Sympathetic regulation of the cerebral circulation remains controversial. Although intravenous phenylephrine (PE) infusion reduces the near-infrared spectroscopy (NIRS)-determined measure of frontal lobe oxygenation (S(c) O(2) ) and increases middle cerebral artery mean blood velocity (MCA V(mean) ), suggesting a-adrenergic-mediated cerebral vasoconstriction, this remains unconfirmed by evaluation of arterial and venous cerebral blood flow.