Pugsy has asked me to add this post about the SleepyHead snore data to this thread since it's a topic that sometimes comes up from newbies and it frequently causes confusion.
Please note the following: The way snores are recorded on the Resmed S9 machines is very different than the way it is recorded on the PR System One machines. This post only applies to the snore data recorded by the PR System One machines and how that data is reported in both Sleepy Head and in Encore.
All about Snoring Data on the PR System One Machines
There's no official guide to how to interpret the Snoring information from the PR System One as it is reported in either SleepyHead or Encore. In looking at Encore numbers, the assumption is that the higher the so-called "VSI" number is, the more serious the snoring is. But exactly how large that number needs to be before it's troublesome is not known. And for reporting snoring in SleepyHead, JediMark had to back engineer the snoring data from the PR machines and the information on why Encore presents the snoring data the way it chooses to present it is pretty scarce ....
And when you start analyzing the
raw snoring data the decisions that Encore makes on how to present the snoring data just seem plain bizarre from a statistical point of view. (More on that later.)
Once JediMark started back engineering the snoring data, he discovered that the PR machines were keeping track of two kinds of snoring data; JediMark has chosen to call these two types of snore data
Vibratory Snores (VS) and
Vibratory Snores #2 (VS 2). Those of us who had access to Encore Pro and had data from both straight pressure mode and auto mode were able to help JediMark figure out just what the significance of those two kinds of snores are in the Encore/PR world are. Here's the run down as we now understand things:
VS snores
VS snores are recorded ONLY when a PR machine is running in Auto mode. If the machine is set to straight CPAP (or straight BiPAP), the machine will NOT record VS snores. If the machine is a model number 450/460 (System One PRO) or 650/660 (System One BiPAP PRO), the machine will NOT record VS snores.
The VS snores have
time stamps attached to them, but they do not have a "magnitude" number. In the Sleepy Head "events" list, when you look at the detailed information for each VS snore event, the number in parenthesis will always be a 0.
But VS snores are the snores that cause the Auto algorithm to respond by increasing the pressure. (On a BiPAP Auto, it's the EPAP that is increased.) For each VS scored, the machine typically increases the pressure by 1 cm. Hence if there's a cluster of VS's, the machine will keep increasing the pressure until either the snoring stops or the max pressure setting is reached.
In Encore, the VS's do NOT seem to show up as tick marks in the Events table. But it's hard to say for sure. Where they do show up is on the wave form when you look at it in Encore Pro (or Encore Basic). Of course, Encore only downloads the wave form for the last night (or sometimes the last two nights) when you down load the data. Encore Pro at least stores all the previously downloaded wave forms in the patient's database, but Encore Basic only stores the last wave form. SleepyHead also puts tick marks for VS snores on the wave form data when a PR machine is running in Auto and the VS data is being recorded.
So---as near as anybody I know who follows such things can tell: The VS snores make up the part of the snoring data that is used by the Auto algorithm when it determines that the snoring is significant enough to warrant an pressure increase. But nobody outside of the PR engineers know what the scoring criteria for a VS snore actually is.
VS 2 snores
VS 2 snores are recorded by all PR machines. They have both a
time stamp and a "magnitude" number attached to them. In the Sleepy Head list, when you look at the detailed information for each VS snore event, there will be a NON-zero number in the in parenthesis for that event. Whether that number represents
the length the snoring went on or
some kind of measure of the loudness of the snoring is anybody's guess. We really do not know the significance of that number.
JediMark's SleepyHead VS 2 graph uses the "magnitude" numbers for the vertical-coordinates in the Snore graph. In other words, JediMark has set the SH VS2 graph up with the assumption that the "magnitude" numbers are somehow related to how bad the snoring is. That's not a totally unreasonable assumption since you can have VS 2 events closely space together with some rather large "magnitude" numbers. But it is an assumption and there's no real way to verify whether this assumption is valid. That's why the units on the Snore graphs are labeled as "Unknown" when you hover the mouse over the vertical scale of the Snore graph.
The VS 2 snores show up in Encore (all versions) as tick marks in the Events table based on the time stamp of the VS 2 event. But the calculation of the VSI index in Encore is not as straightforward as you would expect.
The Snore Indices in Sleepy Head and Encore
SleepyHead calculates the VSnore Index shown in the left sidebar of the Daily Details data as follows:
- SleepyHead VSnore Index = (# of VS scored during the night)/(run time for the night)
And so the SleepyHead VSnore Index is nothing more than the average number of VS snores detected in an hour of sleep (or more technically run time).
