Fuzzing seems like a really useful test for this.
Either way, I agree I'm not really subscribed to the idea that DIY life critical systems are a good idea beyond POC.
Maybe it isn't life critical but only quality of life critical?
If it pumps too much you're dead - which is why I'm considering it life critical.
Not enough is also bad but hopefully they'll notice and can act accordingly - still a threat too though.
It's not that we're all saying this is an unsafe machine, we're saying that a random person DIY'ing and using such a solution is very risky, there's a reason why commercial medical equipment requires rigorous testing/certifications, etc.
There's so many pitfalls here where teams of engineers with the whole part spec and from different disciplines have failed before. It sounds very dangerous.