Is there an evoked vascular response?

Event-related potentials of the brain are enhanced when stimulation is synchronized with diastolic phases of cerebral or cephalic pulse pressure waves. A cerebral vascular event has been found to be temporally consistent with the event-related potential. Averaged evoked vascular responses were measured with bioimpedance techniques from the brain and the arm. Changes in brain blood volume occurred 150 to 250 milliseconds after stimulation synchronized with diastolic but not systolic phases of the cerebral pulse pressure wave. The time course of this phenomenon defies the usually accepted characteristics of metabolic activity. The evoked vascular response may be a neurally mediated event in anticipation of altered metabolic demand, and it offers the possibility of measurement in real time.