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.