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Meaning of VS and VS2 data on PR xPAP machines
#1
Meaning of VS and VS2 data on PR xPAP machines
In different thread, bonjour writes:
(07-08-2017, 09:15 AM)bonjour Wrote: Also disable your VS2 events.  They are of no use since noone knows what they mean.
I beg to differ with this advice.

I apologize for the length of this post, but I do think it's important to establish what is and what is not known about how the PR machines record snoring information and how to interpret that data.

VS2 events are one of two ways that the PR machines score snoring. We don't know exactly what the difference in criteria used for scoring VS and VS2 snores are on the PR machines, but it turns out we know quite a bit about how the PR machines and Encore (the official software) use the VS and VS2 events.


PR machines and recording snore data
If a PR machine is running in fixed pressure mode, only VS2 data is recorded. In other words, if you are using fixed pressure on a PR machine, the only available snoring data is the VS2 data.  

If a PR machine is running in auto adjust mode, both VS and VS2 data is recorded. But only the VS events cause pressure increases.

Anecdotal evidence is that the criteria that PR machines use to score VS2 data is pretty sensitive, and as a result VS2 data can record a lot of "non snoring" stuff as snores. There are reports on other CPAP forums that people have been able to track excessively high numbers of VS2 snores to sleeping with snoring dogs and the hose rubbing against the sharp edge of a night table or headboard.  Nonetheless, if snoring is a potential problem, then the VS2 data, even as mysterious as it is, is important.


SleepyHead and how it uses the PR snore data
SleepyHead does not compute the VS2 index in the same fashion as Encore does. Since Encore is the official software for the PR machines, this is a potential problem with SH data.  Note that JediMark is aware of this, but at the time he was writing SH, we didn't have any ideas at all about how PR machines recorded their snore data, let alone how Encore computed it's "VSI" index.  Heck, we didn't even know there were two forms of snoring data before JediMark started writing SleepyHead.

In looking at lots and lots of raw data, JediMark was able to determine when a PR machine is scoring a ton of VS2 events, they are scored in 2 minute intervals.  In other words, the closest together two VS2 events can be is 2 minutes.

SleepyHead does two things with the VS2 data: It creates the VS2 Index in the usual way:
  • SleepyHead VS2 Index = (Number of VS2 events)/(run time)
SleepyHead also draws a "Snore Graph".  Each VS2 event comes with both a time stamp (when it happened) and a mysterious "number".  You can see these numbers if you click on the Events tab in the left side bar and look at the individual events.  What those numbers numbers actually mean and how they are determined is not known to us because PR is pretty hush, hush about the algorithms its machines use.  However, the common assumption is that the higher the number, the worse the snoring is in some (undetermined) way.  But remember that the VS2's are scored in two minute intervals, and hence  JediMark's Snore Graph is a "step" graph formed by drawing a two minute horizontal line segment for each VS2 snore; the height of the line segment is the number attached to the VS2 snore.

So visually speaking, the more activity there is in the SH Snore graph and the larger the y-axis numbers on the Snore graph, the worse the snoring is.

The VS events have no number attached to them. Hence JediMark had no way of turning the VS data into a visual graph. He reports a SleepyHead VS index computed in the usual way:
  • SleepyHead VS Index = (Number of VS events)/(run time)
If the VS event tick marks are overlaid on the pressure graph, it's easy to see that the VS events are the snoring events that lead to increases in pressure when a machine is running in Auto mode.  

If your SleepyHead VS = 0.0 night after night, it's tempting to think that you are not snoring at all.  But it is critically important to remember VS snores are NOT recorded if the machine is running in a fixed pressure mode.  Hence if you use a PR DreamStation PRO, a System One PRO, a DreamStation BiPAP PRO, or a System One BiPAP PRO, your SleepyHead VS = 0.0 regardless of how much snoring you are doing at night.  If you run a PR Auto CPAP or Auto BiPAP in fixed pressure mode, then your SleepyHead VS = 0.0 regardless of how much snoring you are doing.  

In other words, if you are using fixed pressure on a PR machine, the only available snoring data is the VS2 data.  


Encore and how it uses the PR snore data (Part I)
The SleepyHead VS2 snore data shows up as tick marks in the Encore Event table and is used to compute the Encore VSI, although not in the usual way. The SleepyHead VS snore data does NOT show up in the Encore Event table and it is not important in computing the Encore VSI.

