The Diaphragm and the Phrenic Nerve
"The diaphragm is the muscular equivalent of an umbilical cord, linking us to the environment: it keeps us alive by pulling fresh air into the lungs and returning used air back out into the world. This process is not a mindless one, but is very responsive to our thinking. The word 'diaphragm' is related to the Greek word for mind: the diaphragm muscle is controlled by the phrenic nerve, and its Greek root, phren, designates the mind as well as the muscle. The Merriam-Webster dictionary (1991) definition of the word 'phrenic' is the following: '1. Of or relating to the diaphragm. 2. Of or relating to the mind.' Considering such an odd dual meaning, one might conclude that the Greeks were confused, but the confusion is rather in the modern mind which attempts to separate mind and body into separate compartments. Ancient physicians had only their native senses for observing the action of breathing in themselves and others. This provided what no modern mechanical breathing monitor can offer - simultaneous registration of mental and breathing processes. With this opportunity for observation, parallels and correlations could be drawn between moments of emotion and changes in breathing rate, depth, regularity, and bodily placement. Interruption of attention, style of focusing, state of calmness or distress, degree of mental effort - such 'mental' variables can be observed in oneself and to a degree in others. These variables all interact with the breathing pattern via the phrenic nerve."
Multidisciplinary Approaches to Breathing Pattern Disorders by Leon Chaitow