What about building a negative pressure ventilator?
A negative pressure ventilator (sometimes colloquially called an “iron lung”) is a mechanical ventilator that acts by intermittently lowering the pressure around the patient’s abdomen to less than atmospheric pressure, mimicking the natural function of the muscles and diaphragm to allow the patient to take in air.
This can be accomplished with either a large tank surrounding the patient’s body, or a smaller jacket-like device worn by the patient. These have been widely used for breathing difficulties caused by neuromuscular disorders, but their safety and effectiveness in pneumonia and ARDS is poorly studied.
In addition, most forms restrict access to the patient’s body, and most medical professionals are not familiar with their use.