Implausible and overfunded CPAP machine on Indiegogo • Hacker News Board

Re: Implausible and overfunded CPAP machine on Indiegogo

#51

Post by jwynia » Tue, Jul 14, 2015, 4:54 PM UTC

narwally wrote: post #25

mcphage wrote: post #9

The fact that their anticipated price is $3/day is absurd. I can't see insurance companies rushing to cover this.

"The costs of untreated sleep apnea reach further than just health issues. It is estimated that in the U.S. the average untreated sleep apnea patient's annual health care costs $1,336 more than an individual without sleep apnea. This may cause $3.4 billion/year in additional medical costs. Whether medical cost savings occur with treatment of sleep apnea remains to be determined."[1] So if it turns out that this treat…

CPAP treatment (and no other substantial changes in my life) brought my blood pressure down from 160/110 down to 118/78. Previous doctors had tried, without success, to lower it with massive beta blockers and other medication. I just needed some damned sleep.

Re: Implausible and overfunded CPAP machine on Indiegogo

#52

Post by Alkim » Tue, Jul 14, 2015, 5:13 PM UTC

amluto wrote: post #41

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…

Well now I guess I have to do the math:

W = P(b)V(b) ln(P(a)/P(b))

(https://en.wikipedia.org/wiki/Compressed_air_energy_storage)

CPAP requires roughly 10 cm of water pressure = 0.01 Bar Sea level atmospheric pressure is roughly 1 bar So the device has to pressurize to 1.01 Bar Now I’ve looked it up, and a typical CPAP machine moves 20 to 60 liters per minute Let’s say 30 liters per minute = 1800 liters per hour

W = (1.007)(1.8)ln(1/1.007) = (1.81)*(-00698) = 0.0127 MJ = 3.53 Watt Hour

So assuming perfect efficiency you would still need 28.64 watt hours of battery, just to do the compression.

470 Wh/kg for Zinc-air battery implies this device requires a 60gm battery (2 oz to those of us of a certain age)

I looked up CPU fan efficiency (what they say they derived it from) and PEAK fan efficiency only approaches 25%

http://www.nmbtc.com/fans/white-papers/fan_efficiency_import...

So, you’d really need an 8 oz battery hanging from your nose to make this work, not counting what you need to run the electronics, etc.

Re: Implausible and overfunded CPAP machine on Indiegogo

#53

Post by TylerE » Tue, Jul 14, 2015, 5:19 PM UTC

jwynia wrote: post #49

TylerE wrote: post #33

Earlier quoted context omitted.

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.

Yea, for sure.

Mine can do all that, but I actually have it all turned off...I find I have a much easier time getting and staying comfortable that way...every time the pressure changes my mask would shift...at a constant pressure I can get it "just right" and it doesn't leak at all and I find it easier to fall asleep as the pressure points don't shift around.

Re: Implausible and overfunded CPAP machine on Indiegogo

#54

Post by TylerE » Tue, Jul 14, 2015, 5:22 PM UTC

amluto wrote: post #47

TylerE wrote: post #16

Earlier quoted context omitted.

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.

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.

Re: Implausible and overfunded CPAP machine on Indiegogo

#55

Post by Mz » Tue, Jul 14, 2015, 5:41 PM UTC

I don't think there is an ethical obligation to do anything. I hope people contributing can afford to lose whatever funds they are pledging. They will have to seek FDA approval. If they don't get it, no one is going to be buying some overhyped piece of plastic that doesn't actually work.

One of the challenges we have currently is that the medical field is over regulated and there are excessive barriers to entry. Perhaps you can make your peace with the fact that it isn't your money and if people want to hope against hope for something better and pledge a few dollars, that is their choice. Then the developers might get their shot at developing something new. Maybe it won't meet every criteria they listed. Maybe it somehow will. Maybe it will be a complete flop. (Shrug)

Innovation only happens when there is some leeway for some of it to fail. $100k is a drop in the bucket for medical research. Why do you feel such a strong need to not even let them try? I suggest you let it go.

