ResMed VPAP III ST Algorithm

[rogelah]

Does anyone know how the ResMed VPAP III ST algorithm works in ST mode?

[dsm]

I can try to answer some parts of it.

But, it gets a tad messy when trying to explain the I:E ratio (which is a little more complex & flexible than what is on the Bipaps).
There are a few here who can give some explanations of that part allowing for the extra settings on a VPAP III.

Ask a question & lets see how we go.

Cheers

DSM

[rogelah]

I am interested in the actual algorithm used. I have a low or nil leak rate but RR is high, for example median is 21, 95% is 33 and max is 48, VT median is 500, 95% is 700 and max is 900, MV median is 12.4, 95% is 17.8 and max is 20.6. AHI has a high AI component one night but a low one the next (AHI is 30.8, AI is 3.7, %Time is 1.9 and AHI of 21.5, AI of 13.2, %Time of 8.5). Both days represent 7+ hours. Afterward, I feel like crap with a headache that lingers and I can't keep my eyes open all day.

[dsm]

I am not sure what you might be meaning by 'algorithm' as the breathing rate & volume are driven by you not any software in the VPAP III.
> S mode is 'spontaneous' mode & the machine will only change from epap to ipap to epap when it senses the user is changing from breathing out to in to out etc:.

> T mode adds a backup rate that if the users breathing rate drops below the backup rate, the machine itself switches from epap to ipap to try to keep the breathing rate at the minimum (as set = backup rate).

> (2 added) In Timed mode the clinician can set a breathe-in to breathe-out ratio (i.e he can tune the user's breathing-cycle to set how much of a breathing-cycle is allocated to breathing in (ipap) vs breathing out (epap). This is the 'T' & 'ST' mode MAX I:E setting. A typical ratio of I:E might be 1:2 as most people breath in quicker than they breathe out, but not all. The ratio helps synchronize the users breathing better. (Resmed VPAP Bilevels include this I:E ratio as a setting, Bipaps generally don't as (IIRC) Bipaps use AutoTrak as part of their detection).

See extract of text from clinician manual in a post just below this one.

As 1 example ...
The 'mechanisms' it uses to handle centrals is not so much an 'algorithm' as a simple tracking of the rate at which you are breathing & if that rate drops below a backup rate (set when the machine is in T mode) then the machine 'triggers' that is when the period of time defined by the backup rate, passes & the machine senses the user is still in epap phase, it switches (or 'triggers') to ipap.

The intention of this switch is, assuming the ipap setting is high enough above epap, that switch will trigger the user to breath again. The success of the triggering depends on the epap to ipapa gap being wide enough based on just how much of a gap is needed to get this particular user to breath in again.

The VPAP III does not monitor your volume for any purpose other than to record it as data. e.g. If your tidal volume is say 600 ml and then a few breaths later you only breath in 300 ml. It records the fact but does nothing about it. If this happened when you had an ASV machine, it would immediately ramp up pressure (within 1 breath) to try to get you to maintain at least 90% of the past breathing volume average (or target peak flow) as recorded in a 3min/4min window (depending on brand of ASV (resmed vs respironics)).

If you hyper-ventilate (say breathing in excess of about 25-30 BPM) then also the VPAP III will let you do it & not do anything about it. When I used a Vpap III (in both S & S/T modes) I noticed there were times when my BPM went way up high. What usually causes this is CO2 build up & the body starts to accelerate your breathing rate in order to lower the CO2 in the blood). Breathing too slowly or with very low volume, is the opposite & allows CO2 to build up (hypo-ventilation). The T mode backup rate tries to deal with hypo-ventilation based on what rate you are breathing at, the VPAP III as already mentioned, merely records the volume (tidal flow).

The Bipap AVAPS machine is one that does (in AVAPS mode) track volume & if it falls below a set minimum (set by the RT clinician in the machine setup)
will raise pressure slowly to try to bring the user's tidal flow back up to target..

