A mortal lives not through that breath that flows in and that flows out. The source of his life is another and this causes the breath to flow.
Cycling continuously through day and night, the breath empties the lungs and fills them with air. Each breath rids the body of wastes, replenishes the bloodstream with oxygen, and nurtures the cellular fires of metabolism. Breathing forms a backdrop for every activity.
But exhalation and inhalation, the two great tides of the breath, do not give us a complete picture of breathing. They are connected to a vast system of energy, a latticework of activities all woven around a central hub. Contained in that system are mechanisms that process and put energy to use. Thus, without conscious effort, we are able to maintain body temperature, circulate blood to cells, digest the food we have eaten, and eliminate the wastes accumulating inside us. This mobilization of the entire array of human functions—functions propelled by a living, vital energy—is what we really mean when we say that breathing sustains life. Under the influence of this “inner breath,” the body/mind comes alive.
According to the yoga tradition, this far-reaching system of vital energy functions through five sub-energies called the prana vayus (vayu means “wind, breath, or life force”). Each function has a distinct role, and each is integrated into the total system of human energy. If we understand the role of each prana vayu, we can grasp how the forces of prana serve the whole person and how disturbances among the pranas lead to illness and reduced quality of life. Let’s take a look at each of the five prana vayus.