Cerebral Metabolic Rate of Oxygen During Transition from Wakefulness to Sleep Measured with High Temporal Resolution OxFlow MRI with Concurrent EEG

During slow-wave sleep, synaptic transmissions are reduced with a concomitant reduction in brain energy consumption. We used 3 Tesla MRI to noninvasively quantify changes in the cerebral metabolic rate of O (CMRO) during wakefulness and sleep, leveraging the 'OxFlow' method, which provides venous O saturation (SvO) along with cerebral blood flow (CBF). Twelve healthy subjects (31.3 ± 5.6 years, eight males) underwent 45-60 min of continuous scanning during wakefulness and sleep, yielding one image set every 3.4 s. Concurrent electroencephalography (EEG) data were available in eight subjects. Mean values of the metabolic parameters measured during wakefulness were stable, with coefficients of variation below 7% (average values: CMRO = 118 ± 12 µmol O/min/100 g, SvO = 67.0 ± 3.7% HbO, CBF = 50.6 ±4.3 ml/min/100 g). During sleep, on average, CMRO decreased 21% (range: 14%-32%; average nadir = 98 ± 16 µmol O/min/100 g), while EEG slow-wave activity, expressed in terms of -power, increased commensurately. Following sleep onset, CMRO was found to correlate negatively with relative -power (r = -0.6 to -0.8,  < 0.005), and positively with heart rate (r = 0.5 to 0.8,  < 0.0005). The data demonstrate that OxFlow MRI can noninvasively measure dynamic changes in cerebral metabolism associated with sleep, which should open new opportunities to study sleep physiology in health and disease.