Hope this sort of helps a bit

DSM

(3 altered) Put the clin data in its own post & adjusted wording to confirm to the convention that 'triggering' means epap to ipap & 'cycling' means ipap to epap (it gets tricky when trying to talk about a breathing-cycle as meaning a full breath-in/breath-out event, because cycle has a specific meaning in Bilevel manuals but it is also the best word to describe a full in/out breath).

[dsm]

I am interested in the actual algorithm used. I have a low or nil leak rate but RR is high, for example median is 21, 95% is 33 and max is 48, VT median is 500, 95% is 700 and max is 900, MV median is 12.4, 95% is 17.8 and max is 20.6. AHI has a high AI component one night but a low one the next (AHI is 30.8, AI is 3.7, %Time is 1.9 and AHI of 21.5, AI of 13.2, %Time of 8.5). Both days represent 7+ hours. Afterward, I feel like crap with a headache that lingers and I can't keep my eyes open all day.

My guess here is that your epap may be too low & the gap a little to wide.
What are your epap / ipap settings at the moment ?. Who set them (what qualifications - i.e. Dr or Resp Specialist).

Also, does the data show at ANY time, you dropping into the backup rate (I strongly suspect not).

(2 added) also, it is worth noting your TI values (Ipap Max & IpapMin) ?
They *may* also have an effect on your respiratory rate.

Cheers

DSM

[dsm]

From the manual ....

VPAP
====
VPAP stands for variable positive airway pressure therapy. In VPAP treatment, you may
set two treatment pressures—one for inspiration (IPAP) and one for expiration
(EPAP). The VPAP senses when the patient is inhaling and exhaling and supplies the
appropriate pressures accordingly. The difference between IPAP and EPAP levels helps
determine the tidal volume.

OPERATING MODES
================
The VPAP devices provide a higher pressure during inhalation (IPAP) and a lower
pressure during exhalation (EPAP). The VPAP III ST has three operating modes which
determine how the changes between IPAP and EPAP pressures are made:
Spontaneous, Spontaneous/Timed and Timed. The VPAP III ST also has a CPAP mode
in which a fixed pressure is delivered. The VPAP III (non-T model) can operate in either
Spontaneous or CPAP mode.

• In Spontaneous mode, the VPAP senses when the patient breathes in and when
the patient breathes out. The ventilator follows the patient’s spontaneous
breathing rate to supply the appropriate pressure.

• In Spontaneous/Timed mode (VPAP III ST only), the VPAP will follow the patient’s
spontaneous breathing (as in Spontaneous mode). However, the clinician also
specifies a breathing rate (as in Timed mode) which they do not want the patient
to fall below. This is a backup rate, which will be supplied if the patient’s
spontaneous breathing rate becomes insufficient.

• In Timed mode (VPAP III ST only), the clinician sets a breathing rate and an
inspiratory time (as set by the IPAP Time parameter). This fixed rate and fixed
inspiratory time as set by the clinician is supplied to the patient.
• In CPAP mode, a fixed pressure is delivered.

TiCONTROL™ – INSPIRATORY TIME CONTROL
=====================================
The TiControl™ feature is also unique to the VPAP Series. It allows the clinician to set
minimum and maximum limits on the time the ventilator spends in IPAP. The minimum
and maximum time limits are set at either side of the patient’s ideal spontaneous
inspiratory time, providing a “window of opportunity” for the patient to spontaneously
cycle to EPAP.
The minimum time limit is set via the IPAP Min™ Time parameter and the maximum
time limit is set via the IPAP Max™ Time parameter.


(cycle in this diag means when to switch from epap to ipap)

TiControl’s IPAP Max and IPAP Min Time parameters play a significant role in
maximising synchronization by effectively intervening to limit or prolong the inspiratory
time when required. This ensures synchronization even in the presence of large mouth
and/or mask leak.

