Curious about ResScan "Flow Limitation"

[jerainey]

I wonder what ResMed is measuring when they show the value of "Flow Limitation". There's no numerical value attached, no units, just three little icons that I take to represent an open throat, a partially closed throat and a closed throat. In my detailed graphs all I ever see is a few bumps up from open but way less than even partially closed. Yet I have numerous OA events every night. If my events are indeed O then why no flow limitation? Does anybody know what this indication of "Flow Limitation" or "Flattening" is good for? Does your readout show significant values for this item?

[Physician]

Damn. Excellent question. Maybe we should BOTH read the manual.

See here---- viewtopic/t57346/Flow-graph-in-ResScan-software.html

[robysue]

Well, I've read the manual (but I could re-read it again, I suppose) and have not found an answer to this question myself. And I too have noticed that (1) my flow limitation seldom drops below half-way to "flat" and (2) the S9 registers numerous OA's in my data---usually between 5 and 15 OAs per night (for an AI typically ranging between 0.5 and 2.0 each night, with CA's accounting for very, very few events.) Seems like the the vast majority of my OA's have the flow limitation right at the top most round part of the scale, too, even after I account for time shifts between the flow curve and tha flow limitation curve.

I have noticed, though, that the pressure curve does indicate that my S9 AutoSet does respond to these flow limitations by raising the pressure just like the (clinician's ?) manual indicates that it should.

[jerainey]

Physician - The manual doesn't give me a clue Not that this info would be very useful even if I had it.

robysue - You MUST upgrade to ResScan 3.12 The HUGE change I have noticed is that the limitation icons have switched from top to bottom. When I get a little limitation I get an UP tick, whereas, in 3.11 it used to be a down tick. Those ResMed software engineers are really into it

[Physician]

Those ResMed software engineers are really into it

Hope you are joking. It's a poor GUI and the software is in need of a big overhaul. Yuck.

[robysue]

robysue - You MUST upgrade to ResScan 3.12 The HUGE change I have noticed is that the limitation icons have switched from top to bottom. When I get a little limitation I get an UP tick, whereas, in 3.11 it used to be a down tick. Those ResMed software engineers are really into it

Going up versus going down doesn't much matter to me as a mathematician. And the point remains, my flow limitation seldom crosses the halfway point from "round" to "flat" and the obtructive apneas often occur when the flow limitation is at the "round" end of the vertical axis.

[-SWS]

There's no numerical value attached, no units, just three little icons that I take to represent an open throat, a partially closed throat and a closed throat. In my detailed graphs all I ever see is a few bumps up from open but way less than even partially closed.

And the point remains, my flow limitation seldom crosses the halfway point from "round" to "flat"

That's a halfway point on a proprietary Resmed scale. That half-scale measurement point says nothing about how "arousal susceptible" you happen to be to half-scale, quarter-scale, eighth-scale, or even sixteenth-scale Flow Limitations given Resmed's proprietary measuring scheme. So the more crucial events---resultant sleep arousals---are unfortunately not in the S9 data set.

Depending on patient-unique threshold of arousal, your sleep architecture might severely deteriorate at frequent eighth-scale FL crossings, while my architecture might stay intact despite frequent quarter-scale or half-scale FL crossings. So threshold of arousal relative to FL severity can be unique from one patient to the next. UARS patients, as an example, are thought to be hyper-arousable to flow limitations.

Yet I have numerous OA events every night.

...and the obtructive apneas often occur when the flow limitation is at the "round" end of the vertical axis.

Central-apnea detection specificity is not published for Resmed's FOT detection method. Some of the detected apneas entailing no FL (no "wave flattening" that hints at obstruction) might be ordinary, innocuous central apneas that Resmed couldn't differentiate. Other apneas lacking that "flattening" signature might be quick, obstructive closures having presented no precursor wave flattening immediately prior to sudden obstruction. Not all obstructive apneas present with snore or FL signals.

[robysue]

-SWS,

Thanks for the thoughtful and insightful answer to questions posed by me and jerainey about the flow limitation chart.

You write:

So the more crucial events---resultant sleep arousals---are unfortunately not in the S9 data set.

Is this because the only way to tell if there really is an arousal is through an EEG?

I ask because even though I'm eight week into using CPAP, I'm still feeling as bad or worse than I felt before CPAP and I'm now starting to consciously wake up at night in a way that I wasn't before. And it's not due to mask/leak issue 90+% of the time.

[idamtnboy]

I wonder what ResMed is measuring when they show the value of "Flow Limitation". There's no numerical value attached, no units, just three little icons that I take to represent an open throat, a partially closed throat and a closed throat. In my detailed graphs all I ever see is a few bumps up from open but way less than even partially closed. Yet I have numerous OA events every night. If my events are indeed O then why no flow limitation? Does anybody know what this indication of "Flow Limitation" or "Flattening" is good for? Does your readout show significant values for this item?

You actually pretty much gave the answer in your question, believe it or not! From the "368175_s9-autoset-s9-elite_data-management-guide_amer_eng.pdf". Don't know off hand who to thank for giving the link somewhere here in the forum.

"Flow Limitation
Flow Limitation is a measure of partial upper airway obstruction. This measure is based on the shape of the inspiratory flow–time curve. A flat shape suggests upper airway obstruction."

