AHI — the average number of apneas and hypopneas scored per hour of therapy — is the
number everybody fixates on, because it is a single digit and it goes up and down. It is
genuinely useful. It is also routinely over-read.
Things worth holding onto:
It is an average over a whole night. Two nights with the same AHI can look nothing
alike: one with events scattered evenly, one with a clean first half and a wall of
events at 5 a.m. The second is telling you something the number is hiding.
Night-to-night variation is normal. Alcohol, a cold, a late meal, sleeping on your
back, a bad mask night, or simply more REM will all move it. A single high night is not
a trend; three weeks of drift is.
Your machine scores events its own way. Manufacturers do not all define or detect
events identically, and no home device is doing what a scored sleep study does. Compare
your machine against itself over time, not against a friend's different machine.
A low AHI does not automatically mean you feel well. Leak, arousals, mask discomfort
and plain insufficient sleep are not in that number at all.
The useful question is almost never "is 3.2 good?". It is "what changed, and does the
shape of my nights match how I feel?".
If you want the longer version, the Reading Your CPAP Data section of the Library
covers AHI, RDI and how severity bands are drawn.
Nothing on SomniTalk is medical advice. Talk to your own clinician before changing therapy.
