Man on a ventilator needs a simple modification...

My friend has ALS and is struggling to exhale against the inward air flow from his positive pressure ventilator. We have a spare machine and I want to put in a 3 way valve that opens to the room and eliminate the need to work against the machine pressure. Has Anyone already done something similar?

I would say I am a mid-level Arduino-teer with several successful projects under-belt.

I’ve got a relay plug and 12 v power supply for a 3 way solenoid valve (6 watt). i need to have the relay switch open to exhaust (unrestricted) when he stops inhaling and starts to exhale. Then when he starts to inhale it needs to return to pressurized air, closing the exhaust port. I can’t figure out how to do this with pressure sensors.

  1. Inhalation step: Pressure drops, Relay switch closes, solenoid valve conducts pressurized air to face mask.

3-way
(MASK)<------[—]<-----Pressurized Ventilator
|
X
|
Exhaust

  1. Exhalation: Pressure increases, Relay opens, solenoid valve switches to exhaust to unrestricted ambient room.

(MASK)------>[—]X<----Pressurized Ventilator
|
|/
Exhaust

But a pressure sensor would immediately feel the pressure quickly drop as soon as the valve goes to unrestricted exhaust.
That will make the valve instantly revert back to state 1.
Has anyone done something like this already? I cant figure out the logic. OR is there a better type of sensor…one to detect DIRECTION and Velocity of air flow. I need ensure this works every breathing cycle. One skip and its out of sequence with breathing cycle. Also, we don’t wish to use a simple delay because his breathing rate changes through a 24 hr cycle.

Any advice would be a big help, thanks.

I wouldn't ask Atmel, the last sentence from the ATmega328 datasheet is:

Atmel products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.

Never done this, so all disclaimers apply

First proto would be a measurement device only, learn how the pressure behaves when he is breathing. During day during night, when exited, coughing etc.
is it regular or "chaotic"

next proto version is one in which the relay timing is hard coded. You need to know the average breathing rate (from first test).
although this will give all kinds of trouble it might become part of a safety modus to fall back to.

next I would add a manual override, e.g. for when (s)he is coughing. Then the breathing becomes irregular, that I think you want to shut of the air supply and only have the exhaust open - also to inhale - don't know what is best

Maybe you should have a look how an aqualung(?) from deep sea divers work, they should have a similar mechanism you need.

Hope this helps.

Maybe you should have a look how an aqualung(?) from deep sea divers work, they should have a similar mechanism you need.

Springs and levers.
Don’t trust this new-fangled elastic-trickery.

Also, I would consider the following. Every time you take a breath, your friend will hear a click when the relay turns off or on. Personally that would drive me crazy.

Use solid state relays will prevent that, anyway there will probably some noises from the pressure valves ?.

Diving regulators or demand valves attempt to provide air at the ambient pressure at the depth of the diver's mouth and lungs.
[http://web.mit.edu/scuba-club/www/Everything_about_regulators.pdf/url]

That aim is slightly different to what the Pressurized Ventilator is doing as it seeks to deliver air at above ambient pressure, presumably to help inflate the lungs. I can appreciate it would be quite tiring to breathe out against such a device, even for a healthy person.

Procyan if need be is your friend able to breathe in without the assistance of the Ventilator?

If he cannot then closing the valve to the Ventilator is risky as it becomes essential that it re-opens with 100% reliability. If he can breathe unassisted then you need to ensure that it is physically impossible for both the Ventilator Valve and the Exhaust Valve to close at once. In other words probably a single valve mechanism with two ports where one of the two ports will always be open.

Presumably your friend currently wears a mask which covers both his nose and mouth? This may be a silly suggestion but have you consider the mask design e.g. a mask covering only the nose. Your friend would have to shut his mouth to breathe in and open his mouth to breathe out, but he would have no pressure to overcome to exhale. Of course he would also have the choice of breathing out through his nose against the pressure.

The nose mask might feel a bit weird because with his mouth open air will be flowing in through his nose and and out through his mouth. I am not sure how this would affect speech. Still it would be a relatively easy to conduct an experiment on yourself.

What are the worst case failure modes? It seems to me that this could potentially be fatal under the wrong circumstances and if there is any possibility at all that this could prevent the ventilator from working as designed then you shouldn't be considering any modifications. It would be worth asking the equipment supplier whether this characteristic (of restricting the exhalation) is normal and whether the ventilator is working as designed - if it's not intentional and desirable then the supplier may be able to suggest safe ways to avoid it. DIY solutions involving switching valves in and out do not strike me as safe.

It would be worth asking the equipment supplier whether this characteristic (of restricting the exhalation) is normal and whether the ventilator is working as designed - if it's not intentional and desirable then the supplier may be able to suggest safe ways to avoid it.

You are correct, and it is possible they may have a solution so first port of call is to ask the doctor and the equipment supplier.

To me there seemed a lot of advantages to using a nose only mask, but some down sides particularly if the person fell asleep with one on. The closest thing I could think of to that would be sleep apnea so I looked that up and they have positive pressure nose only masks
http://www.sleepapnea.org/diagnosis-and-treatment/treatment-options/positive-airway-pressure-therapy/choosing-a-mask.html

In this case I am not going to say damn. One day, one day, either I will win the lottery or I will find that nobody has had the same thought before. Of course if nobody has done what I thought about then there must be a very good reason for that so therefore I probably will not do it either - damn, damn, damn.

I used a wind sensor from Modern Device. So a pressure sensor detects end of inhale. Click, and the wind sensor detects end of exhale, Click. Very simple solution. Happy to share details with anyone needing to solve simlar problem. Life goes on... awhile.

thanks
Procyan, not Pro-cyanotic! heh