The Mechanics of Breathing

Simply put, breathing is an exchange of gases; oxygen and carbon dioxide between the air and the blood in the lungs.

Drawing oxygen into the lungs is called inspiration or inhalation. The point of inspiration is to bring the appropriate amount of oxygen into the blood and therefore spark the transformation of nutrients into fuel. Inspiration occurs due to a large parachute-shaped muscle called the diaphragm, which is located underneath the lungs and above the liver, stomach and spleen. As we inhale, the diaphragm drops and intercostal muscles between the ribs contract, expanding the rib cage, which lowers the air pressure in the alveoli to below atmospheric pressure, creating a vacuum inside the chest cavity. Because air always flows from a region of high pressure to a region of lower pressure, the negative pressure of the vacuum causes the air to be drawn in through your nose or mouth, down the pharynx (throat), through the larynx (voice box) and into the trachea (windpipe). The end of your trachea splits into an upside down Y-shape and forms the bronchi. Air passes through the right and left bronchus into the lungs. Inside the lungs, the bronchi branch off into smaller bronchioles, which look similar to branches of a tree. The air flows through the bronchioles, until it reaches the clusters of microscopic air sacs that collect the oxygen, called alveoli. When the air reaches the alveoli, oxygen diffuses through the membrane into small blood vessels called capillaries; this causes the carbon dioxide to diffuse from the blood into the alveoli. Therefore oxygen and carbon dioxide have been exchanged between blood and air.

Releasing carbon dioxide out of the lungs is called expiration or exhalation. Each exhalation is designed to purge the body of the appropriate amount of carbon dioxide, allowing the hemoglobin to release sufficient oxygen to the cells. After the oxygen and carbon dioxide trade places in the alveoli, the diaphragm and intercostal muscles relax and positive pressure is restored to the chest cavity. This returns the thoracic cavity to it’s original volume, increasing the air pressure in the lungs, and releasing the used CO2 out of the lungs, following the reverse of the inhalation path. The deoxygenated blood has therefore flowed out of the alveolar capillary beds, through the venules (very small blood vessels), and back to the heart via the pulmonary veins.


At least, this is how it is supposed to work... and it does, but to varying degrees, depending on our emotional health.

(see Body Breath & Voice Integrative Therapy)

The entire breathing process is repeated, in a normal adult, 6 to 14 times per minute at rest and 12 to 24 times per minute during light activity.