Clear Airway Apnea = Central Apnea?

General Discussion on any topic relating to CPAP and/or Sleep Apnea.
-SWS
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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Fri Jan 01, 2010 4:28 pm

dsm wrote:Also if any cpap manufacturer used reflective wave technology, you would need a doppler radar speed-gun to accurately measure the speed of their apnea
Forgetting about CPAP for the moment... There are diagnostic FOT methods that map airway impedances. Those FOT mapping techniques rely on pressure-pulse wave reflection. ...And I thought that's what Weinmann did as well, before abandonning the technique altogether.

Didn't the Weinmann marketing people formerly draw parallels between their own FOT technique and wave-reflection based SONAR?

dsm wrote:Weinmann appeard to use conventional fot bursts.
Oh? Well that answers that question. So what other details can you share about Weinmann's FOT?

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Re: Clear Airway Apnea = Central Apnea?

Post by dsm » Fri Jan 01, 2010 6:14 pm

-SWS wrote:
dsm wrote:Also if any cpap manufacturer used reflective wave technology, you would need a doppler radar speed-gun to accurately measure the speed of their apnea
Forgetting about CPAP for the moment... There are diagnostic FOT methods that map airway impedances. Those FOT mapping techniques rely on pressure-pulse wave reflection. ...And I thought that's what Weinmann did as well, before abandonning the technique altogether.

Didn't the Weinmann marketing people formerly draw parallels between their own FOT technique and wave-reflection based SONAR?

dsm wrote:Weinmann appeard to use conventional fot bursts.
Oh? Well that answers that question. So what other details can you share about Weinmann's FOT?
SWS

I always understood Weinmann used FOT in the early machines they tried the technique in. I really don't know what is in the SOMNNOVent CR. I suspect you are probably right that they use a variant of SONAR or another technique.

Re reflective wave - I was humously commenting on the radar use - in radar of course, it is reflected waves that detect on object in the distance. With SONAR it is reflected sound waves (some models of the polaroid camera uses SONAR to measure distance). Doppler uses phase shifts to detect change in speed of the target object.

I really have no specialist knowledge of waves used inside the human body but was thinking that it might be possible to measure distance (where is the blockage - at throat or end of lungs) by sending bursts of oscillations (say between 3000-5000 HZ) in 100 or so millisec bursts stepping up by 500 HZ each 100ms(or so) & try to sense the time lag when a particular reflected frequency is detected back during that overall burst. But, reflecting off soft tissue seems such a challenge.

I can't see how a fixed frequency FOT burst could be adequately detected for anything other than is the air moving overall ?. But, this is a very interesting area of new technologies.

Cheers

DSM

#2 Added: Most sonar devices rely on a seperately located (positioned) transmitter & detector. They also send a burst then listen for a bounce back then 'ping' again after a safe period.
For xPAP machines, they basically have to put *both* transmitter & detector in the exit close to where air exits the machine. Sending a same frequency burst from a transducer located next to the detector where distance to the block is 7 to 9 feet (allowing up to 24 ins between throat & bottom of lungs) doesn't seem viable to me - there seem to be lots of timing issues - but this technology is intriguing.
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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Fri Jan 01, 2010 10:48 pm

dsm wrote:I can't see how a fixed frequency FOT burst could be adequately detected for anything other than is the air moving overall ?
Well, as it turns out spectral analysis of fixed-frequency oscillation can actually be used to calculate an overall respiratory impedance:
http://www.nicoletvascular.com/prod_ser ... ra_ch5.pdf

And I thought that's what Weinmann formerly employed before dropping the technique altogether. Perhaps I remembered the Weinmann implementation wrong. Probably did...

Anyway, that technique would be very different than simply detecting a basic "yes forward-pulse-flow" versus "no forward-pulse-flow" condition. For instance, calculating total respiratory impedance (comprised of airway resistance, elastic and inertive lung and chest wall characteristics) now means that central hypopnea versus obstructive hypopnea differentiation becomes technically feasible as well.

One FOT technique works with coarse forward mass airflow, while the other technique works with vibratory or spectral type reflection.
Last edited by -SWS on Fri Jan 01, 2010 11:22 pm, edited 1 time in total.

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Re: Clear Airway Apnea = Central Apnea?

