Pranayama balances, strengthens, and increases life energy. The result is a peaceful mind, the foundation for expanded awareness.
Prana is a Sanskrit word derived from two roots; pra represents "continuous" and na means "movement". Thus prana flows in continuous movement. Svara is the Sanskrit word for the flow of prana. Svara is defined by the qualities of the breath and the pranic flow.
Yogis control the breath in order to have peace of mind.
Citta-Santi
The great Indian scholar, Swami Vivekananda, who originally brought yoga to America is 1893, said, "One of the greatest discoveries of the yogis is that prana follows the mind." This is why the yogic teachings say that one of the greatest ways to control the mind, thus attaining the state of yoga, is through pranayama.
The word 'pranayama' has a rich interpretation. It contains the word Prana, which is the essence of all matter and form in the universe - the life force of creation. It also contains both the words 'yama' or 'ayama'. Yama means restraint. Ayama means expansion. Thus, pranayama includes breathing techniques to control the breath while expanding the life force.
The definition of pranayama should not be limited to breathing practices. Breathing practices are techniques within pranayama to increase the life-force. To increase prana, one must gain greater awareness through the control of thought-waves in the mind. This must be reflected in the way one lives their life. Through greater awareness of prana, consciousness expands. Therefore, pranayama is a way of living in harmony with the body, mind, and spirit.