I think that the main challenge project management for medical devices face is the lengthy time of certain projects. This is mainly due to the rigorous protocols and strict regulations enforced by the FDA or other regulatory agencies alike. Since medical devices are in direct contact with humans, testing can be quite a challenge where specific protocols have to be followed to ensure the validity of the results. Also, since its a system that can be incorporated into a human, testing can yield variable results due to the dynamics of the various organ systems present in humans; where these results can greatly influence the parameters initially set for the device. Add to that the strict regulations enforced by the FDA, due to human subjects; your timeline can be drastically lengthened.