When you download data into Encore, you also get wave flow data (flow rate data in SH) for just the last night before the download. The wave flow data is NOT a standard part of the Encore Daily Detailed Data, but by clicking on the appropriate icon, you can look at it and print it off. When looking at an Encore wave flow, the OAs, CAs, Hs, and SleepyHead VS evens show up as tick marks.  But the SleepyHead VS2 events do NOT show up as tick marks on the Encore wave flow.  The Encore wave flow data also includes a pressure curve, and it is clear that the SleepyHead VS events cause PR machines to increase pressure.

If you look at the wave flow for a PR machine running in fixed pressure mode, there will be NO snore tick marks because the SleepyHead VS events are NOT recorded in fixed pressure mode and the SH VS2 events are not overlaid over the wave flow data in Encore.


Encore and how it uses the PR snore data (Part II)
I'm a long time PR BiPAP user. I also have a known snoring problem: On my bad apnea nights, I snore. According to my hubby, most of the time my snores are not really loud, but they are persistent on the nights when I snore.  And there's some anecdotal evidence that on my worst nights, snores may contribute to the number of wakes I experience.  Hence I've spent a fair amount of time looking at snore data in both SH and Encore trying to sort out just what the VS and VS2 data tells us.

I knew right away (long before SH came out) that the Encore VSI was NOT computed in the same way all the other Encore indices were computed.  In other words, by looking at Encore data, I knew:
  • Encore VSI not= (Number of Encore VS events)/(run time)
And this bugged me for a very, very long time: I really wanted to know what the heck that Encore VSI might mean since my Encore VSI varied tremendously from night to night in my early days of PAPing. And after SH came along, the PR snoring data as presented in SH never even came close to matching up with the PR snoring data as presented in Encore. And that also bugged me (and continues to bug me.)

One assumption that I made in doing my analysis is that PR's programmers are privy to information about what the VS2 data actually means and what the criteria for scoring a VS2 snore is.   PR's programmers are the ones who wrote that abomination called Encore, but for its kludginess, Encore does present the Daily Data in a pretty nice format, except for lack of the Flow Rate data being immediately available.  And since sleep docs rely on Encore to evaluate how effective PR machines are treating their patients, I'm inclined to give some real consideration to how Encore presents the snore data.

It took me a very long time to backwards engineer how Encore computes the so-called Encore VSI.  What was clear to me even before JediMark started writing SH was that Encore's VSI was NOT computed in the usual way. In other words:
  • Encore VSI not= (Number of Encore VS and/or VS2 events)/(run time)
As soon as JediMark had a test version of SH (SH 0.7ish, if I recall), he had discovered what we now call VS snores, but not VS2 snores. And it quickly became apparent that
  • Encore VSI not= (Number of SH VS events)/(run time)
It was also apparent by looking at SH Event Tables and Encore Event Tables, that the VS events JediMark was scoring were NOT the same as the VS events Encore was using in its Event Table and the Encore computation of a VSI.

JediMark kept looking at and analyzing more PR data, and soon found a second type of snore data, what we now call VS2. And the SleepyHead VS2 events in SH match up precisely with the VS events in an Encore Event table. But it was also clear that:
  • Encore VSI not= (Number of SH VS2 events)/(run time)

Eventually I figured it out: The numbers attached to each VS2 event are what is used to compute the Encore VSI.  Encore's programmers have chosen to add all the VS2 numbers together and then divide that total by the run time. In other words:
  • Encore VSI = (SUM of the numbers attached to each SH VS2 event)/(run time)

All of which raises the question: What is the meaning of the Encore VSI?

And I've hit a bit of a brick wall in trying to answer that question in a definitive manner. I have a working hypothesis for the answer to that question, but I have no way to verify whether my hypothesis is accurate or wildly off the mark.  


Robysue's hypothesis about the SH VS2 numbers and the Encore VSI computation
I strongly suspect the number that is attached to each SH VS2 event is the number of individual breaths in the last two minute window that are considered to be "snores" by the PR xPAP machine.  What criteria the PR xPAPs use to decide that an individual breath is a snore is unknown to me; it's got to be something in the shape of the Flow Rate data, but whatever the subtle changes are, they're not enough to pick out visually.

The main reasons that I've come to the conclusion that those numbers attached to the VS2 events are likely the number of individual snores in a two minute window are:
  • The fact that in a long, persistent stretch of snoring, the VS2's are always scored in two minute intervals, and
  • The maximum VS2's that I see in my data (and others data) seems to be roughly twice the RR rate, and 2*RR = maximum number of breaths in a two minute period.

