I've been seeing a lot of ventilator engineers popping up everywhere! It's great seeing such brilliant ideas come to life! However, building a mechanical ventilator is just 1 part of the overall system. The hard part comes in when you have to account for things like injecting precise doses of Oxygen (which vary by the patient) all while controlling humidity (which also varies by the patient). Another challenge to ventilator systems is adding Monitoring/Alarms/Dynamic-Adjustments so you don't have to babysit such a complex feedback loop between it and the patient. Nurses generally have to monitor more than 1 patient at any given point in time. This is where these additional necessities come into play so that they can allocate their care time appropriately. Feel free to add your thoughts.
The big thing I can think of is assisting the patient with breathing when needed, yet allowing the patient to still breathe naturally when they can. Things like not forcing air in when the patient is trying to exhale, or removing air when the patient is manually drawing in a breath..
Great article for non-professionals. Starts with how lungs work and what in lungs needs to be taken into account for a ventilator design. Adds such things as maintaining temperature and humidity - while fighting bacteria which like such an environment. You either spend quite some time working around ventilators (the name is rather misleading - it's a complex device) or you'll learn a few important things when reading this.