[xenablue]

I so badly want to understand the stats I see in ResScan and little by little I THINK I'm starting to understand. I'm an avid manual reader, but could find nothing useful to explain the details and thank you for making it a little clearer to a newbie.

Cheers,
xena

[-SWS]

Is this because the only way to tell if there really is an arousal is through an EEG?

Yes, robysue.

Interestingly Respironics now claims that their PR System 1 can detect RERA's---which are "respiratory effort related arousals". Obviously they're correlating certain flow wave shape characteristics when they do that, since the machine only has one data channel---flow sensing. I am unaware of published sensitivity or specificity numbers for that Respironics RERA detection method. I'm skeptical about those claims. But S9 doesn't endeavor or claim to detect EEG arousals.

I ask because even though I'm eight week into using CPAP, I'm still feeling as bad or worse than I felt before CPAP and I'm now starting to consciously wake up at night in a way that I wasn't before. And it's not due to mask/leak issue 90+% of the time.

Well, CPAP introduces a significant amount of sensory disturbance IMO. And it can take some people many weeks to acclimate, while some never do. But RDI is most often tallied as apneas + hypopneas + RERAs----with those RERAs NOT being associated with either apneas or hypopneas; the latter is most often associated with flow limitations and/or high upper airway resistance. Looking at your tag line, your lab might tally RDI differently. Do you know if they scored flow limitations or associated RERAs?

Anyway, I'm wondering if you're now experiencing plenty of sensory-disturbance type arousals thanks to CPAP.

[jnk]

An old article, but a nice overview, in my opinion . . .

http://www.cda.org/library/cda_member/p ... sting.html

"The spectrum of clinically significant obstructive respirations can include events that are more subtle than hypopneas. These subtle events consist of increases in upper airway resistance occurring from a partial blockage of the upper airway. This results in increased work of breathing, triggering an arousal (or micro-arousal) that fragments sleep. This can occur even without a measured decrease in airflow . . . Identification of arousals requires electromyograph and electroencephalograph signals for proper tabulation. It is possible to identify arousals using other parameters such as sudden fluctuations in heart rate, but these are less reliable. Therefore, sleep studies done without electro-oculograph, electroencephalograph, and electromyograph are not reliably able to quantify sleep, stage sleep, or identify arousals."

[robysue]

I ask because even though I'm eight week into using CPAP, I'm still feeling as bad or worse than I felt before CPAP and I'm now starting to consciously wake up at night in a way that I wasn't before. And it's not due to mask/leak issue 90+% of the time.

Well, CPAP introduces a significant amount of sensory disturbance IMO. And it can take some people many weeks to acclimate, while some never do. But RDI is most often tallied as apneas + hypopneas + RERAs----with those RERAs NOT being associated with either apneas or hypopneas; the latter is most often associated with flow limitations and/or high upper airway resistance. Looking at your tag line, your lab might tally RDI differently. Do you know if they scored flow limitations or associated RERAs?

This is one of the great mysteries of my diagnosis to me: I can't for the life of me figure out what the heck they actually scored as a "hypopnea with arousal" since those things went into the RDI but not the AHI. The only time I had a chance to talk to the doctor, I hadn't seen the sleep study and was still a bit stunned by his saying that I had moderate apnea instead of mild apnea, which is what I really was expecting to hear given what my husband had been telling me before the sleep study; and so I didn't know enough to put the question to him directly. He glossed over the whole issue with the bald statement, "You are stopping breathing about 23 times every hour or about about every 3 minutes or so and you need to be put on CPAP." When I've ask the PA, she's been really vague about this saying something along the lines of "they're probably events that didn't quite make the definition of hypopnea because there wasn't enough of a desaturation or something."

And with all the web searching I've done on the phrase "hypopnea with arousal", I still haven't managed to find a definition. It usually turns up as a "half-definition" of an apparently widely used alternate definition of a hypopnea that requires a 4% desat. One example of this is the paper at http://http://ajrccm.atsjournals.org/cg ... l/159/1/43 for example. And in all these examples I've found, they all seem to indicate that these things should have been part of the AHI as hypopneas.

But whatever the heck they are, I'm sure that these "hypopneas with arousal" were (are?) causing problems with my sleep architecture and I can see why they they were at least put in the RDI and why my diagnosis was based on RDI even though the AHI was well below 5.

Anyway, I'm wondering if you're now experiencing plenty of sensory-disturbance type arousals thanks to CPAP.

I've no doubt that this is part of my current problem. I hope that I manage to eventually get used to whatever it is that's waking me up.

But I also really wish I knew exactly what it was they found in my distrubed breathing patterns and whether the S9 is actually fixing them. On bad nights, which tend to happen at least a couple of times a week, the S9 is registering between 10 and 20 "obstructive apneas" over the course of the night. Since I only had 14 of these on my overnight diagnostic sleep study and since I'm still feeling no better than pre-CPAP and often worse than pre-CPAP, it's left me wondering just what the S9 actually is doing for me as far as those very frequent "hypopneas with arousal" are concerned.

[billbolton]

Since I only had 14 of these on my overnight diagnostic sleep study and since I'm still feeling no better than pre-CPAP and often worse than pre-CPAP....

1. 8 weeks is relatively short period of treatment, so you might need to persist somewhat longer before evaluating the efficacy of your xPAP treatment.

2. You may have other SBDs than OSA, or may have sleep problems unrelated to breathing, which reamin untreated, even if your OSA is being treated by xPAP.

Cheers,

Bill