Please see Johnny Lee’s ventilator project (the video gives a great overview): https://github.com/jcl5m1/ventilator). It's a $50 USD ventilator. It's a working starting point.
The idea here is a make a better $50 ventilator: a more flexible and robust device that could be suitable for production in quantity. A ventilator with a microcontroller, airflow and pressure sensors, and a digitally controlled blower, can potentially perform any ventilation ‘mode’.
There are plenty of good ventilator designs. There are many manufacturers of simpler ventilators (still $thousands) that could increase their output for a couple of weeks. (ICU ventilators probably have complex supply chains, and the tooling may not be set up for high-rate production.)
Consider Egypt, 100m people living on a thin strip of land by the Nile, the Philippines, rural Ukraine, India. A yearly salary wouldn’t cover a Chinese ventilator. This design has potentially few parts. Tooling up means machining a few molds. Email gerbers to a PCB house. Get a few automatic screwdriver machines etc.
This Google doc (https://docs.google.com/document/d/1KpPWYRb1A637Cp5KIhhKtuGFS8Cdm5fGra3TTwwrBKo/edit#) is a proposal for progressive further development of Johnny's design, component by component. There's also some useful resources and information that I have collected from the last couple of days of discussion on helpfulengineering.slack.com , and elsewhere.
Discussion of this proposal has taken place on https://join.slack.com/t/open-ventilator/shared_invite/zt-cwh6py1x-C5tO4JewMUf2tRN7rwWB~g