Using the xenon Xe133 (Xeneisol 133) intracarotid method in man, regional cerebral blood flow (rCBF) was measured in 35 small areas of a hemisphere. it was shown that intracarotid infusion of trimethaphan camsylate (Arfonad) has no effect on rCBF. Marked increases and moderate decreases of perfusion pressure normally cause no measurable change in regional cerebral perfusion pattern nor in absolute flow (rCBF autoregulation). Therefore, autoregulation is impaired when the rCBF changes more than explained by methodologic error. With disease, all degrees of impairment from normal regulation to a completely passive vascular bed may be seen. The derangement may be quantified by the vasoreactivity impairment index (VI): rCBF change, % mean arterial blood pressure change, %. Autoregulation is abnormal in many acute cerebral disorders. The possible diagnostic value of this fact is exemplified and discussed.
Olesen J. Quantitative Evaluation of Normal and Pathologic Cerebral Blood Flow Regulation to Perfusion Pressure: Changes in Man. Arch Neurol. 1973;28(3):143–149. doi:10.1001/archneur.1973.00490210023001
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