Objective: We hypothesized that the cerebral blood flow change induced by sleep might reflect the activation of waste clearance system. We investigated the association between the sleep-related alterations of blood flow parameters and cerebral white matter hyperintensity (WMH) volume on MRI using transcranial Doppler (TCD) monitoring.
Methods: Fifty volunteers with pre-specified inclusion criteria (Thirty-eight males [76.0%] and twelve females [24.0%]) were prospectively recruited and categorized per their ages (age ≤50 years, n=26 and age >50 years, n=24). Along with participants’ sleep profiles and baseline transcranial Doppler (TCD) parameters, mean flow velocity (MFV) of the middle cerebral artery (MCA) was monitored during short-term sleep using TCD with electroencephalograph. Spectral density analysis was performed to analyze the periodic pattern of MFV variation. For the aged subgroup (n=24), WMH volume in the total, subcortical, and periventricular region were measured.
Results: Thirty-eight males (76.0%) and twelve females (24.0%) with mean age of 47.3±12.6 years (range 24–69) were monitored with the mean duration of waking status of 299.4±95.6 seconds and sleep status of 877.1±321.3 seconds. Compared to the waking status, substantial augmentation of the periodic pattern of MFV was observed during sleep (P<0.001). In the spectral density analysis, a peak in the in the very-low frequency (VLF, 0.003−0.04Hz) band in the sleep status was observed, with the mean sleep/waking ratio of this VLF peak of 2.87±2.71 (P<0.001). In the multivariate linear regression analysis for the WMH volume in the aged subgroup, the sleep/waking ratio of VLF peak was negatively associated with both total (B coefficient =-0.517; 95% confidence interval [CI] -0.915−-0.120; P=0.013) and subcortical WMH volume (B =-0.630; 95% CI -1.150−-0.109; P=0.020), but not with the periventricular WMH volume. 
Interpretation: The sleep/waking ratio of VLF peak power was associated with total and subcortical WMH volume. Sleep-related augmentation of MFV oscillation might be an actively regulated process which enhances the cerebral waste clearing during sleep.

AMPLIFICATION OF PERIODICITY IN CEREBRAL FLOW VELOCITY DURING SLEEP AND ITS ASSOCIATION WITH WHITE MATTER HYPERINTENSITY VOLUME