SleepyHead Anomoly

[jdm2857]

See anything strange here?


In BiPAP Auto mode, EPAPmin = 14, EPAPmax = 25, PSmax = 4. On my 750, PSmin is always 2.

Yet in the pressure graph, EPAP starts out at 13, which is less than EPAPmin. And since the initial IPAP is 14, initial PS is 1, which is less than the machine's minimum of 2. EPAP is below EPAPmin for most of the night.

I've looked at the same data in Encore Basic. While the shape of the graphs is the same, EPAP starts out at 14, and IPAP at 16.

I'll see what happens tonight. Has anyone else seen this type of problem?

Oh, BTW, I was awake during the nasty-looking first 20 minutes.

[Pugsy]

Is ramp on by any chance?

[robysue]

@pugsy,

ramp wouldn't explain those very long periods of time in the middle of the night with EPAP = 13.


@OP,

I'd suggest that you also look at the machine's LCD when you first put the mask on tonight. Once you start the BiPAP, the LCD should show you the pressures it thinks its delivering: It should say E 14 and I 16 and switch back and forth as you exhale and inhale.

Can't say I've ever seen this bug in the 2+ years I've been using SH. But then, my min EPAP = 4cm and so there's not really anywhere lower to go.

As for other oddities in your data: That nasty 20 minutes where you were awake at the beginning of the night? It looks like the AHI graph is also wrong since the AHI graph tops out at 3.8 and you clearly had more than 4 OAs during that 20 minute period. Quite frankly, the whole AHI graph looks strange compared to what I typically see in mine. In my AHI graphs, the graph jumps by increments of 1 for each new event and decreases by 1 each time an event turns 60 minutes old and is dropped off the hour time frame. But maybe you have the default settings on your AHI graph set differently than mine. (The preferences for the AHI graph are under the CPAP tab for the Preferences panel. Mine has a window set to 60 minutes.)

[Pugsy]

I had some whacko pressure lines a while back...SH was reporting them being totally less than what they were on the graphs themselves. Like EPAP at 8 when it was at 10...messed up my IPAP also. Encore was reporting them correctly.

Go to Preferences/ Appearance tab and remove the check mark from "use Pixmap caching" and see if the pressure lines correct themselves.

I mentioned maybe ramp because the initial stair step thing looks like ramp to me...it was just an observation that in hind sight was meaningless to your question but I had to think a little bit to come up with the pixmap thing..it was on the tips of my fingers as a possible explanation for the bug but took a little while to materialize (long version of I was trying to remember what I did when SH went whacko on me)
I was thinking out loud.

[jdm2857]

I thought I had turned Pixmap caching off preemptively.
Operative word being thought.

Turned it off now and the graphs are now correct.

Interesting that it only affected the one night.

Thanks, Pugsy.

[Pugsy]

Interesting that it only affected the one night.

Mine was random...sometimes several nights in a row they were whacko and then they would be fine for a while.
I don't know why or what turning that feature off does...but it worked for me. I haven't had it happen since I turned it off.

[DreamDiver]

Do you suppose it might be time to check the blower with a manometer?
Edit: Oh - it looks like it was SH itself in the pixmap cache. Huh!

I've noticed that if you have two oximetry sessions on the same day, I have to close SH and open it again for them both to show. That might be the same fix.

[Pugsy]

BTW...this happened with either brand of machine I was using...so wasn't limited to the PR S1...I saw it with the S9 also.
Since I also used either Encore or ResScan to check pressures and pressures were correct...I knew it was in SH...so just a little bug.

[jdm2857]

I just did a bit of research.

A pixmap is a way (one of may) to store images in computer memory.

A cache is a place in computer memory to store frequently used data.
The benefit is that if set up properly, retrieving data from the cache
is faster than the usual data retrieval methods. (This may be because
the cache memory is faster than regular memory, or because it saves
having to recalculate complex data.)

In this case, pixmap caching is the storing of image data (the graphs) to
avoid having to recalculate them. But somehow, sometimes, the storage
or retrieval is screwing things up.

I think that this explanation is basically correct. If it's not, I'm
sure I'll hear about it.

[DreamDiver]

I think that this explanation is basically correct. If it's not, I'm
sure I'll hear about it.

I think you nailed it. That's why I think it's the same problem I've been seeing in the multiple oximetry session oddness. I'm going to check it out next time I have a day with two saved sessions. Many modern computers probably don't need caching set, but it's nice to have it for really slow machines.