Your post revived some memories of my youth, more than forty years ago.
I had then a long standing relation with a charming and a bit crazy girl who was very much into medfet. She had established the rule that every time we had sex, she would before submit me to a complete médical exam. I accept this game because I loved her and did not want to compromise our relationship.
The first rule of the game was that I had to be stark naked while she kept her clothes on. She was in fact ashamed of her body, considering she was skinny and her breasts were too small
A large place of the exam was devoted to my penis and testicles. She retracted my foreskin several times and occasionnaly, she mesured the length of my pénis.
The exam allways ended with her taking my rectal temperature, usually on her lap, but also some times me standing up, on all four, or in the so called diaper change position
Stheting was of course a large part of the exam. She had borrowed a high quality stethoscope ( Litmann) from her sister who was a doctor. I had told her I was ( I still am) afraid of doctors, but she had answered she knew nothing about cardiology and would not be able to tell if I was diing. Some times she would let me listen to my heartbeat and I must say I found it facinating. On some rare occasions, she opened her blouse and let me listen to her heart and that was even more exciting.
As one of her hands guided the stethoscope on my chest, her other hand very often played with my erect niipples and that was also very exciting.
In fact, those mock medical exams quickly became for us as important and as arousing as the ''real'' sex we had after.