Figure 3

Single-breath test for CO ₂ at ordinary and long postinspiratory pause in subject 4, depicting fraction of CO ₂ at airway opening, FCO ₂ , against expired volume. The blue loop shows the SBT-CO₂ from an ordinary breath, and the magenta loop, a breath with a prolonged T_P. The blue area corresponds to V_TCO₂ of an ordinary breath. The additional volume of CO₂ eliminated at the longer T_P, ΔV_TCO₂, indicated by hatched area, is caused partly by a lower-airway dead space (indicated by interrupted lines) and partly by a higher level of the alveolar plateau.