Day 91 

It is natural to obstruct the flow of breath in an asana. Patanjali said that it is obstructing the natural flow of your breath because it is not natural at all. You have made your breath very unnatural. 

So whatever you feel is natural, is not actually natural. We have to return to the natural way of breathing. We do this by gati, breaking its movement. We break its movement consciously by breathing deep, long and subtle, with counts and by keeping our attention on different parts of the body. 

In just one sutra, Patanjali has described all the pranayamas.

Breathe in, hold, breathe out and hold - with different counts and with attention on various parts of the body. That is all. Most of the pranayamas are there in one sentence; in one sutra. 

But there's one more pranayama, which happens automatically. When all the thoughts and ideas are cleared from the mind, there is a natural pranayama. It throws out all the impurities from the mind. That is the fourth pranayama. Patanjali said that pranayama should be learnt with proper guidance. 

It is not to be done on one's own and anywhere. The pranayama which happens all by itself and without any effort is the fourth pranayama. You go deep and the pranayama starts. It breaks the routine way of breathing. It assumes or forms its own rhythm. This is the fourth type of pranayam.

Gurudev Sri Sri Ravi Shankarji 

PATANJALI YOGA SUTRAS