Long time CPAP user still fatigued

[enigmatic]

If you can tease it out of OSCAR, the ideal would be total expiration time x total expiration volume + total inspiration time x total inspiration volume, as a graph for every breath over the whole night (strictly you would want smoothing to be useful, eg average over every 20 breaths), and then compare that graph over the whole night with SPO2. That will really be a true plot of hyper/normal/hypoventilation over time. If you can get tidal volume and breath time on a breath by breath basis from OSCAR, then you could do it by exporting data to excel. You might want to add sleep stage to the comparison, as the metabolic rate changes according to alertness and sleep stage especially REM sleep.

The more I think about it, isn't that equation basically tidal volume itself? I.e. integrate area underneath flow rate for each full breath.
Tidal Volume (l) = total inspiration_time (min) * flow_rate (l/min) + total expiration time*flow_rate(l/min) at each instant of time. Actually, net is about zero, since it's full volume in and out each breath? I can roughly match displayed tv for insp*flowrate, and exp*flowrate, exp is under curve so net sum is about 0 I think.
Are we looking for net differences from zero?
And what would we see to differentiate hyper/normal/hypo? Are there numerical thresholds?

[Bhante]

The more I think about it, isn't that equation basically tidal volume itself? I.e. integrate area underneath flow rate for each full breath.
Tidal Volume (l) = total inspiration_time (min) * flow_rate (l/min) + total expiration time*flow_rate(l/min) at each instant of time. Actually, net is about zero, since it's full volume in and out each breath? I can roughly match displayed tv for insp*flowrate, and exp*flowrate, exp is under curve so net sum is about 0 I think.
Are we looking for net differences from zero?
And what would we see to differentiate hyper/normal/hypo? Are there numerical thresholds?

Hmm. you're right that I messed up the formula, but no, it's not tidal volume because I had volume up there not flow rate. But it was supposed to be tidal volume divided by time not multiplied, i.e. volume of air per unit time. And no, it does not cancel out because I added not subtracted (and intended both as positive quantities. The reason I expressed it that way (aside from the multiply/divide error) is because the air you take in has to last a certain period of time depending on how fast you are breathing in and out. Also there may be a big imbalance in breathing rate between in and out, especially with EPR. However The formular I gave is also not really correct for another reason: it should be (abbreviating and moving the same terms in my earlier formular): 

inspiration volume / (inspiration time + expiration time)

That gives you the volume of oxygen-bearing air provided per unit time. Tidal volume on its own is inadequate, because the exact same tidal volume is either hyperventilation (at a high breathing rate) or hypoventilation (at a low breathing rate) depending on the breathing rate in each case. For forced ventilation it doesn't really matter as long as the breathing rate is a constant, but here it is not at all constant therefore it has to be compensated for. 

You are half-right that it is the integral of flow rate over time or the area under the graph - but expressed per UNIT TIME, not per breath. Or if you prefer roughly the integral of (inspiration) flow rate graph against time, divided by total breath length (inspiration plus expiration).

Hyperventilation means you are getting oversupply of oxygen per unit time. That may be very fast quite shallow breaths - panting - where the tidal volume is much too small; or it may be moderately slow deep breaths, where the tidal volume is high but the breath time is not sufficient to balance the deep breath - a typical example in my experience might be deep breathing under excessively high pressure. In this case SPO2 should be high, but may not be elevated above normal because normal is already high and no extra oxygen can be absorbed.

