In the early fifties, Paul Reps was studying under Swami Laksmanjoo when Laksmanjoo was beginning the effort to translate the Bhairava Tantra into English. Reps in Zen Flesh, Zen Bones noted two inaccurate things: that the text was 4000 years old and it was the basis for Zen. Fortunately, the person (Jaideva Singh) working with Swami Laksmanjoo on this translation into English project correctly noted the 7th Century origin for this tantra. The text is a product of Kaulism tantrums (of the Kula System). Singh's book came out about 12 years before Swami Laksmanjoo died in 1991.
Around four thousand years ago there were probably concentrative type practices that included breathing exercises by wandering bands (and solo folks) associated with the Vratya Brotherhood. Warrior ascetics. The 112 forms of meditation focusing here are a much more elaborate "system".
A beautiful piece of work.
You don't hold your breath. Just feel the thought free space between the inhalation and exhalation, and enjoy that primal "pulse" or throb or vibration of Consciousness Itself.