Transmural Pressure The difference between the pressure inside the lungs and the pressure...

Transmural Pressure The difference between the pressure inside the lungs and the pressure surrounding the lungs is called the transmural pressure (or the transmural pressure gradient). Figure 1 shows for three different persons how the volume of the lungs is related to the transmural pressure, based on static measurements taken while there is no air flowing through the mouth. (The functional reserve capacity mentioned on the vertical axis is the volume of air in the lungs at the end of a normal expiration.) The rate of change in lung volume with respect to transmural pressure is called the lung compliance.

Figure 1 Lung pressure–volume curves.

Most lung diseases cause a decrease in lung compliance. However, the compliance of a person with emphysema is higher than normal. Which curve (I or II) in Fig. 24 could correspond to a person with emphysema?