FIGURE 4.

Examples of the four types of response patterns for model flow (left) and the calculated resistance response patterns (right) with the reference resistance (black line). The four voxel branch flow patterns (color coded solid lines) are increasing (A, red), inverted U-shaped (B, light blue), declining (C, dark blue) and U-shaped (D, orange), with the accompanying reference branch flow patterns shown as dashed lines. The dotted vertical line indicates the subject’s resting PETCO₂. Note that despite the varying shapes of the BOLD curves, the resistance curves are all sigmoidal in shape as expected except type C, which is unresponsive. The choice of BOLD scaling to model flow of 100 nL/s at the resting PETCO₂ brings the model resistances at resting PETCO₂ to approximately the same value for all patterns.