Figure 1. The bispectral index (BIS) and ventilatory responses to five successive hypoxic pulses during sevoflurane inhalation in a single male participant are shown. (Upper) The BIS. Each circle represents a measurement point. To guide the eye, a line through the data points was drawn by hand. The dotted lines denote a BIS of 94. (Middle) End-tidal oxygen pressure waveform. (Bottom) Ventilatory response. Each dot is one breath. During the second hypoxic pulse, arousal caused an increase in the BIS above 94. Consequently, this response was omitted from the analysis.