How difficult is it to build a respirator?

[pepperbird]

a question for anyone who knows about medical technology.
How difficult is it to actually build a respirator? What were the fist models made from? Are there old models that may not be as efficient as the newer ones, but are quick to make and could make a difference? Can 3D printing be used to make respirators or their components?

[amaysngrace]

Not sure the specifics but Ford is working on a simpler type of ventilator that is using parts from their F-150s.

it should kick ass