Fig. 1.
Timelines for the repetitive cardiovascular response tests in which the participants immersed their hand in cold water (∼4 °C) as pain stimulation for 2 min (CPT). The experiment consists of three trials: the first CPT (CPT[1st]), the second CPT (CPT + CC), and the placebo test with warm water (∼35 °C) (PLCB + CC) under two conditions: room air (RA) and 40 % nitrous oxide/oxygen (N2O) inhalation. Participants performed the 5-min baseline, 30-s countdown (CD) before the stimulation, 2-min CPT/PLCB, and 3-min recovery in each trial.