This drill is notable for its rapid series of forcible expulsions.

In Sanskrit, the word Bhastrika means "bellows." You can inhale and exhale quickly, much like a blacksmith blows his bellows quickly. 

Take a seat in your preferred Asana. Keep your mouth shut. Inhale and exhale rapidly 20 times, as if you were using bellows. When you inhale and exhale, dilate and contract your chest.

A hissing sound is made when you practice Pranayama. Begin with a series of forcible expulsions of breath, one after the other in rapid succession. After 20 expulsions, take a deep breath in and do it for as long as you can safely do so before gently exhaling. This is one Bhastrika round.

Start with 10 expulsions per round and eventually escalate to 20 or 25 per round. The period of Kumbhaka can also be expanded steadily and cautiously. After one round, take a short break before starting the next. Do 3 rounds at first, then 20 rounds in the morning and 20 in the evening after some practice.

After a partial closure of the glottis, advanced students do this Pranayama. They don't make as much noise as the beginners do. Even in a standing position, they will do so.

Bhastrika treats throat pain, improves gastric burning, eliminates phlegm and other diseases of the nose and lungs, and cures Asthma, consumption, and other diseases caused by an abundance of wind, bile, and phlegm. It provides body warmth. 

It is the most powerful Pranayama technique. Prana is able to break through the three Granthis thanks to it. This practice also provides all of the other advantages of Sukha Purvaka Pranayama.

You may also want to read more about Pranayama and Holistic Healing here.