How is auto CPAP supposed to work?

[BeckyLC]

Oh, lordy - now I'm really confused.

Where are you getting these max pressure numbers? Off the machine or using software to see the details?
It is very possible that the machines when in auto mode would increase the pressure because of flow limitations it was seeing.

The max pressure numbers I'm seeing are off the machine. I had Sleepyhead when I first started using CPAP, but don't have the new software.
I don't understand flow resistance - tried looking it up and still don't understand it.

"full blast" is what? It *never* 'blows' harder than it *needs* to. As soon as whatever caused the pressure to increase stops happening, the machine will start lowering the pressure back to the minimum pressure set, or when another breathing disturbance happens.

Seriously? With the Air Mini default settings it was waking me up with my mouth open and the machine blowing as hard as it does if I'd take the mask off with the machine going. I thought it would back off since I was awake and shut my mouth, but it wouldn't. I normally sleep with my mouth closed; I'm sure the pressure was blowing it open.

But bottom line: For you folks that clearly understand all this way better than I do - is there any possible downside with just leaving the pressure at 8 since the machine says my AHI is always 0 or <1? Thanks.

[Pugsy]

The max pressure numbers I'm seeing are off the machine.

What you see on the machine's LCD screen is what we call the 95% number. It is NOT a max pressure number.
95% numbers just mean you were AT OR BELOW that number for 95% of the night. It's just a number and a number easily skewed to the high side by a relatively short period of time at that number.

Get the new software if you want to see the real details.
OSCAR https://www.sleepfiles.com/OSCAR/
http://www.apneaboard.com/wiki/index.ph ... stallation
http://www.apneaboard.com/wiki/index.ph ... rpretation

is there any possible downside with just leaving the pressure at 8 since the machine says my AHI is always 0 or <1?

Not really IF you are sleeping good and feeling good. Without seeing the detailed reports we don't know why the machine wants to go higher but preventing it from going higher may or may not be letting something sneak past the defenses that isn't part of the AHI....but if you are feeling great and sleeping great then it probably isn't a big deal.
I suspect the primary driver for the pressure (since your AHI is low) is the flow limitations and they may or may not be that big of a deal.

[BeckyLC]

Thanks, Pugsy. I'll have to get OSCAR one of these days and see what I can figure out.

[palerider]

Oh, lordy - now I'm really confused.

flow limitations.

I don't understand flow resistance - tried looking it up and still don't understand it.

You *NEED* to use the right terms, if you try looking up something with the wrong terms, you'll get the wrong answers.

"Flow Limitations" is not even remotely close to 'flow resistance' in meaning. One is a condition of your airway, and the other is how much resistance to airflow through things like hoses, filters, humidifiers, masks etc. that the machine compensates for.

"full blast" is what? It *never* 'blows' harder than it *needs* to. As soon as whatever caused the pressure to increase stops happening, the machine will start lowering the pressure back to the minimum pressure set, or when another breathing disturbance happens.

Seriously? With the Air Mini default settings it was waking me up with my mouth open and the machine blowing as hard as it does if I'd take the mask off with the machine going. I thought it would back off since I was awake and shut my mouth, but it wouldn't. I normally sleep with my mouth closed; I'm sure the pressure was blowing it open.

The machine can't even create enough pressure to inflate a balloon. The machine didn't force your mouth open. It *CAN'T* It's physically unable to do that.

The machines measure the pressure many times per second, (I forget what Resmed does, something between 50 and 125 as best I remember) and adjust the fan speed to try and maintain the desired pressure. when you don't have the mask on, the pressure drops, and the fan speed goes all the way up, within a fraction of a second of your putting the mask on, the fan speed drops. If you had your ear up against the machine, you could hear this.

Sure, if you lose the seal in the back of your mouth that keeps the air out of your mouth, then the air will blow into your nose and out your mouth, just close it off. That's something you do unconsciously all the time, when you switch from nasal to oral breathing, or breathing vs drinking eating, or... so many other things. It's part of the same mechanism that allows you to blow up a balloon without having to pinch your nose. ie, your soft palate.

But bottom line: For you folks that clearly understand all this way better than I do - is there any possible downside with just leaving the pressure at 8 since the machine says my AHI is always 0 or <1? Thanks.

Yes. There's more to Sleep Disturbed Breathing than just Apneas and Hypopneas (AHI).

[randye80]

FWIW, I recently bought an AirMini and an Airsense 10 online.

While both were set to the pressure listed in my prescription, neither were set to AutoSet by default. Both were in regular CPAP mode out of the box.

[palerider]

FWIW, I recently bought an AirMini and an Airsense 10 online.

While both were set to the pressure listed in my prescription, neither were set to AutoSet by default. Both were in regular CPAP mode out of the box.

"autoset' mode requires two pressures.

If there's only a single pressure on your Rx, then they're going to set the machine to CPAP mode.

[BeckyLC]

Apologies, palerider - flow limitations is what I looked up and read about, not flow resistance - I typed the wrong thing. It's so irritating when people are stupid, isn't it?

[palerider]

It's so irritating when people are stupid, isn't it?

My concern is for people that are trying to find answers, and are getting wrong ones, or just more confusion when they use the wrong terms.

Flow limitations are a thing that's occasionally hotly debated here, but to rephrase things, they are a limit to the rate that you can inhale air, and result in a characteristic distortion in the air rate flow patterns recorded by the machines.

To get an idea, try a sharp inhale through your nose, then do the same thing with your mouth open... notice how you can fill your lungs quicker with your mouth open? Now, try the same thing only do it through a straw.

Notice how it's harder to get the air through the straw, and it takes longer to fill your lungs?

That's a "flow limitation" in sleep apnea parlance.