Nadi shodhana pranayama is a hatha yoga practice that purifies the nadis (energy channels in the subtle body) through alternate-nostril breathing. Shodhana means “to purify.” The practice balances the flow of vital energy, or prana, through the ida (the left, or moon) and pingala (the right, or sun) nadis, as well as the flow of breath through the right and left nostrils.
This pranayama practice begins and ends by breathing through the left nostril. Some pranayama practices can create heat in the body, but concluding the practice by exhaling through the left nostril neutralizes any excess heat that may have accumulated.
We can also investigate this practice on another level by taking a deeper look at why one should begin and end nadi shodhana with the left nostril. In pranayama practices, the left nostril provides access to the ida nadi, the right to the pingala. One purpose of nadi shodhana is to restore balance to the flow of prana through these nadis. Once balance is restored, the practitioner may have the means to practice hatha yoga, which focuses on resolving one’s past karmas with others as well as one’s own perception of his or her ego-bound self.
The aim of all yoga practice is enlightenment. What is realized in the enlightened state is the Oneness of being. The biggest obstacle to that realization lies in misperception of oneself and others. So the practices must address this misperception of self and others if they are to aid in giving rise to enlightenment.
One of the primary aims of hatha yoga practices is to facilitate the movement of prana into the sushumna nadi (the central energy channel in the subtle body), which would cause consciousness, or kundalini, to rise, ascend, expand or evolve toward the realization of the Oneness of being. In order to do this, balance must first be brought to the ida and pingala nadis.
Everything we do creates karmas. The body we have now is made up of all of our past unresolved karmas. The Sanskrit word karma is derived from the root kr, which means “to act.” Karma means “action.” An action can be a thought, a word or a physical function (like breathing).
Through avidya, “mis-knowing,” we mistakenly view others not as who they really are, and we also mistakenly perceive ourselves as separate and disconnected from others. Avidya is really a case of mistaken identity.
We can be unkind to someone only when we are deluded through avidya and perceive him or her as not part of ourselves. When we are unkind to others, energy that could be moving into the sushumna nadi, and bringing about enlightenment, is instead drawn into the pingala nadi, or sun (surya) channel. When we are unkind to ourselves, energy is drawn away from the sushumna, away from enlightenment, and into the ida, or moon (chandra) channel. Nadi shodhana resolves this energy imbalance.
How we treat others determines how others treat us; how others treat us determines how we see ourselves; how we see ourselves determines who we are.
Nadi shodhana, a practice of balancing the sun and moon, is a metaphoric way of describing the transformation of our perception of self and other. Through yoga practices, we discover who we are. So we begin our pranayama practice with who we think we are, by inhaling through the left nostril, and we conclude by exhaling through the left, where we began, but hopefully with the perception of ourselves somewhat transformed. Through abhyasa and vairagya (consistent and detached practice), we begin to melt away the avidya that keeps us separate from others, from nature, from God, separate from the realization of the Oneness of being, and the truth about ourselves and the reality in which we live, and share, with others.
For best results, nadi shodhana should be done before asana practice, or after shavasana and before meditation, but never in the middle of a sequenced practice of asana.
Use Vishnu mudra to facilitate the passage of air through the nostrils: Bend the first two fingers of the right hand into the palm, using the thumb to control the passage of breath through the right nostril and the ring (or third) finger to control the passage of breath through the left nostril. At the beginning, it is important to equalize your ability to inhale and exhale, using a ratio of 1:1, without retention. Exhale through both nostrils. Block the right nostril and inhale slowly through the left. Block the left nostril and exhale slowly through the right. Slowly inhale through the right, block the right nostril and exhale slowly through the left. That is one round. Practice five to ten rounds every day for at least one month. This is a safe practice level for beginners if all other prerequisites have been met, including the adherence to a vegetarian diet and mastery of asana (the ability to sit comfortably).
The next step would be to add retention using the ratio of 1:1:1:1. Exhale through both nostrils, block the right nostril and inhale through the left, block the left nostril, retain, exhale through the right, block the right nostril, retain, inhale through the right, block the right nostril, retain, exhale through the left, block the left nostril, retain. This is one round of samavritti (equal breathing) nadi shodhana pranayama.
NOTE: For further reference, see the Hatha Yoga Pradipika, Chapter 2, Verses 1 to 20, by Swami Muktibodhananda of the Bihar School.