Can someone explain "Flow Limitation" to me?

[WilsonVilleUSA]

I am new to CPAP and have been learning lots, mostly because of this board and all the helpful people on it.

One thing I haven't found specific info on is "Flow Limitation" can someone explain what exactly it is and what a "good" number is for it?

I did do a search, but didn't find an explanation of the term.


Thanks!

Wayne

[NightHawkeye]

Flow Limitation is a term used by Respironics in Encore Pro software. It is less than a hypopnea but indicates that the machine has sensed, well, a flow limitation. A good number would be, well, zero.

Regards,
Bill

[Ric]

Flow Limitation is a term used by Respironics in Encore Pro software. It is less than a hypopnea but indicates that the machine has sensed, well, a flow limitation.

Good answer NightHawkeye, I actually wondered about that myself. Now I know. (That'z whie eye come hear, two git smart).

I HEREBY NOMINATE YOUR REPLY as an official entry in the CPAPopedia book of wisdom and universal enlightenment. Maybe even a Pulitzer. I suggest also posting that (with your name on it of course) under the HYPOPNEA cpapopedia entry, since that one mentions flow limitation, but sort of leaves the concept dangling in mid-air.

[Guest]

[quote="NightHawkeye"]Flow Limitation is a term used by Respironics in Encore Pro software. It is less than a hypopnea but indicates that the machine has sensed, well, a flow limitation. A good number would be, well, zero.

Regards,
Bill

[Guest]

Flow limitations, flow limitation runs, and hypopneas are collectively the source of debate within the sleep industry and medical/scientific community in general. The above need to be defined according to Puritan Bennett's criteria, but first I want to give you the over-simplified definition that we patients use, that just so happens to not match what Puritan Bennet means by the above. The over-simplified definition is comprised of how much airflow is occuring in a patient's breath:

1) snore=slightest airway obstruction and least stifled airway obstruction
2) flow limitation=slightly more stifled or limited patient breathing
3) hypopnea=even more limited airflow than flow limitation
4) apnea=no airflow whatsoever

The medical community also goes into how long the obstruction lasts as part of its criteria regarding which of the above event types an obstruction will be categorized. Absolutely no airflow whatsoever for a very brief moment might be categorized as a hyopnea rather than an apnea. There are subtle differences in how these events are "scored" throughout the international medical community and among manufacturers.

With that said, the above definitions only speak of degrees of airflow and time durations of obstruction. They do not speak of the underlying nature of the airway failure which can often be determined by the very waveform shape of the patient's limited breath. Puritan Bennet and other AutoPAP manufacturers factor in the waveform shape of a patient's limited breath.

So "flow limitation run with amplitude decrease" is a restricted airflow (several breaths actually, hence "F.L. run") that also occurs with hypopneas (hence the "amplitude decrease" part of the name). This would be an example of what are called "concomitant hypopneas". A concomitant hypopnea is a flow limitation and a hypopnea together, which as you can see just doesn't gel with that over-simplified definition above. But, the underlying failing airway mechanism that causes a typical "flow limitation" is not the same airway failure that causes a "hypopnea". They can, indeed, occur simultaneously, and when they do IFL2 will trigger on it because of the unique waveform shape.

A "flow limitation" is a lesser airway restriction that might be caused by nasal or other airway swelling, or perhaps soft pallate partial closure. The air is restricted, but not as severely as with hypopnea or apnea. The 420e requires but several of these limited breaths before it will trigger, hence it is referred to as a "run" or "flow limitation run". Puritan Bennett defines a run as follows: "a Run is detected after two respiratory cycles with flow limitation or ten intermediate respiratory cycles and ends after two successive respiratory cycles without flow limitation.

With that attempt at a layman's explanation, let me list Puritan Bennett's event definitions below:

Apneas:

This refers to respiratory Apnea during which there were no representative cardiac oscillations.

Apneas / CA:

This refers to a respiratory Apnea where representative and permanent cardiac oscillations were detected.

Hypopneas:

This refers to a decrease in the amplitude of breathing.

Hypopneas+FL:

This refers to a RUN of Inspiratory flow limitation with simultaneous reduction in the amplitude of breathing.

Acoustical Vibrations:

This refers to detection of acoustical vibrations caused by the patient snoring.

Runs :

A Run is an indicator of a respiratory period with flow limitation, defined as follows: a Run is detected after two respiratory cycles with flow limitation or ten intermediate respiratory cycles and ends after two successive respiratory cycles without flow limitation.

Cycle status:

The analysis of the flow form during the inspiration computed at each respiratory cycle allows their classification in Normal (N), Intermediate (I) or at Flow Limitation (FL). On the trend trace, the higher the trace, the closer the inspiratory cycles are to normal (N). Conversely, a low trace indicates a trend of Flow Limitation (FL). A median trace indicates a trend of intermediate cycles (I).

Perhaps a light-hearted metaphor instead?

Apnea="the Grand Daddy of all obstructions"; the "big one" so to speak!

Hypopnea="baby" or "adolescent" obstruction; a lesser obstruction than apnea

Flow Limitation="zygote" or "fetus" obstruction; a lesser obstruction than even hypopnea; not yet a genuine obstructive problem for the vast majority of patients, but a significantly increased liklihood of becoming an obstructive breathing problem

Flow Limitation Run=several breaths, each impregnated with signs of "flow limitation"

UARS/RERA events manifest as flow limitations. However, flow limitations are not exclusive to UARS/RERA events. Flow limitations can also happen because of simple allergic rhinitis, bronchial swelling, incipient hypopneas, etc.

[PEELS]

About two months ago I was wondering about the same thing about Flow Limitation and Hypopnea and Obstructive Apnea. Somewhere I thought I read (and I can't remember where) that Respironics viewed Obstructive Apnea as an 80% obstruction in air flow for at least 10 seconds. An hypopnea was a 40% obstruction (like half an Obstructive Apnea). And a flow limitation was a 20% obstruction (half an hypopnea) and is not even used in the AHI calculation.

Of course, my wife would tell you that I can't remember anything right - and I have to admit there is some truth to that.

George