https://doi.org/10.1140/epjp/s13360-021-01480-2
Regular Article
Inverse correlation of fluctuations of cerebral blood and water concentrations in humans
1
Oulu Functional Neuroimaging Group, Research Unit of Medical Imaging Physics and Technology (MIPT), University of Oulu, Oulu, Finland
2
Department of Diagnostic Radiology, Medical Research Center (MRC), Oulu University Hospital, Oulu, Finland
3
Center for Translational Neuromedicine, University of Copenhagen, Copenhagen, Denmark
4
Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
5
Optoelectronics and Measurement Techniques Research Unit, University of Oulu, Oulu, Finland
6
Department of Diagnostic Radiology, P.O. Box 50, 90029, Oulu, OYS, Finland
a
borchardt.viola@googlemail.com
Received:
24
October
2020
Accepted:
22
April
2021
Published online:
5
May
2021
Near-infrared spectroscopy (fNIRS) measures concentrations of oxygenated (HbO) and deoxygenated (HbR) hemoglobin in the brain. Recently, we demonstrated its potential also for measuring concentrations of cerebral water (
). We performed fNIRS measurements during rest to study fluctuations in concentrations of , HbO and HbR in 33 well-rested healthy control subjects (HC) and 18 acutely sleep-deprived HC. Resting-state fNIRS signal was filtered in full-band, cardiac, respiratory, low-, and very-low-frequency bands. The sum of HbO and HbR constitutes the regional cerebral blood volume (CBV). CBV and concentrations were analyzed via temporal correlation and phase synchrony. Fluctuation in concentrations of and CBV was strongly anti-correlated across all frequency bands in both frontal and parietal cortices. Fluctuation in concentrations of 
and CBV showed neither a completely synchronous nor a random phase relationship in both frontal and parietal cortices. Acutely sleep-deprived subjects did not show significant differences in temporal correlation or phase synchrony between fluctuations in and CBV concentrations compared with well-rested HC. The reciprocal interrelation between fluctuations in CBV and concentrations is consistent with the Munro–Kellie doctrine of constant intracranial volume. This coupling may constitute a functional mechanism underlying glymphatic circulation, which persists despite acutely disturbed sleep patterns.
© The Author(s) 2021
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