How Does CPAP detect AHI events

I use an Airsense 10 by ResMed and continue to get AHI events. For the technophiles here I was wondering if any of you know what the system queues on to determine an apnea event and how it qualifies it? Using SleepyHead software I see the expected ramp-up rise at start up but then the system rises and falls several times from 15-6 mm during the night. I was curious what it is sensing to cause it to swing like that-

Thanks,
Fritz

sonnichs wrote:I use an Airsense 10 by ResMed and continue to get AHI events. For the technophiles here I was wondering if any of you know what the system queues on to determine an apnea event and how it qualifies it? Using SleepyHead software I see the expected ramp-up rise at start up but then the system rises and falls several times from 15-6 mm during the night. I was curious what it is sensing to cause it to swing like that-

Thanks,
Fritz

Due to copyrights and patents, most algorithms in Auto-CPAPs are slightly different, but most of them trigger pressure increases on Flow Limitations and Snores........believing that those events precede apneas. However, not all apneas are preceded by those events. It also takes (at least) 10 seconds of non-breathing for them to qualify an event as an apnea. Hypopneas are categorized as partial decreases in airflow and Flow Limitations in even smaller characteristics (like the "shape" of the breath curve).

They have different responses (time and effort) to those events and also in when they drop the pressure again.

And, most machines don't directly increase pressures on apneas........just the (supposed) preceding events.

Obviously, all of these machines use sophisticated types of sensors to detect these events based on "air flow", too.


Den

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sonnichs wrote:I use an Airsense 10 by ResMed and continue to get AHI events. For the technophiles here I was wondering if any of you know what the system queues on to determine an apnea event and how it qualifies it? Using SleepyHead software I see the expected ramp-up rise at start up but then the system rises and falls several times from 15-6 mm during the night. I was curious what it is sensing to cause it to swing like that-

Thanks,
Fritz

How many events? Everyone gets some events. It's impossible to get rid of events completely. A reportable event is 10 seconds or more. An Apnea is a complete blockage and a Hypopnia is a partial blockage. Swings are the machine chasing events. How about filling in your profile with your equipment and post some Sleepyhead graphs.

sonnichs wrote:I use an Airsense 10 by ResMed and continue to get AHI events. For the technophiles here I was wondering if any of you know what the system queues on to determine an apnea event and how it qualifies it? Fritz

Apneas are a cessation of breathing and are reported if they last for at least 10 seconds on most cpap machines. If the air flow stops (you stopped breathing) the machine tries to determine if you are trying to breathe and can't or aren't trying to breathe. The first is an obstructive apnea and the machine typically sends little pressure pulses down the hose to you and analyzes the effect on pressure and flow. Since the obstructive event blocks the airway, the effect on the pressure in the air hose is greater than if the airway is open to the lungs. So you can't breathe even though your body is trying to - obstructive apnea.

If the airway is open, the machine still makes the same test but this time, the pressure response is reduced because it is dispersed over a much larger volume (the air hose volume plus the lung volume. When that is the case, the event is classified as a central apnea. I.e., you can breathe but you aren't currently.

Hypopneas are apneic events in which the air flow is reduced presumably by a partial collapse of the airway. This partial collapse causes a reduced air flow and the machine can measure the difference and classify it as an hypopnea.

A flow limitation is a tiny hypopnea in which the air flow is reduced just a little.