[Pressure] Mysterious Sleepyhead/OSCAR periodic pressure ramps with DreamStation BiPAP ASV?

[chrisj]

Hi All,

This is my first post after recently starting therapy for complex sleep apnea, so hello everyone!

I'm sure I'll have a lot of questions (and hopefully be able to help others answer theirs as time goes on).  I'm a professional software developer too so many be able to help with tweaks to SleepyHead / OSCAR as it's open source.  I've already written various scripts to convert between pulse oximeter data outputs and also discovered ways to optimize the process of getting data from various sources into SH/O. 

My latest trick is using a Toshiba FlashAir wifi enabled SD card which appears as a network drive in Windows, as if it's inserted directly into my laptop - means I never have to remove it from the DreamStation to get the data straight into SleepyHead/Oscar - if anyone wants tips how to do this I'm more than happy to help!   I also have a pulse oximeter I've set up with a Raspberry PI that does the same - writes pulse/hr data in a SH compliant format to a network drive so it's just available wirelessly automatically every day.

Anyway, I digress...   I was wondering if anyone with a DreamStation ASV unit or similar could help explain why I'm seeing a pressure ramp in my EPAP min almost every 9 mins?  It seems no matter what my EPAP min is set to, even in the absence of any events the machine will sit for 5 mins with the pressure at EPAP Min, then gradually ramp it up by 1.5cmH2O over the course of 3 mins, before ramping it back down again to EPAP Min over 1 minute.   This seems odd to me as these pressure changes shouldn't be necessary if I'm not having any OSAs.   It would appear as if it's an artifact of the ASV algorithm, but that seems like a significant enough regular pressure change to me to indicate it's actually a possible sensor defect or the like - plus, it doesn't /always/ happen... it seems to get itself into that cycle for a period of a hour or two then can be dine sat at EPAP min for 30 mins or so.  I see the same artifact in the thread on these forums 'forums/Thread-Woot-Dreamstation-900-AutoSV-Sleepyhead-Hack'

If you look at the Mask Pressure graph in the above thread, you can see starting at about 13:10 and ending at 14:40 this 'saw wave' happens every 9 mins, ramping the EPAP Min completely independently of what the PS is doing above it.  A screen snip of the same phenomena from my own output last night is attached below.

As you can see, my EPAP min sits comfortably at 6.0cmH2O for 25 mins or so at the start, then this weird repetitive ramping starts and happens every 9 mins over the course of an hour or so

Can anyone explain why this is happening or would this be a question for Philips Respironics?

Thanks so much for any input!


Chris

[Crimson Nape]

Hi chrisj! -

To help with the OSCAR project, please send a PM to the OSCAR Project Manager, Gideon, with your request to join the team. We are always looking for more contributors.

As far as the spikes; I'm guessing here, but the Philips algorithms employs a test pulse every so often to analyze the response. I refer to it as "poking the bear" code. The one I'm referring to is displayed more definitively in the Pressure graph rather than the Mask Pressure graph. Zooming in on the timeline will provide a better view.

Once again, Welcome aboard!

[Sleeprider]

The 1.5 cm increases are a characteristic of the Philips auto-pressure algorithm and is present in all machines capable of changing pressure (Auto CPAP, Auto Bilevel and Auto ASV). These are not pulses but a gradual increase and decrease of pressure over about a 2-minute period. The algorithm analyzes for improvements in flow rate and keeps or rejects the increase. This has been around on Philips machines since Auto CPAP was patented, and while it looks awful on a graph, it is just something you live with if you have a Philips machine. In my opinion it shows a poor sensitivity to flow rate and rate of inspiratory flow increase which is the foundation of the Resmed algorithm. e

The Philips design is not only weird in these periodic pressure increases, it is really slow to get ahead of events, especially in ASV and AVAPS advanced bilevel therapy. If you ever get the chance to change or trial a Resmed Aircurve 10 ASV, you will immediately see what I mean. We can''t tell very much about your therapy from the mask pressure graph alone, but your appear to be using EPAP min 6.0, PS min 4.0 and we don't see a lot of additional pressure support being added. The event at 23:20 shows how long it takes for the Philips to get to higher IPAP pressure to address whatever is going on there. The Resmed can do that in a single breath, prevent the event rather than respond to it, and it's like comparing a Model-T to a Ferrari Enzo.

[SarcasticDave94]

Yep the ScreamStation flaw strikes again. Try a full chart to show us what's going on overall. One change if possible to gain it would fix whatever ails you on this... ResMed AirCurve 10 ASV.

[chrisj]

Thanks both Crimson and Sleeprider for your replies!   I did suspect it might be something like that, it seemed a bit odd though there were long periods where this wasn't occuring at all but who knows what Philips do with their algorithms!

I don't have the finances to switch to an AirCurve 10 ASV unfortunately but that's a good tip for the future if my therapy doesn't yield good results.  I guess given time I'll see how it goes, but my spo2 levels are hugely improved using the DreamStation ASV (I did start with a DS APAP, my AHI remained 5-15 and no significant noticable improvements to my spo2 graph).

My AHI with this machine is almost always below 1 and it doesn't give me any issues sleeping tbh now I've found the right mask (F20).  Just want to make sure I'm not missing any tricks as I'm still experiencing a fair bit of EDS (I do believe there could be a lot of residual sleepiness though after estimated *20* years undiagnosed!).  I have a zeo too which I'll be using soon to see if there's any improvement in deep sleep duration (I was lucky to get 15-30 mins a night prior to treatment) - I just wanted to aclimatise fully to the PAP therapy first before I stick anything else to my face   

I do notice though that no matter what settings I use, my patient triggered breaths always seem to nosedive when I first fall asleep (sometimes this goes on as long as 20 mins or so) causing a relatively big desat in my spo2.  If you look at the attached you'll see this is particulary apparent at 2:00am and (worse) 8:40am (lie-in day ).  My pat triggered breaths, TV, MV, spo2 all dive.  Without the ASV my spo02 typically would drop about 10% lower at this point than it does with the ASV.

