Pranayama (Breath Control)

 

  The fourth limb of Ashtanga Yoga is pranayama. The word pranayama is made of two words: prana, "vital energy" - that which makes all life and all physical activity passable, and ayama, "expansion". Pranayama is a method of breathing through which life-supporting energy is expanded.
 Yoga (union) is achieved by stopping thought waves (vrittis) in the mind. Mental activity is correlated to breath; the more breaths there are, the more thoughts rush through the mind. The practice of pranayama, which involves a series of breathing exercises, drastically reduces the number of breaths taken in a given period. By calming the mind, it thus prepares one for concentration and meditation.
   The practices of pranayama are based on the normal breathing pattern, which has four stages: inhalation, retention, exhalation, retention. Pranayama alters the ratio of these four parts; it is designed to slow down the rate of breathing and, especially, to lengthen breath retention (kumbhaka).

Vayus
(Vital Airs)

The Vayus are five specific manifestations of prana in the subtle body, each having a certain function and location in the physical body.

In the heart region
resides prana vayu, in the anus
region apana vayu, in the naval
region samana vayu, in the
throat region udana vayu, and
in the whole body vayu
prevails.
GORAKSHA SAMHITA, 30.

  Udana vayu (rising air) functions between the throat and the top of the head; its normal movement is upright, and gives strength to the memory and intellect. In Yoga sadhana, it carries kundalini to sahasrara chakra.
  Prana vayu (viral air) functions between the throat and the naval. It controls respiration, speech, swallowing, circulation, body temperature, and perspiration. In yoga it rises kundalini to udana vayu.
  

 

 

  Samana vayu (unchanging air) functions between the naval and the heart, maintaining apana and prana vayus in a balanced state. It controls digestion, regulates digestive secretions in the stomach, liver, duodenum, and small intestines. This vayu distributes the essential parts of food, thereby nourishing the various parts of the body. In Yoga it stimulates apana and prana vayus and pushes kundalini upward.
   Vyana vayu (diffused air) functions throughout the entire body, helping all other pranas to function. It controls body movement, circulation, heartbeat, and aids the function of the gross nerves and the subtle nadis. Vyana appears as the aura around the body.
  Apana vayu (downward air) functions from the naval to the soles of the feet; its normal movement is downward. It controls digestion, excretion, reproduction, and child delivery. In Yoga it carries kundalini upward in sushumna to unite with prana vayu.