Hypoventialtion means that you are getting an undersupply of oxygen per unit time. As far as I can see, that means BY DEFINITION that SPO2 is depressed. If some sleep techie (or machine) is saying that a certain state is hypoventilation just because the tidal volume is below some magical number, then they don't know what they are talking about. Unfortunately most medical professionals are very non-scientific by nature, because the nature of western medical training suppresses rational thinking (and replaces it with trained dogma). Hypoventilation might be light shallow breaths that are a bit slow - low tidal volume - or it might be somewhat deeper breaths that are even slower - high-ish tidal volume. Key is the fact that the oxygen available is inadequate, therefore SPO2 is necessarily depressed. If SPO2 is not depressed, then it is normal healthy breathing not hypoventilation (and not the unhealthy forced breathing that sleep professionals love). Maybe if SPO2 is not significantly depressed the breathing might be marginally hypoventilation rather than fully hypoventilation (i.e. less of a margin of excess O2 than normal) - but in this case I would expect the SPO2 to be likewise marginally (i.e. insignificantly) depressed - because of the nature of SPO2 values I would expect that still to be classfied as "high" SPO2. 

Note that whether oxygen is sufficient or not depends not only on breathing rate and tidal volume but also momentary metabolic needs. If you do 20 pressups and then immediately lie down and try to sleep, your momentary metabolic rate would be extremely high, therefore your breathing rate is very high, your tidal volume is very high, but your SPO2 could be slightly depressed. As you gradually relax the breathing becomes quieter as your metabolic rate decreases and your oxygen consumption decreases, and the SPO2 will come back up to normal. Likewise in REM sleep the metabolic rate is supposed to be very high (i.e. high oxygen consumption), therefore the tidal volume and breathing rate combination ought to be elevated compared to non-REM sleep, and if not sufficiently elevated the SPO2 may be depressed (hypoventialtion, even if both tidal volume and breath rate are higher than in non-REM sleep). 

Under most conditions CO2 levels ought to mirror SPO2, in theory, although with some exceptions. But I suspect CO2 is probably more important for what it reveals about the operation of the heart than the breathing. @Jay51, was the second capnograph in a very stuffy room by any chance? That might be expected to increase expired CO2 (and respiration rates/tidal volume) compared to a well ventiilated room. For the same reason there might be artifacts induced by mask leakage. A change in tidal volume is obviously also going to change expired CO2 levels, because it changes the dead volume of the lungs - that may be very substantial, because the volume of the lungs we normally use is only a very tiny proportion of what we could use. At the moment you woke up and started hyperventilating, was your tidal volume also large? - Maybe because the machine suddenly increased the pressure too much, causing an arousal, and also causing hyperventilating, and also causing more CO2 to be quickly flushed from the dead space so that exhaled CO2 was then depressed, and with the smaller dead volume the CO2 remained depressed for a time.

[Bhante]

Also, I'm not certain if each of those variables is sampled equally (timewise), not sure if it matters though, as I'd use 1 sec intervals anyways. Even though many of the RESMED signals are subsampled much faster than 1sec, I think the machine only writes synchronized samples out at 1 sec to the card.  

...

But unfortunately, if you are gathering the data from ASV machine, I suspect the hypoventilation would not be present or minimized due to the machine (isn't that one purpose?), Bhante thoughts? Again, it would be great to have a link to show what I should expect to see regarding identifying hypo/hyper/normal behavior.

Now here's something interesting. They insisted large was right nasal pillow size. So last night, I started out with that hissing and sounds like leaking and fighting pressures, after about 20 minutes, I said heck with it, I'm trying medium. Put it on -- all those issues vanished.
It was back like smoothly inhaling exhaling, no leaky sounds - no weird machine forcing me to inhale earlier than I want. On the other hand median TV dropped to 440. Almost as if larger size supported larger air volume and TV -- no evidence though (and I'm sure most vendors would dismiss that conjecture).

The Resmed A10 samples the pressure at a very high rate, far higher than 1/sec. But you are wrong (at least as far as A10 is concerned!) that it saves the data to SD every second: it saves the data in RAM memory for numerous minutes, before writing out the data in a big batch. That's why Resmed tells you to leave the machine on for 10 minutes (!!!!!) after use before switching off, otherwise you will lose data. You can see the SD LED flashing when it writes to disk, and if you watch it while breathing through the mask you can see the SD activity goes silent for long periods. Also when you start a session it does not immediately write to disk. Hence if you start breathing through the mask and then quickly realise you forgot to turn back the Resmed clock, after a break (I used to do that to keep subsequent naps in the pre-12 period), you can quickly turn off the power to erase the new data from RAM and when you switch it back on the machine won't be any the wiser for your minor misadventure. On the other hand if you wait until after the first disk access (LED flashing) before switching off it will be too late, you cannot turn the clock back.

