Transpulmonary Pressure. Finally, note in Figure 37-2 the difference between the alveolar
pressure and the pleural pressure. This is called the transpulmonary pressure. It is the pressure
difference between that in the alveoli and that on the outer surfaces of the lungs, and it is a measure of
the elastic forces in the lungs that tend to collapse the lungs at each instant of respiration, called the
recoilpressure.
Compliance of the Lungs
The extent to which the lungs will expand for each unit
increase in transpulmonary pressure (if enough time is allowed to reach equilibrium) is called the lung compliance. The total compliance of both lungs together in the normal adult human being averages
about 200 milliliters of air per centimeter of water transpulmonary pressure. That is, every time the
transpulmonary pressure increases1 centimeter of water, the lung volume, after 10 to 20 seconds, will
expand 200 milliliters.
General Principles of Gastrointestinal Function— Motility, Nervous Control, and Blood
