Might be a silly Question (AHI}

Hi guy's, just a quick one, woke up early this morning and checked my machine {AHA} reading and it was a reading of 2. Back to sleep and woke up at normal time with a different reading of 1. Question is, so my full AHA reading for the whole night is 3????? or is it that I just had 2 Apnears in the first block of sleep and 1 in the latter????

Ahi is the average number of events per hour. So, if you slept 8 hours, an ahi of 1 would mean 8 events all night. An ahi of 2 would mean 16 events all night.

You probably had a few early on and then fewer later so the average went down.

Not a silly question. I too am interested in the variables as to when a machine adds separate sessions and averages them, or when it reports them separately. Is it based on timing and any sessions within a certain time frame get lumped together? Now I'm curious.

Not sure if it is different with other machines, but the Resmed machine counts all data from noon to noon. So, if I wake up after 4 hours and check the data, I will see what I have so far. If I then check it a few hours later, I will have the new total sleep time and new average. After noon, it resets to zero and starts over. I have to use the software to see the data once it passes that time. If I take a nap in the afternoon, that will get added to the next night's data.

I think the Respironics machines update at a certain time, so checking before then doesn't give complete information.

woody74 wrote:Hi guy's, just a quick one, woke up early this morning and checked my machine {AHA} reading and it was a reading of 2. Back to sleep and woke up at normal time with a different reading of 1. Question is, so my full AHA reading for the whole night is 3????? or is it that I just had 2 Apnears in the first block of sleep and 1 in the latter????

As mentioneventsd there are two math variables, (time) / (# of events) so when either variable changes the average will also change.

I know that waking up to check the display is not accurate as the machine may not have closed out the session to do the calculation at that point in time.

I think it is safe to check after the machine has been idle at least 1 hour.

Also worth noting there may also be some rounding errors included in the screen display.

woody74 wrote:Hi guy's, just a quick one, woke up early this morning and checked my machine {AHA} reading and it was a reading of 2. Back to sleep and woke up at normal time with a different reading of 1. Question is, so my full AHA reading for the whole night is 3????? or is it that I just had 2 Apnears in the first block of sleep and 1 in the latter????

The CPAP machine's display will just display (a simple) average over some period (may differ between machines/brands). You won't have a cumulative of three, it's per period. But then you need to be aware that if you have, for example, a low AHI, e.g. 2, for one 'session' — say you slept for 8 hours — then that does not mean you didn't have an episode during that 8 hours where your number of OA's or hypopnea were not high.

That's where averages fall down, we all wake up and want to see that rotten number 'AHI' on the device's screen being nice and low, but it doesn't tell the whole story.

I don't know if you are using any software to review your therapy data, I'm using SleepyHead, here's a screenshot from a session a few nights ago...



it shows the session (6h 22m) AHI average was 1.57, but looking at the AHI graph in SleepyHead shows that at one stage (around 1:00 AM) the AHI index went up as high as 5. But (again showing the value of using the software) looking at the data and seeing that they were all hypopnea events it makes it not so bad.

zoocrewphoto wrote:I think the Respironics machines update at a certain time, so checking before then doesn't give complete information.

I believe they do the same thing, however, their clock is somewhere around GMT, so they roll over at noon, england time