TRIGGERING AND CYCLING
=======================
To provide comfortable treatment it is important to maximize the synchronization
between the breathing rhythm of the patient and the pressure pattern supplied by the
ventilator. Synchronization is achieved by the ventilator quickly and reliably detecting
when the patient inhales and when the patient exhales. The VPAP uses pressure and
flow transducers to accurately sense the patient’s inhalation and exhalation efforts.
The VPAP detects the beginning of the patient’s inspiratory effort by measuring the
increase in flow. When inspiratory flow increases above a certain level the device
changes from EPAP to IPAP. This change from EPAP to IPAP is called triggering.
Similarly, the VPAP changes from IPAP to EPAP when the inspiratory flow decreases
below a certain level. The change from IPAP to EPAP is called cycling.

RISE TIME ADJUSTMENT
====================
Rise Time is the time taken for the pressure to increase from EPAP up to IPAP. Rise
Time can be set to MIN (the fastest Rise Time) and then in 50 unit increments from
150 to 900. This will control the rate of pressure increase when the VPAP switches
from EPAP to IPAP. The higher the Rise Time setting, the longer it takes for the
pressure to increase from EPAP to IPAP. If the patient has a high ventilatory demand
then the Rise Time should be set to MIN, as this is the fastest Rise Time setting.

OPERATING INFORMATION
======================
Note: The Rise Time should not be set so that it is longer than the time spent in IPAP
(otherwise the IPAP pressure would never be reached). For this reason, Rise Time is not
allowed to exceed the IPAP Max time setting.

DSM

[rogelah]

...My guess here is that your epap may be too low & the gap a little to wide.
What are your epap / ipap settings at the moment ?. Who set them (what qualifications - i.e. Dr or Resp Specialist).

Also, does the data show at ANY time, you dropping into the backup rate (I strongly suspect not).

(2 added) also, it is worth noting your TI values (Ipap Max & IpapMin) ?
They *may* also have an effect on your respiratory rate...

The sleep doctor set the IPAP, EPAP and Backup Rate in the Rx...I = 19, E = 14, BR = 15. IPAPmax and IPAPmin were at default values...Imax =2.0, Imin = .10 (IIRC). I have experimented with Imax at 1.5 and at 2.5. There does not seem to be any appreciable difference.

How would I know if I am dropping into Backup Rate? My "gut' agrees with you.

My "gut" feeling is that CO2 is the culprit for my "crappy" feeling and headaches. I wish the VPAP III ST had some statistic that would let me zero in on something. Would an oximeter help in that regard?

[dsm]

...My guess here is that your epap may be too low & the gap a little to wide.
What are your epap / ipap settings at the moment ?. Who set them (what qualifications - i.e. Dr or Resp Specialist).

Also, does the data show at ANY time, you dropping into the backup rate (I strongly suspect not).

(2 added) also, it is worth noting your TI values (Ipap Max & IpapMin) ?
They *may* also have an effect on your respiratory rate...

The sleep doctor set the IPAP, EPAP and Backup Rate in the Rx...I = 19, E = 14, BR = 15. IPAPmax and IPAPmin were at default values...Imax =2.0, Imin = .10 (IIRC). I have experimented with Imax at 1.5 and at 2.5. There does not seem to be any appreciable difference.

How would I know if I am dropping into Backup Rate? My "gut' agrees with you.

My "gut" feeling is that CO2 is the culprit for my "crappy" feeling and headaches. I wish the VPAP III ST had some statistic that would let me zero in on something. Would an oximeter help in that regard?

Based on your current settings, I don't now think it is a case of epap being too low. To provide any other thoughts I'd need to know a lot more about your weight/health & even then it really is outside any expertise I have when we are dealing with neuro-muscular disorders. I still lean toward the AVAPS machine as being the 'logical' choice.

I don't quite know what it is about the VPAP IIIs that seems to provoke hyperventilation but it happen on mine until I re-tuned the epap & ipap. Using an SpO2 meter helps gain some insights but isn't needed to resolve this problem.

RE dropping into backup rate - the nightly data should show when your RR drops to what the back up RR rate is.
At this time, those high RR rates your are reaching, just don't seem right even for someone with neuro-muscular issues.

The best help here would be if SAG (aka Muffy) or SWS could add some thinking & suggestions but I also suspect they would be thinking (we could see this coming - we said go AVAPS).

