Symmetry of cerebral blood flow and cognitive responses to hypoglycaemia in humans

Summary A low blood glucose level is associated with impairment of higher cerebral function and an increase in cerebral blood flow. This study examined whether there are differences in the physiological responses to hypoglycaemia between the cerebral hemispheres. Eight healthy men participated in two hyperinsulinaemic glucose clamp studies: after 60 min at 4.5 mmol/l, blood glucose was either lowered to 2.0 mmol/l and clamped there for 60 min (hypoglycaemia) or continuously maintained at 4.5 mmol/l (euglycaemia). Cardiac output, middle cerebral artery velocity (transcranial Doppler) and cerebral blood flow (133-xenon inhalation) were measured during the studies. Neuropsychological tests were used to determine whether hypoglycaemia caused differential impairment of hemispheric cognitive function. Hypoglycaemia was associated with symmetrical impairment of cognitive function in both cerebral hemispheres and a rise in cardiac output (from 5.5 [0.2] to 8.7 [0.2] l · min^–1p<0.0001, mean [standard error]), middle cerebral artery velocity (from 55 [2.6] to 64 [2.8] cm·s^–1, p<0.002), and global cerebral blood flow (from 56 [2.6] to 69 [2.9] ml·100 g^–1·min^–1, p<0.005 compared to pre-insulin values). There were no differences in the blood flow response during hypoglycaemia between hemispheres and the increase in blood flow did not correlate with either the change in cardiac output or rise in plasma catecholamine levels. After 120 min of hyperinsulinaemic, euglycaemia, global cerebral blood flow rose significantly above baseline (from 58 [2.4] to 63 [2.2] ml·100 g^–1·min^–1, p<0.05). In conclusion, using the techniques described, the physiological and cognitive responses of each cerebral hemisphere to hypoglycaemia were symmetrical. Hyperinsulinaemia, independent of blood glucose level, may be associated with an increase in cerebral blood flow.