The paper International Space Station Medical Operations mentions
Private medical conferences (PMCs) are conducted regularly and upon crew request with the ISS crew via private audio and video communication links from the biomedical MPSR (multipurpose support room) at MCC Houston.
What specific changes to the audio communications loop setup are done to "privatize" the loop?
(Info about the video link would be OK but I'm primarily interested in the Space-to-ground audio loops).
Do the configuration changes take place solely in the Mission Control Center, or are changes to the onboard voice loop configuration required?
Inspired by this question Can an astronaut have a private communication during a spacewalk? to ask something I've been meaning to ask for a while.
An acceptable answer would describe the nominal, non-privatized audio loop configuration inclusive of the astronaut at ISS and the person they are communicating with at MCC, and then describe the specific changes that are made to privatize it.