MJS_ wrote: ↑Thu Apr 06, 2023 8:03 am
ChicagoGranny wrote: ↑Thu Apr 06, 2023 7:09 am
It's common knowledge that sleep/awake cannot be accurately determined without EEG.
If this were common knowledge, ResMed and F&P would not advertise that their machines can be set to ramp up the air pressure after detecting you have fallen asleep. For example:
https://www.youtube.com/watch?v=BrGGgYolGfI
Both Resmed and F&P are using the fact that normal sleep breathing has certain characteristics that are quite different from normal wake breathing to make a decent, educated
guess as to whether there is a high probability that the person using the machine is asleep. With both machines, the idea is not to try to pinpoint the exact moment you fall asleep (or wake up with SensAwake); rather the idea is to increase patient comfort by limiting pressure increases to times when the patient has a high probability of being asleep. (The idea is that once we're asleep, pressure increases should not bother us enough to wake us up. Whether that's a valid hypothesis is a whole different question.)
Information about Resmed's AutoRamp was pulled from
https://www.resmed.com/en-us/sleep-apne ... -pressure/
In the case of Resmed's AutoRamp, the machine is looking for one of the following three things before it starts to ramp the pressure up:
- 30 breaths of stable breathing (roughly 3 minutes)
- 5 consecutive snore breaths
- 3 obstructive apneas or hypopneas within 2 minutes
- 30 minutes have passed since the machine was turned on
It's clear that in choosing those criteria for ending the AutoRamp, Resmed is making the following assumptions:
- Three minutes (i.e. 30 breaths) of stable breathing looks more like good, normal breathing than "wake" breathing. So you are likely asleep (and hence not likely to be disturbed by the pressure increasing.)
- Snoring occurs when the patient is asleep. Now it's important to remember the Resmed PAPs don't have a sound detector built in---snoring is characterized by particular distortions in the flow rate graph. By using 5 consecutive snores, they hope to avoid instances where a person may make a snoring kind of breath once or twice in the process of falling asleep.
- Three OAs or Hs occurring within a short period of time (2 minutes) indicates that if the person is asleep, their airway is unstable and in need of additional pressure. Hence the need to start ramping up the pressure. By using multiple events in a short period of time, Resmed is hoping to avoid ramping up the pressure in response to the occasional false positive OA or H scored during wake breathing that are perfectly normal for the patient's wake breathing patterns. (It's important to realize that some people do see OAs scored when they consciously hold their breath while awake and using the machine.)
- Most people have a latency to sleep of 10-20 minutes at the beginning of the night. So even if 30 breaths of stable breathing has not yet been detected, there's a good chance the patient is asleep and the continued raggedness of the breathing may, in fact, be due to sleep disordered breathing which warrants a pressure increase if that raggedness could be described as "flow limited breathing".
The goal here is to use the machine's one source of data---the flow rate curve---to detect when the patient is most likely asleep instead of still awake at the beginning of the night. And the hope is that
if the machine keeps the pressure at a constant
low pressure while the person is awake, that person will have an easier time falling asleep. Whether that assumption itself is correct is a valid question: Many people here will tell you that they feel like they're suffocating at pressures in the 4-6cm range and they are quick to tell newbies to ditch the ramp and start at a higher pressure when a newbie complains they feel like they're suffocating.
Now I don't know enough about F&P's SensAwake algorithm, and what I could find on line was pretty pitiful. But based on what Rubicon posted, it looks like F&P is looking for restless wakeful breathing (including what is often called Sleep-Wake-Junk around here). And the F&P machines are supposed to lower the pressure (how much?) in an effort to make it easier to get back to sleep. Does that work for real people in real beds? I suspect the answer is
sometimes. If you are someone who has dealt with a lot of aerophagia and is uncomfortable (and worried about aerophagia) anytime you wake up in the middle of the night, knowing the machine is supposed to reduce the pressure a bit may help alleviate the worrying which in turn will help with getting back to sleep. But if pressure doesn't really bother you OR if you dislike low pressure, that pressure reduction probably isn't going to help very much with getting you back to sleep.
In other words, I think both Resmed's AutoRamp and F&P's SensAwake probably do make reasonable guesses
most of the time when they think the person at the other end of mask is likely asleep at the beginning of the night. But neither algorithm is designed to try to measure exactly when the transition between sleep & wake precisely took place at the beginning of the night. And it's not at all clear to me whether the F&P SensAwake algorithm is really going to pick up SWJ breathing well enough to decide to lower the pressure and whether lowering the pressure is even the best thing to do in terms of helping the person get back to sleep.
).