Getting access to devices is definitely a big hurdle, but there are people working in this area already. Maybe you could contribute to framework engineering in collaboration with groups who can get (or reverse engineer, more likely) communication protocols on specific devices. Here are a few links to get started:
http://conferences.sigcomm.org/sigcomm/2012/medcomm.php (google the speakers and organizers)
http://repository.upenn.edu/cgi/viewcontent.cgi?article=1525...
OpenIGTLink is working on something similar for surgical navigation (http://openigtlink.org).
(See this comment for some more general suggestions: http://news.ycombinator.com/item?id=5089663 )