On the ASV and hypoventilation: my understanding is that hypoventilation is listed as an counterindication for ASV (unlike APCV or VAPS), as it can be exacerbated by ASV, so maybe you'll see more hypoventilation rather than less. 

On the pillows: don't forget that using any mask while awake is different from while asleep (also sit-up position completely different from lying position). As you fall asleep your facial muscles relax and that changes the shape of your face, which changes leak conditions. Likewise higher pressures will cause different conditions. "Larger size supported larger air volume and TV" - of course, if the machine is producing a higher pressure because it thinks there is too much leak, it will cause extra flow and an artifact of larger indicated tidal volume (not saying that is necessarily what is happening though).

[Jay51]

I apologize Bhante if I did not make it clear how the capnography test was done.  I did it on room air in my bedroom (with no PAP or Ventilator).  You have a point about a "stuffy" room and rebreathing expired co2 that can build up in a single room.  I once tried sleeping on the floor in my living room (wide open space) and my spo2 numbers were better in the living room than in my bedroom (I leave the door open in my bedroom, but windows closed).  

My best guess as to why I started hyperventilating when I woke up was that I had a build up of Co2 in my lungs.  And when I awakened, I tried to hyperventilate as much co2 out of my lungs as quickly as possible.  I may be wrong here.  

From all that I have learned here at ApneaBoard about hypoventilation; and all I have learned from my RT; and from all the independent research I have done on it, my definition of hypoventilation would be an inability of the body's respiratory system to effectively remove co2 from the body.  Many mechanisms can be in play here to cause that though and at varying degrees.  I think the RT saw that I had a few really low tidal volumes (in the double digits) and a few really low respiratory rates (5 and 6) and decided to do a capnography test on me to see if I was hypoventilating.  I looked at my sleep study again yesterday and I would say my tidal volume probably averaged close to 400, but a little lower.  Respiratory rate looked close to 12 for the average.  I am 6'2 tall.   On room air, these numbers might decrease. 

The standard treatment for hypoventilation is to increase ventilation to rid the body (lungs) of excess co2.  When I tried a bipap (with no back up rate), it helped clear some extra co2 out, but caused me huge amounts of central apneas.  I had to have a back up rate added.  This is one big difference I see in hypoventilators:  most have a lower than normal tidal volume, but can differ in spontaneous respiratory rate.  My spontaneous rate was on the low side.  Others have good respiratory drive, even with hypoventilation (they can possibly be treated decently on bilevel (without even using a back up rate) or even ASV IMO (and assuming that the lungs are working correctly in regards to gas exchange).  But Bhante is right that ASV is contraindicated for someone with diagnosed hypoventilation.  You have a fairly good respiratory drive IMO Enigmatic.  If those machines don't work, a back up rate and volume assured algorithm usually does the trick.  I don't know why my respiratory drive (the desire to breathe) got so low at night.  I have had significant problems breathing through my nose at time.  Laying flat increases congestion and really hinders my nasal breathing.  I plan on having my deviated septum corrected next month.  Along with reducing the inferior turbinates.  Also ENT plans on reconstructing my nose to provide more space in the nostrils for air.  Pulmonologist said my lungs are "good enough" after numerous tests (although I have been exposed to a lot of dirt and dust and a few chemicals).  I am an ex athlete who was almost a professional athlete.  I have pushed my body from 0 to 100 in a split second and have used severely calorie restricted diets.  Co2 is the by product of metabolism.  An increased metabolism produces more Co2.   I was diagnosed with hypothyroidism a few years ago.  I think my body tried to "slow down" my super high co2 production by hypothyroidism.  This is probably another reason for me personally to have the excessive build up of co2 in my lungs from all the physical activity I have done.  But there many other different ways for co2 to build up in the body (lungs).  The problem can occur at different parts of the respiratory system (along with neurological system that controls it).  Neurologically - I have had a few concussions in my life and was involved in 2 major automobile accidents.  Also, my mother had Myesthenia Gravis; and my father's mother died of Parkinson's (and my father may have Parkinson's.)

