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JohnBFisher · Post by **JohnBFisher** » Fri Jul 05, 2013 11:53 pm

I tend to agree with -SWS. In general, if you feel fine to brilliant, then don't sweat the FL or hypopnea values. If you still feel tired, explore it. But remember, being tired may be due to other issues than just sleep.

-SWS · Post by **-SWS** » Fri Jul 05, 2013 11:38 pm

Papit wrote: Here is something I found in the company's literature. On Page 73 (see link below) it seems to be telling us that detected flow limitations are used by at least some S9 machines to adjust pressure and treat (inhalation) flow. Then, (4) Might the FL's simply be indicators of precisely when the machine did what it is supposed to do and treat central apneas before they can fully occur; i.e., might the FL graph in effect be a machine performance monitor that flags when and how many centrals would have occurred were it not for the VPAP Adapt? --p.73, http://www.apneaboard.com/ResScan_Inter ... -Guide.pdf

I don't think residual obstruction (FL) is a benchmark of how well or poorly the central component was addressed.

As a side note the initial S9 ASV model does not offer ASV-auto mode, whereas the most recent model does. ASV-auto mode refers to this obstructive-addressing aspect of the latest S9 ASV algorithm:

Resmed wrote:In ASVAuto mode, the EPAP also responds to flow limitation, snore and obstructive apneas on the next breath, in proportion to the severity of the event.

http://www.resmed.com/us/products/s9_vp ... s&sec=true

That means the initial S9 ASV model will not adjust EPAP in response to FL, snore, or OA. Rather, those must be manually addressed/titrated with a fixed EPAP. Similarly, the latest S9 ASV model will not raise EPAP in response to FL, snore, or OA *if* legacy "ASV mode" is enabled rather than "ASV-auto mode".

Also, I think it's hard to find other doctors in sleep medicine who share Dr. Krakow's views about needing to eliminate all FL in absence of RERA's. Dr. Krakow's FL views are certainly not shared by consensus sleep medicine. Kudos to him for exploring that hypothesis. Many of us are waiting for empiricism and/or peer replication supporting Dr. Krakow's FL views.

avi123 · Post by **avi123** » Fri Jul 05, 2013 2:25 pm

Dr Barry Krakow on Flow Limitations (and UARS+RERA):

https://www.youtube.com/watch?v=_FrxWQBm3iQ

Papit, get rid of it!

-SWS · Post by **-SWS** » Fri Jul 05, 2013 8:40 am

Papit wrote: I notice that my graphed FL's are very short in time duration in every example we looked at, about 2 seconds or a half of one breath (an inhalation). Slightly over two complete cycles are taking 10 seconds on the Flow graph. My respiratory rate is 15 breaths/minute or 4 seconds per complete inhale+exhale. Then, (1) Do I assume correctly that each complete wave (one cycle) is the equivalent of one-half of a breath, an inhalation cycle -- that is then graphically followed by a complete sinusoidal exhalation cycle on the Flow graph? And (2) Are 2-second FL events, that the S9 VPAP Adapt is designed to quickly act upon, a cause for concern?

Flow limitations sometimes result in sleep arousals (RERAs). Hypothetically, if one's sleep is significantly deteriorated by RERA's, then flow limitations are a cause for concern. My view is that residual flow limitations are not a cause for concern if they do not result in significant numbers of sleep-deteriorating RERA's. Please see my comments below about the S9 ASV's pressure response to FL as an obstructive precursor signal.

Papit wrote: Please note. I'm beginning to wonder about the FL graph's applicability to the S9 VPAP Adapt's various mode settings. I see it as relevant to the machine's CPAP mode. However, I'm thinking now that mathematically the FL graph may or may not be useful in both of the ASV modes; i.e., the standard ASV selection and the ASV Auto mode selection. (3) Can you evaluate that? I don't see any clarifying specifics in ResScan's literature so far. I'm still looking. Any thoughts?

Traditionally, sleep medicine has been concerned with flow limitations based on: a) the flow limitation's potential for RERA type disturbances (not all FLs result in RERA's), and b) the flow limitation's association as precursor for more severe obstructive events such as apnea or hypopnea.

