Dynamic Assessment of CSF Mobility and Blood-CSF Exchange During Wake and Sleep Stages: Brain Clearance Study

The brain lacks conventional lymphatic vessels. Instead, it uses the glymphatic
system for clearing solutes, such as metabolites and proteins, by exchanging
cerebrospinal fluid (CSF) with interstitial fluid (ISF) through the
perivascular spaces (Iliff et al., 2012; Nedergaard and Goldman, 2020).
Several physical forces drive brain clearance, including diffusion,
pressure-driven flow, and mixing. Oscillations from arterial pulsation (~1 Hz),
respiratory forces (~0.2 Hz), and vasomotor activity (~0.1 Hz) help enhance
solute movement through perivascular spaces (Iliff et al., 2013; van Veluw et
al., 2020). Brain clearance is most active during sleep, especially slow-wave
sleep (SWS), when interstitial space expands by ~60%, facilitating CSF-ISF
exchange (Xie et al., 2013).

Impaired glymphatic clearance is associated with protein aggregation and
dementia (Nedergaard and Goldman, 2020). As the global dementia burden rises,
understanding brain clearance mechanisms could inform therapeutic strategies.

Techniques such as tracer injection and diffusion-weighted MRI (dwMRI) are used
to study glymphatic flow. Human studies have shown brain-wide CSF enhancement
following intrathecal gadolinium injection, but invasive methods limit
widespread use (Eide and Ringstad, 2015; Ringstad et al., 2017). Non-invasive
imaging, including MRI-based CSF flow measurments, offers a promising
alternative (Fultz et al., 2019; Helakari et al., 2022).

This study aims to investigate how different wake and sleep stages affect CSF
movement/exchange using both 7T and 3T MRI scanners. The 7T scanner provides
high-resolution imaging of CSF mobility during sleep and wake states, while the
3T scanner explores haemodynamic changes and CSF secretion related to brain
clearance (Petitclerc et al., 2021).

Primary Objective:

The central focus of the 7T study is to investigate the influence of sleep and
its various stages, particularly slow wave sleep, on CSF mobility within
perivascular spaces.

The primary aim of the 3T experiment is to explore the influence of sleep,
encompassing various sleep stages, with a particular emphasis on slow wave
sleep, on the exchange of water between blood and CSF.

Secondary Objectives:

In addition, the study aims to explore the correlation between CSF mobility in
perivascular spaces and driving forces like cardiac and respiratory
oscillations, which promote brain clearance. It seeks to clarify how these
physiological phenomena influence CSF dynamics and the clearance of waste
products in the brain.

Furthermore, the study aims to explore the relationship between changes in CSF
mobility and various sleep-wake characteristics prior to the experiment, such
as chronotype and sleep habits. By examining these associations, the research
seeks to understand how individual differences in sleep patterns influence CSF
dynamics in perivascular spaces during wake and sleep. This aspect of the study
is exploratory in nature.

As an additional secondary objective, we will investigate and characterize the
relationship between 'CSF-waves' (Fultz et al., 2019; Eiling et al., 2024) and
CSF mobility, providing a deeper understanding of the potential link between
CSF flow in 4th ventricle and CSF mobility around perivascular space.

3T secondary objectives:

As a secondary objective, we aim to explore how sleep stages influence
perfusion measurements. Additionally, we plan to establish correlations between
alterations in heart rate variability*indicative of sympathetic and
parasympathetic activity*and CSF production during wakefulness and different
sleep stages. Our hypothesis is that a decrease in sympathetic tone and an
increase in parasympathetic dominance will be linked to elevated CSF production
in the choroid plexus. Furthermore, we intend to examine the impacts on CSF
production outside the choroid plexus.

This study will take place at Leiden University Medical Centre using 7T and 3T
MRI scanners. Young, healthy participants (18-40 years) will be recruited via
advertisements and by word-of-mouth by our research team. Information sheets
will be available to any participants who express interest in the study and
will be sent via e-mail.

During the screening visit, informed consent will be obtained, and participants
will complete a medical questionnaire and questionnaires on sleep habits,
including the Insomnia Severity Index, Epworth Sleepiness Scale, Pittsburgh
Sleep Quality Index, and Horne-Østberg Morningness Eveningness Questionnaire.
Participants will also keep a daily sleep diary for a week prior scanning and
wear an Actigraphy device to monitor sleep patterns.

The night before scanning, participants will be asked to restrict their sleep
to under four hours, with adherence confirmed via Actigraphy and a morning
phone call. Before the scan, participants will complete the Karolinska
Sleepiness Scale.

Night-time scanning will begin at 22:00, with a maximum session of 2.5 hours.
Sleep state, heart rate, and respiration will be monitored using EEG, pulse
oximetry, and a respiration belt. If participants cannot fall asleep within the
first hour, the scan will be discontinued.


After scanning, participants will complete a subjective sleep questionnaire,
and a taxi service will be provided for their return home. Participants will
receive a 100-euro gift card for their participation.

The 7T MRI system, widely used since the 1990s, has not reported any serious
adverse events (SAEs) (van Osch and Webb, 2014). Temporary side effects, such
as vertigo, nausea, and involuntary eye motion, may occur due to ion current
forces in the semicircular canals (van Osch and Webb, 2014). Participants are
provided with adequate sound protection for comfort and ear safety. The study
uses modified scanner software, developed and approved under LUMC*s Standard
Operating Procedure (SOP), which does not impact scan safety.

Sleep deprivation might make the participant irritable, however considering the
length of sleep deprivation it should not lead to psychological/physical
consequences beyond the risks encountered in day-to-day life. Risks are
estimated as very low.

Participants will not receive direct benefits from the study, but by
contributing, they help advance understanding of how sleep influences brain
waste clearance, which could lead to future interventions for neurodegenerative
diseases. The MRI sessions will last up to 2.5 hours, with the scan being
terminated if sleep isn*t achieved within the first hour. Given the
non-invasive nature of the scans (without contrast agents), participant burden
is considered minimal. As compensation for their time, participants will
receive a 100-euro gift card