Illustration of the combined BOLD-CVR and task-evoked BOLD-fMRI study protocol in one subject.

Top: Fig 1A and 1B show the CO2 (grey dotted line) and mean BOLD signal time course (black line) during a BOLD-CVR study at CO2 baseline (A) versus hypercapnia (B), respectively. Note that the BOLD signal follows the CO2 increase from normocapnia and quickly returns to baseline levels. However, during hypercapnia, the mean BOLD signal increase with CO2 rise is less than in normocapnia. Bottom: Fig 1C and 1D show the CO2 time course during a task-evoked BOLD-fMRI block protocol. The black short lines represent the task phase of the protocol. The ability of precise CO2 control with the MPET method produced a constant CO2 level at CO2 baseline (C) versus hypercapnia (D), respectively.