Fig. 2.

Grand averages of the time courses of Δ[Hbdiff], Δ[HbT] and Δ[oxCCO] measured by the detector distal to the light source (source-detector separation of 3.5 cm), over the 15 volunteers that participated in the hypoxia (A), hyperoxia (B), hypocapnia (C) and hypercapnia (D) protocols. The corresponding traces of arterial oxygen saturation (SpO₂) (A), end-tidal O₂ partial pressure (B) and end-tidal partial CO₂ pressure (C and D) are also provided for reference. The small symbols on top of each plot indicate statistical significance with respect to time point 1 (P < 0.05) for the parameters plotted in matching symbols and the error bars represent the standard error of the mean. For reasons explained in the text, we performed the statistical tests only for time intervals 1–10 for hypoxia, 1–14 for hyperoxia, 1–11 for hypocapnia and 1–15 for hypercapnia.