I don't know enough about the fan controller chips, though, to do this. Does anyone have an opinion?
Finally here's the best open source project I've seen as a starting point:
https://panvent.blogspot.com/
The problem is that ventilators require tubes to be inserted into the patients lung. This requires a very skilled doctor and has a risk of infection and injury.
So I am making an wooden lung - like an iron lung but made from plywood. I can share the plans and sourcing for the parts if you want.