Is this 'normal'?  For that particulary session I had my EPAP min at 9 and PS at 5 - I found after a few weeks of experimentation that was giving me the best overall basal spo2 and lowest AHI typically (basal spo2 1-2% higher than with epap min 6, ps 4).  That said, I may be misguided and it might be better to just 'set it and forget it' at 8-4 as Philips recommend, and let my body become aclimatised with it over a much longer period to yield ultimately better results - is that what people tend to do?  I know it's what TheLankyLeft advocates quite heavily in his ASV settings YouTube guide.

Or, by setting it up 9-5 after my own relatively extensive experimentation, have I just compensated a bit for the delays in the Philips' ability to catch up and that's why my sp02 levels are more preferable with the higher setting?



Thanks again! 

Chris

[SarcasticDave94]

OK the chart is good overall. FWIW you can close the calendar with the triangle button and then turn off VS2 flags next time. It'll give a better chart view. I think this is about as good as you'll get with the Respironics.

Now that aspect of breathing stats dropping, this sounds like a respiratory condition. What other illness or disease involving the lungs and breathing do you have?

[chrisj]

Hi Dave,

Good to hear the graph looks good all round, that's a relief     Thanks for taking a look.

Re other conditions - none that I'm aware of!   I have no Asthma, COPD or anything suspected cardio-pulminary at this stage.  I had an ECG recently as a precaution which was normal.   I do however sometimes have lower than desirable spo2 in the daytime - but my baseline is around 96 so it's an edge case is anything .  I'm 6'2 and ~200lbs, so my BMI is only really just above ideal.  I'll be speaking to my GP later this week and think my next request will be for an ABG test to see if I'm perhaps retaining too much co2.

The reason I thought it may be a trait of a central condition though is because it happens every single time (well, 99% of them) when I first enter light/REM sleep after being awake, then it resolves itself after those few minutes and remains stable for the rest of the time I'm asleep.  I essentially enter a cycle of stopping breathing then the machine 'jump starts' me back to more regular TV/MV again... and once that short period has passed I'm free-wheeling.  I do intend to set up a camera too to see what position I'm sleeping in when this happens but I don't think it's dependent on that.

SH/DreamMapper seems to mainly indicate hypopneas which I believe to be central, as sometimes I catch myself doing it in the day and this can give me a general feeling of shortness of breath which I've put down to mainly being in my head.  When my AHI has been high in the past, most of the apneas have been centrals.

Cheers,
Chris

[SarcasticDave94]

Yes Hypopnoea can be, and were thought to be only, Obstructive in nature. Hypopnoea are 50-80% of a full Apnea BTW. We've concluded that in some cases, maybe even your own, Hypopnoea can be Central as well.

That pressure ramping is based on the machine and is just part of the brand algorithm flaw if you will.

Note that I've got a ResMed ASV myself and besides CA, I've had a diagnosis of COPD but this year been downgraded to Asthma and a heart condition called PVC, or premature ventricular contraction. I've had feelings of daytime CA but what they were in fact had yet to be determined. So I get your circumstance very well.

Regardless keep tabs on your info. Maybe upgrade your sleepyhead to OSCAR if you'd not done it yet. Maybe note the symptoms you're feeling with in a chronic basis to present to the doc.

As is the SV Auto is treating you OK, not great but acceptable if you are aware of the flaws. And yes if you ever get the opportunity to swap in the ResMed ASV jump on it. The ResMed version is much better.

[Sleeprider]

Something I notice in your chart is a 30 minute ramp, during which your tidal volume and minute vent are quite high. The cluster of machine triggered breaths results in very low tidal volume and a corresponding drop in SpO2 at 02:15 and 08:45. The BiPAP AutoSV is supposed to target tidal volume and this really represents a failure of the algorithm to do its primary job, and yet pressure never exceeds 17 cm or PS 8.0 from the set EPAP of 9.0.

It would help to know what your settings are including any backup rate or tidal volume target is being used, and especially the EPAP min, EPAP max, PS Min and PS max and/or IPAP max. If you can tolerate starting without ramp, I think some of the early problems can be avoided. If you minimize the daily calendar by clicking the triangle in the date line or using the view menu, many of the settings will be included in the graph.

[chrisj]

Hi Sleeprider,

The same occurs whether I use a ramp or not - to be honest I'm usually still awake when the ramp time expires anyway as it routinely takes me an hour or so to get to sleep

The PS is unrestricted and backup rate automatic.  For that particular session these were the full settings, could it be the machine is possibly defective?:

Machine Settings
 
Mode ASV
Min EPAP 9.00 cmH2O
Max EPAP 20.00 cmH2O
Min IPAP 14.00 cmH2O
Max IPAP 30.00 cmH2O
PS Min 5.00 cmH2O
PS Max 20.00 cmH2O
Breath Rate Auto
Flex Level 3
Flex Mode Bi-Flex
Hose Diam. 15mm
Humid. Lvl 3
Humid. Mode Adaptive (System One)
Humidifier Connected
Mask Res. Lock Off
Mask Resist. Off
Ramp Pressure 5.00 cmH2O
Ramp Time 30.00 Minutes
Ramp Type Linear
Show AHI On