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[Pressure] APAP Algorithms for increasing / decreasing pressure?
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NorthernGuy Offline

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Machine: Philips Dreamstation Auto CPAP
Mask Type: Full face mask
Mask Make & Model: F&S Full face
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CPAP Pressure: 8-14
CPAP Software: SleepyHead

Other Comments: New (couple months) APAP user.

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Location: New York State, USA

Post: #1
Question APAP Algorithms for increasing / decreasing pressure?
I realize that the algorithms APAP machines use are probably prized, and highly proprietary, but I am curious about the basics of it.

I assume OA and H events cause the system to raise the pressure on a schedule until apneas/hypopneas decrease (or stop), but then why would it back the pressure down after it finds the level that is working well.

Too many CA or other proprietary signals may cause the machine to decrease the pressure until the OA and H events start to increase.

However, looking at my Sleepyhead data, I can see times when the pressure fails to increase more, even though events continue, and other times, when the pressure falls after being at a plateau for no apparent reason.

My Dreamstation seems to optimize to maintain the lowest pressure, not the most effective pressure at reducing AHIs.

Also, it seems counter-intuitive to start at the lowest pressure each machine start. Why not start at at the mid-point between the upper and lower limits, or even better, the last effective pressure - and then decide to go up or down?

I believe the reason why most people have to keep adjusting their lower pressure limit in APAP (at least for PR machines) is that the machine keeps starting there. From an engineering standpoint starting at the midpoint of the range, or even a random point between the limits, is bound to be "wrong" less of the time than starting at a limit (that's why they are call 'limits'). (Maybe some manufacturer will owe me royalties for one of those ideas in the future.)

Any thought's? Dont-know Do other APAP machines start differently or do they all start at the lower limit, each restart?
(This post was last modified: 07-08-2016 09:07 PM by NorthernGuy.)
07-08-2016 09:06 PM
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rkl122 Offline

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Posts: 74
Joined: Apr 2016

Machine: Philips Respironics System One 560P (Auto, Aflex, 60 Series)
Mask Type: Nasal pillows
Mask Make & Model: PR Dreamware Frame Med, Pillow MW
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CPAP Pressure: low 8.5, high 12.5, expting
CPAP Software: SleepyHead EncoreBasic

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Location: NJ

Post: #2
RE: APAP Algorithms for increasing / decreasing pressure?
(07-08-2016 09:06 PM)NorthernGuy Wrote:  ............
Also, it seems counter-intuitive to start at the lowest pressure each machine start. Why not start at at the mid-point between the upper and lower limits, or even better, the last effective pressure - and then decide to go up or down........
Hi. Your clinical menu should contain a feature called opti-start. Check it out.

-Ron

We are such stuff
As dreams are made on, and our little life
Is rounded with a sleep.
07-08-2016 10:15 PM
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chill Online

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Machine: DreamStation X500
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Sex: Male
Location: Vancouver, Canada

Post: #3
RE: APAP Algorithms for increasing / decreasing pressure?
I think the theory is that the low pressure should be set high enough to deal with most of your events. Then when/if things worsen (say you roll onto your back or go into REM sleep) the pressure increased to address that. If nothing further happens, it drifts back down to see if the conditions have improved. I think the theory behind that is that people tolerate lower pressures better, it is less disruptive to sleep. I bet that would be an interesting software engineering job.
07-09-2016 12:16 AM
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