Longitudinal Changes in Cerebral Perfusion, Perivascular Space Volume, and Ventricular Volume in a Healthy Cohort Undergoing a Spaceflight Analog

Abstract

Background and purpose: A global decrease in brain perfusion has recently been reported during exposure to a ground-based spaceflight analog. Considering that CSF and glymphatic flow are hypothesized to be propelled by arterial pulsations, it is unknown whether a change in perfusion would impact these CSF compartments. The aim of the current study was to evaluate the relationship among changes in cerebral perfusion, ventricular volume, and perivascular space volume before, during, and after a spaceflight analog.

Materials and methods: Eleven healthy participants underwent 30 days of bed rest at 6° head-down tilt with 0.5% atmospheric CO₂ as a spaceflight analog. For each participant, 6 MR imaging brain scans, including perfusion and anatomic-weighted T1 sequences, were obtained before, during, and after the analog period. Global perfusion, ventricular volume, and perivascular space volume time courses were constructed and evaluated with repeated measures ANOVAs.

Results: Global perfusion followed a divergent time trajectory from ventricular and perivascular space volume, with perfusion decreasing during the analog, whereas ventricular and perivascular space volume increased (P < .001). These patterns subsequently reversed during the 2-week recovery period.

Conclusions: The patterns of change in brain physiology observed in healthy participants suggest a relationship between cerebral perfusion and CSF homeostasis. Further study is warranted to determine whether a causal relationship exists and whether similar neurophysiologic responses occur during spaceflight.

FIG 1.

Mean perfusion-weighted images using masks of all participants at each time point throughout the study. Yellow/red indicates greater perfusion on arbitrary scaled units.

FIG 2.

T1 images with examples of ventricular volume enlargement for 2 participants 7 days into bed rest. A and B, Axial section with arrows highlighting areas of gross ventricular enlargement in the lateral ventricles. C and D, Coronal section with arrows highlighting enlargement of the third ventricle. Participants shown experienced a 9.12% and 12.31% increase in ventricular volume, respectively.

FIG 3.

3D mask representation of WM-PVS of a sample participant from pre-bed rest (BDC-7) to the end of bed rest (HDT29). The following participant experienced a 12% increase in PVS volume.

FIG 4.

Global relative perfusion, ventricular volume, and PVS time courses. Gray shaded area represents the duration of the HDT + CO₂ intervention. Data points for scanning days include pre- (BDC-7), during (HDT7 & HDT29), and post- (R + 5 & R + 12) HDT + CO₂ period and are represented with mean z-scores (standard error of the mean). A divergent trajectory is observed with perfusion decreasing while ventricular and perivascular space volume increase during the HDT + CO₂ period.