Here is a link to a book by James Nessor, The Lost Art of the Breath. This link takes you to the introduction of the book and was published by the Guardian. I highly recommend this book!
Here is an interview by Patrick McKeown of Buteyko International of James Nessor about his book and his experience with researching the breath. Patrick is the author of Oxygen Advantage, another book highly recommended. If you have any questions related to the article or the video, I can help. I am a certified Buteyko Practitioner and I currently work with individuals experiencing breathing pattern imbalance and dis-ease.