7-8. DIAPHRAGMATIC (ABDOMINAL) BREATHING
The diaphragm is a thin, but strong, dome-shaped muscular membrane that
separates the abdominal and thoracic cavities. The abdominal wall is elastic in nature.
The abdominal cavity is filled with soft, watery tissues.
a. Inhalation. As the diaphragm contracts, the dome flattens and the
diaphragm descends. This increases the depth (vertical diameter) of the thoracic cavity
and thus increases its volume. This decreases air pressure within the thoracic cavity.
The greater air pressure outside the body then forces air into the lungs.
b. Exhalation. As the diaphragm relaxes, the elastic abdominal wall forces the
diaphragm back up by pushing the watery tissues of the abdomen against the underside
of the relaxed diaphragm. The dome extends upward. The process of inhalation is thus