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You open your pressure chart and the line steps up in the early hours. Nothing is wrong with your machine. An auto-adjusting CPAP is built to move, and the second half of the night is when it often has the most work to do.
Key takeaways
- Auto machines raise pressure inside your set range when they detect more airway resistance.
- Rises late in the night are common, because REM sleep and back sleeping tend to cluster there.
- A pressure line that sits at the ceiling of your range night after night is the pattern worth raising.
What an auto machine is doing
On an auto-adjusting setting your clinician chooses a minimum and a maximum pressure. Inside that range the machine reads your breathing, looks for signs of narrowing such as flattened inspiratory flow, snoring or an event, and steps pressure up. When things settle it eases back. Our guide to CPAP pressure settings explains the range, ramp and EPR.
Why the climb often comes late
Two things line up in the last third of the night. REM sleep is more concentrated in the second half, and during REM the muscles that hold the airway open relax further, so breathing events tend to be more frequent and longer in REM. People also drift onto their backs as the night goes on, which narrows the airway for many sleepers. A machine that sees more resistance at that point will ask for more pressure.
| What the pressure line does | A reasonable first read |
|---|---|
| Gentle rise in the early morning, then back down | Normal auto-CPAP behaviour |
| High only on nights after alcohol or a late meal | A lifestyle trigger, not a machine problem |
| Rises with leak at the same time | Check the mask seal first; leak and pressure interact |
| P95 pressure sits at your maximum most nights | Worth raising with your clinician: the range may be tight |
What to look at
Read the pressure line alongside the leak line and the event markers. The single most useful number is the 95th-percentile pressure, which shows where the machine needed to be during the hardest 5 percent of the night; P95 pressure in plain English explains why it beats the maximum. In Apnealytics the pressure chart shows your set range as a band, so you can see at a glance whether the line brushes the ceiling.
Not medical advice. Apnealytics is a tracking and coaching tool, not a diagnostic device. Machine-estimated numbers are not a clinical diagnosis; talk to your clinician about your therapy.
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Written by
Haniel Singh
Founder of Apnealytics. A CPAP user who builds software, not a sleep physician.
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