Validation of time-domain analysis method of cerebral autoregulation. In this piglet model, cerebral perfusion pressure was manipulated by inflation of a catheter-tipped balloon placed in the inferior vena cava. (A) Laser Doppler (lDoppler) flux–determined cerebral blood flow is plotted against cerebral perfusion pressure (CPP). The point of intersection of two linear regression lines marks the lower limit of autoregulation (lower limit of autoregulation) which is 34 mmHg in this piglet. (B) Near-infrared spectroscopy regional cerebral oxygen saturation is plotted against cerebral perfusion pressure. (C, D) Correlation coefficient between laser Doppler flux and cerebral perfusion pressure and near-infrared spectroscopy derived cerebral oximetry index with cerebral perfusion pressure. When mean arterial pressure is above the lower limit of autoregulation, there is low correlation between cerebral perfusion pressure and laser Doppler index (lDx) and cerebral oximetry index (COx), indicating that cerebral blood flow is independent of blood pressure or autoregulated. In contrast, when mean arterial pressure is lower than the lower limit of autoregulation (34 mmHg), laser Doppler index and cerebral oximetry index approach 1.0 as cerebral blood flow is blood pressure passive. Reprinted with permission from Brady et al.²⁹