An excerpt from a BKS Iyengar interview taken from the Astadala Yogamala, Volume 7, says it all.
“…I had tuberculosis as a young man and bouts of other diseases that had compromised my lungs. In 1984 I was in San Francisco for the first Int’l Iyengar Yoga Convention and some doctors insisted I undergo a test to study my lungs. They wanted to see the chemical changes taking place in my body on account of regular practice of asana and pranayama. “Sir, we are sorry to tell you that you are going to live long and our study has shown that your lungs are that of a twenty-four year old athlete.” So when you have such good lungs. You have a long life in front of you. I was already sixty-six at that time….”
For an amazing demonstration of Pranayama by BKS Iyengar watch this video!