Long time CPAP user still fatigued

[enigmatic]

   
I read many more papers last night, and they do not always use the same baseline method. They even use a specific product to test this non invasively (RVM monitor). The simplest way to calculate a baseline minute ventilation is using predicted minute ventilation (similar to tidal vol for IBW) -- just use your ideal body weight in kg times 100 ml/min. So in my case IBW is 73 times 100ml/min = 7300ml/min or 7.3L/min. 40% of that is just 2.92 L/min, notice on my graph I set the yaxis max to 3 L/min to look for min ventilation events below 3. Since we are only looking backward at explanatory events, I don't think it is necessary to use the real time moving average or even calibrate the beginning baseline, they use those in practice because they want the most recent empirical baseline and the ability to intervene right away (more of a real time predictive baseline).

Also notice that product I mentioned has a very simple criteria of identifying all three states hypo/normal/hyper and they use in ICUs! Just look at specific ranges of minute ventilation. They define hypoventilation as having minute ventilation below 40% (of baseline) for two minutes or more. We get this capability just by having our apnea machines and OSCAR! You could have also noticed my very shallow breaths on the OSCAR chart as well. Only the UF flags identified the shallow breathing. But -- those minute ventilation sub threshold events pointed me to the shallow flow rate segments on my graphs, not the other way around!

@Jay51 just curious why you only look at naps, as opposed to say full overnight?

[Jay51]

Great stuff Enigmatic.  Thank you for all the explanations and research that you have done.  A person who suspects that the might be hypoventilating could simply calculate their own predicted minute vent.  Then multiply by 40%.  Then plot that as a y axis on their minute ventilation charts.  It could work for hyperventilation also just adjusting the math (multiply by 140% for the y axis).  

2 consecutive minutes.  Wow.  That is not that long IMO.  I have seen some charts here with periods like that even greater than 2 consecutive minutes.  I will try to calculate my own predicted minute vent and plot it as the y axis on my minute vent chart.  

The reason I have not slept all night with this ASV yet is because I had some difficulty learning to fall asleep and stay asleep with it when I got it.  I also have to meet the compliance requirements of using the Evo ventilator on a continuous basis.  I plan on dropping the Evo off in January at the RT's to let her download a year's worth of data to my Pulmonologist to look at.  I may have a night or 2 then that I can experiment with an entire night with ASV.  I may try a night with straight cpap at 8 or so just to compare also.

On the math, Enigmatic, I should multiply IBW x 60% instead of 40% right?  Because IBW x .6 = a 40% drop.  Is this correct?  IBW x .4 would equal a 60% drop in minute vent.

[enigmatic]

Great stuff Enigmatic.  Thank you for all the explanations and research that you have done.  A person who suspects that the might be hypoventilating could simply calculate their own predicted minute vent.  Then multiply by 40%.  Then plot that as a y axis on their minute ventilation charts.  It could work for hyperventilation also just adjusting the math (multiply by 140% for the y axis).  

Their criteria is 300%. for hyperventilation. So predicted minute ventilation (ME) X 3 is the threshold above which they classify as hyperventlation. The key is to override the Yaxis setting by setting the override scaling mode, min, max range of minute ventilation on oscar graph. Hyperventilation would be to set the min y scale range at 3*predME and max farily large. Any ME that shows above that min is hyper. Hypoventilation would be set the yrange max to predicted_ME*0.4, and any ME events visible beneath that max are hypo events. We are essentially looking outside the boundaries of normal minute ventilation (ME) ranges, to look for these abnormal behaviors. If everything is normal, you should see no events exist outside of those ranges.

On the math, Enigmatic, I should multiply IBW x 60% instead of 40% right?  Because IBW x .6 = a 40% drop.  Is this correct?  IBW x .4 would equal a 60% drop in minute vent.

The threshold level is 40% of the predicted baseline (technically, a drop of 60% below that baseline), ME_IBW*.4. So, again, if ME_IBWcalc = 7, then the hypo threshold is 7*.4 = 2.8. Force the yaxis max on ME (oscar) to that value as the threshold. It will only display events that occurred below the threshold (which are hypoventilation events). Look back at my OSCAR plot for illustrations of this for clarification (you will see my ME threshold is max 3, and you only see events below). One could still plot the entire default yaxis for minute ventilation, but without a lot of experience, this is a much easier way to visualize and identify the hypo periods (They use colors on the machine plot to signify these areas).

