1-6

[Previous] [Next]

1-6. MECHANICS OF BREATHING

Breathing refers to the process of moving air into and out of the lungs. The process is usually performed automatically (without conscious thought) by the respiratory control center located in the medulla oblongata of the brain stem. The normal range of breathing rates (one cycle consists of one inspiration and one exhalation) in an adult is 12 to 20 breaths per minute. Regular, easy breathing is referred to as eupnea. Difficulty in breathing is referred to as dyspnea.

a. Inhalation. During the inhalation (inspiration) phase of breathing, the diaphragm and the intercostal muscles contract. When the diaphragm muscle (located at the base of the lungs) contracts, it is pulled downward toward the abdomen. This flattening of the diaphragm enlarges the chest cavity. When the intercostal muscles (located between the ribs) contract, they lift the rib cage up and out (chest rises). This also enlarges the chest cavity. This expansion of the chest cavity causes the air pressure in the alveoli to decrease. Air from the outside environment rushes in through the nose or mouth to equalize the pressure.

b. Exhalation. During the exhalation (expiration) phase of breathing, the diaphragm and the intercostal muscles relax. When the diaphragm muscle relaxes, it resumes its dome-like shape (moves upward). When the intercostal muscles relax, they let the rib cage return to its original position (moves down and inward). Both of these actions cause the air pressure in the alveoli to increase and force air out of the lungs, through the airways, and out the nose or mouth.

Continue with Exercises

[Previous] [Next]