Post by Jay K » Fri Jan 01, 2010 11:21 pm

Barry, How do the overall AHI numbers compare between the Autoset II and your new machine? In another thread I just started (having to do with puzzling AHI numbers I obtained from a Resmed Autoset II and a newly-acquired Respironics System One) I noted that in my case the AHIs reported by both have been essentially equivalent, but the Resmed Autoset II gets there by reporting a relatively high HI, whereas the System One gets there by reporting a relatively high CA.

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Re: Clear Airway Apnea = Central Apnea?

Post by dsm » Fri Jan 01, 2010 11:25 pm

-SWS wrote:
dsm wrote:I can't see how a fixed frequency FOT burst could be adequately detected for anything other than is the air moving overall ?
Well, as it turns out spectral analysis of fixed-frequency oscillation can actually be used to calculate an overall respiratory impedance:
http://www.nicoletvascular.com/prod_ser ... ra_ch5.pdf

And I thought that's what Weinmann formerly employed before dropping the technique altogether. Perhaps I remembered the Weinmann implementation wrong. Probably did...

Anyway, that technique would be very different than simply detecting a basic "yes forward-pulse-flow" versus "no forward-pulse-flow" condition. For instance, calculating total respiratory impedance (comprised of airway resistance, elastic and inertive lung and chest wall characteristics) now means that central hypopnea versus obstructive hypopnea differentiation becomes technically feasible as well.

One FOT technique works with coarse forward mass airflow, while the other technique works with vibratory or spectral type reflection.

SWS
Again a great source of info - that article solves a lot of the questions that came to my mind even if the overall technique may or may not be employed brand by brand.

They keep the pulse duration short enough that a reflected wave doesn't get swamped by the transmitter remaining on (it bursts in 30-40 ms packets). If we consider the circuit to a throat block is going to be approx 7.5ft & twice that is 15ft then sound traveling at 1125 ft/sec will take 1/75th of a second to bounce (reflect) back so bursting at 30-40ms allows the transmitter to be off when the detector gets turned on. Then it seems that measuring the returning amplitude and time taken offers information re what the wave encountered.

I see they also talk of stepping thru different frequencies as well as measuring the amplitude received back. Really fascinating stuff !.

I wonder what technique is in the Bipap AutoSV Advanced (still haven't looked thru the patent yet).

Thanks - DSM
Last edited by dsm on Sat Jan 02, 2010 1:40 am, edited 1 time in total.
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-SWS
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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Fri Jan 01, 2010 11:48 pm

dsm wrote:
-SWS wrote:One FOT technique works with coarse forward mass airflow, while the other technique works with vibratory or spectral type reflection.
I wonder what technique is in the Bipap AutoSV Advanced (still haven't looked thru the patent yet).
Well, if there's an acoustical output transducer inside that PAP machine, then it's clearly going to be one of the spectral techniques similar to the PDF document above.

If the FOT pulse is generated by the impeller, on the other hand, then it's presumably a case of only detecting coarse forward airflow...

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Re: Clear Airway Apnea = Central Apnea?

Post by barry15 » Sat Jan 02, 2010 12:07 am

Jay K wrote:Barry, How do the overall AHI numbers compare between the Autoset II and your new machine? In another thread I just started (having to do with puzzling AHI numbers I obtained from a Resmed Autoset II and a newly-acquired Respironics System One) I noted that in my case the AHIs reported by both have been essentially equivalent, but the Resmed Autoset II gets there by reporting a relatively high HI, whereas the System One gets there by reporting a relatively high CA.
Hello Jay,

I saw your thread and read it with interest. I will be interested to see what responses you get over there. To answer your question, I have observed something similar to what you have observed, but with an added twist. In general, my AHI with my Autoset T (not Autoset II, but the older Autoset T model) machine ran about 8 or 10, with the Apnea Index at about 1, or even less sometimes. So, lots of Hyponeas, which my sleep doctor had told me was unusual, many years ago. I used either nose pillows or a nasal mask for all those years. (There is an additional twist, too - my nose, my AHI, and my sleep were always much better when I was traveling, a situation that continues to this day and is a whole other subject for another time.)

