Therapy using Lumis 150 ST

[StuartC]

Overall, I believe what's happening is that while you breath spontaneously, only EPAP is used and you're happy.  Once you start iVAPSing tho you immediately overventilate,  your drive to breathe is shot for the rest of the night and you end up with machine breaths.  I think the first half of Saturday is how you eventually want to look, with iVAPS attacking what I believe to be the first 2 REM periods while you spontaneously breath during NREM.

That sounds quite reasonable. 

Which leads me to wonder whether I could reduce the volume target in order to maintain the target respiratory rate at 12 without overventilating?  Perhaps that target of 580 to 600 ml tidal volume stated in the report is a touch too high?  After all, one characteristic of Saturday night was that the tidal volume was low. 

On CPAP my tidal volume was typically around 450 and my minute vent was less than 6.  So even getting Vt over 500 and MV over 6 should be better than before.

It has just gone midnight for me, so I need to go sleep.  I'm going to set target patient rate to 11, just because I haven't yet, and set the volume target on the low end of the range stated.  Let's see what that does.  I will post charts in the morning.

Thanks again

[Rubicon]

On CPAP my tidal volume was typically around 450 and my minute vent was less than 6.

Which leads me to wonder whether I could reduce the volume target in order to maintain the target respiratory rate at 12 without overventilating?  Perhaps that target of 580 to 600 ml tidal volume stated in the report is a touch too high?  After all, one characteristic of Saturday night was that the tidal volume was low. 

In re:  your first point, CPAP was at 9.0 cmH20.  4/16 Saturday (where desirable behavior was seen) was EPAP 5.0 cmH2O with PS (probably) 4.0 cmH2O, which may have added some overventilation.  That's not necessarily the signal for "Hey let's start with PS=0 and 9.0!!"  There's a lot of variables going on, and pretty soon I think we need to pick some parameters and just let 'em soak for awhile.

Try Learn Targets function to see what "it" thinks the targets should be.  Maybe your idea of targets and its idea of targets are too far apart.

For the next report replace I:time with Minute Ventilation.  Make the parameters tight enough to see as much detail as possible.  We are going to superpose the iVAPS VE (not VA, we need to have a common value) to see if it's where it should be.  It should be slightly under NREM and activated in REM.

Include IntelliRate and VA in every report.

Could you run the Saturday report with this edit too?

Expand pressure to Auto or increase High Limit enough to include the entire waveform.  It looks clipped. 

What is Min PS and Max PS set at?

[StuartC]

Attached are charts arranged as requested from Friday (15th), Saturday (16th) and Monday (18th).  The following settings are the same for all of them:

• Mode = iVAPS
  
• EPAP = 5
  
• PS min = 4 (IPAP min = 9)
  
• PS max = 9 (IPAP max = 14)
  
• Ti min = 1.0 s
  
• Ti max = 2.5 s
  
• T rise = 900 ms
  
• Trigger = Med
  
• Cycle = Med
  
• Height = 175 cm
  
• Mask = Full (F&P Evora Full)
  

The following settings were changed:

Friday (15th):

• Patient Target Rate = 12 bpm
  
• Va = 5.5 L/min (MV = 6.9 L/min, Vt = 578 ml)
  

Saturday (16th):

• Patient Target Rate = 10 bpm
  
• Va = 4.8 L/min (MV = 6.0 L/min, Vt = 600 ml)
  
• Switched to Vitera mask for second period of sleep
  

Monday (18th):

• Patient Target Rate = 11 bpm
  
• Va = 5.0 L/min (MV = 6.3 L/min, Vt = 574 ml)
  

I have overridden the Y-axis settings on all graphs. No the pressure graph is not clipped, PS max is limited.  As indicated earlier in the post, I have experienced aerophagia previously and did not want to allow the machine to shoot up to pressures that I might not initially tolerate, especially during NREM, when I do not need pressures that high.


My mind was obviously working well last night as I slept.  One thing I realized was that your explanation of the machine taking over breathing because CO2 drops too low could explain the difference between the two periods of sleep on Saturday with the change of masks being the key difference - if the Vitera mask is more effective at venting CO2 than the Evora Full.  No, I can't be sure, but it is a possibility.

The other thing I realized is that I have missed a few things that should have been obvious to me because of my previous career as a control systems engineer, when I used to tune control loops in chemical plants.  VAPS uses feedback control to achieve a volume set point by controlling pressure and, if I am over ventilating, it appears to be over controlling.  Frequently this occurs in control loops because the feedback loop is being asked to do too much.  The best approach to rectify this is to establish reasonable open loop control and then use feedback control to make smaller control actions to only achieve set point accuracy and deal with disturbances. 

