Clear Airway Apneas High, Obstructive Apneas Low

Frequently, my AHI readings report low total obstructive apneas but high to very high total clear airway apneas, resulting in a higher than 5 AHI.

I believe that my CPAP machine is just reading irregular breathing when I am awake with the machine on (e.g., before I fall asleep or when I awake in the morning but before I get up) as a clear airway apnea, thus artificially inflating my AHI (which seems to be the sum of total clear airway apneas, total obstructive apneas, and total hypopneas divided by the number of hours of sleep).

Is there any other explanation for high total clear airway apneas with low total obstructive apneas ? How does a CPAP machine measure (decide to record) a clear airway apnea ?

You are correct in that the CPAP machine can report irregular breathing while you are still awake as apnea events. When going to sleep the ResMed machines minimize this effect by not counting any events until the ramp period is over. The newest machines when the ramp is set to Auto for time will detect when you go to sleep and end the ramp time. But, as you suspect when you are waking up this feature is not in effect and that period of time can increase the apnea count. About the only good way to get a handle on that is to use a freeware program called OSCAR which can read the data from the SD card on your machine and produce graphs of your whole night's sleep so you can see when apnea events occur.

Some call these false apnea events "Sleep Wake Junk", and disregard them. However, it is quite possible to have real central apnea (clear airway) events while obstructive events are low. Central and obstructive events are very different. Obstructive events are more common and can be reduced or eliminated by pressure from the CPAP to open the airway. Central events on the other hand occur with the airway open and more pressure is of no value. The better machines like the ResMed do not increase pressure in response to central apnea events. Central apnea events can be caused by many things, but the root element is the body deciding not to breathe. In most cases this is caused by a CO2 and Oxygen imbalance that is not stable. You have too much air, then too little, but the body has trouble bringing the balance under control. This is something you can see with OSCAR graphs.

If you download OSCAR you can post the graphs here for comments on what might be going on. You need a PC or Mac, and an SD card reader. I struggle with this issue and on average my CA events are about double the OA events. I have tweaked things with my CPAP and pretty much gotten it under control with my total AHI averaging currently at 0.82. But it takes time, and is not always successful. Here is a link to an article on potential causes. When you are on CPAP the first suspect is the CPAP itself. Using higher than require treatment pressure can cause CA events to go up.

https://www.mayoclinic.org/diseases-conditions/central-sleep-apnea/symptoms-causes/syc-20352109

I forgot to answer your question about how the CPAP machine detects the difference between CA and OA events. When flow stops it starts to oscillate the speed of the fan. It then watches to see what happens to the pressure. If the pressure does not oscillate with the fan speed or does not oscillate significantly then it determines the airway is open and classes it as an CA event. It holds the pressure the same and does not increase it. And if the pressure does oscillate with the fan speed it determines the airway is obstructed, and then will increase pressure to try and clear it. If the flow stop for 10 seconds or more it gets recorded as an event. If less than 10 seconds it is not recorded. If you zoom in the scale with OSCAR you can see the machine doing this activity. If the machine cannot distinguish between CA and OA, usually when mask leakage is high, then it records it as an unidentified event. Hypopneas are flow restrictions without a complete loss of flow and are determined just based on flow.

Your last sentence ("Using higher than require treatment pressure can cause CA events to go up.") catches my attention. Originally (years ago), the pressure on my machine was set relatively low (5), and my AHI readings were frequently high (over 10). I reset the pressure myself to double the amount and got the AHI to fall consistently to below 5 (but NEVER to as low as your average 0.82). More recently, however, I'm experiencing numerous nights of AHI at 10 or more (e.g., 17.8), driven by some alarmingly big total clear airway apneas (e.g., 78, or 97). On the other hand, my best AHI nights have occurred last week (1.8), when total clear airway apneas have been only 3 or 7 (with total obstructive apneas only 5 and 2). I'm happy when AHI is averaging 5 or below, but concerned when I have more nights with AHI above 5, and trying to explain why -- hence the attention to the total clear airway apneas number.

Do you think the higher pressure setting is causing the high total clear airway apneas number (when I'm falling asleep or waking up but staying in bed) ? (I have the sense that my better AHI nights occur when I fall asleep quickly and/or get out of bed immediately upon waking up.)