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[CPAP] Wakeful time AHIs vs sleeptime AHIs
(03-26-2016, 12:38 PM)FrankNichols Wrote: I am new and have no idea what I am talking about, but since this is the internet, that means I fit right in.

It seems the opposite of what you are saying would be the case. The AHI is the number of events per hour (of sleep assumed). So, assume you have 100 events over night. Assume you stayed in bed with the machine recording for 10 hours, then the AHI should be 10. Now, if what you are asking worked, then if the machine realized that you were only asleep for 2 of those 10 hours, the AHI would be 100/2 or 50!

Now, I don't know if CPAP machines can tell when you are asleep, but I don't think so - I think they only know when you turn them on and off. So, if you are getting very high AHI values, and it is measuring the time from when you turn it on to when you turn it off, then the high AHIs would be worse if it only measured when you are actually asleep.

Uh, but then I am a noob, so what do I know?

Reply: thanks for your reply, to recap, my AHI s was perfection while I slept, only a 1. 2, i.e.one event per hour!! Awesome, right? Then when I could not sleep, I checked the information again for AHI reading, and it had skyrocketed. The point being I guess, that I don't need such high pressure prescribed to me based on the information coming from this machine, it wrong......
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I also experienced the SWJ phenomenon and came to a number of conclusions which Are backed up by other members of this forum. The AHIs recorded while awake are not events as such, just your machine responding to a different breathing pattern and seeing this as possible events. I determined this by keeping a record of the the times I was definitely awake and asleep. I usually wake up once during the night and after going back to bed I see the most events which are in a cluster.

I further tested this out by attempting to simulate a sleep breathing pattern when I went back to bed and the sleep wake junk cluster just didn't occur.

Now that I know what it is it doesn't bother me any more and strangely the SWJ has dropped considerably. Mind over matter???
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(03-26-2016, 03:14 PM)0rangebear Wrote: After making offset adjustments to the clock error in the software. I t compare my experimental flagged events to the Flow Rate and Flow limitations Data sets to identify the sleep sessions with the most SWJ. I exported the Data for those nights vis the CSV wizard in sleepyhead and separated our the SWJ form the real events in a spreadsheet / scatted diagram.

It is unfortunate that neither the sleep study folks or the CPAP manufactures have attempted to refine their method to do this. Since insomnia and SWJ clearly skew the numbers.

The problem is that a CPAP has to earn FDA approval, and that approval is necessarily based on its efficacy in treating sleep disordered breathing, and CPAP manufacturers can demonstrate this without needing to program the machine to try to distinguish wake from sleep. Moreover, there is no way to program the machine to reliably distinguish between normal wake breathing patterns and sleep disordered breathing patterns because there is no way for the machine to reliably determine whether we are awake or asleep; hence a manufacturer would face a long and potentially protracted battle for FDA approval if they claimed that their CPAP could reliably distinguish which "events" it records in the flow rate data are real sleep disordered breathing events and which ones are normal wake breathing artifacts.

The major problem with attempting to use just the flow rate data from a CPAP/APAP to determine wake vs sleep is that normal REM breathing patterns can and often do resemble normal WAKE breathing patterns. In normal non-REM sleep breathing, the respiration rate is exceptionally stable and the sizes of the inhalations and exhalations are also remarkably stable. There's almost no variability from breath to breath. But in both normal REM breathing and normal WAKE breathing, there can be a lot of variability in terms of respiratory rate and the inhalations themselves can vary quite a bit from breath to breath. The basic difference between REM and WAKE breathing being that normal WAKE breathing can (and often does) include a lot of pauses in breathing that meet the 10-second rule for scoring an apnea or series of deep inhalations followed by shallow enough inhalations to trick a machine into scoring a "hypopnea" that's not real.

