Fig. 1. Individual responses to skin incision according to the up-and-down sequence in patients receiving no remifentanil infusion. When a patient showed an increase in either heart rate or mean arterial blood pressure of 15% or more from the preincision value, the end-tidal concentration of sevoflurane given to the next patient was increased (positive response [open symbols ]), whereas in the absence of an increase in either heart rate or mean arterial blood pressure of 15% or more from the preincision value, the end-tidal concentration given to the next patient was decreased (negative response [filled symbols ]).