Resmed VPAP Adapt SV - for Central Sleep Apnea

StillAnotherGuest wrote:

Banned wrote:I assumed, until now, the Respironics BiPAP SV had the ancillary sensor line. I know with my Adapt SV when I stop breathing (hold my breath) the Adapt SV starts ramping to provide much more air by my next breath. When ResMed says on a "breath-by-breath" basis, it's true. Exhalation (EEP) is fixed, but I can watch the Inhalation pressure change with each breath on the Adapts LCD. If I had serious issues with stopping breathing at night (which I do) I would be hard pressed to want to snuggle up to a Respironics BiPAP SV without any feedback from the mask.

Well, my first thought would be that where you take measurements is academic. If you know the characteristics of the machine tubing, planned leaks (mask vent rate) and the unplanned leaks are relatively constant, you could calculate everything you need to know no matter where you take the measurements. Further, the purpose of ASV is simply to supply ventilation during periods of reduction (specifically central apnea) and both machines do this quite well.

The advantage of measuring proximal airway pressure (pressure at the mask), would be that (theoretically) you could match up machine breaths to patient breaths more easily. I believe that measuring breaths at the machine is less sensitive when there is patient effort (patient is actively particiapting in ventilation, rather than letting the machine do all the work), as shown in this graph of pressure measurements taken in an AdaptSV circuit at patient airway (Flow 1) and machine (Flow 2):



When the breath is largely from the machine, both waveforms are similar, but during periods of greater patient effort, changes are seen in the patient waveform that are not reflected in the machine waveform. So if the ASV is trying to recreate a breath pattern that closely mirrors patient effort (more like PAV technology), then this might be a better way to do that.

Now, one might ask, what value is this information? If you're asleep, having a central apnea, and the ASV is simply trying to generate a breath that is tailored not for comfort, but rather to a volume to stabilize breathing, then I'm thinking, "Who cares?" I mean, great, perhaps you can duplicate waveforms so the waveforms "look" the same, but you're ASLEEP! So is this really just another Wake comfort measure, or is there true physiological value to this?

Besides, with the newer bilevel technologies, there aren't any more square waveforms, they're all much more patient-friendly.

Again, this boils down to "what is it you're trying to fix?" If you're trying to fix CSA, you have to see that machine performance is addressing exactly that. While it may be attractive to say. "Look at that proximal patient line, that must really DO something!", you really have to see which machine fixes the underlying problem better.

This is also another good example demonstrating that the waveform out the machine is not necessarily the same as what the patient is getting, so "treating the waveform" can get you in a real rut. If the machine generates a square waveform, and patient effort is passive, then it will have a flat appearance as flow appears constant. This does not signify a flow limitation, only that the machine is delivering steady pressure.

SAG

SAG,

Good points & well put.

So which machine do the patients prefer & which machine delivers best ? that is the bottom line !.

DSM

You nailed it SAG! "The advantage of measuring proximal airway pressure (pressure at the mask), would be that (theoretically) you could match up machine breaths to patient breaths more easily".

I do not see anywhere in the in the Respironics BiPAP SV literature anything about adapting to the patients ventilatory needs on a breath-by-breath basis. It simply cannot be done without sampling the expiratory pressure at the mask on every breath as with the Adapt SV. The Adapt then automatically calculates a target ventilation (90% of the patients recent average ventilation), adjust the pressure support to achieve it, and ensures pressure support is synchronized to the patients own recent breathing rate and flow. I'm not saying the BiPAP SV won't get you there, eventually, and it is precisely when I'm asleep that I would prefer to have the breath-by-breath result. I'm not trying to disuade anyone from getting a Respironics BiPAP SV or having doctors tell the patient, "Here, the Respironics BiPAP SV is good enough for you, enjoy your life."

Cheers

I'm not a medical professional either. In fact, my sleep-lab doc said he would never prescribe a ResMed Adapt SV for me. Some doctors really suck!
Machine: ResMed Adapt SV
Mask: Quattro FF
Humidifier: Sullivan HumidAire (Old style stand-alone)

Another great insight from SAG.

That helps explain why running Learn Circuit is important, as it must be done for any change in tubing, mask etc.

However, it does explain why EERS works while moving the sensing point some distance away from the mask.

I always thought that the return line and the LC process in the Assist AV
calibrated out the effect of the mask and tubing. What SAG is saying makes more sense.

DSM - again the proof of which machine is better, since they do work quite differently is the result of how one reacts in a PSG. For me, I like the ResMed machine because, in part due to your original sleuthing about the motor design concept, told me that I could grasp better what it did. To me,
the ResMed design appeared to be truly innovative and the result of trying something radically different.

I would be willing to try the Respironics machine to determine how it works for me - and that may be an option in the future for me per my MD, just to see how it does. But the ASV to me is a bit more proven.