Papit wrote: Here is something I found in the company's literature. On Page 73 (see link below) it seems to be telling us that detected flow limitations are used by at least some S9 machines to adjust pressure and treat (inhalation) flow. Then, (4) Might the FL's simply be indicators of precisely when the machine did what it is supposed to do and treat central apneas before they can fully occur; i.e., might the FL graph in effect be a machine performance monitor that flags when and how many centrals would have occurred were it not for the VPAP Adapt? --p.73, http://www.apneaboard.com/ResScan_Inter ... -Guide.pdf

I'm fairly certain the S9 ASV algorithm does not intentionally interpret FL as a precursor to central events. Theoretically, severe FL can reduce minute and tidal volumes, which in turn can affect the flow-targeting aspect of an ASV algorithm. When placed in auto ASV mode, the most recent S9 ASV model will interpret FL wave shape (not volume) as a precursor signal to more severe obstructive events. The obstructive-addressing aspect of the auto-ASV algorithm will then adjust pressure in an attempt to prevent subsequent obstructive apnea or hypopnea.

Papit · Post by **Papit** » Fri Jul 05, 2013 2:58 am

-SWS wrote:Hi Papit- The good news is that your minute ventilation values don't suggest hypoventilation. Regarding the events scored as FL by Resscan. Upon closer examination I think those are mostly obstructive FL. I would invite others to share their opinion(s) based on the most recent images and Figure 1 of this article as reference:
http://journal.publications.chestnet.or ... 1079416#f1

Figure 1's class-1 wave shape in the above article is a normal inspiratory curve. Class 2 through class 7 are common flow-limitation wave shapes--thus obstructive. Additionally, the FL classes or morphologies can be combined or superimposed in a single breath.

Here's my take for each of your above graphs, Papit:
graph1- flow limited (tail end of expiration before FL also reflects classic obstructive narrowing)
graph2- flow limited
graph3- sinusoidal (although 3rd full cycle might have class 7 flattening)
graph4- perhaps FL or disorganized breathing associated with wake/shift/arousal---but probably not central
graph5- flow limited
graph6- flow limited
graph7- perhaps central phenomena based on waxing/waning (although minor waxing and waning is fairly common in ordinary OSA)
graph8- perhaps FL or disorganized breathing associated with wake/shift/arousal

Again, other opinions are most welcome...

Hi, -Sws. That's a very informative article and study, particularly in giving those of us trying to discern some interpretation or meaning from our zoomed-in 1-minute or less wave forms.

I notice that my graphed FL's are very short in time duration in every example we looked at, about 2 seconds or a half of one breath (an inhalation). Slightly over two complete cycles are taking 10 seconds on the Flow graph. My respiratory rate is 15 breaths/minute or 4 seconds per complete inhale+exhale. Then, (1) Do I assume correctly that each complete wave (one cycle) is the equivalent of one-half of a breath, an inhalation cycle -- that is then graphically followed by a complete sinusoidal exhalation cycle on the Flow graph? And (2) Are 2-second FL events, that the S9 VPAP Adapt is designed to quickly act upon, a cause for concern?

Please note. I'm beginning to wonder about the FL graph's applicability to the S9 VPAP Adapt's various mode settings. I see it as relevant to the machine's CPAP mode. However, I'm thinking now that mathematically the FL graph may or may not be useful in both of the ASV modes; i.e., the standard ASV selection and the ASV Auto mode selection. (3) Can you evaluate that? I don't see any clarifying specifics in ResScan's literature so far. I'm still looking. Any thoughts?

Here is something I found in the company's literature. On Page 73 (see link below) it seems to be telling us that detected flow limitations are used by at least some S9 machines to adjust pressure and treat (inhalation) flow. Then, (4) Might the FL's simply be indicators of precisely when the machine did what it is supposed to do and treat central apneas before they can fully occur; i.e., might the FL graph in effect be a machine performance monitor that flags when and how many centrals would have occurred were it not for the VPAP Adapt? --p.73, http://www.apneaboard.com/ResScan_Inter ... -Guide.pdf

-SWS · Post by **-SWS** » Thu Jul 04, 2013 11:11 pm

Hi Papit- The good news is that your minute ventilation values don't suggest hypoventilation. Regarding the events scored as FL by Resscan. Upon closer examination I think those are mostly obstructive FL. I would invite others to share their opinion(s) based on the most recent images and Figure 1 of this article as reference:
http://journal.publications.chestnet.or ... 1079416#f1

Figure 1's class-1 wave shape in the above article is a normal inspiratory curve. Class 2 through class 7 are common flow-limitation wave shapes--thus obstructive. Additionally, the FL classes or morphologies can be combined or superimposed in a single breath.

Here's my take for each of your above graphs, Papit:
graph1- flow limited (tail end of expiration before FL also reflects classic obstructive narrowing)
graph2- flow limited
graph3- sinusoidal (although 3rd full cycle might have class 7 flattening)
graph4- perhaps FL or disorganized breathing associated with wake/shift/arousal---but probably not central
graph5- flow limited
graph6- flow limited
graph7- perhaps central phenomena based on waxing/waning (although minor waxing and waning is fairly common in ordinary OSA)
graph8- perhaps FL or disorganized breathing associated with wake/shift/arousal

Again, other opinions are most welcome...

