Ok Matt...My name is Tony. I am a critical care paramedic and flight medic in florida, and I take care of vent dependent patients daily so I have a good understanding of what you may need and need to consider while setting this up. I use the Impact Eagle 754 transport ventilator on the ground and in the air. You may be familiar with it. First of all go for it. Second, I am not yet a certified diver but will be next month, and flight physiology is quite similar. We fly with a pressurized cabin but the pressure is usually 2500 to 6000 feet so we are still susceptable to pressure changes while transitioning altitudes.
Ok dude, I'm going to need some basic information that most folks here aren't going to understand, but it'll be educational.
I'm going to assume you have a tracheostomy...if so what size? Cuffed? Shiley?
If you've already answered this I apologize...why are you on the vent? What other considerations do you have? I.e. do you have an intact gag reflex? I ask because the cuffs on trach tubes probably won't withstand the water pressure. This can likely be taken care of by orotracheal intubation for the dive or even insertion of a 6.5 tube shortened and placed in the tracheostomy since the cuffs are a bit more sturdy.
Are you on any pressure support? Assist control or SIMV? What about PEEP? Can you manage on atmospheric O2(21%)? If you're on an Fi O2 any higher you're going to have to consider how you're going to supply the oxygen.
Now, the Impact Eagle 754 is only about 12 pounds, so if a watertight case could be made for it then your dive buddy could carry it down for you. Just a clear plastic bag would be perfect...I have an idea I'll explain later. An experiment would have to be done on whether the Eagle could handle pressure at depth so you'd have to find someone willing to risk a $9000 ventilator to find out for you. I'll e-mail Impact and ask if anything's been tried with it before and see what they say. Another experiment will have to be done with a vent circuit. Take a look at yours...that plastic tubing is fairly thin and would be possibly susceptable to pressure which could cave it in a little, but depending on your tidal volume you probably don't need half of it's capability anyway.
Ok...here's that bright idea I had. Try not to laugh. Assuming the Eagle canhandle the pressure, it's totally self contained other than it's oxygen supply, which I'm not sure how compressed oxygen would behave at depth. We use standard aluminum D tanks...stainless steel might work better though. Alright...Clamp the Eagle to a small pole that you can also tape the O2 and medical air cylinders to(an IV pole with places for cylinders would be ideal, and you could cut the pole to size allowing the vent to be clamped to it) stop laughing this setup will probably weigh 20 to 24 lbs...attatch your the circuit and the transducer and exhalation valve tubes to the vent and place this in a sturdy clear plastic bag so that the dials can be turned to adjust your FiO2, TV and rate...and trigger manual breaths if needed. The O2 regulator will be your first stage and the ventilator would be your second. A way of sealing this bag to the other tubing including the circuit must be found. Superglue might work as it'll really bond all the plastic together and prevent leakage into the bag. The vent circuit would then attatch to your trach tube or whichever. Coating the trach tube cuff with a little bit of an oil based lubricant like vaseline would probably prevent incidental leakage of water past the cuff, and securing the tube in place would be a really good idea to prevent slippage. Stop laughing or you'll pass out. That's my idea in a nutshell. Call it a brain fart if you wish. I hope I've given you an idea or two that will bring you closer to your dream.
