COMPARISON OF FLOW AND VELOCITY DURING DYNAMIC AUTOREGULATION TESTINGIN HUMANS

Background and Purpose We compared relative changes in middle cerebral artery velocity and internal carotid artery flow during autoregulatio n testing to test the validity of using transcranial Doppler recording s of middle cerebral artery velocity to evaluate cerebral autoregulati on in humans. Methods Seven human volunteers had dynamic autoregulatio n tested during surgical procedures that included exposure of the inte rnal carotid artery. The mean arterial blood pressure and middle cereb ral artery velocity spectral outline (V(max), using transcranial Doppl er, and ipsilateral internal carotid artery flow, using an electromagn etic flowmeter, were continuously and simultaneously recorded during t ransient sharp decreases in blood pressure that were induced by rapid deflation of thigh blood pressure cuffs. The resulting responses of ve locity in the middle cerebral artery and flow in the internal carotid artery were compared. Results Moderate decreases in blood pressure evo ked responses in cerebral autoregulation. There were no significant (P =.97) differences between the responses in middle cerebral artery velo city and internal carotid artery flow to the blood pressure decreases. Conclusions Relative changes in V(max) accurately reflect relative ch anges in internal carotid artery flow during dynamic autoregulation te sting in humans. Therefore, alterations in middle cerebral artery diam eter do not occur to the extent that they introduce a significant erro r in making these comparisons.