AHI

[Gideon]

Thanks Red

[hh9797]

My AHI on the Resmed Apap (Airsense 10) sits between 1 and 3. Whilst I understand what the AHI is, it isn’t entirely clear how the machine arrives at this number.

Many thanks to anyone who can help clarify this apparent mystery.

"Whilst I understand what the AHI is, it isn’t entirely clear how the machine arrives at this number. For example, if the AHI is 2 does this mean I had two apnoea/hypopnoea events per hour that it TREATED or does it mean the machine treated MORE than two events per hour (which aren’t reported) but the two events were the ones it didn’t manage to treat successfully? " - The machine is reporting how many events you had even with the machine, so if your AHI was say 2.0 over 6 hours and 2 minutes that would mean that durring that 6 hours 2 minutes you had 12 events to average of like 1.989 rounded to 2.0. Which means roughly twice per hour you either stopped breathing for at least 10 seconds (wither central or obstructive) or had partial breathing (hypopnea).

 If the former is the case then that would imply that my AHI of 2 is in the normal range and that wouldn’t warrant any treatment? - It is the amount of events you had despite using the machine, even if you were to have that number near 0 for months straight, unless you resolved what was causing the issues you would still need to use the machine to keep them at those levels otherwise they would just return to pre treatment levels. So say most your apneas were caused by obesity and you lost 80 pounds back to a healthy weight you could potentially not need treatment at that point, but the machine itself does not cure anything, it just treats the issue allowing you to not have the symptoms of what is causing the issue, so just because your numbers are in a normal range now does not mean you can stop treatment unless you want things to just return to pre treatment levels if you didn't treat the cause. Think of the machine like taking a cough suppressant if you have chronic bronchitis, it treats the symptom of the cough caused by the bronchitis but it does not treat the chronic bronchitis.

Edit: And just because the machine treats the symptoms and not the cause does not mean that it is not necessary or a waist of time because the symptoms it treats are symptoms that can cause much larger issues if left untreated, just like a rescue inhaler does not cure asthma but does treat the symptoms of asthma that is extremely dangerous. Now saying that makes me realize that maybe I should have used Asthma as an example instead of chronic bronchitis, but regardless I will leave it in so that there are two examples of times you would have treatments for symptoms instead of cures for the causes of the symptoms since there is no cure for asthma or chronic bronchitis, just treatments to keep them managed.

[Gideon]

My AHI on the Resmed Apap (Airsense 10) sits between 1 and 3. Whilst I understand what the AHI is, it isn’t entirely clear how the machine arrives at this number. For example, if the AHI is 2 does this mean I had two apnoea/hypopnoea events per hour that it TREATED or does it mean the machine treated MORE than two events per hour (which aren’t reported) but the two events were the ones it didn’t manage to treat successfully? If the former is the case then that would imply that my AHI of 2 is in the normal range and that wouldn’t warrant any treatment.
My guess is that there may be a predictive algorithm involved that anticipates an event and intervenes before the apnoea/hypopnoea criteria are triggered.
Many thanks to anyone who can help clarify this apparent mystery.

The crossed out portions are not true, the bold stands by itself and is true.

The ResMed AutoSet algorithms see obstructive events and increase pressure when they are seen.  Generally, it will see Flow Limits first (and Obstructive Apnea and Hypopnea) and raise pressure to ward off future obstructive events.  The premise of CPAP is that pressure is high enough to ward off these events, but starting at 4 is too much.  Generally, exhale pressure must be set at a value that prevents most obstructive events then the auto algorithms can do a fair job on the rest.  Even with that, you want at least some EPR because the differential pressure that uses between inhale and exhale offers excellent treatment (prevention of) Flow Limits, RERAs,  and Hypopneas.  The only events that are presented are those the machine failed to prevent.  There is no way to know how many actually were prevented.  Generally, it is assumed/guessed that you would have had the same AHI as your sleep study every day (you will not) and the difference is what is considered prevented.