When I wondered out loud, how such an extraordinary thing could be achieved, Renu - his fiance and a doctor - piped up; they accomplish it by enhanced control of the vagus nerve.
"Never heard of it," was my contribution to the discussion.
"Also known as the tenth cranial nerve, it interfaces with the parasympathetic control of the heart, lungs, and digestive tract."
"Ah, heart and lungs eh?"
"It is a channel by which they can be relaxed by, say, deep slow breathing or even the application of a cold press to the upper area of the sternum."
"I was thinking more of the role of endurance training, central command, reflexes from muscle, and of the carotid-cardiac baroreceptor reflex in changing vagal tone during intense exercise and recovery, but yes, like yoga."
I'm so happy I went down the pub rather than the library opposite. It is more educational.