What is a Pressure Pulse event?

Noticed that my Dreamstation 1 APAP is reporting flagging a thing called Pressure Pulse Event. Checked with the OSCAR glossary and could not find anything there. Here is a shot of the flow rate graph with the pressure pulse event flagged at 04:25:36, What is happening here?

Also attached is full OSCAR report to provide some context: And this listing of these events:

Pressure Pulses

Data available on the Respironics System One machines. Small test probes or puffs of air to help the machine decide if the apnea event is obstructive in nature or clear airway in nature. This number can vary widely and is of no real critical consequence to therapy.

dataq1 wrote: ↑

Thu Oct 28, 2021 9:38 pm

Noticed that my Dreamstation 1 APAP is reporting flagging a thing called Pressure Pulse Event.

They don't "mean" anything at all, as Pugsy says, it's just the machine trying to see if your airway is open. It does indicate that you're having a number of times when you're not breathing, but not necessarily long enough to count as an apnea.

I'm understanding that a pressure pulse is a machine generated puff of air (obviously a positive flow) that is used to distinguish an apnea as either a clear airway apnea or an an obstructive apnea, am I understanding that correctly.

In the above traces, there is an apnea occurring between 04:25:25 and 04:25:35 (ten seconds in duration). Despite the puff generated, the apnea is not classified as either clear or obstructive.

In fact the cessation of flow for that ten seconds is not classified as any kind of event at all.

BTW, I'm assuming that the little blip (red arrow) is the "puff", (as distinguished from an artifact) would you concur?

dataq1 wrote: ↑

Fri Oct 29, 2021 12:36 pm

I'm understanding that a pressure pulse is a machine generated puff of air (obviously a positive flow) that is used to distinguish an apnea as either a clear airway apnea or an an obstructive apnea, am I understanding that correctly.

In the above traces, there is an apnea occurring between 04:25:25 and 04:25:35 (ten seconds in duration). Despite the puff generated, the apnea is not classified as either clear or obstructive.

In fact the cessation of flow for that ten seconds is not classified as any kind of event at all.

BTW, I'm assuming that the little blip (red arrow) is the "puff", (as distinguished from an artifact) would you concur?
puff arrow.jpg

It looks like it's not *quite* 10 seconds to me, so no flag.

Yes, you're interpreting things correctly.

palerider wrote: ↑

Fri Oct 29, 2021 12:45 pm

It looks like it's not *quite* 10 seconds to me, so no flag.

I think you are saying that the "it" is not an apnea because it did not last 10 seconds or more. Am I correctly understanding you? (Looks like 9.5 seconds from the beginning of no flowrate to the end of no flow rate)

So, if the cessation did not have a 10 second duration, then there would have been no reason to have the device generate a pressure pulse to enable the device's software to classify the cessation as a clear airway or obstructive. I would have anticipated the pressure pulse to come immediately after the 10 second duration period not before. (In this case it looks like the pressure pulse was generated 8.5 seconds after no flow-rate - is there some other criterion relative to the timing of pressure pulse?)

I have some other questions about the flowrate graph, that I'll pose after a bit more study.

Thanks,

Funny thing, apparently Philps (and for that matter, Resmed) don't seem to care what you think.

Their machines do what they do, it's best to just accept facts, and not annoyingly argue with them.

dataq1 wrote: ↑

Fri Oct 29, 2021 8:57 pm

So, if the cessation did not have a 10 second duration, then there would have been no reason to have the device generate a pressure pulse to enable the device's software to classify the cessation as a clear airway or obstructive.

Your thinking is flawed...probably from overthinking.

No...the machine decides when/if it needs help figuring out open or closed airway whenever it realizes it might need to.
Not all flow reductions will end up with the machine using the pressure pulse to help.
And not all pressure pulse generated flow reductions end up with a flag.

The pressure pulse is always done prior to the end of the flow reduction though. Never done after a person resumes breathing normally.

The 10 second requirement minimum duration for a flag....but the machine doesn't know ahead of time if the flow reduction it senses is happening is going to resolve prior to 10 seconds...or last longer and earn a flag.
It doesn't have a crystal ball.
So...the air flow reduces or stops...the machine senses the change...fairly quickly at that...then it decides if it needs to use the pressure pulse thing or not...and then the airflow returns to normal....if less than 10 seconds no flag and the pressure pulse wasn't needed but at the time the air flow was reduced the machine had no way to know if the reduction would last 8 seconds or 30 seconds....but it had to figure out if open or closed airway because that does affect the response when using auto adjusting pressure.

dataq1 wrote: ↑

Fri Oct 29, 2021 8:57 pm

I would have anticipated the pressure pulse to come immediately after the 10 second duration period not before. (In this case it looks like the pressure pulse was generated 8.5 seconds after no flow-rate - is there some other criterion relative to the timing of pressure pulse?)

Why would a puff of air generated after the end of an event when the air is moving normally (breathing normally) help identify why the air didn't move prior to the flow reduction?? Think about it.

The little "puff" is done when there is either no air flow or greatly reduced air flow and the machine "listens" for either an echo or nothing. If the puff bounces back....the airway is obstructed with collapsed tissues. If the puff doesn't bounce back then the airway is open.

