The rules for filming what are normally very private conversations must be very strict. I suspect that, as part of an "informed consent" process, people are only permitted to give such consent if they've discussed the matter with a friend or relative first. (It would be somewhat similar to signing a Lasting Power of Attorney, where the donor must discuss its implications with a suitable third party before being able to grant the power of attorney). That person then acts as a chaperone to the patient during the consultation, explaining why there's always someone with a patient when they enter the room.
That's just my guess though!