Implausible and overfunded CPAP machine on Indiegogo • Hacker News Board

Re: Implausible and overfunded CPAP machine on Indiegogo

#41

Post by amluto » Tue, Jul 14, 2015, 4:09 PM UTC

Let's try the math for real.

The site claims that the device can provide 20 cm H₂O (which is ~1961 Pa). Apparently some hypothetical normal man breathes at a rate of 6 liters (i.e. 0.006 cubic meters) per minute at rest [1]. If you pump a volume V of fluid across a pressure difference of ΔP, you've done work V·ΔP, which is 11.76 Joules per minute or 0.1961 Watts. Keep in mind that this is the work done, not the power consumed, but let's be generous and assume a 100% efficient blower. We'll also assume that no power is harvested during exhalation.

In eight hours, that's 1.56 Watt hours.

Duracell's zinc-air chemistry claims up to 442 Watt hours / kg [2]. That's about 3.5 grams of zinc-air goo per night, ignoring packaging, blower loss, etc.

This seems entirely plausible to me.

[1] http://www.normalbreathing.com

[2] http://media.ww2.duracell.com/media/en-US/pdf/gtcl/Technical...

Edit: In the interest of precision, I should add that the analysis is accurate for an incompressible flow. Air is definitely compressible, so, if you pump air, more volume is going into the pump than is coming out, and you're heating up the air (adiabatically if your pump is any good). So, with a compressible fluid, you have to consider not on the work done moving the fluid across a pressure difference but also the energy you've stored in the fluid by pressurizing it. The pressure difference for CAP is tiny here, though, so this would be a miniscule correction to the math above.

Re: Implausible and overfunded CPAP machine on Indiegogo

#42

Post by rebootthesystem » Tue, Jul 14, 2015, 4:09 PM UTC

Buy the right to post comments by pledging the smallest amount possible? Contact indigogo with the concern? Write a blog post and get help having it widely linked? Alert the authorities?

On the other hand, it might br hard to convince a lot of people that this isn't real. After all, most of humanity believes some version of supernatural nonsense which includes such things as people flying, resurrecting, partin seas, singing bushes, talking snakes, 6,000 year old earth, rapture, being chosen, paradise, etc. in other words, there's plenty of empirical evidence to show science and reason don't stand a chance. Yet.

Re: Implausible and overfunded CPAP machine on Indiegogo

#43

Post by PuffinBlue » Tue, Jul 14, 2015, 4:13 PM UTC

Alkim wrote: post #22

jerf wrote: post #13

"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…

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.

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!

Re: Implausible and overfunded CPAP machine on Indiegogo

#44

Post by PuffinBlue » Tue, Jul 14, 2015, 4:21 PM UTC

amykhar wrote: post #36

I work in the sleep industry, and noted that the company making this device did not attend Sleep 2015 in Seattle. The fact that they were not present at the largest gathering of sleep professionals in the country this year made me really doubt their credibility.

Noting whether a company has been to their industries largest gathering of professionals doesn't seem like a particularly robust metric upon which to judge future success.

Re: Implausible and overfunded CPAP machine on Indiegogo

#45

Post by awinter-py » Tue, Jul 14, 2015, 4:31 PM UTC

You guys are awesome for doing this, but are enabling a dangerous kind of startup: 1. post bullshit to indiegogo 2. hackernews designs it for you 3. profit

Re: Implausible and overfunded CPAP machine on Indiegogo

#46

Post by jwynia » Tue, Jul 14, 2015, 4:39 PM UTC

PuffinBlue wrote: post #43

Alkim wrote: post #22

Earlier quoted context omitted.

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.

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 a…

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.

Re: Implausible and overfunded CPAP machine on Indiegogo

#47

Post by amluto » Tue, Jul 14, 2015, 4:44 PM UTC

TylerE wrote: post #16

jerf wrote: post #13

"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…

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…

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.

Re: Implausible and overfunded CPAP machine on Indiegogo

#48

Post by jwynia » Tue, Jul 14, 2015, 4:50 PM UTC

anonu wrote: post #35

If anything, this underscores the importance of this field. Sleep is an under-studied phenomenon. Sleep apnea is even more so... Consider the current field of options, none of which may be any better than the one proposed on Indiegogo. All you need to do is flip on some infomercials or flip through a SkyMall magazine to see that there are dozen of gizmos and gadgets that don't work: chin straps, sprays, OTC mandibula…

I believe my neurologist was one of those who helped develop that device (Cornelius). Can't log in to see, but sounds like the same thing. But, he keeps me on an adjustable CPAP machine instead because of how my sleep apnea works.

Re: Implausible and overfunded CPAP machine on Indiegogo

#49

Post by jwynia » Tue, Jul 14, 2015, 4:51 PM UTC

TylerE wrote: post #33

skilesare wrote: post #30

There is breathing going on here so is there any chance that the breathing out could help recharge the battery in a similar way that a hybrid car charges your battery when you brake? I also don't think it is 'disposable'. I think it is recyclable and from what I've seen the $3 is dependent on recycling them.

No. To be effective CPAP has to be continous, even during the exhale.

Most of the machines sold now are continuous, but not at constant pressure. Mine's set to detect apnea events and adjust between 5-15 for pressure and to adjust that further based on exhalation.

Re: Implausible and overfunded CPAP machine on Indiegogo

#50

Post by OopsCriticality » Tue, Jul 14, 2015, 4:52 PM UTC

> The question I’m asking here is what should we do as engineers? Ethically, I mean. I really hate to see people taken in by such an obvious scam.

Skepticism is certainly warranted based solely on the timeline presented and my experience in medical devices.

As to the rest, you're operating on incomplete information. According to the NSPE, "Engineers may express publicly technical opinions that are founded upon knowledge of the facts and competence in the subject matter." You say, "what should we do as engineers", so I'll make the implicit assumption that you're an unlicensed "software engineer" like many on HN. If so, consider that you may be operating outside your area of expertise without complete knowledge of the device. I would make careful public statements: I, for example, wouldn't say "I performed a first-principles analysis and, as an engineer, I find the device claims are impossible."