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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.

-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.

-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...

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?

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?

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

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

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.

JohnBFisher wrote: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.

Papit wrote: So if anyone's sleep doc floats the notion of upgrading from a cpap machine to ASV after less than stellar treatment effectiveness on cpap for several months, I would say go for it. And don't linger.

NateS wrote: I was very lucky to be able to persuade my doctor to let me go straight to ASV. It only happened because I first came to cpaptalk, read and learned to insist upon a copy of my full sleep report(s) before accepting the machine first prescribed for me, learned what to look for when I got my report, followed up on recommended reading and then wrote my sleep doctor a letter quoting from my first and second studies re centrals and politely making my argument to go straight to ASV, which resulted in a very amicable phone conversation with him, a 3rd study to support my/his request for authorization to Medicare.
Best wishes, Nate

Papit wrote:... Do I still feel tired and sometimes sleepy during the day despite my new ASV having almost fully reduced my sustained high centrals, and the few obstructives I had, to near zero? Yes, I do. I notice no significant change in that after nearly a month. ...