IMPORTANT NOTE: The VS 2 events are not used to compute this index. This is important because:
- If you are using a PR System One PRO or BiPAP PRO, your SleepyHead VSnore index will always be 0.0 even if you are snoring like a freight train because these machines record only the VS 2 snores; they do not record VS snores.
- If you are using a PR System One AUTO or BiPAP AUTO in FIXED pressure mode, your SleepyHead VSnore index will always be 0.0 even if you are snoring like a freight train because these machines record only the VS 2 snores when run in FIXED pressure mode; they do not record VS snores.
In other words, the SleepyHead VSnore Index will always read 0.0 if you are using a PR System One machine in FIXED pressure mode.
Encore calculates the VSI shown on the right sidebar of the Daily Detailed data in a really bizarre way. I can illustrate this with data from my own data. On July 31, 2013, I had 3 VS 2 snores scored for the entire night. In SleepyHead, the data looks like this:
Code: Select all
Vibratory Snore #2 3 events
#001: 06:43:58 (2)
#002: 06:54:13 (3)
#003: 08:27:51 (1)
Vibratory Snore 1 event
#001: 06:53:41 (0)
Total run time for the night was 5:31:47, which is 5.53 hours. In Encore, the VSI on the right side of the Daily Detailed Data panel is reported as VSI = 1.1. Now Encore only shows
three snore tick marks in the Events table on the daily data---one for each of the VS 2 snores. And the Encore Pro wave form shows only
one snore tick mark---the one for the VS snore. So the total number of (relevant) snores is either 3 or 4 depending on whether the VSI is computed using just the VS 2's in the Event table or both the VS 2's and the VS snores shown only in the wave form.
But it's obvious that 3/5.53 is NOT equal to 1.1 and 4/5.53 is NOT equal to 1.1. Hence Encore is not computing its VSI by simply dividing the number of VS2 snores recorded during the night by the time the machine was running. Nor is it dividing the total number of snores recorded during the night by the time the machine was running.
Instead, with a bit of mathematical backwards engineering, we can figure out that Encore computes the Encore VSI for the night as follows:
- Encore VSI = 1.1 = 6/5.53 - (2 + 3 + 1)/5.53 = (Sum of the "magnitude" numbers of the VS #2)/(run time)
And I've checked this "formula" out on many other nights---some with rather large numbers of snores and some with small numbers. And it always seems to be the case that:
- Encore VSI = (Sum of the "magnitude" numbers for the VS 2's as shown in SleepyHead)/(run time for the night)
Why would Encore define the VSI (Vibratory Snore Index) in this way? I have no idea. Mathematically it makes no sense. If the snores are being scored as "discrete" events (the same way the Flow Limitations are scored as "discrete events") then the intuitive meaning of VSI would be the average number of events per hour, and VSI ought to be (number of snores)/(run time)
So that then leads to the following speculation: Is it possible that the "magnitude" number on the VS2 snores represents something
other than loudness (severity) of the snoring? Perhaps the "magnitude number represents the length of time measured in (seconds? minutes? number of breaths?) that snoring was being detected? In that case, the Encore VSI would then represent the average amount of "snoring time" in each hour of sleep measured in (seconds? minutes? number of breaths?)
How does the machine detect snoring anyway??
The PR System One does not have a microphone attached to it. So it's not listening to the sound of your snoring. So how does it actually detect snoring?
It analyzes the wave form. When a person is snoring (at least when they're snoring loudly or persistently) there are some characteristic changes to the wave form, and the PR's analysis algorithms can pick that up. Exactly what the difference between the changes needed to score a VS and the changes needed to score a VS 2 are is anybody's guess. But some of the machines can be pretty sensitive to picking up vibrations that are coming from sources other than the patient's own airflow. Pugsy says that her VS 2 numbers are strongly correlated to whether or not her snoring dog is sleeping in the bed with her. Other folks have noticed that they can make the machine score VS2's by causing the hose to rub against a sharp edge of the nightstand or the headboard. And so on and so forth. But that said, real snoring is picked up by the PR System One as well as false snoring. You basically have to look at patterns in your own data and learn to interpret based on what you know is going on at night and what you think might be going on at night.
I'm aware that this post has likely provided you with both far more (technical) information than you may have wanted. But hopefully this will give you some things to think about when looking at your own snore numbers.
