Before commencing pranayama, any imbalance in the dosha should be removed – excess body fat should be reduced, mucus blocking the respiratory tract should be removed, gas in the stomach and intestines eliminated, etc. In hatha yoga there are six particular practices which were specifically designed for this purpose. They are called shatkarma. Shat is ‘six,’ karma is ‘action.’ These techniques regulate the production of the doshas.
:- Hatha Yoga Pradipika