Fig. 4.

Example records for the first section of the nitrogen washout phase of the experimental protocol. A–C: end-tidal N₂ fractions ($F_{\text{ET},{\text{N}}_{\text{2}}}$) plotted against lung turnover. D–F: the normalized slope of the N₂ record during phase III of expiration. A, D: young healthy participant. B, E: old participant. C, F: participant with COPD.