Carotid blood flow during REM sleep

Objective: The present study was aimed at directly appraising, in the rabbit, the decrease in common carotid blood flow, the occurrence of which during REM sleep was indirectly suggested by previous studies of preoptic-hypothalamic temperature changes during sleep. Methods: In 5 unrestrained male rabbits, polygraphic recordings of electroencephalography, electromyography, ear pinna temperature (degrees C), common carotid mean and peak blood flow (mL/min), and heart rate (beats/min) were carried out across ultradian wake-sleep cycles. In each cycle, epochs of 60 seconds were selected for analysis at the end of non-rapid eye movement (NREM) sleep, at the beginning and end of rapid eye movement (REM) sleep, and at the beginning of the subsequent period of wakefulness. The time basis of measurements within each epoch was a 5-second period (5x12=60 seconds). The mean values of the cardiovascular variables in such epochs of 5 animals underwent nonparametric statistical analysis of their changes across epochs. Conclusion: A conspicuous decrease in common carotid blood flow is a constant feature of REM sleep in rabbits during several months of recording. This decrease is the result of a marked depression of both peak flow and heart rate. In spite of the unstable systemic hemodynamic conditions revealed by this study, several independent functional and morphologic factors concur to increase the vertebral blood supply to the brain'during REM sleep. This increase raises preoptic-hypothalamic temperature, since vertebral artery blood is warmer than carotid artery blood.