So, three and a half weeks ago I got the new Respironics System One Auto. I don't have the software to read my data every day, but my sleep doctor's office will print it out for me, and I have been having them do that each week so far. My AHI was about 2.5 to 3 for the first two weeks, with CA's about 0.5, OA's about 0.5, and H's about 1.5 to 2. That seemed great, and it also seemed consistent with the things I have read here about Resmed machines reporting higher H numbers than Respironics machines. My older machine made no attempt to identify CA's, of course.

The twist came in the third week, when I switched to a Quattro full face mask (earlier, I mistakenly thought it was an Ultra Mirage full face mask, but it is a Quattro, brand new). With the Quattro FF mask, suddenly my CA index jumped up to about 3. This seems to be consistent with what you have seen, which is very interesting to me. I guess you read this thread, in which it was discussed.

I have a lot more data to gather, and maybe things will change with more data, but this is what I know so far. I'll be interested in your thread on the subject, to see what people have to say. I tried switching back to my nasal mask this week, to see if the numbers went down again, but last night my nose got so bad that I had to switch to my full face mask in the middle of the night, and I think I will just use that for now, since it is more comfortable for me and I feel like I sleep better with it, despite the CA numbers being reported. I'm working on getting the Encore Pro 2 software, and that will make it much easier to gather data and try thngs out.

Barry

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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Sat Jan 02, 2010 12:13 am

Well, if there's an acoustical output transducer inside that PAP machine, then it's clearly going to be one of the spectral techniques similar to the PDF document above.

If the FOT pulse is generated by the impeller, on the other hand, then it's presumably a case of only detecting coarse forward airflow...
The current Respironics FOT technique falls under that second coarse forward-flow detection method above (undoubtedly a technique that is much easier to sleep through):
Respironics Marketing Literature previously submitted by socalmonkey wrote:After several seconds of significant flow reduction, the device delivers test pressure pulses and determines the airway to be clear if this pulse generates a significant amount of flow.
That's clearly not one of the spectral or even time-domain analysis techniques mentioned much earlier. And so much for my bad memory about Weinmann having possibly used time-domain reflectometry. They probably used spectral analysis instead... if they even used a wave reflection method that is.





Again, thanks to socalmonkey for this marketing literature:
Image

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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Sat Jan 02, 2010 1:16 am

dsm wrote:Weinmann appeard to use conventional fot bursts.
As it turns out the Weinmann technique really did match that more sophisticated single-frequency FOT method in the PDF document I linked several posts above:
http://content.karger.com/ProdukteDB/pr ... tNr=224278
Recording of the impedance signal and application of the nasal CPAP pressure were carried out with the Somnosmart® device manufactured by Weinmann, Hamburg, Germany.

Figure 1 shows a diagram of the system. The patient breathes via a standard nasal mask (Respironics, Sullivan, Weinmann; No. 1 in fig. 1) which is connected in parallel to a CPAP generator (2), a pump for generating an oscillating flow at a frequency of 20 Hz (3) and a sensor to record the mask pressure (4). The pressure signal is passed on to the processor (central processing unit, CPU) via an analog-digital converter (5). The CPU (6) calculates the impedance from the pressure signal and regulates the CPAP generator and oscillation pump. Via a digital-analog converter (7) the calculated impedance, called 'FOT', can be presented in analog form. The pressure given by the CPU is called 'control pressure', the pressure taken from the mask and given besides the APAPFOT unit to the polysomnograph is called 'CPAP'...

Impedance (Zrs) designates a complex resistance: in addition to the real component (resistance, R) it also includes an 'imaginary' component (reactance, X) [11, 12, 13, 14]. Recording of the impedance signal and application of the nasal CPAP pressure were carried out with the Somnosmart® device manufactured by Weinmann, Hamburg, Germany.
Unlike the basic Respironics FOT method in the marketing literature above, the Weinmann FOT technique actually determines complex airway impedance. At least my memory about Weinmann's FOT is not completely shot.

And at least we know what Respironics is up to with their more basic FOT as well.

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dsm
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Re: Clear Airway Apnea = Central Apnea?

Post by dsm » Sat Jan 02, 2010 1:43 am

SWS

You are a champion - very very good info - thanks

DSM

( Just wish I had access to your sources of info - you really do get access great info )
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Re: Clear Airway Apnea = Central Apnea?

Post by Muffy » Sat Jan 02, 2010 4:04 am

Morning, -SWS!

Are you up yet?

How about now?

Now?