Papit · Post by **Papit** » Thu Jul 04, 2013 8:54 pm

-SWS wrote:
Papit wrote:
-SWS wrote:
JohnBFisher wrote: I think the "flow limitation" is an artifact of the algorithm used to identify possible limitation of flow and a precursor to snoring.
John's guess might be spot on. Papit, that hypothesis is fairly easy to test. . . .
Are the 1-minute flow curves rounded at the tops, or severely distorted?
Thank you for the guidance, -SWS. I chose to examine two very elevated graphed 'flow limitations' that occurred at 8:39:25am and 8:40:00am in yesterday's (7/3/13) sleep.

-SWS wrote: Hi, Papit. At this point I'm favoring John's hypothesis (central phenomena falsely scored as FL).

Of those six 1-minute graphs, Rescan scored FL-positive on the fourth and fifth graphs but not the others. Would you mind changing y-axis scale on that pair of graphs and perhaps add a couple more FL-positive 1-minute graphs? You can change scale in Resscan by selecting Tools=> Options=> Preferences (tab)=> Detailed Graph Ranges (button)=> Flow (graph selection). Then change the "lower" and "upper" values to -45 and +45 respectively.

While you're in there, what Minute Ventilation values does Resscan return during moments scored as FL-positive? Just place the mouse cursor over the Minute Ventilation graph to get a popup box with recent-averaged and current minute ventilation values.

See the images below. I annotated Minute Ventilation readings on the images of the FL events in the graphs and, for relative perspective, at other times during flow as well. For additional FL examples, I picked a cluster of four (marked A, B, C, D), two very strong, one medium and one low strength. They occurred in my most recent sleep (7/4/13). I also added images of the Flow between the FL events. The cluster occurred between 10:12am and 10:16, well after sleep onset and well before awakening. In addition, for whatever correlation value might exist, Pressure and "High Rate" Pressure graphs are included (although I must admit I have not found a definition of "Pressure (High Rate)". The two pressure graphs differ. Eight images follow. The first two have been updated as you indicated.

==================================================================================================

>> FOUR ADDITIONAL FL EVENTS taken from today's 7/4/13 sleep <<

Dreamingofsleep · Post by **Dreamingofsleep** » Thu Jul 04, 2013 12:48 pm

Papit!!
How amazing and awesome Congrats and congrats you are obviously doing something or a lot of things right!

Dreaming

-SWS · Post by **-SWS** » Thu Jul 04, 2013 8:25 am

Papit wrote:
-SWS wrote:
JohnBFisher wrote: I think the "flow limitation" is an artifact of the algorithm used to identify possible limitation of flow and a precursor to snoring.
John's guess might be spot on. Papit, that hypothesis is fairly easy to test. In Resscan's top window panes set up the FL and detailed flow graphs at 8 hours resolution, one graph on top of each other. Use the mouse to drag the individual graphs either higher or lower. Then, in the bottom window panes, set up the FL and detailed flow graphs in 1 minute resolution---also one graph on top of the other. Now click the top graphs right where severe FL is scored. Then use the left and right arrows at the bottom of the 1-minute graphs to scroll back and forth for detailed viewing.

Are the 1-minute flow curves rounded at the tops, or severely distorted? If the 1-minute flow graphs are nice and rounded, then you are probably looking at reporting or interpretation artifact in the algorithm as John suspects. If, on the other hand, the 1-minute flow graphs are moderately or severely distorted at the tops, then you are probably looking at obstructive flow limitation. Generally, central phenomena will have rounded flow tops while obstructive phenomena will have distorted wave tops (deviating from sinusoid). Mixed phenomena can have both over the course of several breaths. Additionally, mixed and central phenomena will often present with flow-amplitude waxing and waning known as periodic breathing. Cheyne-Stokes is one of many possible periodic breathing types. I also think your periodic breathing does not fit the classic Cheyne-Stokes pattern.

Back to FL analysis. If you observe FL by examining wave tops at 1-minute resolution, AND you now see more severe residual FL than you have on past xPAP treatment platforms, then your residual FL might be iatrogenic vocal cord closures thanks to much larger PS values on ASV. Even "normal" test subjects tend to present vocal cord closures/adduction in response to high PS values . . .