Lubman

Does anybody know what kind of information you might see with the RESMED software with/without the reslink gadget?

Donf,

Having the ResLink - which contains an SD smartcard - will allow you or your DME to move about a month's worth of data into the ResMed ResScan software, where reports can be generated on the type of items Wayne mentions in the information "card" delivered with his (and my) machine.

By the way, I believe the Assist AV manual (but not the clinical manual) is online at the resmed web site.

Lubman

Banned,
Noticed you said a while back that the MD wouldn't give you and ASV and you are using it without having had a PSG.
First of all, are you from down under - where the machine might be more readily available without a test?
Second, care to elaborate a bit more?

Lubman

Lubman! Long time! How ya’ been!

Banned wrote:You nailed it SAG! "The advantage of measuring proximal airway pressure (pressure at the mask), would be that (theoretically) you could match up machine breaths to patient breaths more easily".

I do not see anywhere in the in the Respironics BiPAP SV literature anything about adapting to the patients ventilatory needs on a breath-by-breath basis. It simply cannot be done without sampling the expiratory pressure at the mask on every breath as with the Adapt SV.

Well, it's a little early to draw some conclusions yet, we ain't even through the prologue.

The components of generating waveforms include patient effort, lung compliance, resistance of patient airway, presence of planned and unplanned leaks, resistance of device tubing and response of the machine. The waveforms generated above were made using pressure transducers, and if machine calculations are based on flow (and BTW, BiPAP AutoSV is a lot more flow-oriented), then we have additional considerations.

But let's say proximal airway pressure (Flow1) takes into account more of the patient characteristics, and Flow2 represents more of machine response. If we blow up these waveforms:



then we have to ask, "OK, AdaptSV has all this great information from proximal pressure, what did it actually do with it?"

In order to match up on a "breath-by-breath basis", the pressure signal has to pass through the proximal pressure line (takes some time), be analyzed by the microprocessor (OK, electricity travels pretty fast), the flow generator must respond, and then the resultant flow/pressure has to get out to the patient. Now I know time is relative, but a lot of stuff has to happen here.

So let's superimpose the 2 signals:



and now ask, "Did AdaptSV really do anything different with proximal airway pressure data?"

I would offer that the placement of the pressure sensor at the proximal airway had more to do with being able to calculate leaks with a greater degree of accuracy (you don’t have to account for the tubing resistance, which would have been plugged into the formula as a constant).

Yet, in performing Learn Circuit, you’re calculating actual tubing resistance. So one may now wonder if the chief purpose of measuring proximal pressure is simply to account for tubing resistance and increase the accuracy of volume measurements. This accuracy is essential in a volume-based ASV algorithm.

Ya think if we asked Michael in nice way, he’d tell us?

SAG

SAG,

" I would offer that the placement of the pressure sensor at the proximal airway had more to do with being able to calculate leaks with a greater degree of accuracy (you don’t have to account for the tubing resistance, which would have been plugged into the formula as a constant). "

Agree - have always said that sensing at the masks gives the most accurate info on leaks and to try to perform servo ventilation requires very accurate leak data.

Thanks
for the charts - these have been very helpful

Cheers

DSM

This may be redundant and inconsequential, but as I understand, the Adapt algorithm measures and adjusts over a 100 second traveling interval, so the proximal tube data is averaged and not reactive specifically to an individual event other than maintaining ventilation within the 90 percentile range for a perceived central event. Sort of a 90 percentile ventilation based on an average of an average taken over the previous 100 seconds of data collection. Without a clear time line and ability to calculate or measure this running average, speculation on specific curve data is not completely insightful without the previous data available; though isolated curve data may have some relative interest with this limitation noted.

In order to match up on a "breath-by-breath basis", the pressure signal has to pass through the proximal pressure line (takes some time), be analyzed by the microprocessor (OK, electricity travels pretty fast), the flow generator must respond, and then the resultant flow/pressure has to get out to the patient. Now I know time is relative, but a lot of stuff has to happen here.

SAG, you are awesome! Allot has to happen in a very short time for the Adapt SV to measure the expiration volume at the mask via the proximal sensor tube, then calculate a target ventilation which is 90% of the recent target ventilation, then adjust the pressure support to achieve (thank you dual-impellers), while synchronizing the patients recent breath rate and flow on a breath-by breath basis. In comparison, the extra algorithm squeezed into a a run-of-the-mill Respironics BiPAP machine to create a a 'BiPAP SV' would be the functional equivalent of the fat lady coming down the stairs while the fireman is squeezing past her coming up the the stairs. You may get there before the building collapses, but it certainly isn't going to be on a breath-by-breath basis.

