They must use a hart rate monitor or some device that measures blood flow to the vagina like you suggest. I think Sexologists usually use a full EKG and measure a collection of different physiological responses, like hart rate and respiration, for both men and women.
Just horrible. And people always like to talk about the 1990s like it was some sort of perfect time in history. This show seems to match with how many of these people are just gay men who want to be come women as part of their gayness. Also the "women" guest on the show looks like a man. The whole show is just tranny propaganda trying to normalise the idea in a seemingly joking way.
It's always gay men who want to live as women or Autistics who can't tell the difference between conflating feelings with the physical body and reality. There is of course individuals in the military who are brainwashed by the military to undergo the procedure, so it really is just Nazi level mad scientist experiments. What else would you expect from the mind of a New Zealander?