What exactly does flow limitation mean? and leak rates ?

Greets All -

One the pro report it says a FLI of 4.2 total last night.....also my leak rate seems to be going higher now with the zzz mask..max leak was 120lpm with a 90% rate of 40 lpm...and an avg of 29 lpm...anyone happen to know what the leak rate on a zzz mask should be? Appreciate any info thank you

I can't help you with the mask leak rate, but I would suggest you try google or the search function on the top of the cpaptalk page. A flow limitation can best be explained this way.

An Apnea occurs when your airway is completely or nearly completely blocked for more than a few seconds.

A Hypopnea occurs when your airway is substantially but not completely blocked for more than a few seconds. One definition of a hypopneas is that is a "wannabe" apnea.

A Flow Limitation is an even milder restriction of the airway resulting in a reduction of airflow, or if you will a "wannabe" hypopnea.

While eliminating apneas is the most important thing, hypopneas and flow limitations can result in some of the same problems just milder, so its good to eliminate them as well. But it can be difficult and frustrating, and some would argue not worth getting too worked up about.

For more accurate definitions and information feel free to search this site or Google. Good luck.

thanks for the reply..I did use the search engine on the flow topic but it was very vague.....i dont know what the mask leak rate is either on the zzz but i know that 40lpm has got to be higher than normal.......seems like I am having alot of these mild hypopneas..interesting.......might boost pressure just a little to see what happens

I'll add another perspective on both ...


The masks all have a fixed leak rate (through vent holes at the front) that allows air to exit - the need for this is to help clear excess CO2 that is breathed out on each exhale.

It is normal to re-breathe a small amount of CO2. The leak vent holes are intended to set a balance for cleared vs rebreathed CO2. Some exhaled air sits in the area between your nose/mouth and the vent holes. So, each mask has an area called its' 'deadspace' that is the area inside the mask that can hold exhaled air, on a full face mask that area is larger than on a nasal mask & is even smaller on nasal prongs. Deadspace can be adjusted for some people by adding an extra bit of tubing which allows for more exhaled air to be rebreathed as some people need it.

As for flow limitations (this is a simplified description - no ref to SPO2 desats) ...

When our breathing starts to get restricted by our throats or whatever, the flow of air drops. The rate of drop over a set period (usually 10 secs) is categorized.

A small drop is a flow limitation, a greater drop (50% over 10secs) is called a hypopnea but a greater drop (80% or greater over 10secs) is classified as an apnea. In recent times as machines became more sophisticated, they began including flow limitation data as this is starting to be looked at more closely than it used to be.

UARS (Upper Airway Resistance Syndrome) is a name some OSA researchers & some in the sleep profession use to describe a set of reduced breathing situations. One such situation is where repeated flow limitations occur - flow limitations can be classified as a syndrome within the UARS spectrum of conditions. Medicare doesn't yet accept UARS or flow limitations alone as justifying needing OSA therapy but some researchers believe it should. So someone can suffer daytime sleepiness because of excessive flow limitations but these FLs may never get so bad as to become hypopneas/apneas (the classic and medical definitions of OSA syndrome). For some UARS sufferers, OSA therapy (xPAP) is quite effective. Some other types of UARS conditions don't respond to OSA therapy (xPAP).

DSM

Both Resmed and Respironics offer some words on Flow Limitations, in balance the 1st linke explains it in better detail

http://www.resmed.com/ja-jp/clinicians/ ... clinicians

http://sleepapnea.respironics.com/techn ... ation.aspx

D

Excellent Links and Information..Thank You DSM

alnhwrd wrote:While eliminating apneas is the most important thing, hypopneas and flow limitations can result in some of the same problems just milder, so its good to eliminate them as well. But it can be difficult and frustrating, and some would argue not worth getting too worked up about.

I disagree. Whether an apnea or a hypopnea is milder totally depends upon what happens during that time. This board has a belief that is completely and utterly wrong, that somehow hypopneas don't matter as much as apneas. Some people think they don't matter at all!

The correct statement would be that you need to eliminate ALL events that are creating a problem.

