Samana Vayu is one among the five principal vayus. Samana Vayu in Yoga is the vital airs or vital energies. The five principal vayus are prana, apana, vyana, udana and samana. The vayus are supposed to flow along the nadis or channels inside the body and bring about various life activities by supplying the vital energy required for them.
Like other four vayus, Samana Vayu is also derived from prana. Prana is the one single source of all vitals airs. It is universally present life principle. Prana can be imbibed from the atmosphere by every living being through the process of respiration.
As per Darshana Upanishad and Vedantasara, the Samana Vayu is said to be the supplier of nutrients to all body parts such as muscles, glands, conducting tissues, bones, skin, etc., taking them from the food which is digested by it in the stomach with the help of prana.
Importance of Samana Vayu is also mentioned in Trisikhi Brahmana Upanishad (81 and 86) and Yoga Yajnavalkya (IV – 48-72).
Shankaracharya defines samana as which supplies equitably (samain nayatiti samanah) – (Chandogya Upanishad Bhashya 3/13/4).
In the human body there are said to be 72 thousand nadis spread over all parts and samana vayu flows through them all. Hence, through the agency of samana vayu, nutrients can be supplied to every part according to their needs, supporting the life activity. If there is any obstruction in these nadis, this activity is hampered, causing disorders and diseases.
As per Hatha Yoga Upanishad (II:3-4), practice of pranayama helps to purify the passages of the nadis and makes for perfect health.