Simple Question about the BPM and TI on BiPAP ASV System One

Since I have the Philips Auto SV Advanced System One model and all of the sleep lab titration guides are for Resmed I have a few questions.

1. Does the Ti setting for the System One correspond to a maximum inspiration time, a minimum inspiration time, or other?

2. Does the Backup BPM setting correspond to a maximum or minimum inspiration/expiration time?

The reason that I ask: It is set for 11 BPM, and Ti = 2.0 sec. and occasionally my maximum inspiration time reaches 4.3 sec, and my minimum BPM reaches 10 BPM. Patient triggered breath percentages are usually high, but have minimums in the neighborhood of zero.

The good news: no obstructive or "clear airway apneas" for two weeks. There are still the occasional clusters of hypopneas that wake me up (presumably during REM) at night, and there are also varying amounts of flow limitation events. My highest leak rate is < 75 L/min, with a median of 46 L/Min.

Though the AHI is below 5, I'm trying to minimize wakings, at this time.

RE,
I can answer a few of your questions. Ti is maximum inspiration time (hence the i) and is the maximum inspiration time before pressure is switched to epap.

BPM is breaths per minute. It's the number of breaths that is used by the machine to determine when the machine should kick in and breath for you. For simplicity of explanation, lets use 10 BPM as an example. That means the machine allows 6 seconds (from beginning of inspiration) before kicking in with a machine triggered breath.

I don't understand how or why you're getting a 4.3 second breath reading. Max setting for T1 is 3 seconds. Could it be you over-rode the epap change and continued a forceable inspiration? I mean...that's a long inhalation.

If you have some times where PTBs are zero...it could be a cluster of centrals where the machine is triggering breaths for you.

ASVs are difficult machines...or can be, and it sounds like you're doing pretty good. Just hang in there and allow both the machine to get used to you...and vice versa.
Jamis

Thank you very much for your reply.

One more thing: generally speaking the number of breaths per minute (BPM) is set to be 2 less than the patient's average BPM, right?

RationalEntropy wrote:Thank you very much for your reply.

One more thing: generally speaking the number of breaths per minute (BPM) is set to be 2 less than the patient's average BPM, right?

You're welcome RE...

And yes, that's correct. I believe that's how the machine does it if you have the BPM set on "auto". I have a slightly different take on that though. Telling you this just to enhance understanding...not to suggest you change your BPM rate.

Using my example BPM rate from my previous post. 10 BPM which leaves 6 seconds between machine triggered breaths. Well say your inspiration takes 2 seconds and then another 2 seconds to exhale. Then that leaves only 2 seconds from the end of exhale before the machine kicks in with a breath. I run my BPM rate at 8...just personal preference. I get 98% to 100% PTB.

In general, if you have your BPM rate set too high...the machine will kick in too often and you'll see a low PTB (patient triggered breaths).

Resmed adapt machines don't even have the capability of setting bpm and Ti...only auto. But your machine is more flexible.
Cheers,
Jamis

I know my machine is different, but I run it similar to what Jamis is saying. BPM is set to 8 and Inspiratory Time is set to 1.5. If BPM is any higher, it rushes me. Like Jamis, with this setting, I usually get 96-99% PTB, which is good for me.

RationalEntropy wrote:... generally speaking the number of breaths per minute (BPM) is set to be 2 less than the patient's average BPM, right? ...

In addition to what the others said, I would like to add that you might want to ask the your sleep doctor why they did not want to use the AUTO setting on the Breaths Per Minute (BPM) setting. If that is set to auto, it tries very hard to encourage you to breathe on your own. It will kick in if you fail to breathe, but uses sliding averages to determine your current average BPM and inspiratory time. That allows the machine to be a little more flexible to your breathing styles, rather than forcing you to a specific minimum breathing pattern.

Just a thought ... for your next appointment with your sleep doctor.