Lubman, I look forward to your feedback on the respironics BiPAp SV, when you get it. I'm in northern California. I got my Adapt SV when my young Indian sleep-lab doc with his medical degree from Bombay looked at my CPAP study and decided he would ignore my complaints of gasping for air while on CPAP and my ensuing chest-pain in the morning. Since it was a huge HMO, I was fortunate to get a prescription for the ResMed Adapt SV from another doctor who was equally as disinterested in seeing patients as my Bombay doctor was in practicing medicine. Since I had learned to hate Apria from the onset and vowed I would always purchase my own equipment outright, funding an Adapt SV out of pocket (fortunately for me) was not a problem.

The myth of the difficulting in setting up a Resmed Adapt SV machine and without bi-level SV titration is seriously over-rated (at least for me). There simply is not an easier machine on this planet to setup. Set your 'Mask', set the 'EEP', Set the 'MIN PS', Run 'learn Circuit', strap in, enjoy the ride, and leave the driving to the Adapt SV. All of this can be done from a simple CPAP Study, reading some Adapt SV case-studies, and experimenting with the machine.

When the Adapt SV was originally created it was so totally automated that the medical community complained that there were no clinical controls (hence no money for them). ResMed added a few simple controls to the Adapt and slid it through the (USA) FDA via a loophole in the process. Respironics subsequently took a stock BiPAP, rushed to modify it into a 'BiPAP SV' with an additional algorithm, and slid it through the same FDA loophole. Philips/Respironics has the marketing base to flood the world with the Respironics BiPAP SVs. ResMed will always fight fiercely for there patents. In the end, it will likely be many years before Respironics can introduce an ethical BiPAp SV.

Cheers

On the topic of Servo Ventilation. The issues (including the sensing at the mask) that strike me as important include (from my own observations) ...

That none of the current Bipaps using auto-trak ever try to list leak as zero. They all report total leak and I have strongly believed (rightly or wrongly) that this is because they can't accurately tell the difference between accidental leak and fixed mask leak.

Anyone reading their nightly data does not want to have to take their average nightly pressure, look up the leak rate chart for the mask subtract the number provided from the nightly average total leak in order to come up with a real average nightly leak. Even then average nightly leak is still a poor datum. Accidental leak, minute-by-minute is what most people want to know.

The Bipap SV as best as I can tell (from taking all the other models apart) is the Bipap S/T box - appears to have the same hardware and includes the software perfected on the Bipap Auto plus includes a timed mode algorithm perfected on the Bipap S/T. That is what the Bipap SV appears to be. An amalgam of the Auto & S/T. That in itself could be good.

But one other test I can do with my Bipaps that has me questioning the lack of mask sensing in the Bipap SV, is that with the current Bipaps (Pro II, Auto, S/T) if I nose breathe, the ipap will switch far too early (well under a max INSP of 3 secs) to epap but if I mouth breathe, the ipap to epap switch is normal. When I try this test on other past & present Bilevels, interestingly the older Bipaps (have 2) without auto-trak, all switch ipap to epap ok for both my nasal and mouth breathing (they will reach max INSP). The PB Bilevels (PB320, PB330) all switch ipap to epap ok, the Healthdyne Bilevel switches ipap to epap ok the vpaps (Vpap III S & Vpap III S/T) all switch ok. It is only the current Bipaps with auto-trak that seem unable to work with my slower nasal flow.

That in itself is no big deal. We all know that different machines will deliver different results for different people based on things like their restricted nasal flows. But I do see a clear correlation between being unable to accurately report leaks and not being able to accurately handle low tidal flow patients. Also in my mind is that the current Bipaps are in my opinion, poor at reporting hypopneas and this is going to be obvious anyway as if they are not good at accurately identifying accidental leaks then they can never accurately quantify hypopneas.

The main point I am making is that from all I have learned and from what I can demonstrate repeatedly myself, I am convinced that the only accurate way to determine accidental leaks is with mask sensing and the only accurate way of reporting hypopneas is with accurate leak data (both accidental and fixed) and the only safe way to servo ventilate a patient is with accurate leak data (both accidental and fixed).


Charts of waveforms can identify instantaneous activity but won't necessarily show up weaknesses in the algorithms.

Cheers

DSM

(these topics are a good debating issue)

#2 clarified some aspects of the points.

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, auto

Just wanted to add some other experiments that raised issues in my mind about sensing at the machine vs sensing at the mask.

I modified a Bipap S/T to sense at the mask (ran an ancillary line to the mask & taped it into the machine where it sends the pressure at the air exit port).

The machine couldn't run because the whole circuit got into a pulsing mode that varied depending on the space in the mask used. This brought home to me the criticality of where the pressure info is sensed.

