For some more scientific based explanation of how Wim Hof's breathing and cold meditation methods work, you may enjoy checking out a blog/podcast by a neurosurgeon named Jack Kruse.

He gets very detailed and in depth about the physiology involved with cold and why it's good for humans. He can be hard to read since I personally don't have the biology background needed to understand all of his terms and explanations, but in his podcasts he usually presents his information in ways a person of normal scientific literacy can understand.

Thanks for the piece on a very interesting subject!