Re: Implausible and overfunded CPAP machine on Indiegogo

#56

Post by amluto » Tue, Jul 14, 2015, 5:42 PM UTC

Alkim wrote: post #52

amluto wrote: post #41

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…

Well now I guess I have to do the math: W = P(b)V(b) ln(P(a)/P(b)) ( https://en.wikipedia.org/wiki/Compressed_air_energy_storage ) CPAP requires roughly 10 cm of water pressure = 0.01 Bar Sea level atmospheric pressure is roughly 1 bar So the device has to pressurize to 1.01 Bar Now I’ve looked it up, and a typical CPAP machine moves 20 to 60 liters per minute Let’s say 30 liters per minute = 1800 liters per hour W =…

Where does that 30 liters per minute go? I'm reasonably sure it's not going into the user's nose or mouth.

Part of the claimed innovation here is that the thing sticks directly into the user's nose. If it seals well, it's plausible that there's very little wasted air, which would account for the factor of roughly five.

(Also, you used the formula for isothermal compression, I think. A tiny little device like they showed would probably move air quickly enough through its fan that it would be closer to adiabatic. This doesn't matter much for the small pressure change involved.)

Re: Implausible and overfunded CPAP machine on Indiegogo

#57

Post by mcphage » Tue, Jul 14, 2015, 5:51 PM UTC

TylerE wrote: post #20

mcphage wrote: post #9

The fact that their anticipated price is $3/day is absurd. I can't see insurance companies rushing to cover this.

Insurance for CPAP is actually fairly generous. Mine will pay for a new mask (~$150) every 3 months, and a new machine every year (~$1k). Have to meet my deductible first of course, but I suspect most insurance would LOVE to be paying only $3/day.

> Mine will pay for a new mask (~$150) every 3 months, and a new machine every year (~$1k).

Wow... that's some great insurance! I've got decent insurance, but mine will only cover 80% of costs, on a mask every 6 months, and a machine every 5 years.

Re: Implausible and overfunded CPAP machine on Indiegogo

#58

Post by jerf » Tue, Jul 14, 2015, 5:54 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…

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.

Re: Implausible and overfunded CPAP machine on Indiegogo

#59

Post by Alkim » Tue, Jul 14, 2015, 5:57 PM UTC

OopsCriticality wrote: post #50

> 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 knowle…

Well I never took the PE exam, and it is a couple of decades since my undergrad and graduate engineering degrees that included a couple of courses in thermo, so things are a little rusty, but prodded by a few of these posts I've just dusted off the math and made a go of it. BEST case, requires an 8 oz zinc-air battery. And they are going to sell that, and the device itself for $3..?!

Part of my reaction is that I am a patent attorney, and every patent attorney gets 'inventions' that come through the door from well-meaning but essentially clueless people. After a while you get to develop a bullsh*t detector. This one just rang my gong. I suffer from sleep apnea and I know what a real thing it is, and the idea of these guys just walking away with $$ from desperate people, just, again, rang my gong.

I will say that it has been fun seeing these posts--thank you!

Re: Implausible and overfunded CPAP machine on Indiegogo

#60

Post by TylerE » Tue, Jul 14, 2015, 5:59 PM UTC

mcphage wrote: post #57

TylerE wrote: post #20

Earlier quoted context omitted.

Insurance for CPAP is actually fairly generous. Mine will pay for a new mask (~$150) every 3 months, and a new machine every year (~$1k). Have to meet my deductible first of course, but I suspect most insurance would LOVE to be paying only $3/day.

> Mine will pay for a new mask (~$150) every 3 months, and a new machine every year (~$1k). Wow... that's some great insurance! I've got decent insurance, but mine will only cover 80% of costs, on a mask every 6 months, and a machine every 5 years.

Gold level Blue Cross plan via Obamacare. So yea, while not the absolute best it's pretty good.