Figure 5. Representative records of haemoglobin oxygen saturation during hypoxia–reoxygenation with different durations of the hypoxic phase.

During the four consecutive 60 s cycles, the hypoxic phase was progressively lengthened (15, 20, 30 and 40 s). The black line corresponds to the oxygen saturation of haemoglobin, the red line to FIO₂ in the inspired air. The three graphs represent the cycles with different FIO₂ values during the hypoxic phase (A: 12%; B: 9%; C: 6%).