Figure 6.

Resistance sigmoid measures (top) and their corresponding anatomical maps (bottom). The vascular model is that described in Figure 5. Various aspects of the resistance-PETCO₂ relationship are expressed in the sigmoidal shape of the relationship. The graph shows some of these parameters diagrammatically, and the maps show their anatomical distribution. The amplitude shows the full extent of the vasodilation and vasoconstriction. The midpoint of the sigmoid is the PETCO₂ at its steepest slope, and the range is the span of PETCO₂ over which the response can be considered linear. The reserve and sensitivity show the vasodilatory reserve available from the subject’s resting baseline PETCO₂ and the response sensitivity (sigmoid slope) at resting PETCO₂. The quality map shows the r² fit of the examined voxel resistance sigmoid.