All credits go to Hall, J., 2020. Guyton And Hall Textbook Of Medical Physiology
Chapter 38 - Pulmonary ventilation
There are four important components of respiration:
1. Pulmonary ventilation (in and outflow of air)
2. Diffusion of oxygen and carbon dioxide between alveoli and blood
3. Transport of oxygen and carbon dioxide in the blood and body fluids
4. Regulation of ventilation
Mechanics of pulmonary ventilation
The lungs can be expanded and contracted in two manners:
1. Abdominal breath - downward and upward movement of the diaphragm: The relaxation of the
diaphragm and the elastic recoil of the lungs, chest wall and abdominal structures compresses
the lungs and causes expiration. During heavy breathing (e.g. Exercising) the elastic recoil of the
lungs, which normally suffices, are not powerful enough to expel the air from the lungs, so extra
force is generated by contraction of the abdominal muscles.
2. Chest breath - elevation and depression of ribs: All muscles
involved in the elevation of the rib cage are classified as muscles
of inspiration (external intercostals, sternocleidomastoid muscle,
anterior serrati, scaleni), and vice versa for expiration (abdominal recti, internal intercostals).
Except for the attachment of the hilum from the mediastinum the lungs 'float' freely in the thorax in
pleural fluid. This pleural fluid lubricates the movement of the lungs within the cavity. Due to the
continual suction of excess fluid into the lymphatic vessels, this creates a constant pleural pressure
which makes it seem as if the lungs are 'glued' to the chest
wall (similar to two glass objects with fluid in between). This
pleural pressure is negative (due to suction) and is about -5
centimeters of water. During inspiration, the expansion of the
lungs creates an ever more negative pressure, to an average of
-7.5 centimeters of water.
When no air is flowing in or out of the lungs, the alveolar (air
sacs in the lungs) pressure is equal to the atmospheric
pressure, which is considered to be zero reference pressure -->
0 centimeters of water pressure. For inward flow of air into
the lungs, the pressure must decrease slightly below
atmospheric pressure. Even -1 centimeters of water is enough
to pull 0.5 liter of air into the lungs. During expiration the
opposite happens, and the alveolar pressure rises to about +1
centimeter, forcing the 0.5 to be expelled.
Transpulmonary pressure is a term used to denotate the
Source: Hall, J., 2020. Guyton And Hall Textbook Of
difference between alveolar and pleural pressures. It is a
Medical Physiology
measure of the elastic forces in the lungs that tend to
collapse the lungs at each instant of respiration, also called recoil pressure. The extend to which the
lungs will expand for a single unit of transpulmonary pressure is called the lung compliance (simply put:
Chapter 38 - Pulmonary ventilation
There are four important components of respiration:
1. Pulmonary ventilation (in and outflow of air)
2. Diffusion of oxygen and carbon dioxide between alveoli and blood
3. Transport of oxygen and carbon dioxide in the blood and body fluids
4. Regulation of ventilation
Mechanics of pulmonary ventilation
The lungs can be expanded and contracted in two manners:
1. Abdominal breath - downward and upward movement of the diaphragm: The relaxation of the
diaphragm and the elastic recoil of the lungs, chest wall and abdominal structures compresses
the lungs and causes expiration. During heavy breathing (e.g. Exercising) the elastic recoil of the
lungs, which normally suffices, are not powerful enough to expel the air from the lungs, so extra
force is generated by contraction of the abdominal muscles.
2. Chest breath - elevation and depression of ribs: All muscles
involved in the elevation of the rib cage are classified as muscles
of inspiration (external intercostals, sternocleidomastoid muscle,
anterior serrati, scaleni), and vice versa for expiration (abdominal recti, internal intercostals).
Except for the attachment of the hilum from the mediastinum the lungs 'float' freely in the thorax in
pleural fluid. This pleural fluid lubricates the movement of the lungs within the cavity. Due to the
continual suction of excess fluid into the lymphatic vessels, this creates a constant pleural pressure
which makes it seem as if the lungs are 'glued' to the chest
wall (similar to two glass objects with fluid in between). This
pleural pressure is negative (due to suction) and is about -5
centimeters of water. During inspiration, the expansion of the
lungs creates an ever more negative pressure, to an average of
-7.5 centimeters of water.
When no air is flowing in or out of the lungs, the alveolar (air
sacs in the lungs) pressure is equal to the atmospheric
pressure, which is considered to be zero reference pressure -->
0 centimeters of water pressure. For inward flow of air into
the lungs, the pressure must decrease slightly below
atmospheric pressure. Even -1 centimeters of water is enough
to pull 0.5 liter of air into the lungs. During expiration the
opposite happens, and the alveolar pressure rises to about +1
centimeter, forcing the 0.5 to be expelled.
Transpulmonary pressure is a term used to denotate the
Source: Hall, J., 2020. Guyton And Hall Textbook Of
difference between alveolar and pleural pressures. It is a
Medical Physiology
measure of the elastic forces in the lungs that tend to
collapse the lungs at each instant of respiration, also called recoil pressure. The extend to which the
lungs will expand for a single unit of transpulmonary pressure is called the lung compliance (simply put:
