Up to 70% of astronauts develop Spaceflight Associated Neuro-ocular Syndrome (SANS), a constellation of ocular structural changes, in microgravity; the mechanisms are unknown but have hypothesized to stem from elevated CO 2 , glymphatic dysfunction, and other processes. In this preliminary study, we examined whether brain and ocular tissue signal enhancement on MRI at delay following intravenous gadolinium differs when participants breathe elevated CO 2 versus ambient air across two counterbalanced sessions. We scanned 12 participants at baseline using structural MRI and at 90 and 360 minutes following intravenous gadolinium administration. We observed that parietal and occipital lobe white matter showed a significant main effect of gas versus ambient day, with greater T 1 tissue enhancement when participants were breathing elevated CO 2 . The vitreous chamber of the eye showed larger enhancements on the T 1 sequence for 1.0% and 2.0% CO 2 conditions. The findings suggest that some brain and ocular regions show delayed glymphatic clearance with elevated CO 2 .
Seidler et al. (Wed,) studied this question.