Reliably determining sleep vs. wake requires both EEG data and some data measuring movement or muscle tone. Home EEG data (such as what the Zeo used to record) can have a real tough time distinguishing WAKE from REM since REM EEG patterns look very much like WAKE EEG patterns. The makers of the Zeo only claimed about 75% accuracy in distinguishing REM from WAKE, and that may have been part of what led to the demise of their product. (As an aside, SH is able to "import" Zeo data and line it up with the CPAP data.) The actimetry sensors used in things like FitBits track wake/restless periods based solely on how much you are moving around. But it's possible to do a lot of moving around in normal stage 2 sleep for some people so a FitBit set to "sensitive" mode may over estimate the wake time quite a bit. Conversely, setting the FitBit to "normal" mode may over estimate the sleep time if you actually have a real sleep disorder that leads to a large number of arousals and/or microwakes that last less than a couple of minutes.

On a sleep test in a lab, they use all of the EEG data, movement data (in particular eye movement and facial muscle tone data), and respiratory data to determine the sleep stage and, hence whether any breathing "irregularities" represent normal wake breathing or abnormal sleep breathing. In particular, the movement data can be critical in distinguishing REM EEG from WAKE EEG: In REM, all muscle tone except for the eye movements is essentially gone---i.e. our bodies almost act as if they are paralyzed in REM so that we don't start physically acting out our dreams.

The upshot of all this is the following:

Unless we're willing to sleep with most of the apparatus associated with a formal home sleep test every night, there's just not a reliable way to definitively determine sleep stage (including WAKE) from the data that can easily be gathered in our own beds at night.

But it is possible for us (as individuals) to learn how to read our own particular flow rate data well enough to make some good educated guesses about when we're most likely asleep vs awake. This requires some subjective data on our part ("I know I was pretty restless last night" vs "I can't remember waking up at all during the night") as well as a good understanding of what kinds of pattern(s) are common in our normal sleep breathing. It also requires having a sense of what a normal hypnograph looks like (i.e. REM cycles occurring roughly every 90 minutes or so with short REM cycles at the beginning of the night with longer REM cycles near the end of the night.) But even armed with all this additional data, at times we may still have to "just guess" whether a particularly nasty cluster of events is just SWJ or real sleep disordered breathing.

Questions about SleepyHead?  
See my Guide to SleepyHead
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(03-26-2016, 05:17 PM)Earthfuture Wrote: Reply: thanks for your reply, to recap, my AHI s was perfection while I slept, only a 1. 2, i.e.one event per hour!! Awesome, right? Then when I could not sleep, I checked the information again for AHI reading, and it had skyrocketed. The point being I guess, that I don't need such high pressure prescribed to me based on the information coming from this machine, it wrong......
You cannot make any assumptions on why a high pressure was prescribed to you based on the information coming from your machine.

If you had a formal titration study done in the lab, the tech running the sleep study manually adjusted the pressure on the CPAP in response to events that s/he knew represented real sleep disordered breathing because of all the data being collected. And under ideal circumstances, the recommended pressure is the lowest pressure at which all hypopneas and obstructive apneas disappeared in REM supine sleep. And the pressure didn't create any obvious problems with excessive numbers of spontaneous arousals. And the pressure didn't create any obvious problems with emergent central apneas.

Of course, a lot of the time they don't get to actually see what happens to you if you hit REM sleep while sleeping supine. So sometimes the script will bump up the final pressure from the sleep study by 1 or 2 cm.

There are two ways to find out if you really need the prescribed pressure from your titration sleep study at home:
  • Use an APAP with the min pressure set at least 2-4 cm below the prescribed pressure and the max pressure set well above your prescribed pressure. If the 90% (or 95%) pressure level is less than the prescribed pressure on almost all nights after a 2 week APAP trial AND the AHI is acceptable, that's solid evidence that the prescribed pressure may be too hight.

  • Use an APAP with the max pressure set 2cm below the prescribed pressure OR use a CPAP with the pressure set 2 cm below the prescribed pressure. If the AHI goes up significantly, that's solid evidence that you really do need the prescribed pressure to control all of your apnea.

And why might the prescribed (titrated) pressure be more than you need in the first place? Perhaps you had an extra bad night during the titration study. Or perhaps the tech was more aggressive than needed when it came to increasing the pressure near the end of the night.

Questions about SleepyHead?  
See my Guide to SleepyHead
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