I wouldnt want to use anything that has to do with health care that runs linux, because stuff from the background can interrupt it. you really should look into Microcontrollers, not microprocessors for such kind of task. Maaaaannnyyy Low power bluetooth devices run the nrf51822, and you also should take a look at it (maybe pair up with an electronics engineer student?) And no, its definatly not compact enough to be worn on a wrist, let alone the battery you would need to have to run it for half a day or so