Hackaday Prize Entry: CPAP Humidifier Monitor Alarm

CPAP (Continuous Positive Airway Pressure) machines can be life-changing for people with sleep apnea. [Scott Clandinin] benefits from his CPAP machine and devised a way to improve his quality of life even further with a non-destructive modification to monitor his machine’s humidifier.

With a CPAP machine, all air the wearer breathes is air that has gone through the machine. [Scott]’s CPAP machine has a small water reservoir which is heated to humidify the air before it goes to the wearer. However, depending on conditions the water reservoir may run dry during use, leading to the user waking up dried out and uncomfortable.

To solve this in a non-invasive way that required no modifications to the machine itself, [Scott] created a two-part device. The first part is a platform upon which the CPAP machine rests. A load cell interfaced to an HX711 Load Cell Amplifier allows an Arduino Nano to measure the mass of the CPAP machine plus the integrated water reservoir. By taking regular measurements, the Arduino can detect when the reservoir is about to run dry and sound an alarm. Getting one’s sleep interrupted by an alarm isn’t a pleasant way to wake up, but it’s much more pleasant than waking up dried out and uncomfortable from breathing hot, dry air for a while.

The second part of the device is a simple button interfaced to a hanger for the mask itself. While the mask is hung up, the system is idle. When the mask is removed from the hook, the system takes measurements and goes to work. This makes activation hassle-free, not to mention also avoids spurious alarms while the user removes and fills the water reservoir.

Non-invasive modifications to medical or other health-related devices is common, and a perfect example of nondestructive interfacing is the Eyedriveomatic which won the 2015 Hackaday Prize. Also, the HX711 Load Cell Amplifier has an Arduino library that was used in this bathroom scale refurb project.

31 thoughts on “Hackaday Prize Entry: CPAP Humidifier Monitor Alarm

  1. Isn’t this a good solution to the wrong problem? The real problem is either that the reservoir itself is too small to last the night and/or the user hasn’t checked the reservoir before use.

    A better application would warn the user at the start that the reservoir needs filling so that the user is not woken because the reservoir is low.

  2. Did anybody else think at first that this was a way to somehow combine cigar storage with a CPAP machine or monitor their cigars using a CPAP machine?

    Strange that the actual functionality isn’t built into what is most likely at least a $1000+ medical device as a standard thing that it should be monitoring to function optimally?

    1. I made a simple CPAP for less than $300 using stacked fans to generate the pressure differential and a pressure sensor for PID control.
      The person who uses it says it works as well a “Real” one.

    1. These things can hold plenty of water but many users (myself included) only put in one or two night’s worth. Reason 1: the water gets funky fast. Reason 2: you have to use distilled water.

      1. There’s also the fact that ambient humidity can have a large effect on how much water is consumed in a given night. I fill my reservoir to the same level every night and sleep roughly the same number of hours. There are mornings when I wake up with my nasal passages feeling like they’ve been sandblasted because the reservoir dried out halfway through the night, and other mornings when I could swear that I wake up with more water in the reservoir than I started with.

        1. That requires you to ensure that the holding tank materials can hold up to UV over time and also that the dose of UV that is being created is actually detrimental to bacteria, mold and other pathogens. Doesn’t UV light also create ozone? Breathing that in for hours at a time could be a potential issue.

      2. Sounds like the “funky” water would be pretty dangerous to inhale directly into your lungs.. Mould spores etc. No way I’d use the same water every day.

        This is one of the reasons I don’t use the humidifier on mine anymore.. I don’t find I really need it anyway, it hardly makes a difference. I still have it on the CPAP because it muffles the sound a bit :)

        But yeah they hold plenty of water.

  3. One modification I’d consider is measuring how much water is used, on average, during one night, and set the system to sound the alarm during the day if the water is below that level. One could also replace the alarm with an indicator LED, which presumably the user would notice before going to bed, which would remove the need of detecting the right time to sound the alarm.

    1. You could take it one step further by monitoring ambient humidity/temperature and correlating that with gathered water use statistics to build a system that beeps when you’ve put in enough water for the night based on current conditions +10% or so.

  4. I’ve had this same model of CPAP for years. I have to fill the reservoir once every 3-4 days, and that’s living in Dry-as-rice Alberta, Canada. It has a small window at the top, which you can peek down and see your water level. If it’s low, top it up before sleeping. It’s a quick, 5-second-habit each night that prevents me from ever running it dry. Might be why the functionality isn’t included, as asked by Internet.
    If your CPAP is running dry within 1-2 days, use the system menu to check your mask fit as you might just be leaking a ton of air.

