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Respironics 9 minute cycle with no events.
I have a respironics system one. Generally, everything is working fine, according to sleepyhead AHI is usually less than 2. My main problem is compliance, as I already have a strong tendency towards insomnia, and cpap tends to make it worse. However, when I can fall asleep with the mask on, everything is good. I have pressure set at 5 to 15.

My question relates to what the machine records: whenever I'm asleep for an extended period with no events recorded, the machine seems to go through a 9 minute cycle where it ramps the pressure up from 5 to 6 over a 3 minute period, then ramps it back down to 5 over 1 minute. Then it waits 5 minutes before repeating the process. According to sleepyhead, no events are recorded during this time, and I can't see anything in the recorded data that looks different.

Does anyone know why the machine is doing this? Once again, it's not causing a problem, I'm just trying to get a better understanding of how the machine is working.

I've attached a screen shot showing the pulses.

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Hi, pixpop. I have a PR System One machine and asked the exact same question the first time I ran it in Auto-Trial mode (my machine is a 460, a fixed-pressure CPAP).

I think it's called a "search algorithm", with the machine making changes in the pressure to try to determine whether or not an improvement in breathing is detected. I know that the machine can detect less-than-perfect breathing that still doesn't meet the requirements to be scored as apnea events or even flow limitation. I'm not clear whether the search algorithm's pressure changes are in response to something it detects or whether it just automatically tries higher pressure to see what happens.

There's a short bit about the search algorithm in the Beginner's Guide to SleepyHead wiki:
Quote:Question: Why is my pressure increasing when there don't seem to be any events?
Answer: APAPs (and Auto bi-levels) increase pressure in response to OAs, Hs, snoring, and flow limitations. The Philips Respironics System One APAP and BiPAP Auto also increase pressure in response to RERAs. The Philips Respironics System One also has a "search" routine built into its Auto algorithm, and it will periodically increase the pressure as a "test" to see if the shape of the wave flow improves, even if nothing is being scored. Those test increases show up as saw-teeth on the pressure curve.

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Hi pixpop,
WELCOME! to the forum.!
Good luck to you as you continue your CPAP therapy.
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