It's really a complicated subject. One of the best reads I've seen these days is https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/

It's really a complicated subject. One of the best reads I've seen these days is https://hackaday.com/2020/03/25/ventilators-101-what-they-do-and-how-they-work/ https://hackaday.com/2020/03/25/ventilators-101-what-they-do... and they explain how many factors there is to consider: it's actually "very" complicated to make right.