Fig. 4

Volumes identified with volumetric capnography (based on Tang et al. [19]). The line a–b defines equal area q and p as in Fig. 3. The line c–d is created so that area A equals area B. The distance from b to d defines alveolar dead space (VDalv). Tang et al. did their analysis with the Enghoff approach which uses PaCO₂ instead of PACO₂ as in the Bohr approach. If PACO₂ were used instead the line c–d would be more to the left and the value of VDalv smaller. VDaw is the anatomical dead space, VDalv is the alveolar dead space, VDphys is the physiological dead space, VTalv-eff is the efficient alveolar tidal volume, VTalv is the alveolar tidal volume, VT is the tidal volume