I was recently reading about Paul Alexander, one of the last polio survivors to need regular treatment with an iron lung.

This is a fascinating device with a function and name from another era. It's also completely the wrong way around. The basic principle of operation is that your body is sealed in a chamber while your head remains outside. Then, the pressure in the chamber is decreased - this means that the pressure outside, where your head is, is now relatively high and air will rush into your lungs to try and equalize that pressure. The pressure in the chamber is then reversed and the air rushes back out again.

The critical part is that there is an artificial difference in pressure, delta p, between the lungs and the openings in the head that connect to them. It's totally logical that the iron lung does it this way around, since its replacing the function of the diaphragm, a big muscle that increases/decreases pressure in the lungs to move the air about.

However, being in an iron lung looks like somewhat of an inconvenience. While your head is outside, free to watch TV or recite poetry with a somewhat mechanical rhythm, the rest of your arms & legs etc. is in a big metal chamber being exposed to pressure changes that are largely irrelevant to their function*. This means that you can't do much with your arms, hands, legs etc. to interact with the world - not even scratch your nose, while your head is totally free. But your head is mostly just concerned with information input/output. Information can pass through pressure chambers quite a lot easier than physical objects, like nose scratchers. So, how do we modify this?

Simple, we put the head in the chamber and change the pressure in there. We make the chamber out of clear polycarbonate** Seal it around the neck in the same way as the original device, equip it with a microphone/headphones and have a pump increasing/decreasing the pressure rhythmically. Crucially, the air will have to be replaced on each cycle since the O2/CO2 will quickly get out of balance, but that's easy to do.

The whole arrangement would end up being more like a helmet with backpack, and the person would be free to move around and function in the world. The downside of course, is that you still wouldn't be able to scratch your nose, and we might need to seal off the ears if the ear popping is too much.

*the bowels likely respond, if air travel is any indication. Those chambers have to smell a LOT of fart after a session.

**Prescription chambers available at supplementary cost.
-- bs0u0155, Sep 19 2022

Wouldn't this destroy your inner ears? Like traveling to 20,000 feet and back every 2 or 3 seconds?

Ahh, the dreaded "somebody was typing the same thing as me" syndrome.
-- doctorremulac3, Sep 19 2022


//pressure effects on eyeballs and eardrums?//

Obviously, I've now read a little more on the general subject, in an attempt to get some numbers on the actual pressures involved. I haven't succeeded in that, but it's apparent that the iron lung is mainly there to generate NEGATIVE pressures on the body. So the helmet would therefore be generating net positive vs. the general atmosphere. For this reason the eyes will be fine, they're fine when I squash them with the heels of my hands when tired, they're fine when people suddenly dive 15' under water.

The ears might be tricky, hence some sealed tubes around/into the ears referenced to outside pressure might be needed. You'd probably learn when a good time swallow or whatever it is that opens the Eustachian tubes up for pressure equalization, you wouldn't be eating much since your heads in a fish bowl anyway. Just like pilots, you'd want to make sure your dental work is close to perfect.

Apparently, you can get away with a lot smaller pressure swing if you do it faster - which will be easier with a helmet since it's a smaller volume.
-- bs0u0155, Sep 19 2022


What if you just had a mask covering nose and mouth that looks remarkable like a CPR mask (since it has the same function). then it wouldn't affect the eyes or ears.

Wait.... Googling... Okay, it's called NPPV or NIPPV Non-invasive Positive Pressure Ventilation.
-- scad mientist, Sep 19 2022



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