EFFECT OF STEPPED HYPOGLYCEMIA ON REGIONAL CEREBRAL BLOOD-FLOW RESPONSE TO PHYSIOLOGICAL BRAIN ACTIVATION

The effect of vasoactive stimuli on cerebral blood flow (CBF) has been variously reported as normal or impaired by hypoglycemia. We measured regional CBF (rCBF) in contralateral somatosensory cortex at rest and during vibrotactile stimulation of one hand in four normal awake huma n volunteers during fasting euglycemia (5.1-5.2 mu mol/ml) with 0.9% s aline infusion, euglycemia (5.0-5.2 mu mol/ml) with hyperinsulinemic c lamp, mild hypoglycemia (3.2-3.6 mu mol/ml) with hyperinsulinemic clam p, and moderate hypoglycemia (2.3-3.2 mu mol/ml) with hyperinsulinemic clamp. No changes in mean arterial pressure, arterial PCO2 or arteria l oxygen content occurred. There was no change in the magnitude of the normalized rCBF response to physiological brain stimulation with prog ressive arterial hypoglycemia (r = 0.10, P = 0.73). We interpret this to mean that there was a progressive reduction in cerebral glucose del ivery to the area of physiological activation as arterial glucose conc entrations fell. Therefore, the increase in rCBF during physiological brain activation is not regulated by a mechanism that matches local ce rebral glucose supply to local cerebral glucose demand.