VISUALLY EVOKED CEREBRAL BLOOD-FLOW VELOCITY CHANGES IN DIFFERENT STATES OF BRAIN-DYSFUNCTION

Background and Purpose By assessment of metabolically induced cerebral blood flow velocity changes, transcranial Doppler sonography offers t he opportunity to evaluate vaso-neuronal coupling in different states of brain activation and in critically ill patients. Methods With simul taneous transcranial Doppler monitoring of the posterior cerebral arte ry (PCA) and the middle cerebral artery (MCA), 27 control subjects, 11 patients under general anesthesia, 5 patients in the vegetative state , and 12 patients with aneurysmal subarachnoid hemorrhage were stimula ted with a 10-Hz flashlight for 30 seconds. Ten cycles of stimulation were averaged, and a specific flow response (SFR) was computed as the normalized ratio of PCA/MCA mean flow velocity. Results Maximal SFR wa s 14.2% in control subjects. Eye closure significantly reduced maximal SFR (11.6% versus 15.4%, P<.01). In subarachnoid hemorrhage, SFR was markedly decreased in the early phase (4.8%, P<.01) but became normal later on. Four of 5 patients with abolished SFR suffered delayed ische mia due to vasospasm. Of 7 patients with preserved SFR, 5 had vasospas m but none had delayed ischemia. No SFR was observed in patients under general anesthesia or in the vegetative state. Conclusions Although r eflecting fast and local neuronal activity patterns, metabolically ind uced blood Row response is highly dependent on stimulus-directed atten tion. In subarachnoid hemorrhage, decreased metabolic flow response su ggests severe depression of vasoneuronal coupling, and abolished SFR m ight indicate increased vulnerability to vasospasm and a higher risk f or delayed ischemia.