AfibApnea,
I'm not sure that I'll actually answer any of your questions. But I'll give some of them a try.
AfibApnea wrote:I know basically how BiPap ASV machines work, and I have some fairly rudimentary ideas how one might implement such an algorithm (set of rules the software follows).
It is my understanding that the approach (algorithm) RedMed and Philips take is a bit different.
- How does a BiPap machine work from the algorithmic point of view?
Are you talking about BiPAP/VPAP, Auto BiPAP/Auto VPAP, or the ASV machines? It makes a difference.
In general, BiPAP and VPAP used a fixed IPAP and fixed EPAP. They record events, don't respond to them.
Auto BiPAP/Auto VPAP allow the IPAP and EPAP to vary within certain parameters. In this mode, the machines respond to obstructive events (OAs, Hs, FLs, Snores, and RERAs) by increasing the pressure. Exactly how the pressure(s) are increased differ between the two brands. CAs are recorded and the machine does not raise the pressure or do anything else in an effort to prevent further CAs.
Bilevel machines with a "trigger mode" include the ASV machines as well as the somewhat cheaper BiPAP ST and VPAP ST machines can be run in a mode that allows the machine to respond to breathing patterns that are typical of long strings of CAs. Essentially these machines can and do attempt to "trigger" an inhalation when certain criteria are met. Since I do not use one of these machines, I don't have a strong understanding of exactly how the "trigger breath" algorithms work--as in I don't know what must be present in the breathing pattern to make the machine "trigger" a breath. I do know that the way they trigger inhalations is by quickly and drastically increasing the IPAP while leaving the EPAP alone. The max PS and max IPAP settings are critical in determining just how high the IPAP can be increased in order to "force" an inhalation.
The AUTO versions of ASV machines allow the machine to vary the EPAP in response to obstructive events. The non-auto modes for ASV-type machines use a fixed EPAP and only vary the IPAP in response to the need to "trigger" breaths.
Does the algorithm just monitor one’s breathing pattern or does it take into account Central events, Obstructive events, periodic breathing, calculated values for AHI, etc.
In general the answer is "yes". But there are a lot of caveats and you have to know exactly which machine and which model you are talking about. Some of the ASV machines, for instance, don't seem to flag apneas as CAs and OAs, but just as As. I know the PR machines typically flag periodic breathing; I'm not sure about the newer Resmed AirCurve machines.
Does the machine change what it does based on feedback-over-time? If so, what are the longest time periods it considers?
Not sure what you mean here. Do you mean feedback over the last several minutes of breathing? Or do you mean feedback over the last several nights? or longer?
What different approaches might the software take (more than 2?)?
I don't understand what you are talking about here. Are you talking about how the machines respond to things? Or are you talking about how the data is represented and displayed?
What role does ASV play in that algorithm?
The ASV algorithm is tied to how and when the machine decides to start "triggering" inhalations. The ASV algorithm also is tied to how the machine actually raises the IPAP in an effort to trigger inhalations. And finally, the ASV algorithm is tied to what criteria the machine uses to decide that the breathing has stabilized to the point where "triggered" or "timed" breaths are no longer needed. Essentially the ASV algorithm is designed to treat the problem that leads to long strings of CAs.
What set of rules does Philips employ? What set of rules does ResMed employ?
For Auto Bilevel or for ASV?
What is AVAPS??? I thought my BiPap ASV was as far as the technology went.
AVAPS stands for Average Volume Assured Pressure Support. This is a ventilator term and it refers to one particular kind of algorithm that can be used to determine when to trigger breaths and how much IPAP to add in the triggered breaths. Essentially the machine compares your inspiratory volume to a target volume, and when the actual volume gets too low, the machine starts triggering inhalations.
It's important to note that bilevel ST machines, ASV machines, and AVAPS machines are all considered noninvasive ventilators. CPAPs/APAPs and plain bilevels and auto bilevels without a T mode are NOT considered noninvasive ventilators.
My somewhat vague understanding of the difference between the "trigger" or "timed" breath algorithms get increasingly more complex as you move from the ST machines to the ASV and ASV Advanced machines to the AVAPS machines.
