I really like this as DIY - I also found this video https://www.youtube.com/watch?v=okg7uq_HrhQ - explaining how the virus eventually kills by causing failure of the lungs. After explaining the functional parts he goes on to explain what seem like some interesting things to consider when designing a ventilator with respect to how they were used during the SARS outbreak. e.g. tidal forces causing iteration and more inflammation, which then cuts off more air flow. So thinking about how you maintain a constant air pressure instead of more pushing force... at least the explanation made sense intuitively but I'm not a doctor and don't know if this video or your Ventilator are safe - but I do like the DIY aspect of it and figure thinking about or sharing ideas can't be bad...