Earlier quoted context omitted.
There is a narrow range of pressure where you're not damaging the alveoli from underpressure, but not bursting the lungs from overpressure. You need a mechanical scalpel, not a butcher's knife.
Honest question: is the pressure range actually that narrow? People can survive at high altitudes, which will see pressure of 70% sea level (or less, especially when considering mountain climbing). Additionally, when SCUBA diving, something like 30 feet of depth = 1 atmosphere. I feel like I'm missing something here. Any ideas?
The pressure that must be narrowly controlled in a ventilator application is the relative pressure: the difference between the absolute pressure outside the lung (in the room) and the absolute pressure inside the lung. This relative pressure is what does all the work --- mechanically opening airways and alveoli --- and could cause all the injury.