The machine decides when to do the "puffs" and how long to use the pressure pulses when it decides it wants/needs to use the pressure pulse/puff. I have never seen any documentation that goes into any detail like you seem to be wondering about. Probably in the patent somewhere.
How these algorithms work are closely guarded secrets.

Pugsy wrote: ↑

Fri Oct 29, 2021 9:38 pm

the pressure pulse is always done prior to the end of the flow reduction though. Never done after a person resumes breathing normally.

Why would a puff of air generated after the end of an event when the air is moving normally (breathing normally) help identify why the air didn't move prior to the flow reduction?? Think about it.

The little "puff" is done when there is either no air flow or greatly reduced air flow and the machine "listens" for either an echo or nothing. If the puff bounces back....the airway is obstructed with collapsed tissues. If the puff doesn't bounce back then the airway is open.

Thanks for taking the time to clarify this, but I think you might have misunderstood me (or I didn't explain myself well enough)
You are entirely correct that a pressure pulse generated after normal breathing results is non-sensical. What I should have been more specific about is that I would anticipate a pressure pulse to occur the criterion for some sort of apnea is present (10 sec of non-flow) and prior to the resumption of normal breathing. (This thought is based on your prior description of the pressure pulse being employed to distinguish between clear airway and obstructive apneas)

I am intrigued by your remark that a pressure pulse "bounces back". What would that "bounce back" look like in the above case (where I've indicated a pressure pulse with red arrow)?

Just so I don't misunderstand you, from what you've said, should be a pressure pulse for each OA or CA ? (there could be other pressure pulse events but there should always be a pressure pulse for each clear or obstructed.
Thanks

dataq1 wrote: ↑

Fri Oct 29, 2021 10:27 pm

should be a pressure pulse for each OA or CA ?

From my understanding (and past use of a Respironics machine) the machine may or may not decide to do a pressure pulse for anything...I saw flagged events with and without pressure pulses. I saw pressure pulses with no flag because whatever caused the reduction didn't last 10 seconds.

Respironics never really explains how pressure pulses work in an real detail.

You can't see the "bounce back" on the graphs. Maybe "echo" would be a better term.

dataq1 wrote: ↑

Fri Oct 29, 2021 10:27 pm

but there should always be a pressure pulse for each clear or obstructed.

That's not what I said. The machine uses pressure pulses when it thinks it needs to to distinguish type of flow reduction or stoppage. It doesn't always need help in figuring out what is going on. I saw evidence of that myself back when I used the System One machines.

And don't go asking me how it decides because again....Respironics doesn't go into any real detail explaining the "why" behind much of anything it does. I don't know and have no desire or need to know.
I am sure it's in the patent though. I guess you could go patent digging.
Call up Respironics and see if you can get a straight answer....good luck with that BTW.

dataq1 wrote: ↑

Fri Oct 29, 2021 8:57 pm

So, if the cessation did not have a 10 second duration, then there would have been no reason to have the device generate a pressure pulse to enable the device's software to classify the cessation as a clear airway or obstructive. I would have anticipated the pressure pulse to come immediately after the 10 second duration period not before. (In this case it looks like the pressure pulse was generated 8.5 seconds after no flow-rate - is there some other criterion relative to the timing of pressure pulse?)

No.

You are making the assumption that the device must wait 10 seconds in order to determine why the Air Flow has stopped (or severely reduced). That's not necessary.

The Air Flow reduction must be 10 seconds or more to be considered an Apnea, but these devices can (and do) determine why the flow has stopped earlier than that. For example ResMed's use Forced Oscillation Technique (FOT) to determine if the the event is Central or Obstructive in nature. This occurs 4 seconds after the air flow has stopped.




Why do you think that CPAP algorithms *must* wait 10 seconds, before they can attempt to determine the cause of the reduced air flow rate?

I have also heard, but not verified, that FOT and Pressure Pulses can stimulate breathing. As Pugsy stated, because manufacturers don't publish a lot of detail about their algorithms, this is difficult to verify.

Dog Slobber wrote: ↑

Sat Oct 30, 2021 9:26 am

The Air Flow reduction must be 10 seconds or more to be considered an Apnea, but these devices can (and do) determine why the flow has stopped earlier than that.

And I agree with that, and it makes sense to do that. That is actually demonstrated quite well in my trace (above) where the pressure pulse seems to have occurred at about 8.5 sec, but the flowrate reduction ceased at 9.7 sec or so.

I might have been more correct for me to have said that a pressure pulse (used to distinguish CA and OA) ought to occur before the 10 second mark, but becomes critical to occur immediately after 10 sec and while still in the no flow period.

That suggests to me that the number of pressure pulse events ought to exceed the number of OAs and CAs combined.

Recall that I am using an auto-titrating device, so my device reacts to OAs but not to CAs. Consequently how my device distinguishes between the two is useful for me to understand why my device is reacting.

Thank you all for your input, as this question has definitely expanded my understanding of what goes on in the the " black (or white) box".

To Dog Slobber: Your posting of your FOT trace will also help me to better understand my wife's Resmed device. Thanks.