I am not an expert by any means, but my understanding is that as you get past 4 hours of sleep, the length of your REM cycles go up quite dramatically, and REM sleep is often associated with breathing disturbances, including apnea. I often find that I wake up at 5-6 hours with an AHI <2, and then I go back to sleep and wake up with an AHI that has jumped up dramatically during the last two hours of my sleep cycle.
Since you have a Respironics Autoset machine, every time that you have an apnea lasting > 10 seconds, you get a pressure pulse that the machine uses to detect whether you're having a central apnea. Those pulses may disturb your sleep and even wake you up, especially when you have several in a row. Imagine your wife/spouse/partner grabbing your mask and bouncing it everytime that you have an apnea, and you'll get the picture. You might want to try a machine that doesn't do central apnea detection. Without those pulses, you may find that you sleep better during the last few hours. I know that I do.
Finding a machine that doesn't send those pulses isn't easy. Resmed's machines actually send MORE pulses - they start at 3 seconds into the apnea and continue until you start breathing again. Only the entry level Resmed CPAP and the entry level Respironics CPAP machines send no pulses. The Resmed AirStart 10 CPAP ($349 at
Supplier #1)
Commercial Link Removed also sends no pulses. However, all of these machines are bricks - they give no detailed data at all. And the AirStart gives NO data, not even a summary showing AHI at the end of the night.
The Resmed AirCurve 10 VAUTO can be configured NOT to send the pulses (in S mode with Easy-Breathe Off). I use that and love it, but I hate that I had to pay double the price of a CPAP machine just to turn off the pulses. I believe that ST and ASV machines also do not send the pulses, but they're even more expensive. These machines do give both detailed data AND summary data, but they are all super expensive.
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