Central Detection Driving Me Nuts!!

[Walla Walla]

Well I just tested my VAUTO on S mode without Easy breath and it recorded CA events when I held my breath with my mouth open.

Which means it must of been using FOT.

I assure you that you are mistaken.  You either had Easy Breath ON, or you were not in S mode.  

You can **feel** the pulses if you're laying down.

Also, another side effect that I've noticed is that the FOT pulses interfere with hypopnea detection.  The machine will score hypopneas as apneas when FOT is on because the pulses prevent the machine from seeing the shallower breaths.  As a result, things that would have been scored as hypopneas get scored as apneas when FOT is on.

Well you were right I think. I had the settings right but Sleepyhead recorded it wrong. Maybe due to the short time frame. I checked on the machine and ResScan and they both didn't report CA events. The other thing that could have happened is both the machine and Rescan filters out the CA report when it's in S mode and sleepyhead continues to report it. I'll let someone else figure it out and just assume it doesn't report CA's on S mode. Thanks Reznik for the info.

[isuckatsleeping]

My personal experience with FOT is that I have never noticed it. I do know some people are extremely disrupted by it and even complain about it "shaking the mask".  I have no idea how our experiences can be so different, but it is and I accept that there are sensitive individuals. It seems that central apnea detection could be a reasonable option in the clinical menu to enable or disable. Advanced machines in the ST series do not use FOT,and apnea is reported as UA.  It seems like a reasonable request to have an on/off for FOT.  Who have you contacted and did you get a reply?

For a deep sleeper, the only way to notice it would be to turn ramp off, put your mask on, and start up the machine - after about 1 min of using the machine, hold your breath for 5 or so seconds. There's literally no way you can't notice it when it kicks in (at least with a full face mask). My mask literally moves on my face with the beat of the pulses. I should probably just take a video of it and show what I mean. I tried adjusting the tightness of the mask and it made no difference. 

BTW It was so disruptive that I thought that my machine was broken because I had dropped it onto hard ground from a full standing position previously in the day. I literally went out and bought a whole new autoset because I thought no way that is a "feature" - I must have broke the damn thing. When I woke up to pulsing on the new machine, I was not happy. Then I found out what FOT is after researching.

I'm moving back to the N20 with a chin strap tonight to see if that will cause less of a disruption to my sleep. Now I just have to fight the mouth breathing battle 

[joesetx]

the apnea itself is causing your arousal, not the pulses trying to detect if your airway is open or not.

[logit]

Many members have felt the pressure pulses from the machines.  They don't mean much as there may be a transitional central upon arousal.  Your graph should show whether you received a FOT pulse.

What graph / pattern would indicate a FOT pulse?

[Crimson Nape]

What graph / pattern would indicate a FOT pulse?

You zoom in on the Flow Rate graph.  It is basically akin to a radar or sonar signal. It sends out a pulse and looks for a return pulse. If it receives a return pulse, then it is probably an airway obstruction(OA), otherwise it's a Clear airway(CA).

Here is an image of a FOT waveform:

[Reznik]

the apnea itself is causing your arousal, not the pulses trying to detect if your airway is open or not.

That is incorrect.  The impact of the FOTs is quite obvious with me.  If I use a machine that has FOT, my AHI will consistently be less than 3.  That's because everytime I start having apneas, the pulses disrupt my sleep architecture.  If I use a machine with the same settings but without FOT, I sleep deeper and longer, and my AHIs go up.  

If the apneas were causing my arousals and not the FOTs, the opposite would happen:  I'd get poorer sleep when I had higher AHIs, and the presence of FOT pulses would have no impact on my AHI.

