Purpose of nadi shodhana
Nadi shodhana pranayama is also a term coined by Sri Swamiji. In kriya yoga, inhalation and exhalation are known as arohan and awarohan, ascending and descending breath. In the language of classical pranayama, nadi shodhana is known as anuloma viloma, inhalation and exhalation, or anuloma and viloma, respectively. These are the names you will come across in the yogic literature: anuloma viloma and arohan awarohan. You will not find the name nadi shodhana.
Sri Swamiji gave the name nadi shodhana to the pranayama of arohan awarohan or anuloma viloma as it indicates the purpose of the balancing pranayamas. The nadis are the conductors of prana shakti; shodhana means to clean, to purify. What is being purified and cleaned here are the passages that conduct the prana shakti throughout the body. In most other traditions, the practice of alternate nostril breathing is spoken of only as anuloma-viloma, which means inhalation-exhalation.
However, Sri Swamiji used the term nadi shodhana, for that is the term indicating the purpose and depth of the practice. It is not only about breathing in through one nostril and out through the other. The nadis are the conductors of prana shakti; shodhana means to clean, to purify. Through this practice you are purifying and cleaning the passages that conduct the prana shakti throughout the body.
You will have learned that there are 72,000 nadis in the body. Many people think of the 72,000 nadis as nerves in the body, or as channels like the arteries and veins, but nadis are more subtle; they are the pathways of prana. Nadis were originally defined in marma vijnana, the knowledge of marma, which was the forerunner to acupressure and acupuncture. Marma vijnana is the original practice, which was developed further by the Chinese and named acupuncture and acupressure.
These flows of prana are controlled and guided by two major nadis: pingala and ida, the solar and lunar energies, prana shakti and chitta shakti. Prana shakti manages the physical behaviour of the body and chitta shakti manages the subtle behaviour of the mind. They are not two different things; they are part of the same. You have muscles and you have strength.
A muscle is physiological, made up of fibres; strength is not physiological, it is just the strength of those physiological fibres. If you see a muscle, there is bound to be strength; they are part of the same structure, although the muscle and strength can be experienced separately as well.
Prana is like a muscle and chitta is like the strength of the muscle; they function together. Prana is the one managing the body: the movement, nourishment and sustenance of annamaya kosha, and chitta is the subtle one managing the internal, mental functions and the psychological and psychic behaviour.
Ida and pingala are the two main pathways for the flow of prana, one gross, the other subtle; they control all the nadis in our body. Every other nadi flows out of them and purification of these two nadis is the primary purpose of nadi shodhana pranayama.
From the book “Progressive Yoga Vidya Training, Series 4”, pg. 22-23, Sw. Niranjanananda Saraswati