Fig. 4

Correlations between the changes in time and volumetric capnography indices to alterations of breathing frequency measured by mainstream (MS, horizontal axis) and sidestream capnography (SS, vertical axis). Linear regressions for the transitions from medium to low (black), high to medium (green) and high to low (magenta) breathing frequencies are shown as continuous lines, grey dashed lines indicate the lines of identity. Pearson correlation coefficients (r) and p values for each change in breathing rate are shown separately in each panel with the corresponding colors. *: r values p < 0.05 versus normal to low, #: r values p < 0.05 versus high to medium. ETCO₂: end-tidal CO₂; Sn2_T and Sn3_T: normalized phase 2 and 3 slopes in time capnogram, respectively; Sn2_V and Sn3_V: normalized phase 2 and 3 slopes in volumetric capnogram, respectively; VnDF: Fowler (anatomical) dead space fraction; VnDB: Bohr (physiological) dead space fraction.