To get reasonable open loop control in PAP therapy, I would need to plot volume (take your pick of tidal, minute or alveolar) as a function of pressure support.  If I set a particular pressure support value, what  volume would be delivered? Once I establish the characteristic curve, I should be able to choose an appropriate PS value to become the PS min in VAPS mode.  This should let me breathe freely in NREM with the controller only altering IPAP to the (hopefully small) extent that the volume set point has not yet been achieved and to deal with whatever disturbance REM throws my way.  PS max needs to be high enough to allow sufficient change of IPAP to deal with REM without allowing it to overshoot.

So, how do I establish my relationship between pressure support and volume?  The manual way is to switch back to ST mode, fix EPAP at 5 and and progressively increase IPAP (over several nights), recording the resultant volumes (and respiratory rates) as I do so.  ST mode is better than S mode as it will take over breathing if I set IPAP too high and over ventilate.  That point, where the percentage of spontaneous breaths starts to decrease, is also useful knowledge because it sets the maximum value for PS min.

When I started with the machine, I ran for a few days in S mode with PS between 3 and 5.  Tidal volumes were  still generally less than 500 ml.  Following the logic of the process above, PS min probably needs to be higher than 5.  Interestingly, there was a suggestion in the sleep study from the sleep tech, but not the specialist, that IPAP min should be 11 (PS min = 6).   Maybe.

I could feel this last night.  When I was awake enough to control breathing, I breathed deeply and IPAP stayed at IPAP min.  But as I started to drift off and my tidal volume decreased, the pressure controller stepped in to increase IPAP.  It was noticeable, I could feel it, it roused me before I got to sleep and the cycle started again.  I even worked out how to inhale a little sooner to reset the action of the controller and bring IPAP down to IPAP min.


In the meantime, I will try Learn Targets this afternoon and get back to you with what it comes up with.


Final thing.  The appointment that I had this morning provided one piece of information, which you might find relevant.  I had a basic lung function test done a while ago.  The results were summarized as "normal spirometry, elevated gas transfer".  Full report will be mailed to me.

[StuartC]

Results of learn targets are:

• Target Patient Rate = 13
  
• Target Va = 5.7 L/min
  
• MV = 7.2 L/min
  
• Vt = 558 ml
  
• Vt/kg = 8.1 ml/kg IBW
  

Test was run with EPAP = 5 and PS = 4

[Rubicon]

Attached are charts arranged as requested from Friday (15th), Saturday (16th) and Monday (18th).  The following settings are the same for all of them:

[*]PS max = 9 (IPAP max = 14)

I have overridden the Y-axis settings on all graphs. No the pressure graph is not clipped, PS max is limited.  As indicated earlier in the post, I have experienced aerophagia previously and did not want to allow the machine to shoot up to pressures that I might not initially tolerate, especially during NREM, when I do not need pressures that high.

OK that's fine and offers some explanation on why things are going the way they are.  The way Oscar reported the PS as IPAP 9.0 - 24.0 cmH2O made it look like you could go to peak pressures of 39 cmH2O.  iVAPS wants to drive your VT up but PSmax prevents that.  So by assigned parameters, rate is fixed, now VT is fixed, consequently MV is fixed.  If we want to stop iVAPS that leaves rate to be changed.

Before we go there let's reaffirm that what's happening is NBD.  The results that iVAPS gives you are fine and your sleep looks continuous so all we're really doing is making iVAPS work the way the book says it should work.  But who follows instructions anyway?

Since you know what your sleeping parameters are, going to S/T is similarly NBD.  Just match everything up.

Returning to rate, I believe your sleeping rate with PS=4.0 EPAP=5.0 based on the Saturday result is more like 15.  Do you have the results when you had rate at 14?

[Rubicon]

Do you feel like uploading the Oscar files to dropbox to similar so I could see them?  It would help me to make some shots coloring in a Target VA and reading values along the waveform.  I think if you left PSmax to go crazy iVAPS would eventually equilibrate (but don't do that it's not necessary.  Your PSmax limit makes your therapy safe and effective, even if it's in a roundabout way).  But I'd also like to examine breath by breath why it appears that although iVAPS has hit Target it won't back down.

[StuartC]

Ah, yes.  OSCAR has been reading EPAP as a 5 to 15 range, not just fixed at 5.  That affects the way it displays the IPAP range as well.  I have reported it in the software forum and uploaded data to be looked at.  Fix in a future release, I am sure.

Sorry, NBD? Not familiar with that acronym.

Screenshot attached for night with RR = 14.  Did not like that rate though, too fast for comfort.

Happy to supply data by Dropbox.  If you have one you would like me to use, pm the details.  Otherwise I will arrange to share a folder off mine and send you a pm with the link.  Might be easier that way anyway should others also need access.

[Rubicon]

NBD = No Big Deal aka things are fine.

Understand about rate feeling too high.  Wake likes 12, sleep likes 15.  Starting to get a little constrained in our options tho--  "NBD", there's at least 2 more tools in the toolbox.

Yup, Loop Gain, the key to all things CompSAS.

You are going to find this FASCINATING!!

[Rubicon]

Can you see it yet?

[Rubicon]

You are oscillating!!