Background and Purpose-We sought to describe the dynamic changes in the cerebrovascular system after traumatic brain injury by transfer function estimation and coherence. Methods-In 42 healthy volunteers (meanϮSD age, 37Ϯ17 years; range, 17 to 65 years), spontaneous fluctuations of middle cerebral artery blood flow velocity and of finger blood pressure (BP) were simultaneously recorded over a period of 10 minutes under normocapnic and hypocapnic conditions to generate normative spectra of coherence, phase shift, and gain over the frequency range of 0 to 0.25 Hz. Similar recordings were performed in 24 patients with severe traumatic brain injury (Glasgow Coma Scale score Յ8; meanϮSD age, 50Ϯ20 years) serially on days 1, 3, 5, and 8 after trauma. Cranial perfusion pressure was kept at Ͼ70 mm Hg. Each blood flow velocity/BP recording was related to the presence or absence of middle cerebral artery territory brain parenchyma lesions on cranial CT performed within a close time frame. Results-In

When CA is intended to be assessed by use of phase shift, the hyperventilation setting needs its own reference values. In MCA territories containing a traumatic lesion greater than 3 cm in diameter phase shift at 0.1 Hz will detect a high frequency (44%) of a disturbed state of CA.