Originally Posted by
Flight Alloy
...Now at external pressure that is lower than internal lung pressure, which are being pressurized by, for sake of argument, a continuous air supply, our lungs are inflated like a balloon. This force could be multiples of the normal inspiration force that is normal. Our lungs have a limited expansion capacity before injury occurs, linings are torn, intricate alveoli and arteries ripped, they explode, baro-trauma?
Even in a decompressed aircraft, the pressure differential between the external environment and the internal lung pressure is not going to be anywhere near enough to cause damage. We are talking about low flow rate supplementary oxygen, maybe 10 litres/min, not connecting the patient to a high pressure air-line. Baro-trauma is usually the result of being too near the shockwave of an explosion, or other such high pressure events.
If you manually ventilate a patient in respiratory arrest - where the diaphragm and intercostal muscles are dormant - you can feel when you have met the elastic limit of the lungs, and any excess volume will be expelled round the seal of the mask. But even in a fully intubated patient using an automatic ventilator, you would be unlikely to cause any baro-trauma.
To try and drag this discussion back to some sort of relevance, the purpose of the passenger air masks is not to ventilate the patient, but simply to increase the partial pressure of oxygen within the mask, and therefore the lungs, to the point where anoxia does not occur.