Good luck

DSM

(2 added) One other thought I have is that your tidal volume seems highish for someone with your condition. You may be averaging more ml of volume than me & I am very fit & healthy. I am wondering if the hyperventilation shown (when RR goes above say 25) is the cause of the highish tidal flow numbers.

[rogelah]

I am 6' 1" and last time I was weighed I was 180 (my guess is closer to 195 now). Other than FSHD, I am healthy. No heart problems, my appetite is good, I am never depressed (no nagging wife:)), I have great friends and a close family for support.

I don't drink, chew, smoke, toke, eat Alice B Toklas brownies. My thoughts are pure (:)), my bills are paid and I don't worry about anything except what came before The Big Bang.

One thing more, last night I removed the mask after 4 hours and haven't had the pernicious headache and sleepiness. Let's say I keep getting this feeling that CO2 is involved but because there is not a good record of my breathing pattern I keep looking for ways to back into it. My live in caretaker says sometimes she has check closely to see if I was breathing (before BIPAP).

Today, I finally got the release for the PSG and titration and faxed it back immediately. Hopefully, there will be more info but the sleep doc said he was having a problem figuring it out. He wanted me to use a ResMed VPAP Adapt SV and I said Respironics SV (more options for different therapies) and the DME won because, I think, they only do ResMed.

I have a followup appointment on Monday and will ask if possible to switch to Respironics SV if not AVAPS.

I have found a fellow FSHer in the UK who uses a portable respirator on the arm of his wheelchair during the day (don't know yet what he uses at night) and have asked him what protocol(s) he went through.

[dsm]

Ask them if you can trial the AVAPS but if they don't supply Respironics gear due to their affiliations, ask for the Resmed equivalent
(which isn't a Vpap AdaptSV ).

As posted much earlier, Resmed have a few volume - hybrid/volume ventilators (I am just not sure what models are available in the US).

DSM

[rogelah]

New insight. Last night, my caregiver was instructing her replacement for her weekend off and I put the mask on early. Normally, I just zone our and fall asleep. Last night I lay the contemplating then Zen of the Universe when I noticed something...my spontaneous breathing was shallow and had, what I would call, a long waveform. Normally, I would have consciously countered with deeper normal breaths. The VPAP, however, was countering with high pressure and timed cycling. I decided to lay low consciously (if that's really possible) and see what happened. I theorized that the VPAP had not had time to get situated with its 100 second moving average and five breath calculations and was using defaults as initial values. I theorized that the next morning's graphs would show marked apneas and that later times would be less or nil (I had some day graphs that, indeed, did show this, but not all). I guessed that my breathing was less than 25% of what the VPAP was using for my norm. This could also explain why on some graphs there is a high hypopnea count and low apnea count (if my breathing rate was between 25% and 75% of what VPAP considered normal.)

I eventually went to sleep and when I woke up 6 1/2 hours later the VPAP was cycling at a comfortable rate and no matter what I tried to do it kept on plugging away. This morning's graphs did show many apneas coincidental with the theoretic test. End of the graph also showed some apneas, but only a few. Since I noted the times of the two periods I am certain my observations match the graphs.

I do have apnea events on some that are indeed in areas where sufficient time for the VPAP to normalize occurs. However, they all have an unusually high apnea or hypopnea count at the beginning. Some have similar, but less intensive, numbers at the end.

[dsm]

New insight. Last night, my caregiver was instructing her replacement for her weekend off and I put the mask on early. Normally, I just zone our and fall asleep. Last night I lay the contemplating then Zen of the Universe when I noticed something...my spontaneous breathing was shallow and had, what I would call, a long waveform. Normally, I would have consciously countered with deeper normal breaths. The VPAP, however, was countering with high pressure and timed cycling. I decided to lay low consciously (if that's really possible) and see what happened. I theorized that the VPAP had not had time to get situated with its 100 second moving average and five breath calculations and was using defaults as initial values. I theorized that the next morning's graphs would show marked apneas and that later times would be less or nil (I had some day graphs that, indeed, did show this, but not all). I guessed that my breathing was less than 25% of what the VPAP was using for my norm. This could also explain why on some graphs there is a high hypopnea count and low apnea count (if my breathing rate was between 25% and 75% of what VPAP considered normal.)

