Pranayama is important in Hatha Yoga because only by controlling breath a Yogi is able to bring about steadiness of his mind. Breath is important in the body because as long as breath stays in the body there is life, the moment it comes out it is Death. Pranayama can be performed by a Yogi only when the intellect is free from all kinds of tama and raja activity or sloth.
Pranayama is performed sitting in the position of Padmasana. The yogi should inhale the air from the left nose (chandra) and should exhale it from the right one (surya). The next time air should be taken in from the right nose and should be exhaled from the left one. The process of inhalation and exhalation in Pranayama should be performed in a relaxed manner and not in a forcible manner. The inhalation and exhalation of air should be continued alternately that is once the air should be taken from the right nose and once it should be taken from the left one.
The constant practise of such breathing cleans the nadis. They become free of all impurities. Kumbhakas should be practised by the yogi in the process of Pranayama daily. In the beginning Kumbhakas may bring about perspiration and quivering but ultimately it brings about steadiness. In the stage of steadiness the breath is made motionless and steady.
In the first stage of the Pranayama there are certain restrictions which the Yogi should adhere to. For example a diet of milk and ghee is recommended but once when the practise becomes established no such restriction is required.
Proper practice of the Pranayama eradicates all kinds of diseases but improper practise of Pranayama may generate disease in the body of the Yogi. Diseases which are caused by the improper practice of Pranayama are hiccough, asthma, and cough, pain in the head, the ears, and the eyes.
It has been mentioned in the Hatha Yoga Pradipika that proper practise of the Hatha Yoga are sometimes seen outwardly like the individual gains a lean and glowing body. When such signs appear a practitioner can be sure of success of the Pranayama that is practised. With the proper practise of the Hatha Yoga ones appetite is increased, body becomes healthy and the divine sound gets awakened. It has been said that those who have excess fat in the body should practise the six kinds of duties which are namely Dhauti, Basti, Neti, Trataka, Nauli and Kapalbhati. These six kinds of actions should be kept secret in order to achieve success from them.
Pranayama has the capacity to eradicate the fear of death from the minds of a Yogi. Moreover as long as breath is restrained within the body till then the mind is undisturbed and calm. Steadiness of mind is attained in Pranayama with the help of Kumbhaka. In fact it can be said that Kumbhaka is the best way to attain success in the process of Pranayama. There are eight kinds of Kumbhaka. They are Surya Bhedan, Ujjayi, Sitkari, Sitali, Bhastrika, Bhramari, Murchha, and Plavini.
Thus, it can be said that Pranyama brings about control of the breathing process and as the breathing process is controlled the mind of the yogi also gets gradually controlled and there are outside manifestations of a successful Pranayama like lean and glowing body, clear eyes and a growing appetite.