Whatever you can get parts for, I suppose. We chose parts you can get from Home Depot and Amazon/Ebay only, except for the PCB, which you will be able to make

Whatever you can get parts for, I suppose. We chose parts you can get from Home Depot and Amazon/Ebay only, except for the PCB, which you will be able to make with hand-soldered components. Also: make sure you choose a design where it is not possible to over-pressure the lungs. Even so much as 1.5PSI can damage them permanently. As well, the design must never allow the pressure to drop below about 300 pascals (above STP), or the patient will eventually suffocate due to alveoli collapsing.