Breathing is a very basic phenomenon concerning life. It is intimately concerned with the biochemical process of obtaining energy from digested food materials. Every cell and tissue of an organism's body depends continually for its life activity on the energy derived from oxidation of the digested food materials, and as this process cannot go on without a continued supply of oxygen to the cells and tissues, almost all forms of life seem to depend very largely on the process of breathing. For the sake of description, this process may be conveniently divided into two parts, one connected with the external environment, the other with the internal environment. Taking oxygen from the external environment into the body constitutes the first part of breathing, while making the oxygen available to every cell and tissue, is a function of what may be called internal breathing. In human beings, as we have noted earlier, the first part is played by the respiratory system, and the second by the circulatory system.
We do not know if our ancient masters of yoga were aware of the fact that the air we breathe in is a mixture mainly of three gases, namely, nitrogen, oxygen and carbon dioxide. They knew it fully well however, that life activity depends fundamentally upon the vital air which they called "Prana".They distinguished ten different forms of this vital air. These were supposed to be responsible for performing different functions in the body. Five of these ten vayus were supposed to be more important. They are: Prana, Apana, Vyana, Udana and Samana. As declared by the great Shankaracharya "one and the same prana becomes known as the five vayus due to diversity of functions."
The location and functions of the ten vayus are found described in many yoga texts, (e.g. Trishikhi-brahmanopanishad, mantra ; Yoga Yajnyavalkya ; Chhandogya Upanishad,; Amritanado-panishad and so on). We do not have space here to go into the details of these. We should note one fact, however, namely, that the word prana was in use in the Sanskrit language since very ancient times, and has been referred to at several places in the Vedic literature. It is said in the Atharvaveda that the activities in the body are based on prana and apana. The same text at another place has compared the relation of prana with the world of living beings to that of a father with his son,declaring that "prana is the fundamental basis of whatever is, was, and will be". The word "Pranayama", however seems to be of a later origin.