I eventually went to sleep and when I woke up 6 1/2 hours later the VPAP was cycling at a comfortable rate and no matter what I tried to do it kept on plugging away. This morning's graphs did show many apneas coincidental with the theoretic test. End of the graph also showed some apneas, but only a few. Since I noted the times of the two periods I am certain my observations match the graphs.

I do have apnea events on some that are indeed in areas where sufficient time for the VPAP to normalize occurs. However, they all have an unusually high apnea or hypopnea count at the beginning. Some have similar, but less intensive, numbers at the end.

Roger,

When you started this thread you asked for info on the VPAP III S/T but in your above post your appear ? to be describing the behavior of a Vpap Adapt SV.

Just want to be sure what machine you have ?

Thanks

DSM

[rogelah]

Roger,

When you started this thread you asked for info on the VPAP III S/T but in your above post your appear ? to be describing the behavior of a Vpap Adapt SV.

Just want to be sure what machine you have ?

Thanks

DSM

Says VPAP III ST on the hood.

[dsm]

Roger,

When you started this thread you asked for info on the VPAP III S/T but in your above post your appear ? to be describing the behavior of a Vpap Adapt SV.

Just want to be sure what machine you have ?

Thanks

DSM

Says VPAP III ST on the hood.

One comment ...

"The VPAP, however, was countering with high pressure" - The Vpap III only switches between Ipap & Epap & doesn't vary that all night. The only time it will do anything a bit different is if your RR drops below the dialed-in backup rate. Then it just switches from epap to ipap on its own rather than waiting for you to do so. so am not sure what you mean by 'higher pressure' other than it went to IPAP (as it does every breath).

Also, "VPAP had not had time to get situated with its 100 second moving average and five breath calculations " - The Vpap really has no moving window ? (the Vpap Adapt SV does). It normalizes irregular breathing (PB) within 3 or so breaths.

The Vpap III is really very very mechanical & doesn't vary anything until your RR drops below the backup rate at which time the machine will 'trigger' by itself (go from epap to ipap). The 'cycling' (going from ipap to epap) always occurs because we all (even when having centrals) breath out first. i.e. a Central can really only occur at the end of breathing out phase as the body contracts and expels air. A central typically happens because no signal is sent to the respiratory musculature to act such as to draw in the next breath. Thus he RR is seen to be dropping below the backup RR number & the machine 'triggers' from epap mode to ipap mode which normally pushes air into the user's lungs (if the epap to ipap gap is set correctly - if the epap/ipap gap is too low for the user's condition, the user may just do nothing & lay there ignoring the increase in pressure when the machne 'triggered' to ipap pressure). A *min* gap of 4 is the norm & some folk are given gaps as high as 8 CMs. It typically depends on a number of factors related to the person's type of CA & their physiology. But I don't believe you have CA as such, just weakness in breathing ?.

Hope this clarifies some of the info for you.

Cheers

DSM

(2) Corrected reverse use of 'cycle' & 'trigger' (I always seem to reverse these in my mind & only realize it when I read what I wrote a day or so later )

I have to keep reminding myself that 'triggering' is when a breath-in begins (the sucking in of a predetermine small amount of air 'triggers' ipap mode - the machine will remain in epap until 'triggered' by a breathing in or by 'timed mode' being activated due to RR dropping below backup). Cycling is when the machine flops out of ipap mode into epapa mode due to no more air being breathed out.

[rogelah]

Color me confused. The manual says the RR and VT are a 5 minute moving window. There is no graph for RR and VT just median, 95th percentile and max. MV has a detailed graph and is the product of RR and VT. My "gap" is 5 (19 - 14)? There are settings of low, med and hi for Cycle and Trigger but the manual says nothing about them.

Also, there does seem to be a difference in the IPAP at the beginning and ending of the night and I took into consideration the mask leak test at the start.

Is there anything to be gained from tweaking things like Rise Time, IPAPmin, IPAPmax, ???