From Richard Rosen’s “The Yoga of Breath”:
“How does an inefficient breather breathe? She’s inclined to breathe too shallowly, mostly high in the chest because the diaphragm is stuck, and too fast – she hyperventilates, which makes the flow of breath turbulent. She often breathes through the mouth, which is universally censured because it reinforces hyperventilation, and under extreme stress she’ll tend to hold her breath. Shallow, fast breathing reduces carbon dioxide in the body, which constricts blood vessels and slows the circulation of blood and oxygen to the body and brain. Oxygen starvation chronically excites the the sympathetic branch of the autonomic nervous system and the fight-or-flight response. So the heart beats rapidly or irregularly, she’s by turns forgetful or confused, anxious or fearful, tense or irritable, and she’s always tired and emotionally drained or flat.”
Rosen asks us, “How well do you breathe?”
I highly recommend this book if you’ve ever been curious about the emphasis we place on the breath in yoga.