Emptying patterns of the lung studied by multiple-breath N2 washout.

Changes in the nitrogen concentration seen during the single-breath nitrogen washout reflect 
changes in relative flow (V) from units with differing ventilation/volume ratios 
(V/V0). The multiple-breath washout provides sufficient data for the V for 
units with varying V/V0 to be plotted as a function of 
the volume expired. Flow from the dead space may also be 
determined. In young normals the emptying patterns are narrow and unimodal 
throughout the alveolar plateau with little or no flow from the 
dead space at the end of the breath. Older normals show 
more flow from the dead space, particularly toward the end of 
the breath, and some show a high V/V0 mode early in 
the breath. Patients with obstructive lung disease have a high flow 
from the dead space which is present throughout the breath. A 
well ventilated mode at the end of the breath is seen 
in some obstructed subjects. Patients with cystic fibrosis showed a poorly 
ventilated mode appearing at the end of the breath as well 
as a very high dead space. 