Figure 2.

The relationship between cerebrovascular reactivity (CVR) and steady-state CVR (ssCVR). Data from the same patient as presented in Figures 1 and 5. CVR and ssCVR values are expressed in %S/mm Hg. (A) Plot of blood oxygen level-dependent (BOLD) signal versus convolved end-tidal partial pressure of CO₂ (P_ETCO₂) and line of best fit (green dots and line, same data as Figure 1); and the signal versus actual P_ETCO₂ with its line of best fit (black dots and line), both from the same voxel with slow response. (B) Similar graph of signal versus convolved PETCO₂ (red dots and line, same data as Figure 1) and signal versus actual PETCO₂ (black dots and line). Note that when the time course of response is rapid, little convolution of PETCO₂ is required and the CVR is close to ssCVR.