One thing that clearly made a difference with me (only using ASV a few days) was using the small cushion, even though they wanted me to use large (all those nasty leaks, hissing, instability arousals disappeared, and my sleep is much smoother, less fragmented, and stable). One other thing I came across in my research, is ASV (particularly RESMED) is very good at treating hypoventilation (even better than IVAP, AVAP in many respects, particularly, stability of signals - hence smoother sleep).

BTW,Jay, if you are indeed sleeping without the ASV machine, and you have an older cpap/apap machine that you tolerate overnight (ah I think you can't simultaneously use the EVO ventilator), you could still gather the data and run the tests on that. It's even better, because (as in my case), you can compare hypo therapy between machines.

Sorry if anyone gets confused by ME = Minute Ventilation (one would expect MV), but they use that nomenclature as Expiratory Minute Ventilation in most of the literature, so I just stuck with it.

[Jay51]

Thank you for explaining that again Enigmatic.  I thought it was a 40% drop from baseline.  But it is 40% of baseline.  Got it.  300% seems very high for hyperventilation, but they are the experts I guess.  

I want to run something by you.  It seems to me like a person could get a rough estimate of how they would perform on a capnography test by:  1.  Calculating their predicted minute vent. and multiplying that by 40%.  Then plot that as a y axis on OSCAR's minute vent chart.  
2.  Calculate the total time spent either at that line or below it during sleep (this would take some time and a lot of counting to get the total in probably minutes).  3.  Figure out the total time asleep.  If it was 8 hours, then it would be 480 minutes.  The divide 480 (for example) by the total minutes at or under the y axis line (of 40% of predicted minute ventilation).  if this number was greater than or equal to 25%, then that would roughly equate to the capnography home test I took:  25% of the total sleep time or greater spent hypoventilating was a diagnosis of hypoventilation.  

Philips encrypts the data for this Evo ventilator, so it won't work with OSCAR.  This s9 Adapt ASV has a straight cpap mode also.  I have some experiments to do in the future now.  I will try to post a few naps in a day or couple of days just to look at.  My numbers are:  8.2 for normal minute vent. and 3.25 for the hypo threshold (I'm 6'2).  But from personal experience, when my RT used 8.2 or so when she set up my ST (A) and Resmed Astral IVAPS, it felt way too high for me to ever sleep with.   It felt like my lungs were going to pop.

[enigmatic]

   
Jay, That sounds like a great test. My only problem (for me) is I can't get any capnography data (and for whatever reason, my sleep dr. won't do it, instead relying on ASV). You on the other hand can, but you need both the capnography and minute ventilation data in sync to compare. I think there are several papers where they do this too, and they find this test even better than capnography at early classification and intervention. I was in the process of writing a script to tabulate that percentage of hyp events time/ total sleep time, over my recent history.  25% seems like a really high hurdle, but I don't have enough data to say just yet. I admit, the ASV pressure is a bit heavy for me too at the beginning, but I am getting better at tolerating, as I see the results (as well as cause effect, higher pressure = higher TV, MV). One scary thought is - I was reading they used to use really high pressure, and people's lungs were getting damaged. It took some time to figure that out. Things like that are one reason I don't want to just 'try' things, without solid justification (but again, beggards can't be choosers).

edit. Just ran the script and can you guess which %mv under 40 matches the motor replacement period? Look all the way to the right. Those huge spikes are within the 25% range you were talking about, so not out of the ballpark and confirms further my hypoventilation theories (including explanations for the extremely tired, lethargic daytime behavior not explained by very low AHI). And just remember, if two minutes is hypoventilation, those periods of >10% are into hours.

[Jay51]

   

This thread has taught me some things about hypoventilation.  I appreciate that Enigmatic.  I am glad the ASV is working for you and keeping you a pretty good distance from hypoventilation territory.  

