Prachhardana vidhaaranaabhyaam va praanasya
Vidhaaranaabhyaam: Preventing from entering
Va: Or / also
Praanasya: Of the prana
Patanjali lists one more way to purify the chitta.
(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.