Fig. 1. Means and standard errors of self-reported anxiety and minute-by-minute mean end-tidal pCO₂ for the three groups over the course of the experiment. BASE is the baseline. 6 x FB/REC refers to the six 1-minute fast-breathing periods and 1-minute recovery periods, the following FB refers to the 3-minute fast-breathing period, and REC refers to the 10-minute final recovery period. Anxiety ratings were not evaluated during the initial six recovery periods. a marks the first time point where the panic disorder patients differ from the other groups (ANCOVA with last 2 minutes of FB as covariate: F(2,53) = 4.01, p < .02).