Thank you all for the helpful replies, and support. The minor tweaks I've made had to do with expanding the range of EPAP and the lower end of the PS, and even that was in the range of what I had been prescribed from the sleeping titration. I also did look at my BPM rate, and the setting initially was 12, and I dropped it to 11 to see what would happen. The result: an increase in PTB and fewer times waking up. It was pretty awesome, so, I've not really messed with timing other than that. I confess, it may not have been the best things, but it was a minor tweak.

Honestly I do not know what many doctors know about ASVs, since they don't seem to be commonly prescribed to patients. I am all about asking questions and learning. Perhaps the backup rate was set to 12 because the BiPAP caused central episodes left and right, and perhaps wanted to minimize "clear airway events" with certainty, also 12 BPM is a fairly common breathing rate (when asleep). I'm not sure. They just gave that rate as a backup.

I do want to know why, as well. I may read up on the Auto BPM settings, because I do wonder how much it is a trial and error sort of thing with the machine.

RE,
As long as you're keeping things within your titration parameters...you should be OK. But random setting changes on an ASV are not at all like messing with a simple cpap. You can mess things up. And always take notes recording old settings so you can return to them if things get worse.

If your PTB aren't very high...you could do a little test dropping your BPM to 10 or probably even better...trying things out on auto like John suggested. I have seen ASV therapy improve noticeably switching to auto.

Do you live anywhere near Northern new Mexico? In Albuquerque, there's a sleep Doc named Krakow who is one of the leading experts on ASV use. If you have the money (or insurance)...a titration at his sleep lab could be very valuable. Or so I've been told.
Cheers,
Jamis

jamiswolf, Agreed. The ASV has far more moving parts, and is definitely more complex than a CPAP. I do not know the algorithms in these little "black boxes". I may have ideas about them, but have no idea how much it will increment up, how quickly the unit will react to an event, or anything. So, I don't really mess with it much. My average PTBs are in the neighborhood of high 60's to mid 70's and are sometimes as low as 59%.

I do not really want to take a lot of chances with my treatment, but many of the people on this forum are very insightful, and offer good advice. At times some of the best advice is, "go see the doctor". At some times, "see another doctor" or "analyze your data and be your own longitudinal case study" is another feasible approach. I can always talk to my doctor and tech. They are very approachable, and understanding. Also, they are quick to answer questions. Probably doesn't hurt that my tech has narcolepsy and OSA, and is very understanding and diligent as a result.

RationalEntropy wrote: My average PTBs are in the neighborhood of high 60's to mid 70's and are sometimes as low as 59%

I would doubt that all those machine triggered breaths are from apneas...probably just from your respiratory rate dipping a little lower.

John Fisher has been using asv machines for quite awhile...and truthfully his advice is worth much more then mine.

If you're into tweaking, and with those PTB numbers, I would seriously consider trying out John's suggestion for a few days. See what auto BPM does for you for a few days...can't hurt. You can always turn it back.
Jamis

Thank you guys for the answers. Unfortunately, I caught myself starting to chase numbers. I should have been thankful with the numbers I had.

I did try the auto. Not nearly as much aerophagia, and the PTB did improve. The AHI did increase a touch (still 2-4 is a good range, especially when they are hypopneas). I unfortunately did an immature thing, and got caught up in chasing numbers (wanted a consistent less than 2). Thankfully I do have the parameters that were given to me by my doctor, and the minor tweaks made previously over the last few months. Another example of why keeping good notes is helpful.

The thing is I thought that I was doing so in an informed manner by consulting my data, looking at ranges, and averages. The truth: I was blinded by my own biased number chasing self. Thankfully nothing too terrible happened. Just woke up a bit more tired than I normally would after good therapy a few times.

I owe you guys an apology, because originally I was merely curious, and then decided to try to optimize my therapy. Now, I've got to exercise my best judgement, since this is a complex machine, with many variables, it is difficult to make informed judgments on this without being very well versed in the ways of these machines.

If I make any changes from now on they will require more than one to two nights of sleep before changing them (more like a week if AHI <5). I also need to actually make time, and talk to my doctor. It has been a couple of months. I owe them an update.

Again, everyone, I'm sorry and thank you. I'm just here to learn, and be more helpful the more I learn.