Cerebral autoregulation is visualized as a correlation plot between cerebral blood flow (CBF) and cerebral perfusion pressure (CPP). CBF remains stable between the lower limit (LL) and the upper limit (UL) (portion B, plateau). CBF is pressure passive at the CPP range below the lower limit (portion A) and above the upper limit (portion C). This illustration uses a CPP of 60 mmHg as the lower limit, a CPP of 150 mmHg as the upper limit, and a CBF of 50 ml/min per 100 g as the plateau. However, these regularly quoted numbers are not fixed; rather, they vary interindividually and intraindividually depending on a variety of factors. Therefore, we take a note of SD to emphasize that these parameters have a wide range of distribution. The cerebrovascular reactivity is also illustrated.