How about now?
-SWS wrote:
Well, if there's an acoustical output transducer inside that PAP machine, then it's clearly going to be one of the spectral techniques similar to the PDF document above.

If the FOT pulse is generated by the impeller, on the other hand, then it's presumably a case of only detecting coarse forward airflow...
The current Respironics FOT technique falls under that second coarse forward-flow detection method above (undoubtedly a technique that is much easier to sleep through):
Respironics Marketing Literature previously submitted by socalmonkey wrote:After several seconds of significant flow reduction, the device delivers test pressure pulses and determines the airway to be clear if this pulse generates a significant amount of flow.
And I think because of that, it's probably inappropriate to call the Respironics methodology FOT because the frequency is so slow (at about 0.14 Hz, there's going to be plenty of breaths where there's only one pulse, so you really can't call it "oscillating"), pulse duration is long (about 2 seconds vs the traditional 30 - 40 msec) and the analysis is based on flow (so they say. Grossly, it appears that pressure waveform analysis could easily be used)(or volume, when you really think about it) instead of resistance.

Other than that, though, they're pretty much identical.

Muffy
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-SWS
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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Sat Jan 02, 2010 9:20 am

Hey, Mr Lark, this bad owl is finally up.
Muffy wrote: And I think because of that, it's probably inappropriate to call the Respironics methodology FOT because the frequency is so slow (at about 0.14 Hz, there's going to be plenty of breaths where there's only one pulse, so you really can't call it "oscillating"), pulse duration is long (about 2 seconds vs the traditional 30 - 40 msec) and the analysis is based on flow (so they say. Grossly, it appears that pressure waveform analysis could easily be used)(or volume, when you really think about it) instead of resistance.

Other than that, though, they're pretty much identical.

Muffy
I agree. Although the most fundamental distinction between those two methods, in my mind, is that the Weinmann FOT technique relies on vibratory particle mechanics while the Respironics technique relies on mass particle flow. The difference between those two types of particle travel can be roughly demonstrated by a wacky home experiment:

Aim a quiet source of airflow at the wall (a silent leaf blower if one existed). Run to the other side of that wall and observe absolutely no particle movement by the way of mass air flow on the other side of that wall. Then aim a loudspeaker at that same wall. Once again run to the other side and note that particle movement or sound managed to travel through the wall. Both devices generated pressure waves. Yet one method resulted in mass airflow that cannot pass through walls, while the other method resulted in vibratory mechanics or particle excitation that managed to partially reflect and at the same time partially pass through walls.

I wonder if Resmed's soon-to-be-released implementation is more like Weinmann's or more like Respironics. I still think the more coarse mass airflow technique should be easier to sleep through. So I'm guessing that's what Resmed might soon deploy...

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Re: Clear Airway Apnea = Central Apnea?

Post by Rebecca R » Sat Jan 02, 2010 10:41 am

-SWS wrote: Aim a quiet source of airflow at the wall (a silent leaf blower if one existed). Run to the other side of that wall and observe absolutely no particle movement by the way of mass air flow on the other side of that wall. Then aim a loudspeaker at that same wall. Once again run to the other side and note that particle movement or sound managed to travel through the wall. Both devices generated pressure waves. Yet one method resulted in mass airflow that cannot pass through walls, while the other method resulted in vibratory mechanics or particle excitation that managed to partially reflect and at the same time partially pass through walls.
How will you ever get any sleep if you are always running back and forth?

r

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Re: Clear Airway Apnea = Central Apnea?

Post by -SWS » Sat Jan 02, 2010 12:08 pm

Rebecca R wrote:How will you ever get any sleep if you are always running back and forth?

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Re: Clear Airway Apnea = Central Apnea?

Post by dsm » Sat Jan 02, 2010 5:37 pm

SWS

A great experiment - it does have an interesting angle & that is the transmitter is on one side of the obstruction (wall) & the detector keeps running to the other side - poor old xPAPs txmtr & detector have to remain on the same side. But if the technique is to measure the loss of energy of the signal (that component of energy that leaked through) by analysing the amplitude of the reflected wave, I can see how it could work

But I have to say, these techniques are extraordinarily complicated - but that is medicine today

Cheers

DSM
Last edited by dsm on Sat Jan 02, 2010 6:28 pm, edited 1 time in total.
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