Following prolonged stays on the International Space Station (ISS), some astronauts exhibit visual acuity changes, ophthalmological findings, and mildly elevated intracranial pressures as part of a novel process called spaceflight-associated neuro-ocular syndrome (SANS). To determine the pathophysiology of SANS, NASA conducted a multi-investigator study in which 11 healthy participants underwent head-down tilt bed rest, mimicking microgravity-induced cephalad fluid shifts, combined with elevated ambient CO2 levels similar to those on the ISS (HDT+CO2). As part of that study, we examined the effects of HDT+CO2 on cerebral perfusion.
Using arterial spin labeling, we compared cerebral perfusion before, during, and after HDT+CO2 in participants who developed SANS (n = 5) with those who did not (n = 6).
All participants demonstrated a decrease in perfusion during HDT+CO2 (mean decrease of 25.1% at HDT7 and 16.2% at HDT29); however, the timing and degree of change varied between the groups. At day 7 of HDT+CO2, the SANS group experienced a greater reduction in perfusion than the non-SANS group (p =.05, 95% CI:-0.19 to 16.11, d=.94, large effect). Conversely, by day 29 of HDT+CO2, the SANS group had significantly higher perfusion (approaching their baseline) than the non-SANS group (p = .04, 95% CI:0.33 to 13.07, d=1.01, large effect).
Compared with baseline and recovery, HDT+CO2 resulted in reduced cerebral perfusion which varied based on SANS status. Further studies are needed to unravel the relative role of HDT vs hypercapnia, to determine if these perfusion changes are clinically relevant, and whether perfusion changes contribute to the development of SANS during spaceflight.
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Availability of data and material
Data is available by request to NASA at https://lsda.jsc.nasa.gov/.
Data was processed using the open-access FMRIB Software Library version 6.0.3 (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/)
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Research reported in this study was facilitated by the Spaceflight Standard Measures Cross-Cutting Project of the Human Research Program of the National Aeronautics and Space Administration. We thank Grant Gauthier, Ali Freitas, and Lexus Hartung for assistant with data analysis. We also thank the entire VaPER study staff.
This study was funded by the National Aeronautics and Space Administration (NASA), grant # NNX13AJ92G.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the local ethical commission of the regional medical association, Ärztekammer Nordrhein, and the University of Florida, Medical University of South Carolina, and Johnson Space Center Institutional Review Boards.
Informed consent was obtained from all individual participants included in the study.
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Roberts, D.R., Collins, H.R., Lee, J.K. et al. Altered cerebral perfusion in response to chronic mild hypercapnia and head-down tilt Bed rest as an analog for Spaceflight. Neuroradiology 63, 1271–1281 (2021). https://doi.org/10.1007/s00234-021-02660-8
- Healthy participant
- Head-down tilt bed rest
- Human spaceflight
- Spaceflight-associated neuro-ocular syndrome