I have maybe 25 naps or so recorded in OSCAR.  I chose this one because it is probably a better representative of my sleep than even a nap.  I remember on this one, I didn't sleep well that night.  I was very tired, so I switched over to the ASV to see how it would work for me (I just couldn't get going that day, so I laid back down and tried this).  

I didn't put in the 40% hypoventilation threshold, but you can see my minute vent spikes down a few times through it when I am asleep (3.25 is my 40% threshold of hypoventilation).  The pressure goes back and forth from about 19 IPAP to 7 EPAP for this period also.  Since the ASV recalculates every minute or so, my breathing would have dragged the target minute vent down lower and lower and lower the longer I slept with it.  (On most naps though, since they were so short, I usually had an AHI of around 0 and better numbers than this).  

One trick to use with the ASV that I learned here at ApneaBoard is this:  before masking up to go to sleep, make sure you are completely relaxed and not breathing hard from doing something physically right before you lay down.  This is how I finally learned to fall asleep with it.  I would lay down and hold the mask in my hand.  Then just as I was about to doze off (my breathing would be at its lowest and slowest), I put on the mask and turned on the machine.  The ASV algorithm calculated the target minute vent (and RR and tidal volume) based on the 1st minute or so when you 1st put the mask on and turn on the machine.  If it is ever hard to fall asleep, try this technique.  

I can think of 2 exceptions to the Anesthesiologist's protocol for determining hypoventilation.  1.  A person who has a problem with their gas exchange in their lungs may start hypoventilating at a higher % than 40%.  Say 50% or even 75% etc.  2.  A person with metabolic acidosis (their body produces more co2 at rest) may be hypoventilating at a number higher than 40% of their predicted minute vent.  

When you recommend me syncing this with one of my capnography tests, I don't think the 2 are equal because when using the ASV, it artificially inflates my numbers because the EPAP is opening my airway more; and the IPAP is improving my natural tidal volume more.  Also, my minute vent will be inflated (for the better of course, but different than my room air (no pap or vent use) breathing.  

I had a 30 or 45 minute meeting with my RT and the lady in charge of testing at my DME.  They thoroughly explained the capnography to me and interpreted it.  They could tell when I was alseep or awake, etc.  When I sleep, I am usually close to the top of the 35mm/HG - 45mm/HG channel.  Any disturbance can push me up above 45 into hypoventilating.  And I agree with you, 25% of the time is a very large amount.  I did not realize that my breathing was that bad.  

I have tried cpap, bipap, bipap with back up rate, S, ST, IVAPS, and AVAPS, and personally like AVAPS best because with a 500 assured tidal volume with each breath all night, I have some wiggle room with my respiratory rate.  The AVAPS "auto" breathing rate algorithm is like the dynamic ASV's algorithm for determining respiratory rate.  Even when it drops some, the 500 assured tidal volume keep my minute vent up enough.  You have a good spontaneous respiratory rate, so you can get by probably with a slightly lower tidal volume than normal  (your minute vent would then still be acceptable).

[Bhante]

Since we are only looking backward at explanatory events, I don't think it is necessary to use the real time moving average or even calibrate the beginning baseline, they use those in practice because they want the most recent empirical baseline and the ability to intervene right away (more of a real time predictive baseline).

Sorry I can't keep up with you two! I started posting a response 2 days ago but got diverted and couldn't finish it. 

Minute volume would be a measure somewhat along the lines of what I was suggesting in my formula, but it would be worth finding out how OSCAR calculates it (i.e. how it combines minute volumes/times for inspiration and expiration, or whether it only includes one of the two. There are various ways you could look at it - none of them exactly wrong but some may be more useful than others. If inspiration time and expiration time are approximately equal then it will not matter, but if you have a significant difference between the two then it will make a significant difference to the result - aiming for a measure of how much available oxygen is being provided per minute averaged. If you inspire deeply and quickly, and then expire slowly, the inspiration has a high minute volume but the expiration a low minute volume, and both affect the average availability of oxygen over time - the quick inspiration provides more oxygen, but the slow expiration delays the time before the next breath. Therefore both are part of the picture.