Doctors look mostly at AHI. They don't get too worked up over the exact mix. You shouldn't, either. Both kinds of events are bad.

well thats disturbing to me......i'm having all 2 events each night......trying a new mask today I got from the auction to see if numbers change at all....... somehow I feel this zzz mask i'm presently using is not doing the job correctly.....the mask really seems to leak a lot and has no forehead support.....will see how it goes

LoQ wrote:

alnhwrd wrote:While eliminating apneas is the most important thing, hypopneas and flow limitations can result in some of the same problems just milder, so its good to eliminate them as well. But it can be difficult and frustrating, and some would argue not worth getting too worked up about.

I disagree. Whether an apnea or a hypopnea is milder totally depends upon what happens during that time. This board has a belief that is completely and utterly wrong, that somehow hypopneas don't matter as much as apneas. Some people think they don't matter at all!

The correct statement would be that you need to eliminate ALL events that are creating a problem.

Doctors look mostly at AHI. They don't get too worked up over the exact mix. You shouldn't, either. Both kinds of events are bad.

LoQ
I can follow the point you are making but why did you say this ?
"This board has a belief that is completely and utterly wrong, that somehow hypopneas don't matter as much as apneas."

Quoting one person's post (that was generally ok) then warping that into 'this board' is stretching it a bit

Cheers

DSM

No, I see this false belief all the time, and variations of it. If you paid attention, you would notice it, too.

LoQ wrote:No, I see this false belief all the time, and variations of it. If you paid attention, you would notice it, too.

Thank you kindly for that admonition I'll do my utmost to pay better attention

DSM


Hmmm where do I start .....

Sorry, I wasn't trying to say that you needed to pay attention to this. It doesn't matter if you pay attention or not, unless you really want to know whether or not the board has a false belief (or maybe bias is a better term). You asserted that I was stretching a single comment into a generalization. I am telling you that I am not, because I have seen it any number of times from a variety of people. Since you think it was a single statement that I based my comment on, you apparently haven't seen the others. The "paid attention" statement was just pointing out that if you aren't paying attention to that particular thing, you won't notice it. Plenty of stuff I'm not paying attention to that I miss, I'm sure.

I think there are a lot of reasons why people think that hypopneas are not as much of a problem as apneas. Part of it is just that to stop breathing entirely sounds so much worse than to have only a partial obstruction of breathing. Yet the reality is that hypopneas can drop the O2 to dangerously low levels.

I normally try to refrain from commenting on this, because I know many on the board does not agree with me. I will try to stifle in the future. It is hard, though, to see this false belief come up time and again and not say anything. I would hate for people who have hypopneas only to think that they didn't have a real problem.

LoQ wrote:Sorry, I wasn't trying to say that you needed to pay attention to this. It doesn't matter if you pay attention or not, unless you really want to know whether or not the board has a false belief (or maybe bias is a better term). You asserted that I was stretching a single comment into a generalization. I am telling you that I am not, because I have seen it any number of times from a variety of people. Since you think it was a single statement that I based my comment on, you apparently haven't seen the others. The "paid attention" statement was just pointing out that if you aren't paying attention to that particular thing, you won't notice it. Plenty of stuff I'm not paying attention to that I miss, I'm sure.

I think there are a lot of reasons why people think that hypopneas are not as much of a problem as apneas. Part of it is just that to stop breathing entirely sounds so much worse than to have only a partial obstruction of breathing. Yet the reality is that hypopneas can drop the O2 to dangerously low levels.

I normally try to refrain from commenting on this, because I know many on the board does not agree with me. I will try to stifle in the future. It is hard, though, to see this false belief come up time and again and not say anything. I would hate for people who have hypopneas only to think that they didn't have a real problem.

Actually,

You summed up a POV very nicely with this well made point "you need to eliminate ALL events that are creating a problem"

That really hits the nail on the head.