[Reznik]

Tonight, I was reading a brochure from DeVilbiss about their auto-titrating methodology.  They mention the FOT technique used by ResMed in the following paragraph:

"Determining central and non-obstructive apneas is a controversial subject among manufacturers of Autotitrating devices. Some Autotitrating units are limited to flow signals. Due to this limitation, some manufacturers do not attempt to define non-obstructive apneas. Others use questionable definitions such as – any apnea occurring at pressures greater than 10 cmH2O. (Lab reports substantiate the presence of REM- or position-induced obstructive apneas at 10+ cmH2O. Obstructive apneas require a therapy response.) Others, using a clinically unsubstantiated echo concept, pulse pressure into the patient’s airway. If the pulse is not returned, the apnea is considered central based on the assumption that ‘no echo’ indicates an open airway. (This method entirely ignores CSDB or non-obstructive apneas caused by a PAP-induced reduction of carbon dioxide.)"

http://www.devilbisshealthcare.com/files...T-2089.pdf

[Sleeprider]

First, the DeVilbiss article has a lot of very thought-provoking information in it, and thanks for bringing it to our attention. I think that using that quote without the preceding paragraph in that section, misrepresents what is being discussed. DeVilbiss attributes

Non-Obstructive Apneas (NOA) Non-obstructive apneas, including complex sleep disordered breathing (CSDB), may occur during OSA therapy. These non-obstructive apnea events occur if the PAP’s pressure reduces carbon dioxide levels in the patient’s system. Without the proper CO2 stimulus, the brain will fail to trigger breathing and a non-obstructive apnea will occur. Most Auto-titrating manufacturers do not increase pressure in response to non-obstructive apneas because higher pressures will reduce CO2levelsfurther; however, it is important to report non-obstructive apneas for two reasons: clinically, if the NOA incidence is high, clinicians may want to investigate central apneas in a lab setting; and mechanically, if pressures are not rising as expected, checking the non-responding event index(NRI) may eliminate returning the unit for repair when it is operating normally.Non-obstructive apneas mimic central apneas. Central apneas occur when the autonomic nervous system fails to trigger breathing as a response to the CO2stimulus. Sleep labs are able to properly identify central apneas using muscular effort, EEG readings and pulse oximetry in combination with the defined lack of breathing. NOTE— Primary central apneas follow the waxing and waning pattern defined as Cheyne-Stokes breathing. Clinical consensus today indicates primary central apneas are best treated using bilevel PAPs with timed backup.

The DeVilbiss makes an argument to consider "non obstructive apnea events" as being caused by hypocapnea affecting respiratory drive, rather than central nervous system failure to trigger breathing.  That is a very fine point to make considering the mechanisms of respiratory stimulus.  Whether a NOA results from central apnea or hypocapnea, the fact remains that increasing pressure is not appropriate. So determining whether an event is obstructive or non-obstructive remains a valuable input to the auto CPAP algorithm. 

We frequently see Complex Sleep Disordered Breathing (CSDB) on the forum, where thanks to the pulse echo or FOT, we can see the mix of events.  While a CPAP has no means to address this problem, its signature as presented by clusters of mixed apnea events is valuable knowledge that is used to either modify the therapy approach (limit pressure or consider Enhanced Expiratory Respiration Space EERS), or recommend a more advanced bilevel therapy such as ASV.  You cannot conclude that this is an argument against the use of FOT or pulse echo, simply because DeVilbiss calls it "unsubstantiated".  More often than not, the indication of obstructive or central apnea is accurate, and points to a need to modify therapy.  It certainly is a valuable tool for auto-adjusting pressure machines to decide whether the event response should be an increase in pressure or not.

I recognize that a few individuals are sensitive to the pressure pulses or FOT, but the vast majority of CPAP users never notice the pulses.  I think you're cherry-picking an article to find fault with using pressure pulse control of auto CPAP.  DeVilbiss takes the position that an auto CPAP cannot differentiate between the types of clear airway event, and such events may be low CO2, complex apnea or central apnea.  In my opinion, this does not diminish the value of differentiating these events from obstructive apnea.  DeVilbiss acknowledges the value of this differentiation, but the paper does not appear to explain how the machine identifies NOA events.  If I missed it, please point it out to me, but it appears their approach at least is disruptive to your sleep if sensitivity to pressure pulse or FOT arouses you.

