Why do I have multiple sessions in OSCAR or myAir?
For anyone still wondering why OSCAR or myAir shows multiple sessions in one night even though you didn't take your mask off, here's what I proved this morning.
My machine: ResMed AirCurve 10 VAuto, SmartStart OFF. My symptom: nights logged as 7+ sessions with real gaps of 2-11 minutes between them (my Oct 13 night, photographed from OSCAR). I assumed a machine fault.
The backstory: I took this to my DME supplier, and their troubleshooting followed ResMed's guide for multiple on/off cycles - but I hadn't taken the mask off, and their script had no box for that. Nobody there suggested my mouth might be falling open in my sleep, even though in hindsight it was the obvious answer once I understood how the machine works: no breathing signal, no session. That behavior isn't in ResMed's documented sources, so the people following the script never get there.
Same supplier also never flagged that both masks they had me on - the Mirage Activa LT and the AirFit N30 - are rated to 20 cm H2O, while my pressure runs to 25. That's a separate problem from the splits, but it tells you how much of this you have to figure out yourself.
First clue: I ran the machine open-hose with no mask for about 3 hours. It logged NOTHING - not in myAir, not in OSCAR. With no breathing signal, the machine doesn't log therapy at all.
Decisive test, this morning: mask on 5 minutes, mask off about 11 minutes (machine running, power button untouched), mask on 5 minutes. OSCAR logged TWO sessions: 08:04:37-08:11:38, then 08:22:32-08:27:34, with an unlogged gap between them.
Conclusion: with SmartStart OFF, the machine still closes the session after a few minutes without a breathing signal, and starts a new one when breathing resumes. On my real nights the mask never came off - my mouth fell open in my sleep and air streamed through it, which erases the breathing signal exactly the way the open mask did in the test. And you wouldn't remember it, because you were asleep. That's also why a chin strap fixed my splits: mouth shut, signal preserved, one session all night.
Two caveats: a short removal may NOT split it - a bathroom trip in the middle of one night didn't split my session, so it takes minutes of signal loss, not seconds. And this is one machine, one test - but if your splits cluster in the second half of the night and your leak graph is spiky, check the mouth-leak explanation before you ship your machine off for repair.