Central Apnea vs Clear Airway

[Eishan]

Hi guys

I had done 3 sleep studies prior to use of APAP and below were the results

1st study : AHI - 32.8, CAI - 1.8, OAI - 23.1, HAI - 0
2nd study : AHI - 20.7, CAI - 0,   OAI - 5.2,   HAI - 14.9
3rd study : AHI - 22, CAI - 0.1, OAI - 2.4, HAI - 19.3

Based on the above, it seems that I may not have any significant central apnea events .

Nevertheless, upon using APAP, I noticed a description called CA which I understand is called central airway events being captured in my Oscar reports although the numbers are also always below 1.0. 

So are they both the same ? My initial thoughts are that they may not be both the same.

My understanding is that central apnea happens when the brain instructs the body not to breathe without the aid of any pressure. A high number ( more than 5.0 ) may be of concern since this could be due to a neurological problem.

As opposed to a clear airway event which happens with an aid of pressure using an APAP / CPAP whereby the brain will automatically think that i dont have to breathe and doesnt send a signal to breathe. The machine detects no breathing and sends a burst of air and depending on how it is received if the airway is blocked or clear. A clear airway is deemed when there is no obstruction. So am I right to conclude that technically it is  not a central apnea event as this is not a neurological problem per se ? So even if my  clear airway numbers in OSCAR are high , there is not much of a concern ?  

Seeking some clarification as I am confused about both terms. To make it simple, do I still have to monitor my clear airway events even if my sleep study didnt show any significant central apnea events ? If so, is it ( the CAI in OSCAR) still supposed to be less than 5.0 ?

P/S : Apologies for my rambling of words as I cant seem to express myself well when it comes to differentiating between a central vs clear airway event.

Thanks

[DeepBreathing]

G'day Eishan.

Yeah it's a bit confusing, but basically "clear airway apnea" is a more general term for all apneas which occur when the airway is open (not obstructed). "Central apnea" is more specifically a term for when the brain does not send the "breathe now" signal to the lungs. In practice the terms are used more-or-less interchangeably.

A non-central clear airway event could occur, for instance, if you have a brief arousal which causes you to move in the bed while not breathing. You can stop for 10 seconds or more so it counts as an apnea but it's not a true central apnea.

New CPAP users can experience true central apneas caused by the fact they are breathing more efficiently, which lowers the level of CO2 in the blood. This in turn causes the brain to think it's not necessary to breathe just now. This is called a treatment-induced or treatment-emergent central apnea and is quite common.

Provided the number of central or clear airway apneas is low, then there's no need to worry.

[Eishan]

Thanks DeepBreathing.
May I know your definition of low ?
Should the CA index  based on the Oscar reports be not more than 50% of the total AHI or must it be not more than 5.0 on its own ?
Is there a standard guide just for CA monitoring ?  If so, this could actually help me as I am currently in the process of "playing" around with my pressure settings. I was told by my Doc to ensure that the clear airway index number be always lesser  than the obstructive index number  to get the optimal pressure setting. Is this true ? For your information, I did not go through a titration study. Hence the pressure experimenting .

[JoeyWallaby]

CAs should be low/very low unless you have idiopathic central apnea, which you don't. Below 1.0 is not concerning unless they're long events.

[Gideon]

The medical community says 5 events per hour. The Medicare guide to get an ASV machine says 5 Central events per hour plus your obstructive events.
Around here we like to see at least half that.
Long events are a concern but they show as oxygen desats and an approach for them is needed if they are prevelent
}We try to minimize centrals because they are harder to treat, in fact CPAP, APAP, and BiLevel without backup (forced breathing) ignore Central events and literally do nothing

[SarcasticDave94]

As one who's been diagnosed with pre-existing CA (myself), I need all apnea events addressed via the machine. Some people are more or less sensitive to any events. There are some patients who will be more disturbed by events, and others are less disturbed regardless of event type. I think it's best practice to get all apnea events below 5, but a zero AHI isn't required. Once apnea therapy gets you below 5 fairly consistent, then our focus is gaining comfort while not allowing AHI to go up if possible.

[Sleepster]

Another thing you want to look at is how long those CA events last. 10 seconds is pretty low, and that's all it takes to score a CA. On the other hand, if they last for 60 seconds, that's more of a concern.

[ApneaQuestions]

One other comment on treatment-emergent CAs...

If you are getting CAs due to the use of a PAP machine, they can spontaneously resolve themselves after 2 or 3 months of usage (but not always).
The theory is that your breathing is more efficient with a PAP machine and decreases the C02 levels in your blood.
This causes the brain to suppress the breathing reflex since there is a low C02 level in the blood and therefore no "need" to breathe for the time being.
After 2 or 3 months, the body often acclimatizes to the new lower CO2 levels and the breathing response self-regulates and the CAs disappear.
If CAs persist at a high level then an advanced machine such as the ASV may be indicated.

I also have link in my sig for treatment-emergent CAs

[Sleepster]

After 2 or 3 months, the body acclimatizes to the new lower CO2 levels and the breathing response self-regulates and the CAs disappear.

Not always. Sometimes it persists and has to be treated, but in most cases it does go away as we adapt.

Also, if you have a bi-level machine, too much pressure support can induce CA's.