I wouldn't worry about that phenomenon if you are sleeping better and feeling better by day. And if you are experiencing iatrogenic vocal cord adduction in response to high PS values, you may very well see those go away with time and physiologic adaptation. Alternately, you might want to eventually experiment by limiting PS max.
Thank you for the guidance, -SWS. I chose to examine two very elevated graphed 'flow limitations' that occurred at 8:39:25am and 8:40:00am in yesterday's (7/3/13) sleep. As you can see below, as usual, lots of FL spikes were graphed during the sleep. Also pictured are a series of 1-minute duration detailed views of the 1-minute resolution Flow and FL graphs that I scrolled through to examine my breathing flow wave tops before the two strong FLs' occurred, during the FL's, and after the FL's. Please check me on this. (1) It appears that my Flow wave generally is fairly sinusoidal in shape with relatively minimal distortion at the tops in the absence of FL's. (2) Also, the two FL's examined (typical, after looking at many others during this sleep) had minor/no significant affect in causing distortion to the Flow waves when they occurred. Again, thanks for the clear explanation and the time you took on this.

Hi, Papit. At this point I'm favoring John's hypothesis (central phenomena falsely scored as FL).

Of those six 1-minute graphs, Rescan scored FL-positive on the fourth and fifth graphs but not the others. Would you mind changing y-axis scale on that pair of graphs and perhaps add a couple more FL-positive 1-minute graphs? You can change scale in Resscan by selecting Tools=> Options=> Preferences (tab)=> Detailed Graph Ranges (button)=> Flow (graph selection). Then change the "lower" and "upper" values to -45 and +45 respectively.

While you're in there, what Minute Ventilation values does Resscan return during moments scored as FL-positive? Just place the mouse cursor over the Minute Ventilation graph to get a popup box with recent-averaged and current minute ventilation values.

Papit · Post by **Papit** » Thu Jul 04, 2013 1:26 am

-SWS wrote:
JohnBFisher wrote: I think the "flow limitation" is an artifact of the algorithm used to identify possible limitation of flow and a precursor to snoring.
John's guess might be spot on. Papit, that hypothesis is fairly easy to test. In Resscan's top window panes set up the FL and detailed flow graphs at 8 hours resolution, one graph on top of each other. Use the mouse to drag the individual graphs either higher or lower. Then, in the bottom window panes, set up the FL and detailed flow graphs in 1 minute resolution---also one graph on top of the other. Now click the top graphs right where severe FL is scored. Then use the left and right arrows at the bottom of the 1-minute graphs to scroll back and forth for detailed viewing.

Are the 1-minute flow curves rounded at the tops, or severely distorted? If the 1-minute flow graphs are nice and rounded, then you are probably looking at reporting or interpretation artifact in the algorithm as John suspects. If, on the other hand, the 1-minute flow graphs are moderately or severely distorted at the tops, then you are probably looking at obstructive flow limitation. Generally, central phenomena will have rounded flow tops while obstructive phenomena will have distorted wave tops (deviating from sinusoid). Mixed phenomena can have both over the course of several breaths. Additionally, mixed and central phenomena will often present with flow-amplitude waxing and waning known as periodic breathing. Cheyne-Stokes is one of many possible periodic breathing types. I also think your periodic breathing does not fit the classic Cheyne-Stokes pattern.

Back to FL analysis. If you observe FL by examining wave tops at 1-minute resolution, AND you now see more severe residual FL than you have on past xPAP treatment platforms, then your residual FL might be iatrogenic vocal cord closures thanks to much larger PS values on ASV. Even "normal" test subjects tend to present vocal cord closures/adduction in response to high PS values . . .

I wouldn't worry about that phenomenon if you are sleeping better and feeling better by day. And if you are experiencing iatrogenic vocal cord adduction in response to high PS values, you may very well see those go away with time and physiologic adaptation. Alternately, you might want to eventually experiment by limiting PS max.

Thank you for the guidance, -SWS. I chose to examine two very elevated graphed 'flow limitations' that occurred at 8:39:25am and 8:40:00am in yesterday's (7/3/13) sleep. As you can see below, as usual, lots of FL spikes were graphed during the sleep. Also pictured are a series of 1-minute duration detailed views of the 1-minute resolution Flow and FL graphs that I scrolled through to examine my breathing flow wave tops before the two strong FLs' occurred, during the FL's, and after the FL's. Please check me on this. (1) It appears that my Flow wave is fairly sinusoidal in shape with relatively minimal distortion at the tops in the absence of FL's. (2) Also, the two FL's examined (typical, after looking at many others during this sleep) had minor/no significant affect in causing distortion to the Flow waves when they occurred. Again, thanks for the clear explanation and the time you took on this.