Cheers

DSM

Any events that results in a drop in blood O2 levels needs to be avoided. Flow Limitations can fall into that events arena. When I look at my data I add FL's to my AHI and look to get the sum to be less than <1 - it is when I feel the best also. So for me AHI + FL = <1

LoQ wrote: I normally try to refrain from commenting on this, because I know many on the board does not agree with me. I will try to stifle in the future. It is hard, though, to see this false belief come up time and again and not say anything. I would hate for people who have hypopneas only to think that they didn't have a real problem.

Any contribution, from anyone is welcome. I find it very weird to hear you say you will refrain from commenting on something just because many on the board do not agree with you - most of us are here to learn, and letting wrong ideas perpetuate themselves is a disservice to all.

Comparison of apnea and hypopnes definition form different machine makers - Velbor's chart



You'll find definitions from a company that makes PSG tracking software and equipment here:
Glossary of PSG terms

Flow Limitation – the partial closure of the upper airway impeding the flow of air into the lungs.

Hypopnea – shallow breathing in which the air flow in and out of the airway is less than half of normal-usually associated with oxygen desaturation

Apnea – Literally means "no breath"; the cessation of airflow at the nostrils and mouth for at least 10 seconds

What the machines measure is not what a PSG measures.

If you pay attention to it, you will see that people using Resmed machines consistently have their machine report more hypopneas that people using other machines.

I agree - hypopneas can drop O2 levels dangerously low. That does not mean that for people on Resmed machines, O2 levels are consistently dangerously lower that they would be at the same pressure on other machines.

You may also notice that some people using Puritan Bennet machines have far more flow limitation reported than people using Respironics machines.

The following is from:
Event Descriptions by Puritan Bennet, from the 420E manual:

• When is apnea said to have occurred?
  An apnea event occurs when there is no airflow for a time equal to at least 10 seconds plus 5/8 of an average breath period.
  When is central apnea said to have occurred?
  A central apnea event occurs when cardiac oscillations can be detected during an apnea event. The cardiac oscillations indicate an open airway, which is not an obstructed situation.
  When is hypopnea said to have occurred? A hypopnea event occurs when there is a period of at least 10 seconds where hypopneic breathing occurs. Hypopneic breathing is considered to be a reduction in breathing peak airflow by at least 40% when compared to the average of the preceding eight breaths, but not enough reduction to be considered an apnea. A hypopnea event is terminated when the patient delivers 2 consecutive non-hypopneic breaths.
  When is snoring said to have occurred?
  A snoring event is declared by the microcontroller when there has been an acoustical vibration for at least 7% of the average breath period time of the three preceding breath cycles and if the time between snoring doesn't exceed 120% of the average breath period.
  When is flow limitation said to have occurred?
  Flow limitation events are determined from breath wave shapes. Flow limited breaths occur when the es (thus reducing airflow) during the middle stage of inhalation.

Hypopneas in this definition, may be nice and rounded, but have too little flow. A flow limited breath has a jagged shape.

O.

Once again, I'll step in where angels fear to tread.

I'll speak only from my own experience with a ResMed Autostat II and a CMS50 pulse oximeter. Over the past month, my CPAP reports an AI averaging .2 and an AHI averaging less than 5.0 which still represents about 40 times a night in which my breathing has been severely restricted ....... certainly enough to cause concern if it should be reflected in my blood oxygen levels.

Without dragging out charts and endless stats, the long and short of it is since going on the APAP, my night-time blood oxygen levels fluctuate between 94 and 98 versus a low of 56 when I had my sleep study done at the hospital 45 days ago. My pressure settings have been tweaked to a range of 14.2 - 18 versus a titrated pressure of 16 and I don't see a lot of upside in worrying about my HI numbers since they don't seem to be adversely affecting either my blood oxygen levels or my resting heart rate to any degree. Let's put it this way, the act of turning over from sleeping on my side to my back seems to have a greater momentary impact than the hypopneic events identified by the equipment.

Am I missing something else that I should be worried about? Should we be trying to exceed an average blood oxygen level of 97% over the course of a night time sleep? So far, I'm inclined to side with those that preach an objective of zero AI events and less than 5 hypops per hour as having reached a successful treatment for our sleep apnea.

Paul