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Ventilator loss of power alarm

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Ventilator loss of power alarm

Postby Electrons-R-Fun » Tue Feb 28, 2017 2:11 am

Hi all,

I got an email from a person who has advanced ALS but can still use her DynaVox to communicate. She wrote in her email some very scary information about how her mom was visiting her and they were playing cards and her ventilator just shut off. If her mom wasn't there in the "nursing facility" playing cards in the room with her she would have suffocated to death because there was no power to the vent to set off any alarm. So her mom was able to run down the hall screaming for help and the nurses came with Ambu bag to breath for the patient until a different vent could be hooked up.

My question relates to electronics this way. Is there a device that detects current (not voltage, because the vent had 110 voltage available but was not drawing any current.) Is there a device that already exist for this purpose so an alarm could sound if a vent stops drawing current. Or would one need to be built. I have heard of something called a current shunt but don't really know what that is. The device would, obviously be in series with vent but could not interfere with vent operation in anyway. I was also thinking since some vents charge batteries while plugged in and they all might differ on their current draw to do the charging it might be a good idea to have the current alarm adjustable so different vent could use the device.

Ok thanks for the suggestions and tips and possible links to read.

Jason

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Re: Ventilator loss of power alarm

Postby Granz » Thu Mar 02, 2017 10:12 pm

Electrons-R-Fun wrote:Hi all,
... I was also thinking since some vents charge batteries while plugged in and they all might differ on their current draw to do the charging it might be a good idea to have the current alarm adjustable so different vent could use the device.
...
Jason
Do you know what kind of current a ventilator would draw? How about the range of current ratings? Will future ventilators use similar current draws? Would the typical caretaker have a clue of how to adjust the alarm levels?

I'm thinking that these may be difficult questions, maybe even too difficult to be practical. Perhaps the way to do this would be to sense the air flowing through the breathing tube (hose?). Every ventilator (no matter how much current it draws) has to push air through a tube to inflate the patient's lungs. Something that can sense the air flow, and sound the alarm when it doesn't detect the air flowing for a few seconds (that timing may need to be adjustable) might do better than sensing the current draw.

You would also want the device to have a trickle-charged battery of its own, so that it can still alert medical personnel if the ventilator failure is from a power failure. The battery would not need to be very big - if the alarm goes off for more than about 5-10 minutes, the patient is already dead. I would guess that ventilators should be on some type of UPS - external if not built-in, so hopefully a power failure would not cause the ventilator to quit, but the idea of the alarm system is for failure anyway.
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Re: Ventilator loss of power alarm

Postby Electrons-R-Fun » Sat Mar 04, 2017 2:20 pm

Hi Art,

Thanks for the reply.. :D


Do you know what kind of current a ventilator would draw? How about the range of current ratings? Will future ventilators use similar current draws? Would the typical caretaker have a clue of how to adjust the alarm levels?


I can answer some of those questions. Lisa's vent has a sticker on the bottom reads 2.1 Amps. I have a device that measures the watts, amps, and voltage, it is called KILL A Watt (http://www.harborfreight.com/kill-a-wat ... 93519.html) I took several measurements with the device. The vent off charging the batteries (0.08 Amps 7.9 Watts). Vent on working and charging the batteries (0.10 - 0.30 Amps) I have to admit that was much lower than I expected.

LIsa has a newer generation ventilator, here is one on ebay? can you believe it....
(http://www.ebay.com/itm/Philips-Trilogy ... 2533437820) I could never guess about other vents or their power needs or draws so I just don't know.

My thinking was, a vent pulling power through a cord and no power running through the power cord (because it failed, but the vent could be still charging the batteries I don't know if that could be true.) is an easy difference to detect . Now that I write it down (say it out loud in a sense) I feel, I could almost use a compass or a Hall sensor to "detect" the magnetic field being created from the current moving through a conductor.

As far as other caregivers ability to "adjust" the vent alarm. I was thinking the current draw used by the vent while working and the current draw used by the vent charging batteries could be measured and the vent alarm could be set to a current draw between those two values.
The procedure could be as simple as:
1.) Plug vent in.
2.) Make sure vent is off and charging.
3.) Adjust screw (potentiometer) until alarm turns off.
I realize the above may be over simplified but I hope it gets my thinking across.

I was also thinking the device could just be set to a specific value like 750 mA, so any current draw under 750 mA would set off the alarm.

Perhaps the way to do this would be to sense the air flowing through the breathing tube (hose?). Every ventilator (no matter how much current it draws) has to push air through a tube to inflate the patient's lungs. Something that can sense the air flow, and sound the alarm when it doesn't detect the air flowing for a few seconds (that timing may need to be adjustable) might do better than sensing the current draw.


The above is certainly the main goal, I did not think about this for a few reasons. The air that flows through the tube has to be humidified, so the sensor would have to be in contact with moister 24/7. The sensor housing could not interfere with the flow and could not allow for any leaks in the system. Also the sensor housing would not be allowed to increase something called "dead space" in the overall circuit, increased dead space (basically volume, is very dangerous to vent patients) Also the sensor would have to stay in a somewhat sterile condition because it is part of the biological breathing process now.

Buts it's still a great idea. I was thinking a vibration sensor attached to the outside of the tubing could work. As air passes through the tubes they vibrate, so something like a missing pulse detection circuit might work. I don't recall for sure, but I believe a piezoelectric element can detect voltages by generating voltages as the element deflects (vibrates). Hopefully I don't look like a idiot in anything I said in the above paragraph.