In other tests I measured the pressure losses between hoses of varying lengths and at varying pressures & was able to see a distinct pressure loss the faster the air moved down the tube. (this is predictable to those who understand airflow in a tube) but when I wrote about this - one serious cpapper mocked the data while claiming that any 3rd grade student understands that pressure in a container is equal at all places (at the time I tried to get that person to explain static pressure vs dynamic pressure in a 6ft tube when the air is still vs when being moved by force - it never sank in as far as I could tell).

The ancillary airline provides accurate pressure data because the air is static (air is not moving) the air circuit has air moving very rapidly and the variations & losses & effect of other aspects of the mask & leaks skew the data substantially. Again I come back to the (in my mind) fact that sensing at the mask via an ancillary line is the safest way to drive a servo ventilator.

DSM

#2 - also meant to mention the difference that exists for measuring pressure in fluids in a tube vs air in a tube. Liquids are not very compressible (why hydraulics in tubes work so well) whereas air in a tube is compressible & air not moving will establish a static pressure from end to end but air that is being pushed from one end (and in a varying fashion) is going to compress and the pressure wave even in as short as a 6 foot tube, combined with tube resistance can cause a drop of 1-2 CMS from one end to the other without adding in the nature of the activity at the other end. When the activity at the far end is included (sucking and pushing back) the pressure data is very different end to end.

The static air line can be telling a quite different story to the dynamic and much larger air circuit hose.

D

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap

Banned,

The myth of the difficulting in setting up a Resmed Adapt SV machine and without bi-level SV titration is seriously over-rated (at least for me). There simply is not an easier machine on this planet to setup. Set your 'Mask', set the 'EEP', Set the 'MIN PS', Run 'learn Circuit', strap in, enjoy the ride, and leave the driving to the Adapt SV. All of this can be done from a simple CPAP Study, reading some Adapt SV case-studies, and experimenting with the machine.

Okay, now I understand. When the machine was first brought to my state, the initial DME's and sleep lab staff briefed were told that for some people, setting the EEP = 6 brought considerable results without further efforts.

Others, if that initial setting didn't work, and they suggested EEP=8.
And for others, it was my understanding the algorithm didn't do much.

So I can see why you were able to get it to work. Thanks for the clarification.

DSM & SAG

The main point I am making is that from all I have learned and from what I can demonstrate repeatedly myself, I am convinced that the only accurate way to determine accidental leaks is with mask sensing and the only accurate way of reporting hypopneas is with accurate leak data (both accidental and fixed) and the only safe way to servo ventilate a patient is with accurate leak data (both accidental and fixed).

It makes one wonder why ResMed (and Respironics) FF masks don't have something to restrain chin movement build into the mask, similar to the
F&P mask. Because I can't think of a faster way to get an unwanted leak
on my NV FFM than to move my chin to change how the mask seals on my face.

No manufacturer has recommended a chin strap - yet I think dsm is right,
the assist sv algorithm isn't tolerant to accidental leaks. Yet how does one know if they might open their mouth, move their jaw and create a large leak -on numerous occasions through the night.

Lubman

[quote]Okay, now I understand. When the machine was first brought to my state, the initial DME's and sleep lab staff briefed were told that for some people, setting the EEP = 6 brought considerable results without further efforts. [Quote]

8/5 is the factory default setting on the Adapt SV. 8cmH2O would be the EEP. 5 cmH2O would be the MIN PS. When you add 8cmH2O (EEP) and 5cmH2O (MIN PS) the result is 13cmH2O which is the factory default inspiration pressure. With my CPAP study I knew I needed a minimum inspiration pressure of 14cmH20. i had read various case studies on the Adapt SV. Patients in those studies were prescribed an EEP of 9cmH2O, and sometimes 10cmH2O by their doctors. I tried EEPs from 6cmH2O to 8cmH2O and it was too much back pressure for me to exhale comfortably against. I chose an EEP of 9. Some sleep lab doctors automatically prescribe an EEP of 10cmH2O which I probably would not recommend. I adjust to 10cnH2O only when I'm stuffy and have a head cold and can benefit from the maximum expiratory pressure relief. From my experience, and in most cases I would recommend an EEP of 9cmH2O. Don't forget to set the MIN PS accordingly, and i generally run the Learn Circuit after I change EEP and MIN PS, just for the hell of it.

Cheers

That none of the current Bipaps using auto-trak ever try to list leak as zero. They all report total leak and I have strongly believed (rightly or wrongly) that this is because they can't accurately tell the difference between accidental leak and fixed mask leak.

If Regular Resmed machines are so smart at sensing things from the mask, how come you have to tell them which (Resmed only) mask it is they're sensing? How come the Adapt SV can only use specific (Resmed only) masks? Shouldn't those machines be capable of telling the difference betwwen accedintal leaks and fixed mask leak without being given a crib sheet with the masks' fixed leak numbers?
O.