(another sneak peak from Mug’s book)
Sarva means “all”, dvara means “door”, and baddha means “bound.”  All the doors or gates where prana can escape are closed.
Sit comfortably and apply shanmukhi mudra (cover the ears with the thumbs, eyes with the index fingers, nose with the middle fingers, upper lip with ring fingers and lower lip with the baby fingers.) Keep the finger pressure light the nostrils to allow for breathing.
Breathe in slowly through both nostrils, visualizing the prana flowing all the way down to the muladhara chakra and filling the space up to the throat chakra. During the “pause” at the top of the inhalation, concentrate on the ajna chakra. Then begin a slow, controlled exhalation through both nostrils, releasing the power of the senses with the breath. Repeat several times, if comfortable.
00 LettersYogaMastersCoverA more advanced version of this pranayama is to have intentional breath retentions while visualising the ajna chakra. This pranayama leads one to pratyahara (withdrawal of the senses). As we withdraw the senses from the outward-moving consciousness, we awaken the inward-moving consciousness and the divine light of the third eye. Awakening the third eye gives us knowledge of the Self.

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Excerpted from Letters from the Yoga Masters: Teachings Revealed through Correspondence from Paramhansa, Yogananda, Ramana Maharshi, Swami Sivananda, and Others by Marion (Mugs) McConnell, published by North Atlantic Books, copyright © 2016 by Marion (Mugs) McConnell. Reprinted by permission of North Atlantic Books.