What is an effective way to obtain use case information from preoccupied professionals?

Question

When designing a novel system in a hospital or other clinical setting, I think it would be important to gather information from doctors, nurses, pharmacists, technicians, et al on use cases for the system.

Aside from the fact that all of these are also busy professionals, what is a good way to get them to share information pertinent to their (possibly chaotic and time sensitive) workflow that would be usable in a software engineering design?