In Pranayama one begins first by observing and getting acquainted with the breath in order to perceive the sensations that arise in the lungs during the breathing process.
Pranayama is the practice of observing, refining and extending the breath. It is a way of controlling your life force energy. It is the fourth limb of Asthanga Yoga, right after asana.
I used to be a Vinyasa Yoga teacher. Over the past several years, I have been gradually changing my teaching style. Because I felt that the style of yoga I had been practicing was injurious to my body, I decided to go back to my Iyengar roots.