Figure 3. Ensemble averages of PETCO2(top) and V with dot sub I (bottom) of the last 90 s of transcutaneous electrical stimulation (TES) and the subsequent 2 min during air breathing of the eight participants. The averages were calculated with linear interpolation at 3-s time intervals between breaths of the individual responses. By indexing on the time of the last breath with TES (time t = 0), the first “nonpainful” breath was set at t = 3 s. We plotted the averages +/- 2 SE, which constitutes an approximate 95% confidence interval. For presentation purposes, the averages are plotted at 6-s intervals. The dotted lines represent prestimulus baseline values.