That's a good question. I view them as separate but interrelated, and often times I'll practice pranayama without doing a corresponding meditation (e.g. after asana).

Pranayama in many ways is exercise which readies you for meditation. The Anapanasati Sutta makes reference to a form of it as a preparatory practice. It has helped me investigate and understand bodily sensations that arise in meditation that previously would have been distracting to me. Or to not be overwhelmed with fear or thoughts in meditation when occasionally you realize "hey, I actually haven't been breathing for a while".

Happy to talk about it more off thread if you'd like (email in profile).