Re: Patient circuits/Patient connection/Applied parts
An applied part is a part of the equipment which needs to contact the patient in normal use. Issues associated with applied parts include electric shock, burns (thermal) and biocompatiblity.
A patient connection is a part of the applied part through which current can flow, so it is purely an electrical issue. Also it is possible that a single applied part (such as an ECG) can have multiple patient connections (e.g. RA, LA, LL, etc).
A patient circuit was a defined term in the 2nd edition, but this has been left undefined in the 3rd, and only appears twice and one time seems to be a mistake and the other in the rationale. The idea was to capture the electrical circuits that extend into the medical device, such as an ECG circuit. It's still a good concept, but not one that needs to be written into the standard (you don't have to have a patient circuit, in other words).