[enigmatic]

The Resmed A10 samples the pressure at a very high rate, far higher than 1/sec. But you are wrong (at least as far as A10 is concerned!) that it saves the data to SD every second: it saves the data in RAM memory for numerous minutes, before writing out the data in a big batch. That's why Resmed tells you to leave the machine on for 10 minutes (!!!!!)

interesting. I always thought told us to to us to keep it on a few minutes so it can release some mask pressure. Anyways, unless I have a need for sub second data, it's a heck of a lot harder to process and sync, so sec sample rate is how I'm processing for now.

On the ASV and hypoventilation: my understanding is that hypoventilation is listed as an counterindication for ASV (unlike APCV or VAPS), as it can be exacerbated by ASV, so maybe you'll see more hypoventilation rather than less.

problem is I sitll don't even know how to 'see' hypoventilation at all. You keep mentioning equations but no papers or visual images as evidence. Kind of hard to follow your explanations as they are. I could easily plot insp time/(insp time+exhale time), but still don't see how I get ventilation state out of that signal.
Outside of capnography, which I don't have, other than looking at SPO2 I don't know how to 'see' hypoventilation. But I certainly would like to. 
I understand concepts much better by looking at signals in practice along with explanations (and knowing what type of signal classifies what).

@Jay51. Good info. I found out even with ASV, higher pressure support does increase tidal vol. Not only through my dr. and literature, but empirically as well. I also found a paper that
showed they use really big tidal volumes (like 10ml/kgibw) to clear out hypoventilation. I'll link if you are interested. I do also think your background makes more sense with hypoventilation, who knows, I may have had a concussion one or two times dropping tree branches and tools and things like that on my head. Never diagnosed though.
I also came from a fairly physically intensive background, but after college, sat on a desk with computer for years. When you talk of excess buildup of CO2 in lungs from years of above average activity, it seems like we should see that in daytime bicarbinate cO2 blood test, as it is accumulated over years, no? I've also had fine thyroid tests.


anyways, for the first time the new 'ASV' machine is reporting some hypopneas (never saw on old machine kind of matches bhante comment) which IS a common attribute of hypoventilation patients, I've read
(assuming those are even real hypoventilations on resmed/oscar).
I am also feeling more refreshed and energy lately with ASV/pressure/ higher TV. Too early to draw conclusions, but good start. It is weird also that the mask fitting size
changes pressure and tv. They never tell you that, but I am seeing it empirically.

[enigmatic]

So I saw that regarding hypoventilation, "Slow and shallow breathing characterizes this breathing disorder, sometimes as low as 8 to 10 breaths per minute. The normal breathing rate is between 12 and 20 breaths per minute."
@Jay51 have you looked at your respiratory rate on OSCAR? Does the time you had hypoventilation show small ranges like this? Mine do not. Maybe not that simple, but sure seems like an easy metric to look at.

[Jay51]

Thank you for that Enigmatic.  I just looked at my OSCAR's for several naps with my S9 Adapt ASV.  Surprisingly, my respiratory rate averaged around 12 or 13 (higher than I thought it would be).  It was only for 30 or 45 minutes naps though, so not completely sure how it would look for 8 hours.  

My minute ventilation chart, tidal volume chart, and respiratory rate chart all went up and down back and forth like a continuous roller coaster.  As one of them would fall, the ASV upped PS, and then it would rise above the moving average line.  Then it would peak and drop right back down to a low below the moving average line (in all 3 - minute vent., tidal volume, and respiratory rate).  The ASV seemed to be doing the job of ventilating me more.  The downside was the back and forth up and down pressure also:  from a low EPAP of 7 or 8 to an IPAP max or around 20.  About a PS of 12 or 13 so for me.  Back and forth and back and forth, etc.  I did learn how to fall asleep and stay asleep with this, but this Evo ventilator keeps me closer to it's moving average lines in minute vent., tidal volume, and RR.  without as many huge ups and downs.  

