[ASV] Timed breaths and Patient Triggered Breaths

[tmoody]

The SH data on my PRS1 ASV include a line for "patient triggered breaths", min, med, 95%, and max. I understand PTBs to be breaths initiated by me, as opposed to the machine. I don't understand how the numbers work, however. If, for example, my PTB min value is 50, does that mean that 50 PTBs was the least number of PTBs that occurred in any 60-minute interval, regardless of start and stop time? Or is it a percentage of something? It seems likely to be a percentage because the max value is never over 100. Indeed, if the PTB max is 100, as it always is, does that mean there was at least one 60-minute interval during which 100% of my breaths were initiated by me?

I understand "timed breaths" to be breaths initiated by the machine after I failed to inhale for a certain interval. If so, it would seem that they are the opposite of PTBs. The higher the PTB, the lower the TB should be. That seems to be roughly, but not exactly, the case. And once again, I don't know how to interpret the SH number for PB. I'm assuming it's a number of TBs per hour, rather than a percentage, but I'm not sure.

[justMongo]

Let's see if we can get an ASV "expert" on this question.

[tmoody]

Tried to edit the original post but failed.
So...

Edit: As I look over my pre-ASV APAP data, I see that on a bad night I'd have 75 to 80 centrals. On ASV, the number of Timed Breaths is much higher, on just about any given night. Since I started ASV on March 23, the highest TB number I've seen is 810, which is pretty high. On that particular night, there was one central.

It looks to me like most of my TBs would not have been centrals, if they hadn't timed out. That suggests to me that the machine may be a bit too aggressive in finding centrals. But as far as I can tell, this isn't an adjustable setting; it's built into the algorithm. Is that correct? It would be useful to be able to tweak this.

[justMongo]

As a "preferred Member," you have 90 minutes to edit a post.

Really need a person whose an expert at a PR ASV to help with your questions.

[richb]

Hi tmoody.

My machine is a Resmed Aircurve 10 ASV. It doesn't count "timed breaths" or "Patient Triggered Breaths". So, I looked at a 10 minute segment of data from last night and counted the higher pressure pulses "timed breaths" vs low pressure pulses "patient initiated breaths". I counted 108 timed breaths and 77 patient initiated breaths during that 10 minute segment. This gives me a respiration rate of 18.5 BPM during that 10 minute segment. I have other times during the night when the machine isn't working so hard but for the most part my machine is stimulating my breathing pretty actively throughout the night. By the way I had an AHI of 0.0 last night. For those of us with Central Apnea the ASV machine provides enough breathing to prevent desaturations of O2 and seems to help with deeper levels of sleep. (I am frequently sleeping through the night.) The ASV machine doesn't cure Central Apnea. It relieves the symptoms so the fact that it is working is a good thing. I hope this helps.

Rich

[robysue]

I want to preface this with the fact that I am not an ASV user. But I do think I can shed a bit of light on one of your questions:

Edit: As I look over my pre-ASV APAP data, I see that on a bad night I'd have 75 to 80 centrals. On ASV, the number of Timed Breaths is much higher, on just about any given night. Since I started ASV on March 23, the highest TB number I've seen is 810, which is pretty high. On that particular night, there was one central.

The triggered breath (ASV) algorithm kicks in whenever the machine thinks you are at high risk of developing a CO overshoot/undershoot cycle, which is what leads to CAs. Given an average of 80 CAs on the APAP and about 810 triggered breaths with the ASV but almost no actual CAs, that means that the ASV algorithm is triggering about 10 breaths to prevent each CA from happening. That's not necessarily unusual since a typical CO overshoot/undershoot cycle can involve 10-15 breaths with a CA at the nadir of the cycle.

It looks to me like most of my TBs would not have been centrals, if they hadn't timed out. That suggests to me that the machine may be a bit too aggressive in finding centrals.

Maybe. Maybe not. The ASV algorithm is supposed to kick in before the CAs can develop in the first place. And some of what looks like normal airflow in the flow rate graph may look normal only because the ASV algorithm is triggering the inhalation just in time to keep the CA undershoot part of the abnormal breathing cycle from developing. In other words, the ASV algorithm is kicking in before your breathing slows down and decreases enough to cause the CA from occurring a few breaths down the line.

But as far as I can tell, this isn't an adjustable setting; it's built into the algorithm. Is that correct? It would be useful to be able to tweak this.

