Yesterday morning I read this in this post on apneaboard:
“Beginner's Guide to SleepyHead
“How APAP machines respond to events.
New PAPers are sometimes surprised by the fact that their PAP did nothing when an apnea was in progress. There's an assumption that the positive air pressure provided by the PAP is supposed to "blast" through the obstruction and restart the breathing. But pressure is not used to try to "end" an on-going event. It's not even clear that 20cmH20, the maximum pressure delivered by a CPAP, would even be effective at trying to "blow" a collapsed airway open: 20cmH20 is not enough pressure to effectively blow up an ordinary balloon. In fact, 20 cmH20 is about the difference in atmospheric pressure between a very stormy, low pressure day, and a bright sunny high pressure day.
The basic idea in PAP therapy is to provide (a small bit of) positive air pressure through the entire breath cycle to make it more difficult for your airway to collapse. This system is very good at preventing apneas and hypopneas from occurring, but it is not perfect: A few events will likely occur each night, but the overall number of events will be low enough to keep your treated AHI under 5.0, and probably well under 5.0, each night you use the machine. In other words, a well-adjusted PAP makes it difficult, but not impossible for your airway to collapse.
CPAPs, of course, cannot respond to OAs and Hs by increasing pressure since they have one fixed pressure setting. APAPs do respond to OAs and Hs, but it's important to realize that an APAP will wait until the apnea or hypopnea is over before it increases the pressure. And even then, a typical APAP won't raise the pressure after each and every OA or H. Rather, APAPs will only raise the pressure in response to OAs and Hs if two or more events occur in a relatively small amount of time like 5 minutes or so. The rationale for this behavior is based on the AASM Clinical Guidelines for Manual Titration Sleep Studies. Isolated OAs and Hs are not necessarily indicative of a badly compromised airway: Even normal people have the occasional (frank) OA or H during their sleep. But two or more OAs or Hs occurring close together indicates that the current pressure may not be sufficient to prevent the airway from collapsing in the (very near) future. And since more pressure is needed to prevent future events from happening, the machine increases the pressure after the second (or latest) event in the cluster ends.
APAPs also respond to snoring and flow limitations by increasing the pressure. Snoring and flow limitations are considered precursor events to OAs and Hs. In other words, snoring and flow limitations are thought to indicate that the airway is compromised: It may be partially collapsed (but not far enough to score an H) or it may be just barely beginning to collapse. More pressure at this point will help hold the airway open and prevent further collapse, and hence, prevent OAs and Hs from occurring. It's worth noting that some brands of APAPs are very aggressive in how fast and how far they increase pressure in response to snoring or flow limitations.
So the overall goal in every manufacturer's Auto algorithm is to increase the pressure just enough to prevent more events from happening in next few minutes and allow the breathing to stabilize. The idea is to avoid jacking up the pressure unnecessarily: That can lead to more unstable breathing, discomfort, and more pressure than is needed to keep the airway open most of the time. And once the machine is satisfied the breathing is indeed stable, the Auto algorithm will decrease the pressure until there is evidence that the airway is once again in some danger of collapsing.
Each manufacturer's Auto algorithm handles the details of how to handle the pressure increases and decreases in its own proprietary way. Some machines are more aggressive and increase pressure faster in response to snoring, flow limitations, and events. Some take small 1cm steps in increasing the pressure and then wait for a minute or more before increasing the pressure further. The PR machines even have a search algorithm that periodically tests what happens to the Flow Rate curve when a modest pressure increase is applied even when there are no scoreable events (OAs, Hs, FLs, RERAs, and Snoring). And likewise, each manufacturer's algorithm has a different way of deciding when to start decreasing the pressure and how fast to decrease the pressure.
It's clear from reading informational material aimed at clinicians, that each manufacturer believes that they have the "best" algorithm. But what little information that has been published about independent bench trials seems to indicate that while real differences in the auto algorithms can be quantified, the clinical significance of those differences is much harder to evaluate. This may be one reason that some sleep docs are so reluctant to prescribe APAP therapy as the first course of treatment for ordinary OSA.”
Sorry for the large quote BUT I really feel it is needed in its total.
Based on it I considered my settings, and considered I might be running my exhale too low. So I tried raising it as high as possible for me. I had been running as low as possible based on the idea if I get Complex apnea caused by the use of CPAP which is why I have a AVS machine then I needed the lowest exhale pressure.
I think that is wrong as the machine may not be able to blast open any blockage as reported in the notes above.
So I changed my low exhale from 4 to 6 and I saw a sleep season with ZERO AHI and higher O2 and calmer graph’s on all but for my breathing rate.
With things looking better I changed again to an exhale pressure of 7cm. and again reset PS lower to keep my inhale pressure at 12cm.
Here are the pictures: Note I do wake up a few times..mainly due to forcing myself to sleep on my side as I have seen major apneas when I get on my back..I will have to see if that will still happen with these new settings.
The only part of concern is my breathing rate..but with such good O2 readings with its average nice and high and looking so much more stable I am kind of thinking of allowing that as all the rest are looking so much better.
The final proof will be how today goes (10/29/14) I will follow up on this.