You seem to have a better spontaneous respiratory rate (and probably tidal volume, too) than me, so you charts in these 3 metrics would not have as large of pressure swings.  

I changed to CPAP mode once and tried to sleep with it, but couldn't.  There I had a much lower respiratory rate, etc.

[enigmatic]

   
FWIW, to anyone trying to observe hypoventilation with only RESMED/Oscar signals, I did find a method (they use this method to identify hypoventilation in patients under sedation, in order to intervene with titration). It primary requires expiratory minute ventilation, which means
it would take some processing to get expiratory only. You could just filter minute ventilation on expiratory breaths only. Their criteria is 40% drop of EMV (expiratory minute ventilation) relative to a baseline (could just use rolling average over some bars or daily average I would suspect, or target minute ventilation) are considered hypoventilation periods. What's great about the plots they show, is you could clearly see the second plot  (they call frequency) is just respiratory rate, and when they intervene (plot B) , the respiratory rate and EMV rises consistently higher than non-intervention. Another takeaway, is we could look at big dips in minute ventilation and respiratory rate (which look like they correspond with hypopneas in OSCAR) as a rough estimate of hypoventilation events (not just looking at average respiration rate over the evening session, but total time in hypoventilation is significant).

The only problem with all of this, is our machines are likely significantly improving these events already, but I suppose it could be a measure of how bad hypoventilation is, if machine is not helping under settings. Or comparing one result to another. If I have time I'll go back and run this on bad motor period.

-----------
"A new noninvasive respiratory volume monitor (RVM)
has been shown to overcome limitations associated with
pulse oximetry and capnography.1...
Although the ability of the RVM to accurately measure V˙ E, VT, and f and to
detect hypoventilation has been verified,13 its use by anesthesiologists to improve patient safety has yet to be tested
in a randomized controlled trial." The paper goes on to demonstrate this is valid.

[enigmatic]

   
Looking at it more, I don't think it needs to be as complicated as I earlier mentioned.

Here's a simple illustration of the concept mentioned in the prior thread. Looking back on a horrific day (when motor replaced and tidal volume average very low).
Note I can easily calculate predicted VE (minute ventilation) and set the hypoventilation threshold at 40% of VE or about 3.0. Notice RR was (mostly) ok here, but Tidal Volume dropped to the 50s and VE dropped close to 1. Had about 10 minutes of very shallow breathing. Those are all signs of hypoventilation just using graphs from oscar (which is what I've been trying to find). All this with a very lovely AHI = 0.41

I don't see that behavior at all on the new ASV (which benefits hypoventilation, esp. resmed machine) and I'm starting to feel better too.

This was the kind of evidence I was looking for (without the benefit of capnography or ABG).
@Jay51 would be great to see if you can corroborate any of this on bad days.

[Jay51]

Thank you very much for all of that Enigmatic.  Thanks for doing the research to find that paper.  I think I grasp the concept.  Basically look for a 40% or so drop in minute vent (also watch RR and Vt).  It looks like it can possibly be "eyeballed" in a chart without having to calculate so much.  40% is close to 50%, so just a tad bit less than a 1/2 reduction.  I like the rolling average line in OSCAR also for reference also.   This sounds logical because a 40% reduction in minute vent. would likely cause the accumulation of more co2 in the lungs.  

That bad motor really did a number on you.  I am glad you have a better machine and motor.  

Another thing I found in the literature concerns the kidneys.  Co2 is acidic.  The kidneys have to filter this excess acid out of the blood.  A person suspecting hypoventilation; and then had abnormal kidney test results, might have another confirmation on hypoventilation (without having to do the overnight capnography study).  

I will try to post a nap or 2 of mine in the future here just for reference.