Not the person you're responding to, but my experience as a runner and someone who practices breathing is that it does engage some specific mechanisms that promote certain kinds of blood flow. I think your intuition here is off, and you're treating the body as a pretty simple machine rather than something that has some pretty sophisticated feedback mechanisms between the mind and the body.
As I said, I am open to explanations that this is a mind/body effect.
I am not open to explanations that breathing fast/deep in itself, through the extra blood flow that it can obviously generate, are directly therapeutic for arthritis. This was, by my understanding, GP's preferred explanation.
