Pranayama is the fourth limb or step of ashtanga yoga, as set out by Patanjali in the Yoga sutra. It is made up of two words prana means breath or bio energy in the body and yama means control hence pranayama is the control of breath or bio (pranic) energy. It is done by regulating the breathing and holding the breath in between for certain periods of time to calm the mind and relax the body to experience higher states of consciousness. The practice is an integral part of both hatha yoga and ashtanga vinayasa yoga in the execution of asanas. Patanjali in yoga sutras mentioned pranayama as means of attaining higher states of awareness, holding of breath is an important practice of reaching Samadhi.
FIVE TYPES OF PRANAYAMA
Prana, Apana, Vyan, Udana and Samana are responsible for various pranic activities in the body. Out of these prana and Apana are most important. Prana is upward flowing and Apana is downward flowing. Practice of pranayama achieves the balance in the activities of these pranas, which results in healthy body and mind.
The breathing procedure of the pranayama should be taught to the practitioner to avoid any harmful effects. Pranayama involves mainly of two activities inhaling and exhaling. In Yogasutras of Patanjali, inhaling is termed as Rechaka. The state when these two activities are made to halt has been termed as Kumbhaka. The breathing rate may be: 
(1)- QUITE BREATHING: smooth continuous naturally without any efforts.
(2)- DEEP BREATHING: First, the movements concerned with inhaling and exhaling are to be controlled in order to further slowdown the breathing at the same time the need of oxygen for the body is to be lessened. So that the speed of breathing can be further slowdown. The constitution of the body is such that if the need or use of oxygen is not reduced it becomes difficult or rather impossible to control the process of breathing. The easy way to reduce the need of oxygen is to stop the movements of the body and try to relax all the muscles. After some times the practitioner finds it difficult to do the deep breathing further, at this junction he or she should return to the neutral breathing and rest for a while. After taking rest the deep breathing should start again. After practising deep breathing with equal time and speed successfully one should start studying it by increasing the for exhaling. If inhaling (Puraka) is in four seconds, then exhaling (Rechaka) shell take 5 to 6 seconds instead of four. This need special efforts. When a person succeeds in doing inhaling and exhaling at the ratio of 1:1 for 10 to 15 minutes. He should double the time for exhalation. The ideal ratio for inhaling-exhaling is 1:2. 
(3)- FAST BREATHING: When the speed of the inhaling and exhaling is more than the deep breathing is termed as fast breathing. In the fast breathing the practitioner should increase the speed of inhaling and exhaling, however short breathing is not practised. The practitioner has to practice continue the cycle of quick breathing with constant practice. This short of breathing is easy to understand and to practice also. The fast breathing clears the nasal passage and exercise the part involved in the respiratory system. During fast breathing there is a feeling of whirling sensation in the head which may be considered to be normal, but soon as it occurs the practitioners should return to the quite breathing and then after sometimes comes back to the fast breathing. Making habits of the fast breathing can remove such kind of sensation. To practice the fast breathing the practitioner sits in one of the following asasna: Padmasan, Vajrasana or Swastikasana. The eyes are closed and the practitioner concentrates in the breathing to achieve maximum results.