The effects of elevated CO₂ on brain and ocular signal intensity with intravenous contrast MRI

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 CO₂, 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 CO₂ versus ambient air across two counterbalanced sessions. We scanned 12 participants at baseline using structural MRI and at 90 and 360 min 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 T₁ tissue enhancement when participants were breathing elevated CO₂. The vitreous chamber of the eye showed larger enhancements on the T₁ sequence for 1.0% and 2.0% CO₂ conditions. The findings suggest that some brain and ocular regions show delayed glymphatic clearance with elevated CO₂.NEW & NOTEWORTHY In this study, we investigated the effects of elevated CO₂ on delayed signal enhancement in brain MRI following gadolinium contrast injection. We found CO₂ effects on brain white matter and vitreous chamber of the eye, with higher tissue enhancement at 90 min relative to when participants breathed ambient air. These findings suggest delayed glymphatic clearance with elevated CO₂.