Difference between central and clear airway apnea

[PaytonA]

FOT is a little more than an attempt. There are over 20 years of data backing it up in other ventilation scenarios. Chest belts are a secondary measurement also and are not 100% accurate.

The subject of this thread is Central apnea versus clear airway apnea not central apnea versus obstructive apnea.

Sleepster:

Great job on your tweaking.

Best Regards,

PaytonA

[PaytonA]

Yes, but ....

It's also possible for there to be no signal to breathe and then the airway collapses and so the machine classifies the apnea as an OA, when it would be classified as either a central apnea or a mixed apnea on an in-lab sleep test.

And real mixed apneas are very likely to be misclassified as OAs by CPAP machines.

Now I have an off topic question or two.

At what point of the FOT does the machine decide whether or not the airway is open. For example:

Breathing cessation for 10 seconds
FOT starts after 4 seconds (for arguments sake)
The first 3 seconds of FOT show open airway
The next 3 seconds show blockage from the airway collapsing
At what point during the FOT does the machine decide and why??

Another question that this brings up relates to the cause for a central apnea turning into an obstructive apnea. Is it just coincidence or is there a thought that the central apnea allows the collapse? Against the continuous pressure of the CPAP?

Best Regards,

PaytonA

[0rangebear]

OK I have been following this thread very intriguing but you lost me on FOT

I thought he was a Nordic king in 9th century !

please explain

[PaytonA]

FOT, if I remember correctly, stands for Forced Oscillation Technique. It is what Resmed uses to determine if the airway is clear or obstructed. They send a series of small pressure pulses (about 1 cm at 4 cycles per second if memory serves me correctly) and analyze the return-kind of like sonar.

Best Regards,

PaytonA

[FrankNichols]

OK I have been following this thread very intriguing but you lost me on FOT

I thought he was a Nordic king in 9th century !

please explain

"Forced Oscillation Technique"

The CPAP machine pulses the air pressure and if the pulses echo back to the machine there is an obstruction, if there is no echo the pulses continue into the lungs and disappear - no echo.

You can see these as tiny 1 cm pulses in the flow diagram/Preasure diagram just before the CA.

Darn: PaytonA beat me -

[palerider]

Wasn't the subject clear airway versus central apnea?

indeed... but I didn't even see any reference to that in the first post... unless I missed it, it was like apples and oranges between the post and the subject.... *scratching head*

[palerider]

The CPAP machine pulses the air pressure and if the pulses echo back to the machine there is an obstruction, if there is no echo the pulses continue into the lungs and disappear - no echo.

it's not an echo, rather it's a difference in flow and pressure response.

if the airway is open, there's more flow with the pressure oscillation, and there's less pressure response, because the lungs are absorbing the pulses of pressure, like a pair of balloons.

if the airway is closed, then there's much *less* flow, and a sharper pressure response, because there's not as much to absorb the pressure fluctuations.

you can usually see this, if you zoom in on the flow and mask pressure traces. sometimes there's more flow and a fuzzier mask pressure trace, and that's a central, sometimes there's very little flow variation, but spikier mask pressure.. and that's an obstructive.

there's a lot of videos out on youtube, here's one that explains FOT and how it works:
https://www.youtube.com/watch?v=4GW97Xk06N8

[eseedhouse]

The CPAP machine pulses the air pressure and if the pulses echo back to the machine there is an obstruction, if there is no echo the pulses continue into the lungs and disappear - no echo.

it's not an echo, rather it's a difference in flow and pressure response.

4 hz is an extremely low frequency, well below the limits of human hearing. A 4hz tone has a wavelength at sea level of 282.5 feet, or 86 meters. This is a lot longer than your airway so 4hz is well above resonance and no standing wave can form. Any reflection would be too fast to detect, basically lost in the noise from the original pulse, I think. I believe that, rather, they measure the impedance of the airflow, which will increase as the "pipe" is shortened.

But I might be mistaken.

[palerider]

I believe that, rather, they measure the impedance of the airflow, which will increase as the "pipe" is shortened.

But I might be mistaken.

what they do is explained, quite clearly in the video linked...

if you want more detail, you'll have to read resmed patents.

[0rangebear]

Thanks-I get it -didn't mean to start a third topic in this thread.