You would also want the device to have a trickle-charged battery of its own, so that it can still alert medical personnel if the ventilator failure is from a power failure. The battery would not need to be very big - if the alarm goes off for more than about 5-10 minutes, the patient is already dead. I would guess that ventilators should be on some type of UPS - external if not built-in, so hopefully a power failure would not cause the ventilator to quit, but the idea of the alarm system is for failure anyway.
\

Power failure was not what I was worried about. Most if not all vents have battery back up system, so when the vent gets unplugged ( on accident or purposely to move patient) or the AC power is lost at the wall receptacle from a storm, breaker tripping, or what ever, the vent automatically switches to the battery back up system.

As far as powering the device I was thinking about building ( the loss of power vent alarm) I was thinking about running a parallel line going through a step down transformer, sending it through a rectifier, decoupling capacitors, through a DC regulator, through another DC decoupling capacitor and into the micro-controller. So the power circuit would be part of the device.

My vision of how the device would look would be, it has a length of cord that gets plugged into the wall and the cord goes to a box that has the alarm circuit, the measuring circuit, and the power circuit all included. The box would also have a place to plug in the vent power cord.

Ok I think that covers everything.

Jason

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Re: Ventilator loss of power alarm

Postby Granz » Sun Mar 05, 2017 7:22 am

Electrons-R-Fun wrote:...I can answer some of those questions. ...

My main point is that it is impossible to predict all current draws for all current (and future) ventilators. It is even possible that a future ventilator product could go into some kind of very low-power mode where it doesn't even draw power to charge the batteries when they are fully charged. So, I was just pointing out that it may be better to try to measure something other than current draw.


Electrons-R-Fun wrote:...The above is certainly the main goal, I did not think about this for a few reasons. The air that flows through the tube has to be humidified, so the sensor would have to be in contact with moister 24/7. The sensor housing could not interfere with the flow and could not allow for any leaks in the system. Also the sensor housing would not be allowed to increase something called "dead space" in the overall circuit, increased dead space (basically volume, is very dangerous to vent patients) Also the sensor would have to stay in a somewhat sterile condition because it is part of the biological breathing process now.

Buts it's still a great idea. I was thinking a vibration sensor attached to the outside of the tubing could work. As air passes through the tubes they vibrate, so something like a missing pulse detection circuit might work. I don't recall for sure, but I believe a piezoelectric element can detect voltages by generating voltages as the element deflects (vibrates). ...Jason

YES, A vibration sensor! That would work: it would not depend on the ventilator drawing power; it would not be subject to temperature and humidity issues of the breathing air; it would not interfere with the air flow; and, it would not introduce any harmful substances (bacterias/molds/poisons/etc.) to the patient's air supply.

As I thought about this, I remembered a device that I played with years ago: the Radio Shack Removable Telephone Pickup. This is just a microphone (which is a kind of vibration sensor) placed inside a suction cup - you used to stick it onto a telephone handset to record the phone calls. I found one on E-Bay (http://www.ebay.com/itm/Radio-Shack-Rem ... Sw-CpX~Twt) for only $0.99 (plus $7.50 S/H, current bid.) If you search, you may find it even lower (although you will certainly find it higher - someone actually wanted like $30 + S/H :roll: .) This could be fed into an A/D converter and the microcontroller could just "listen" to the mic and alert when it does not find any sound. The microcontroller would act like an intelligent monostable multivibrator - every time it "hears" breathing, it delays the alarm for another few (several? many?) seconds. You would need to account for outside noises - perhaps wrapping an Ace bandage around the microphone and the breathing tube would dampen out the room noises enough to "hear" only the breathing.

You could try this on Lisa's ventilator without any worries about hurting her. If she is a fan of horror movies, make sure that you explain what you are doing so she doesn't worry about you suddenly turning psycho and trying to murder her. :lol: See what kind of data you receive at the microcontroller. If you have any spare breathing hose, you could set up a "broken ventilator" mock-up; wrap the mic around that spare hose, place it into Lisa's room, and wrap it with your sound dampener - bingo, you have a broken ventilator. Take some reading from that, and you will have a cut-off noise level to detect when the real ventilator dies. Of course, before you trust that, move the "broken" unit into several different rooms, and take measurements at many different times. Then you will be able to account for the alert system to be set up in different places, for different patients. If the sound from the broken ventilator gets up high enough to match the sound levels from Lisa's real ventilator, then you will need to find a better way to dampen out the outside noises.
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Re: Ventilator loss of power alarm

Postby Electrons-R-Fun » Mon Mar 06, 2017 7:10 pm

HI Art,

I'm digesting everything about the ideas right now. I actually had found a few of those mic's around here at one time. I always wondered what they were for, to bad I discarded them. I do have Parallax sound impact sensor around here somewhere, maybe I try that just for trial, set up, and learning process.

I am also concurrently working on a different project for the Chaffey College Car Club. It is a trophy for first place made out of the flywheel out of my Shelby GT500. I thought I would learn a little about multi plexing 16 segment displays and incorporate that into the clock project. The clock is actually a analog clock with four digital numbers and some segments put together to spell some stuff. I have some test code working and will likely post some pictures and the code. I wanted to stream line my code anyway and thought I would ask everyone if they can tell me how to think about the code in a more efficient manor. I also still need how to post pictures on this website, the sizes always get messed up so maybe I'll just make a YouTube video.

Jason

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Re: Ventilator loss of power alarm

Postby Granz » Wed Mar 08, 2017 5:34 am

Granz wrote:...If you have any spare breathing hose, you could set up a "broken ventilator" mock-up; wrap the mic around that spare hose, place it into Lisa's room, and wrap it with your sound dampener - bingo, you have a broken ventilator. ...

One more thought about this "broken ventilator"; with both ends of the tube open, it may not kill off the external sounds as well as a working ventilator would. If you get confusing readings, you may need to stuff some cotton in both ends, or something like that.
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