If my assumption about the meaning of the SH VS2 numbers is correct, then meaning of the Encore VSI also becomes both clear and intuitive. Recall:
  • Encore VSI = (SUM of the numbers attached to each SH VS2 event)/(run time)
If the SH VS2 snore numbers are counting individual snores in a two minute window, then
  • (SUM of the numbers attached to each SH VS2 event) = total number of snores during the night
and that means
  • Encore VSI = the average number of snores per hour of run time
and, since "run time" is a (crude) approximation of "sleep time",
  • Encore VSI = approximation of the average number of snores per hour of sleep
Questions about SleepyHead?  
See my Guide to SleepyHead
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#2
RE: Meaning of VS and VS2 data on PR xPAP machines
That is so far above me that I didn't even feel the breeze when it passed overhead.
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#3
RE: Meaning of VS and VS2 data on PR xPAP machines
I bow to your knowledge.
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
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#4
RE: Meaning of VS and VS2 data on PR xPAP machines
Hi robysue,
Thank you so much for the post, it was very interesting.
trish6hundred
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#5
RE: Meaning of VS and VS2 data on PR xPAP machines
This is really interesting - thanks very much for your work Thanks

Have you ever compared the numbers between what you would get out of SH (if you sum them up) to encore?
(I believe the csv-exporter does the sum for you - in daily or session scope mode)

depending on the maximum value this Encore VS Index can get, the time-base might not be a complete hour - but that should be clear if there is always the same factor between the encore VSI and the values from the sum of VS2 from SH.

So it would be more "meaningful" if VS2 would move out of the events and get its own graph?

Just out of curiosity is there always(!) a correlation between VS and VS2? I mean, can there be a VS2 value / event without any VS scored in the last 2 minute-window?
and / or: is there always(!) a VS2 value, if there was an VS event in that 2 minute window?
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#6
RE: Meaning of VS and VS2 data on PR xPAP machines
(07-13-2017, 03:58 AM)TBMx Wrote: This is really interesting - thanks very much for your work Thanks

Have you ever compared the numbers between what you would get out of SH (if you sum them up) to encore?
That's exactly what I did.

The numbers attached to the VS2 snores in SleepyHead do not appear anywhere in an Encore report.  So back in the pre-SleepyHead days, there was no way for me to figure out how Encore was computing the Encore VSI.  It was clear from my data that the Encore VSI was NOT equal to the number of VS ticks in the Event Table divided by the run time.  And that's all I knew at the time.

It's been several years, and I don't know what actually made me think about summing up the SleepyHead numbers and dividing by the run time.  But as soon as I did, *bingo*, I had finally figured out how Encore computes it's VSI. To be clear:
  • Encore VSI = (Sum of numbers attached to individual VS2 in SleepyHead)/(run time)


Quote:depending on the maximum value this Encore VS Index can get, the time-base might not be a complete hour - but that should be clear if there is always the same factor between the encore VSI and the values from the sum of VS2 from SH.
Encore provides no hint as to how the VSI is computed.  All the other Encore indices are "average events per hour" and there's no reason to believe that Encore would arbitrarily change the definition of "index" for snores and not document the definition in the manuals meant for the clinicians who use the program.

Quote:So it would be more "meaningful" if VS2 would move out of the events and get its own graph?
Not really.  VS2 has it's own graph (the Snore graph), but that graph is difficult for people to interpret because the y-scale's units are (correctly) labeled as "Unknown."  

There are two reasons I think that the VS2 tick marks should remain:

1) That's how the snore data is presented in Encore.  And I think it is important that those of us who are into data to understand how the data looks to our doctors. And most docs will use Encore, not SleepyHead, when looking at data from PR machines. (It's a liability issue among other things; PR has to run everything, including the software, through accepted testing procedures for one of their products to be used in a clinical setting. SleepyHead doesn't have an official approval from anywhere, let along the FDA.)

2) The tick marks give a nice visible way of seeing when the snoring happens in relation to all the events without having to look at multiple graphs at the same time.


Quote:Just out of curiosity is there always(!) a correlation between VS and VS2? I mean, can there be a VS2 value / event without any VS scored in the last 2 minute-window?
My data shows that it is possible for VS2s to be scored without a VS in sight.  Indeed, in my data, it's not uncommon to have VS2s scored without a VS anywhere near it.

Quote:and / or: is there always(!) a VS2 value, if there was an VS event in that 2 minute window?
I'm not so sure about this: A quick perusal of my most recent data seems to indicate that whenever there is a VS, there are one or more VS2s close by.  But it's not possible to try to correlate which VS2 seems to be connected to which VS.

Also in my data, I've noticed that in a whole string of VS/VS2s mixed together, it is possible to have to more than on VS inside of a single two-minute gap between the VS2's.

I don't have time to post the screenshots now, but I'll try to post some this evening.
Questions about SleepyHead?  
See my Guide to SleepyHead
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