(02-24-2015 04:17 AM)archangle Wrote: ...You're only fooling it because you're awake, which we know the machine can't tell.
...Are you talking about pressure induced central apnea? That's pretty well understood. CPAP pressure can cause your tidal volume and minute ventilation to increase. The increased minute vent can cause "washout" of CO2. Your respiratory drive is mostly based on your CO2 levels, not oxygen. Low CO2 makes some people stop breathing for a while until your CO2 picks back up and your respiratory drive makes you start breathing again. Another theory is that your lungs become more inflated and the stretch receptors in your lungs gives feedback that reduces your respiratory drive.
Google "Pressure Induced Central Apnea" and you'll find a lot of info.
What I found is this article:
Which seems to have some of the exact phrasing you are using in your post, which makes me think you might have read it, too. But what you left out is this:
"Clinical experience has suggested that these events resolve spontaneously over time, since ongoing CPAP therapy is not a recognized cause of central sleep apnea. The pathogenesis of treatment-emergent central apnea, however, is unknown and is poorly studied.5 Several theories have emerged, based largely on speculation."
And that would imply that it is not at all "pretty well understood".
What we can take from this is exactly what I suspected, which is that a pressure-induced central event is quite different from a spontaneous central event that is not pressure-induced.
Here is how I am interpreting this, and full disclosure will add that there is a lot of speculation in my theory:
Respiration is governed by a feedback system. While it is not as simple as this, essentially the body knowing what the 02 saturation is, is induced to automatically inhale when the saturation lowers to a particular point. CPAP pressure can mess with this in many ways, such as those you mentioned and are mentioned in this article.
But a central that happens without PAP can only have one cause, which is a failure of the feedback system. A pressure-induced central does not necessarily point to a failure of the feedback system, because the PAP skews the system's operation. The respiration system may actually be working just fine.
So a pressure-induced central event is very different than a normal central event, because one implies a problem with respiration while the other really doesn't, at least not definitively.
Failure to inhale is scary when you are the cause; not so scary when the therapy itself is ironically the cause.
If I am looking at this correctly, this supports my earlier statement that "the centrals are not coming from me, they are coming from the therapy itself".
I don't think there was ever a question about being awake while fooling the machine; the point was that I CAN fool the machine
, and it is therefore not perfect and really not even all that smart. That I might have been awake while doing it is beside the point, but even so, it underlines how imperfect the machine is, if it is flagging events that aren't real and dithering the accuracy of the AHI report.
And this is a prime indicator of how smart the machine isn't, and how inaccurate AHI can be as a result: the xPAP can't tell the difference between a pressure-induced apnea and a non-pressure-induced apnea, two very different things that have very different indications as to respiratory health.
Instead, it lumps them both together and treats them the same, counts them as equals, and summarizes them in a single dumb AHI number.
As in anything else, it is always important to understand and have respect for the margin of error you are dealing with. xPAP isn't magic and we should not be sheep and assume it is perfect and that the AHI it is reporting is an ironclad certainty; xPAP is great and sophisticated, but still flawed.