:?: How does the CPAP detect central vs obstructive events?

Hi, I'm new to this, tonight will be my 7th night with the CPAP. I'm very glad to have found this board!

I had a home sleep study with an AHI of 22 (which they called very severe but I'm seeing higher numbers posted here). According to the study those were all OSA. This little machine is reporting a mix of obstructive and central apneas. How is it measuring that, from a technical standpoint? Is there any reason to think that is actually happening?

thanks much
Betsy

(I have a Resmed Airsense 10 and two masks, a nasal pillow and a full face ,haven't settled on which one yet)

Like this: https://www.youtube.com/watch?v=4GW97Xk06N8

The machine will inject a wave of varying pressure. If it sees the same wave at the flow sensor input, it knows that there is an obstructed airway. If it doesn't see the wave, it assumes the airway is clear.

From what I have read, true central apneas are rare as hell. If you have a problem with them, somebody is going to tell you and do a lot of investigations. So don't worry about it at all.

EDITED: to clarify that the machine is looking for the pressure wave on the flow sensor

mrCanoehead wrote: ↑

Sun Feb 17, 2019 3:06 pm

The machine will inject a wave of varying pressure. If it sees the same wave at the sensor input, it knows that there is an obstructed airway. If it doesn't see the wave, it assumes the airway is clear.

Not really.

mrCanoehead wrote: ↑

Sun Feb 17, 2019 3:06 pm

So don't worry about it at all.

That's most likely true, though.

palerider wrote: ↑

Sun Feb 17, 2019 3:08 pm

Not really.

To me, if the machine is pumping into a confined, relatively limited, relatively rigid channel that is foreshortened by an obstruction, the pressure wave will be seen at the flow transducer. If the air is making it into the lungs, the volume expansion will attenuate the pressure signal.

EDITED: to clarify that machine is processing the flow signal to look for evidence of the pressure wave

mrCanoehead wrote: ↑

Sun Feb 17, 2019 3:20 pm

palerider wrote: ↑

Sun Feb 17, 2019 3:08 pm

Not really.

To me, if the machine is pumping into a confined, relatively limited channel that is foreshortened by an obstruction, the pressure wave will be seen at the pressure transducer. If the air is making it into the lungs, the volume expansion will attenuate the pressure signal.

How it works is clearly described in the video Iinked. It's a combination of the flow and pressure results in response to the 4hz pressure fluctuation.

Pretty sure my description of the pressure bit is correct, or at least that is what I see in my Sleepyhead data. Do you know the patent number?

Thank you both, that makes sense. So central apnea the air way is open, and the machine doesn't have an O2 sensor - so is it just saying there is too big a time gap between breaths?

betsys wrote: ↑

Sun Feb 17, 2019 3:36 pm

so is it just saying there is too big a time gap between breaths?

That is correct.

mrCanoehead wrote: ↑

Sun Feb 17, 2019 3:34 pm

Pretty sure my description of the pressure bit is correct, or at least that is what I see in my Sleepyhead data. Do you know the patent number?

Pretty sure it's *clearly described in the video*.

Find your own patent numbers. patents.google.com

Spare me from know-it-all newbies. :sigh: Been here half a month, can't figure out how to connect a mask without help, but knows all the answers, willing to argue to the death.

I give up.

Be kind.

Thank you all for the info!

Hi Betsy - the video that palerider posted is the explanation from the manufacturer so it applies to your machine. this paper is one I found very helpful if you want to understand things from a rather technical standpoint, and the differences between the algorithms of different brands or versions of machines.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4629962/

These seem to be the most recent patents if anyone is interested:

http://www.freepatentsonline.com/9028423.html

https://patents.google.com/patent/US7730886

This is the key part:

or (c) there is patency of the airway, determined by the steps of:
(i) applying an oscillatory pressure waveform of known frequency to the patient's airway;
measuring respiratory air flow from the patient; and
determining that the airway is patent if there is a component of said air flow at said known frequency induced by said oscillatory pressure waveform;
or (ii) measuring respiratory air flow from the patient; and
analysing said measured air flow to detect the presence of cardiogenic air flow, and if so then the airway is declared patent.

Hope that helps.

mrCanoehead wrote: ↑

Mon Feb 18, 2019 6:15 am

These seem to be the most recent patents if anyone is interested:

http://www.freepatentsonline.com/9028423.html

https://patents.google.com/patent/US7730886

This is the key part:

or (c) there is patency of the airway, determined by the steps of:
(i) applying an oscillatory pressure waveform of known frequency to the patient's airway;
measuring respiratory air flow from the patient; and
determining that the airway is patent if there is a component of said air flow at said known frequency induced by said oscillatory pressure waveform;
or (ii) measuring respiratory air flow from the patient; and
analysing said measured air flow to detect the presence of cardiogenic air flow, and if so then the airway is declared patent.

Hope that helps.

As clearly stated *in the video*.

Are you unable to access youtube?