[jerf]

"People breath about 5 liters of air per minute at a low activity level. That’s 2400 liters in an-8 hour period. Air weighs about 1.2 gm/l = 2.88 KG moved in an an 8 hour period."

I'm not sure if this device is plausible, but I know this calculation is not useful. You're calculating the mass of air moved, which, first of all, does not itself say much about the energy required to do so; for instance, horizontal motion doesn't require any net energy (though any real device doing so will of course need to do something to accelerate and decelerate, there's nothing to say it can't be very, very cheap). Second you appear to be discussing it as if there isn't a pair of lungs right there providing motive power. I do that much moving of the air every day (plus a bit, probably, I'm a tall guy) with no batteries at all.

This thing is not responsible for "moving all that air"... it's responsible for a pressure increase of the air, which is at least somewhat equivalent to saying it's responsible for "moving air" but only a fraction of the value you computed. They say it is supposed to do from 1 to 20 "centimeters of water". According to the Great and Mighty Internet, 20 cmH20 is 0.02 atmospheres, just to give some perspective. I do not have the math to calculate the energy requirement that represents when the air is in motion itself; my physics would only be sufficient to calculate the energy implied in pressurizing a closed container from 1 to 1.02 atmospheres, which is useless in this case. Perhaps someone else can pop up for that.

(Bear in mind I took a full standard College physics-for-non-majors course set, using full calculus, and what I know from that is that what I know is inadequate... if that also describes your experience, your education is inadequate too. We're going to need to hear from someone with more specialized education.)

My suspicion is that yes, this device is plausible, but the final version is going to be larger than the versions shown. Whether it crosses over the invisible line where people become unwilling to wear it is anybody's guess, but... sleep apnea sucks and those masks do suck too, so there's some room for these guys to work in. I'd classify this as a "considered risk" rather than "two orders of magnitude impossible". I reserve the right to change this assessment as more data comes in, especially a (good!) physics analysis of the real energy required to do this.

[TylerE]

20 centimeters of air is a LOT more than it sounds like. I personally run a pressure of 14 cmH20 and the airflow needed to maintain this is a LOT higher than that needed for breathing. I run a full face mask and my machine averages flow of around 30 liters a minute. The air needs to be "turned over" constantly since you don't want to be re-breathing stale air.

(As a side note to GP: Reducing/stopping pressure on the exhale is problematic also... for some of us many of our problems are actually on the exhale.

[amluto]

I know basically nothing about how CPAP devices work, but why does it need to move so much air? There are snorkels on the market with little check valves so your exhaled air goes out a different pipe than your inhaled air. They cost maybe $20. I can't imagine that a super-expensive CPAP machine doesn't have a similar pair of valves.

[TylerE]

Basically, because you're sleeping, and even a good mask seal will leak a fair bit, and there is also a lot of intentional leakage around the valves because you don't want stale air hanging around, or condensation building up, and you have to make sure that the person can breathe sort-of normally if the power fails or something like that.

[amluto]

As a guess: with a plugged-in device, the manufacturer doesn't care about power consumption, and the thing already needs to be be able to supply enough air for the peak flow while you're inhaling, so it doesn't really matter if it leaks.

If they cared about power consumption, they could presumably make it less leaky and use check valves to prevent issues with stale air or inability to breathe if the fan stops working.

I've used snorkels with separate in and out tubes and check valves to route the air correctly. It solves stale air problems (which are irrelevant for snorkling because the total air volume is much less than the amount of air you breathe in per breath) and causes serious suckage (because you really want your exhaled air to displace water that comes in the intake, and check valves prevent that), but for CPAP it might make sense.

[jerf]

As I suggested, I won't be shocked if it is infeasible in the end, or if it practice it only works on the lower end of the scale, or that it has significant issues with the other considerations you laid out in your deeper reply, such as condensation. I just know that we can't do the math as if we expect this little thing to be doing all the work.

[Alkim]

Well it has been a few years from when I took my Thermo course, and yes the proper way to do this is to compute the work required for compression. I'd invite this thread to do a proper job with the math. And if you've used a CPAP as I have you know that it actually assists your chest in moving, which is even a more considerable mass--there's a lot of energy being used in my CPAP device.

[PuffinBlue]

Does the CPAP need to do that? Assist in moving your chest I mean? It seemed from the video that they are targeting the collapse of the soft tissue in the throat. Perhaps the energy required to do that would have the side effect of assisting to raise the chest?

I've never used on of these devices so I'm curious about it.

How do you exhale? If it's forcing air in at a decent pressure then does it detect an exhale or are you expected to just push on through?

It seemed like from the video they airing would add pressure to the inhalation and switch off for the exhalation, or at least that's what I'd try and do, but then I don't know much about these things!

[jwynia]

My ResMed S9 machine detects exhalation (configurable levels) and backs off of the pressure. The mask that I wear (covers mouth and nose) has small holes that vent both exhalation and the pressurized air. The air flow out of those holes is relatively stable during both inhale and exhale, with the machine adjusting pressure to keep fresh air flowing through the mask and maintaining the pressure.