DYNAMICS OF CEREBRAL BLOOD-FLOW VELOCITIES DURING NORMAL HUMAN SLEEP

Bilateral flow patterns of the middle cerebral artery (MCA) were recor ded continuously throughout the night in 18 healthy male subjects (mea n age 27.4 years) by a computer-assisted pulsed Doppler (2 MHz) system together with simultaneous polysomnography. After inception of sleep, mean flow velocity (MFV) decreased steadily during deepening sleep st ages reaching -15.0 +/- 3.6% (p<0.001) in the right MCA and -16.2 +/- 3.4% in the left MCA (p<0.001) in stage 4 of the first sleep cycle com pared to the waking state. Lowest MFV values were found in stage 2 pre ceding the last REM period (right MCA: -19.2 +/- 4.1%: left MCA: -19.7 +/- 5.1%). Changing from non-REM into REM sleep, a sudden rise of MFV , which varied from 8.9% (first sleep cycle, left MCA) to 18% (last sl eep cycle, right MCA), could be consistently detected indicating a cou pling of cerebral electrical activity and cerebral perfusion in REM sl eep. During non-REM sleep this concomitant change of MFV and EEG activ ity was only found in the first sleep cycle, whereas no parallel chang es could be observed in later sleep cycles. These results indicate a d ecoupling of EEG measured cerebral electrical activity and perfusion a nd suggest that factors other than metabolic mechanisms contribute to the regulation of cerebral perfusion during human non-REM sleep.