-SWS · Post by **-SWS** » Wed Jul 03, 2013 9:16 pm

No, Avi. Those "normal" subjects in the study I linked don't have VCD. And Papit probably doesn't have VCD either.

Rather my comment to Papit was that *if* he notices more FL using ASV than previous xPAP platforms, then perhaps ASV's higher PS values are inducing vocal cord adduction. More importantly, the scored FL might be perfectly benign given improved sleep and daytime symptoms.

avi123 · Post by **avi123** » Wed Jul 03, 2013 6:08 pm

-SWS, do you mean Vocal cord dysfunction (VCD)?

http://emedicine.medscape.com/article/137782-overview

See also:

viewtopic/t16612/Vocal-Cord-Dysfunction ... -Cpap.html

-SWS · Post by **-SWS** » Wed Jul 03, 2013 3:54 pm

Hi Avi. This is an exercise in applying heuristic judgment to validate/invalidate Rescan's FL scoring. The algorithmic artifact (or interpretive scoring error) that John spoke of stands to show up in the FL graph---not the raw flow graph. Why? The "flow limitation" graph reflects Rescan's algorithmic scoring or interpretation. By contrast the raw "flow" graph reflects unscored measurement. So the idea here is for Papit to examine his unscored flow graph at 1-minute resolution, in an attempt to validate or invalidate Rescan's FL scoring.

When we see significant flattening, one or more shoulders, or other distinct deviation from rounded sinusoid on the flow measurement graph, then we're looking at some kind of obstructive narrowing rather than central phenomena. Residual or even iatrogenic breathing phenomena are not always worrisome. Recall that periodic breathing, central apneas, obstructive apneas, flow limitations, hypopneas, etc. all occur with subclinical frequency/severity in the "normal" non-SDB population.

So if Papit's sleep and daytime symptoms are much improved, then a little residual or even iatrogenic FL here and there might be nothing more than benign.

avi123 · Post by **avi123** » Wed Jul 03, 2013 12:45 pm

-SWS, how can I tell if the following out of roundness of my respiration wave shapes were true or artifacts? Notice that the Flow Limitation graph did respond by rising:

(Use un zoomed Window to see the following graphs)

At other times the wave shapes are rounder:

But, there were occasions when my wave shapes were really flat although the FL graph (above it) has not shown it to be so:

-SWS · Post by **-SWS** » Wed Jul 03, 2013 12:00 pm

JohnBFisher wrote: I think the "flow limitation" is an artifact of the algorithm used to identify possible limitation of flow and a precursor to snoring.

John's guess might be spot on. Papit, that hypothesis is fairly easy to test. In Resscan's top window panes set up the FL and detailed flow graphs at 8 hours resolution, one graph on top of each other. Use the mouse to drag the individual graphs either higher or lower. Then, in the bottom window panes, set up the FL and detailed flow graphs in 1 minute resolution---also one graph on top of the other. Now click the top graphs right where severe FL is scored. Then use the left and right arrows at the bottom of the 1-minute graphs to scroll back and forth for detailed viewing.

Are the 1-minute flow curves rounded at the tops, or severely distorted? If the 1-minute flow graphs are nice and rounded, then you are probably looking at reporting or interpretation artifact in the algorithm as John suspects. If, on the other hand, the 1-minute flow graphs are moderately or severely distorted at the tops, then you are probably looking at obstructive flow limitation. Generally, central phenomena will have rounded flow tops while obstructive phenomena will have distorted wave tops (deviating from sinusoid). Mixed phenomena can have both over the course of several breaths. Additionally, mixed and central phenomena will often present with flow-amplitude waxing and waning known as periodic breathing. Cheyne-Stokes is one of many possible periodic breathing types. I also think your periodic breathing does not fit the classic Cheyne-Stokes pattern.

Back to FL analysis. If you observe FL by examining wave tops at 1-minute resolution, AND you now see more severe residual FL than you have on past xPAP treatment platforms, then your residual FL might be iatrogenic vocal cord closures thanks to much larger PS values on ASV. Even "normal" test subjects tend to present vocal cord closures/adduction in response to high PS values:

V F Parreira, et al wrote: Increases in inspiratory pressure did not always lead to increases in effective ventilation reaching the lungs. This was due to a significant narrowing of the glottis by adduction of the vocal cords in all subjects.

http://www.atsjournals.org/doi/abs/10.1 ... .5.8630611

I wouldn't worry about that phenomenon if you are sleeping better and feeling better by day. And if you are experiencing iatrogenic vocal cord adduction in response to high PS values, you may very well see those go away with time and physiologic adaptation. Alternately, you might want to eventually experiment by limiting PS max.

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