  5. or automatically tops up. from an external resivior.

    Many humidifiers used in the hospital use a float valve in the humidifier bowl, water is supplied from an IV style bag hang above the unit, so there is only around 200mL of water in the humidifier at any one time.

    Low water is detected by monitoring the heat rise of the chamber heater plate. When the water has evaporated the temperature of the heater plate is insufficiently cooled by the evaporating water and the temperature increases and trips the low water alarm.

    If the weight change as the water evaporates was logged through the night perhaps that data could be useful.

    Maybe an increase in water consumption could trigger a separate room humidifier, perhaps increasing the room humidity would reduce the water consumption of the humidifier??

  6. Having tried a CPAC machine and rejecting it on the grounds of safety, there is no filter on the machines. If your house fills up with any type of gas, CO2, carbon monoxide, radon, propane exhaust from the bbq, etc,, the machine will pump you full of it. There are no sensors on any CPAC machine to let you know that its pumping more than just air.

    1. If the deadly gas is already in the house to be pumped through the CPAP would it not still be in the house to breath without using the CPAP?

      I doubt that the CPAP pumps much more air into your lungs than you would get from a normal breath so you probably would not get much more air with the CPAP than without.

      1. You’re right, it doesn’t. It does not make you breathe more air. It just helps to keep your airway open.

        Depending on the prescription it doesn’t do much at all anyway – Some people have a prescription for Auto CPAP which works at a low pressue and only ramps up when your airway becomes restricted.

    2. Not that it really resolves the problem of not ensuring the ambient air is clean, there are at least gas, CO2, CO and radon sensors available commercially that could be used in the same room that could be easily added as separate devices. Using a CPAP machine or not, those are not good gasses to be inhaling and many US building codes at least require some degree of detection equipment near bedrooms.

      Your house is also not likely to fill up with radon gas as an immediate hazard either though it is still obviously not good to breathe in over time.

    3. you say that as if normal sleeping won’t do the same thing – most gas content/detection sensors don’t like warm moist places so they’d have just as hard of time in a CPAP as they would in other applications and require constant replacement/calibration.

    4. Every CPAP machine I’ve seen and used had a dust filter. No CPAP machine will protect you from those gases, and your own lungs will do the same thing if those gases are present. If those are really a concern, you should invest in alarms for each of the various ones you’re concerned about. Most homes have smoke and carbon monoxide detectors already (if not, they should), radon isn’t really an issue unless you’re sleeping in an unsealed basement and you should have tested for it already anyway, and anyone operating the BBQ should be responsible enough to use it properly or they shouldn’t touch the thing.

      Also, a CPAP machine isn’t a respirator. It can’t “pump you full of it”, as your lungs and diaphragm are still doing most of the work. CPAP is only providing just enough additional pressure to keep your airway open. If your home is that hazardous, the CPAP machine is the least of your worries.

  7. I have this exact machine, and while it’s wonderful when it works, what isn’t wonderful is that the stupid pipes split so damn easily. I move a _lot_ in my sleep, i will sometimes wake up and find I’ve wrapped the cord around my neck (it’s never tight, but I think that may really not help the fact they split).

    If anyone out there, has any idea on how to make a better tube for these devices, I’d actually kiss you, with my dried out, tired, CPAP’d mouth.

    1. I’ve never had this issue. I can see the white hose that connects directly to the CPAP being more prone to splitting, but the hose that comes from the humidifier is a pretty impressive quality.
      One thing to consider might be that you move a lot because you’re still having sleep interruption events. I had the same issue for a while as I was using the nose cover mask and I have a beard (trimmed close, but still leaked a bunch of air). I switched to the nose pillows and my air leakage is minimal, my events went down to less than 1 per hour, and I barely move now.
      Maybe give a different mask a shot. Worst you stand to lose is a small bit of money, compared to the gain of a really good sleep.

      1. I’m already on a full face mask – I’ll ask at clinic next time they call me if there’s anything else or if it’s worth re-monitoring me. As it’s through the NHS it costs me nothing, but takes awhile to get anywhere.

  8. A nice feature for CPAP would be if it would notify you when there was some problem. On most of them you have to look at a screen, push buttons, whatever to see how things were last night. What it should do is let you set conditions, and notify you when the conditions are met. (e.g. leak over certain amount, so many apneas, …) Then one wouldn’t have to check it regularly (or, what many people probably do – fail to check it.)
    This would be easy to do if they had wifi or bluetooth built in – send basic stats (or the whole shebang) to a cell phone app.

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