RELATIONSHIP BETWEEN CEREBRAL BLOOD-FLOW VELOCITIES AND CEREBRAL ELECTRICAL-ACTIVITY IN SLEEP

The dynamics of cerebral blood flow velocity during sleep were measure d in the right and left middle cerebral artery of 12 and 10 healthy ma le volunteers, respectively. A computer-assisted pulsed (2-MHz) Dopple r ultrasonography system was modified for continuous long-term and on- line recording of cerebral hemodynamics in combination with polysomnog raphy. Mean flow velocity (MFV) decreased steadily during deepening no nrapid eye movement (NREM) sleep and increased suddenly during rapid e ye movement sleep, corresponding to changes in brain function. However , spontaneous or provoked changes in sleep stage patterns as well as a wakenings from NREM sleep were not regularly accompanied by correspond ing changes in MFV. Differing values for MFV in subsequent sleep cycle s could be shown for several sleep stages. Furthermore, MFV values in sleep stage II at the end of an NREM-sleep period were lower than in p receding slow-wave sleep. After application of short acoustic signals the electroencephalogram frequency rose, indicating an arousal, wherea s MFV rapidly decreased for several seconds and then gradually returne d to the prior level. These results imply an uncoupling between cerebr al electrical activity and cerebral perfusion during sleep and support a dissociation in the activity of central regulatory mechanisms. In l ight of the proposal that cortical energy consumption can be accounted for by cerebral electrical activity, the concept that cerebral perfus ion during sleep is regulated solely by the metabolic rate must be rec onsidered.