The increase in mean arterial pressure (MAP; Panel A), middle cerebral artery blood velocity (MCAv; Panel B), and absolute (Panel C) and relative (Panel D) cerebrovascular conductance index during rebreathing-induced increases in end-tidal carbon dioxide (PETCO2) in healthy non-depressed adults (HA; n = 14; 9 women) and adults with major depressive disorder (MDD; n = 16; 11 women). The absolute breath-by-breath increase in PETCO2 throughout rebreathing was determined for each individual and presented at each 3 mmHg increase in PETCO2 up to, and including, the highest common magnitude of hypercapnia achieved by all subjects (ΔPETCO2 = 9 mmHg). Outcome variables were analyzed using two-way (group x. hypercapnia) mixed-model ANOVA, with post hoc corrections (Tukey) applied for specific planned comparisons when appropriate. Data are presented as mean±standard deviation; effect sizes are reported as partial eta squared (ηp2). *p<0.05 vs. baseline.