AHI Computation

I was wondering if the AHI is computed on the time the machine is on, or
the time you are sleeping or the some other indicator.

I ask this since my Resmed seems to know the time i go to sleep. (SmartStart function does not turn on your pressures till it senses that you are asleep).
Does it also factor out any wake up times? Could it know that in the same manner as your sleep commencement?

If you read in bed with the machine on for any length of time, would that affect the AHI?

These machines have no clue if we are asleep or not.
SmartSense is only for breathing...has nothing to do with sleep. The machine senses a human is breathing on the other end and it turns itself on and has nothing to do at all with sleep vs wake.
Now the Auto ramp thing...maybe it can but that's just for ramp.
In general the AHI you see is base on an average for when the machine is turned on and then off. You could lay awake for 4 hours using the mask and machine and the machine still will factor those 4 hours into the calculations.

Sometimes awake breathing is irregular and these machines only measure air flow and sometimes our irregular awake breathing will trigger a flag from the machine. If you are reading and you hold your breath for 10 seconds (and we pause our breathing all the time and not realize it) the machine will likely give you a 10 second central apnea flag. So yes, reading in bed with mask on might impact the AHI a little...probably not a lot though.

AHI

Instead of using AHI, it's best to use Sleepyhead to view individual events, how long they are and when they happen.

Allessio77 wrote:I was wondering if the AHI is computed on the time the machine is on, or
the time you are sleeping or the some other indicator.

I ask this since my Resmed seems to know the time i go to sleep. (SmartStart function does not turn on your pressures till it senses that you are asleep).
Does it also factor out any wake up times? Could it know that in the same manner as your sleep commencement?

If you read in bed with the machine on for any length of time, would that affect the AHI?

The AHI is calculated by dividing the time the machine is on divided by the number of events. The machine does not know if you are sleeping or not. It just knows you are breathing. Example....If you have the machine running for 8 hours and you were reading for 2 of those hours, with 16 events the AHI calculation would be 2.0. In reality you were sleeping for only 6 hours and the true AHI is 2.66.

I just wanted to add that the PA at my sleep Dr. told me that the hypopnea identification is not that great on xPAP's. Her advice was to take the hypopnea number with a grain of salt.

LSAT wrote:It just knows you are breathing.

... or not breathing:

TASmart wrote:I just wanted to add that the PA at my sleep Dr. told me that the hypopnea identification is not that great on xPAP's. Her advice was to take the hypopnea number with a grain of salt.

ResMed S8's notoriously over counted hypopneas. I haven't heard the same about S9's and later.