I really would not use blue tooth or usb for that matterfor such a simple project.Mostof the design work is going to be dedicated to writing stcks forthosedevicesand its going to be a pain in the bum.
All I would do is use a medical,scientific,technical radio link using one of the many available radio modules and the jobs is done.
My reason for saying this is blue tooth is a REALLY REALLY nasty protocol with huge overheads i would forget all about using it if i were you,but thats just me.