You need to check the clinical manual for your machine. It should list every single adjustable setting in the ASV mode. If you find adjustable settings that you do not understand, post here with their names and what the clinical manual has to say about them. Then somebody might be able to tell you what they mean.

[richb]

I want to preface this with the fact that I am not an ASV user. But I do think I can shed a bit of light on one of your questions:

Edit: As I look over my pre-ASV APAP data, I see that on a bad night I'd have 75 to 80 centrals. On ASV, the number of Timed Breaths is much higher, on just about any given night. Since I started ASV on March 23, the highest TB number I've seen is 810, which is pretty high. On that particular night, there was one central.

The triggered breath (ASV) algorithm kicks in whenever the machine thinks you are at high risk of developing a CO overshoot/undershoot cycle, which is what leads to CAs. Given an average of 80 CAs on the APAP and about 810 triggered breaths with the ASV but almost no actual CAs, that means that the ASV algorithm is triggering about 10 breaths to prevent each CA from happening. That's not necessarily unusual since a typical CO overshoot/undershoot cycle can involve 10-15 breaths with a CA at the nadir of the cycle.

It looks to me like most of my TBs would not have been centrals, if they hadn't timed out. That suggests to me that the machine may be a bit too aggressive in finding centrals.

Maybe. Maybe not. The ASV algorithm is supposed to kick in before the CAs can develop in the first place. And some of what looks like normal airflow in the flow rate graph may look normal only because the ASV algorithm is triggering the inhalation just in time to keep the CA undershoot part of the abnormal breathing cycle from developing. In other words, the ASV algorithm is kicking in before your breathing slows down and decreases enough to cause the CA from occurring a few breaths down the line.

If one has idiopathic Central Apnea it is most likely that the overshoot undershoot cycle would still include shallow breathing and would be characterized as Hypopneas or Periodic Breathing. Standard CPAP machines usually escalate the Hypopneas converting them to full blown Central Apneas. Your ASV machine detects changes in breathing associated with Periodic Breathing and Central Apnea and intervenes providing higher pressure pulses of air at a rate determined by your previous normal breathing pattern. It will intervene whenever it detects abnormal breathing. That means it will kick in quite frequently because not every sequence of abnormal breathing would be long enough to be scored as a Hypopnea or Central event. This is also why the machine winds up providing so many "timed breaths". You will also not see many Hypopneas or Central events in your data. What you do see is your machine working to keep you breathing.

Rich

[tmoody]

The triggered breath (ASV) algorithm kicks in whenever the machine thinks you are at high risk of developing a CO overshoot/undershoot cycle, which is what leads to CAs. Given an average of 80 CAs on the APAP and about 810 triggered breaths with the ASV but almost no actual CAs, that means that the ASV algorithm is triggering about 10 breaths to prevent each CA from happening. That's not necessarily unusual since a typical CO overshoot/undershoot cycle can involve 10-15 breaths with a CA at the nadir of the cycle.

If one has idiopathic Central Apnea it is most likely that the overshoot undershoot cycle would still include shallow breathing and would be characterized as Hypopneas or Periodic Breathing. Standard CPAP machines usually escalate the Hypopneas converting them to full blown Central Apneas. Your ASV machine detects changes in breathing associated with Periodic Breathing and Central Apnea and intervenes providing higher pressure pulses of air at a rate determined by your previous normal breathing pattern. It will intervene whenever it detects abnormal breathing. That means it will kick in quite frequently because not every sequence of abnormal breathing would be long enough to be scored as a Hypopnea or Central event. This is also why the machine winds up providing so many "timed breaths". You will also not see many Hypopneas or Central events in your data. What you do see is your machine working to keep you breathing.

Rich

First, I want to thank both of you for these explanations. I wish we had a "thank" button.

Second, I need to learn more about this overshoot/undershoot phenomenon. I don't really understand it. I take it we're talking about CO2 and not CO, and the centrals are somehow caused by some kind of blood gas homeostasis failure. That's all news to me, and I hope I can learn more about it.

Concerning Timed Breaths... I've noticed that the number of TBs reported by SH tends to track the AHI, though not perfectly. My AHI last night was 1.7, one of my lowest yet, and the number of TBs was the second lowest ever. Zero centrals and only 14 hypos for the night. If the TBs are the machine preventing events, I'd expect to see higher TB counts with lower event counts, but that's not what I see, as a general thing.

[FrankNichols]

I wish we had a "thank" button.

Agreed, thank you, like, or karma button would be very nice.

Frank

[justMongo]

we do have one!