what the machine reports, which in the case of resmed is a number from 0.0 to 1.0.
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#6
RE: Definition of Flow Limitation and Flow Limit
I found this thread because I was looking at OSCAR data from last night and I see a couple of periods with increased Flow Limitation.  I didn't know what that meant so I did some googling – and here I am.

I've read through the thread and understand Flow Limitation reasonably well, but I have some questions.  During the periods where Flow Limitation values were > 0.0, there were no events.  I would have thought that "partial closure of the upper airway, which impedes the flow of air into the lungs" would be either caused by or at least accompanied by an apnea, RERA, or other event.  If not caused by this kind of event, what are some typical causes of measurable flow limitation?

I'm also curious about the "Flattening Index".  I guess this isn't the same as the ResMed measure.  Given that this thread is a year and a half old I was wondering if there is any more clarity about the relationship between the two measures.
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#7
RE: Definition of Flow Limitation and Flow Limit
ResMed uses a "Flattening Index" as a means of identifying flow limitations that require action (raising pressure). Look at the Flow Limits and the Pressure charts and see a flow limit correlates with a pressure increase. Think of flow limits as part of a continuum

Apnea (80-100% restriction)(min 10 sec)
Hypopnea (50-80% restriction)(min 10 sec)
Flow Limit(<50% restriction)(not timed),

Technically flow limits would include <10 second events or that Apnea and Hypnea are more significant subclasses of flow limits.

Think of Flow Limit as the basic event and the others as more significant.
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#8
RE: Definition of Flow Limitation and Flow Limit
This is very clear and very helpful!  Thank you.
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#9
RE: Definition of Flow Limitation and Flow Limit
I just read your signature – Looks like you would be a good person to thank for OSCAR.  I use it every day.  I can't tell you how much it has contributed to my learning about how I'm sleeping.  I've had a challenge finding a good mask.  I've used OSCAR as the empirical basis for how well various masks work.  

I've also had poor support from my doctor.  He started me out on a pressure range of 5-20 and then left me to my own devices.  Through help from several sources I learned more about the relationship of pressure setting to event occurrence.  I have learned to set my machine based on what OSCAR is telling me.  I'm typically now in the 0.5 or less range.

I'm really grateful for such a comprehensive tool.  Thank you.
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#10
RE: Definition of Flow Limitation and Flow Limit
(05-10-2021, 11:04 AM)Gideon Wrote: ResMed uses a "Flattening Index" as a means of identifying flow limitations that require action (raising pressure).  Look at the Flow Limits and the Pressure charts and see a flow limit correlates with a pressure increase.  Think of flow limits as part of a continuum

Apnea (80-100% restriction)(min 10 sec)
Hypopnea (50-80% restriction)(min 10 sec)
Flow Limit(<50% restriction)(not timed),

Technically flow limits would include <10 second events or that Apnea and Hypnea are more significant subclasses of flow limits.

Think of Flow Limit as the basic event and the others as more significant.

Since I'm suffering incredibly from Flow Limit issues, does this mean that a flow limit is a reduction in oxygen to the lungs but under 10 seconds long which would then become a Hypopnea?  

Could this explain someone having issues with daytime wheezing in the lungs?  And brain fog during the day?
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