DeVilbiss is not unique in defining or reporting non-obstructive apneas but the AutoAdjust has had this ability as early 1996. In a clinical study comparing DeVilbiss AutoAdjust to sleep lab equipment,Martin Scharf et al found that the AutoAdjust device’s definition of non-obstructive apneas had an85% correlation to the lab’s definition of central apneas.11The AutoAdjust is NOT attempting to diagnose central apneas; it is, however, able to recognize therapy-induced non-obstructive apneas and, following common lab procedures, stop all pressure increases while these events are present.(Increasing pressure during central apneas can cause further reduction of carbon dioxide levels along with further increases in central and non-obstructive apnea densities.) By defining and reporting non-obstructive apneas, the AutoAdjust offers clinicians a view of non-obstructive apnea density so that they can determine if clinical intervention is appropriate.

Non-Obstructive Apneas (NOAs)
Cause: Non-obstructive apneas may occur during OSA therapy if the PAP pressure reduces the normal carbon dioxide accumulation and degrades the CO2 stimulus response. NOAs also may be primary central apneas that cannot be properly defined by an Autotitrating device alone.

[Reznik]

I only quoted that paragraph for the purpose of discussing DeVillbills's proposition that FOT is clinically unsubstantiated when used to differentiate between obstructive and non-obstructive apneas.  I agree that the preceding paragraph is helpful to understand DeVillbiss's discussion of the difference between the two types of non-obstructive events.  However, for purposes of my concern, the ability to differentiate between the two types of non-obstructive events is irrelevant.  My concern is only that FOTs may be unsubstantiated and not very accurate, which you seem to acknowledge.

You only propose that FOT is accurate "more often than not."  IMHO- "more often than not" is nowhere near enough for a medical device, particularly when the method disrupts the sleep architecture of some of its users.  Ideally, you'd have 100% accuracy in a medical device.  Even acknowledging that 100% accuracy is not possible, "more often than not" could mean as little as 51% accuracy.  That's far too low, given how important the issue is.  I agree that being able to distinguish between obstructive and non-obstructive events is important.  My point is that it is too important to be left to a potentially unsubstantiated mechanism that both disrupts sleep and whose accuracy is described using the words "more often than not."

The fact that most users don't notice FOTs is the problem.  FOTs may be disrupting sleep architecture even though the user never notices them.  People who use ResMed's machines may well be sleeping, but not getting the best sleep that they could get.  They may be sleeping better than they did when they were experiencing apneas (which most people also never notice but are still very bad), but the fact that they don't notice the FOT pulses doesn't mean that they are getting the best sleep that they could get.  Most users never notice their sleep apnea, and yet we treat the sleep apnea in order to help them get better sleep.  Yet, ResMed chooses to treat the sleep apnea by pulsing patients with pulses that are (according to DeVilbiss) "clinically unsubstantiated," nowhere near as accurate as other alternatives, and which patients may never realize are disrupting their sleep architecture.  Apneas are bad even though the patient may never notice them because, among other things, they disrupt sleep architecture.  FOT pulses may be bad for the same reason.

Devilbiss, like Fisher Paykel, uses a passive mechanism to detect obstructive vs. non-obstructive apnea, and so it would not disturb my sleep (or anyone's) but would provide patients with the important benefits that you highlighted.  If their method is more accurate than ResMed's FOT pulses, then it would seem that switching machines would be doubly beneficial.

BTW- just for clarification, I have never used a DeVillbiss or F&P machine.  I use a ResMed that has the ability to disable the pulses.  My purpose in posting is to have an academic discussion and to alert others to the hidden risks and potential downsides of using machines that generate these pulses.  I do hope that ResMed switches to another method of detecting obstructive vs. non-obstructive apneas in future devices.

[Sleeprider]

While DeVilbiss dismisses pulse and FOT detection, the methods have been researched and verified in scientific studies as accurate methods of determining open or obstructed airway. I remain uncertain what method DeVilbiss is using.
https://www.atsjournals.org/doi/full/10.....5.9902085
https://www.atsjournals.org/doi/full/10.....3.2006168
https://erj.ersjournals.com/content/17/3/456

There is a lot more out there, and most find the technique valid.