(Chitta gets purified) by expelling and preventing entry of breath also.

Breath is often called the doorway to the inner world. We are constantly exchanging prana with the world outside through the medium of breath, taking in pollution of thoughts and matter, which interfere with our own pranic frequency. By gaining control over prana, one can control what he/she has to absorb and expel and thereby keep the mind and body toxin free.