There is a good reason for the moving average - the metabolic rate CHANGES! As the metabolic rate changes, the need for oxygen changes, and the breathing has to change with it. If you have an arousal and wake up, there is a good chance the metabolic rate will increase so you need more oxygen. Hypoventilation has to be measured relative to the metabolic needs of the moment, not compared to some arbitrary statistic. Take those body weight statistics with a large truckful of salt - they take no account of variation in metabolic needs over time - which are HUGE!! They dwarf momentary changes. 

By taking a rolling average baseline AND requiring a sustained response for at least 2 minutes, you cancel out changes in minute volume due to metabolic rate changes (MR). If MR changes the body will force the breathing to find a new balance very quickly. Only if it fails to do so, or minute rate drops without a corresponding drop in MR, then THAT is hypoventilation - i.e. it is causing a tension in the absorption of oxygen. If it is not causing any tension in the absorption of oxygen then it cannot be considered to be hypoventilation.

If you fall into REM sleep from non-REM sleep, the metabolic rate increases substantially, and the breathing minute volume has to responde quickly by increasing to fill the gap. if it does not, that is hypoventilation. Enigmatic when you see claims by non-experts like that woman on the verywellmind website (or whatever it was called) claim that breathing rate drops in REM sleep, that is almost certainly them misunderstanding what is going on. Because the metabolic rate INCREASES in REM sleep, the need for oxygen increases, and therefore the breathing MUST increase to fulfill the metabolic needs of the body. If it does not, or even if it INCREASES but it does not increase enough, then that is hypoventilation. That is why they need to take a rolling average. 

I can't remember how much the MR increases in REM sleep, but don't be surprised if it is 300% or more. If the MR increases 300% and the minute volume increases only 50%, then you have serious HYPOventilation despite a 50% increase in minute volume. If the breathing is functioning correctly it will respond very quickly to the new requirements. Hence the two minute minimum requirement will filter out momentary changes in MR and alow for a new MR.

MR changes very quickly - even in response to a momentary thought!! (Probably also in response to dream events). In wakefulness, if you are relaxed and comfortable, and are having comfortable thoughts, your MR will be relatively low and your breathing will be quiet. If you then suddenly think about a very aggrevating event that took place during the day, INSTANTLY your breathing will change - within a fraction of a second - it will become short, shallow, fast and rough, and the heart rate also instantly increases. 

In exactly the same way as minute volume and MR, using tidal volume without breathing rate will give wrong results. You need to use a minute volume measure of some kind. But even that alone is not enough - because you have to take account of changes in metabolic rate.

You can take a look at this video Oxygen - Haemoglobin Dissociation Curve - Physiology https://www.youtube.com/watch?v=BYGPkRFvzOc by Armando Hasudungan - he also has numerous other good videos on breathing.

[Bhante]

I would lay down and hold the mask in my hand.  Then just as I was about to doze off (my breathing would be at its lowest and slowest), I put on the mask and turned on the machine.

I'll give you a little tip. After lying down and when you are ready to sleep, but before putting on the mask, take TEN very deep breaths. Very deep means VERY DEEP - use the WHOLE of your lung volume for each and every one of the ten breaths - probably at least 10 times as much volume for each breath as normal breathing. Your chest should expand and your shoulders heave up with every inspiration, otherwise it is not what I call a very deep breath. You will be strongly tempted to return to normal breathing after 3 to 5 deep breaths, but make sure you do all 10 at full volume. Speed of breathing doesn't matter, it is easy to breath quite quickly. After the 10th very deep breath is completed, just breath completely naturally. The result is very dramatic - it REALLY QUICKLY quietens down your breath! Even if you do jogging for 5 minutes, then lie down and take TEN very deep breaths, you'll find after the 10th deep breath your breath will quieten down very quickly.

You can do the deep breathing lying down, or sitting up (it is easier to do the really deep breathing while sitting up).

[Jay51]

Bhante, thank you very much for the tip about taking 10 very deep breaths when I am ready to sleep.  I will try it next time.

[Bhante]

Bhante, thank you very much for the tip about taking 10 very deep breaths when I am ready to sleep.  I will try it next time.

You're welcome. You can use it also any time you have hyperventilation. (Maybe you think forced hyperventilation is not the solution to hyperventilation, but ... it works!)