Here is an interesting commentary on breath, and how it can lengthen our lives, from the following link: http://www.yogabound.com/yoga-asthma-pranayama-yoga-breathing-for-asthma-relief/
Breathing and Life Span
Slow, deep and rhythmic respiration sublimates, and is stimulated by calm, content, states of the mind. When you breathe incorrectly it disrupts the rhythms of the brain. This leads to physical, emotional, and mental blocks. This in turn leads to inner conflicts, imbalances, personality disorders, destructive lifestyles and disease. By establishing regular breathing patterns through your Pranayama practice, the process is reversed, and negative cycles are broken. In yogic terms this is essential for concentration (Dharana) and meditation (Dhyana). In practical terms this leads to happier, healthier and more balanced states of mind.
In addition to influencing the quality of life, the length, or quantity of life is also dictated by the rhythm of the respiration. The ancient yogis and rishis studied nature in great detail. They noticed that animals with a slow breath rate such as pythons, elephants, and tortoises have long life spans. Where as, those with a fast breathing rate such as birds, dogs, and rabbits, live for only a few years.
From this observation they realized the importance of slow breathing for increasing the human lifespan. Those who breathe in short, quick gasps are likely to have a shorter life span than those who breathe slowly, and deeply. On the physical level, this is because the respiration is directly related to the heart. A slow breathing rate keeps the heart stronger, and better nourished, and contributes to a longer life.