Spaceflight-Associated Neuro-Ocular Syndrome (SANS) describes a constellation of ocular structural changes exhibited by ~33% of astronauts returning from long duration-spaceflights [1, 2]. These changes include optic disc edema, choroidal folding, globe flattening, and hyperopic refractive error shifts. The etiological mechanisms behind SANS remain insufficiently understood; it is thought to be linked to headward fluid shifts, increased intracranial pressure, altered glymphatic drainage, hypercapnia-related volume and pressure disturbances, and a number of other potential mechanisms . Traveling beyond the confines of Earth’s atmosphere is accompanied by various health stressors such as microgravity, ionizing radiation, and disrupted circadian rhythms ; insight into the various complex interactions of these induced stressors on brain fluid dynamics, glymphatic exchange, and brain health is necessary to develop effective SANS countermeasures.
The glymphatic system functions to distribute solutes and clear waste from the brain via cerebrospinal fluid (CSF) circulation and interstitial fluid flow along its perivascular spaces.
Glymphatic clearance has been implicated as a key determinant of brain health, acting to remove or redistribute metabolic products, inflammatory and immune-mediated molecules, as well as additional solutes for disposal . Glymphatic dysfunction may cause the failure of interstitial solute clearance or derangement of cranial fluid dynamics resulting from the mismatch between CSF influx and interstitial fluid efflux, with negative impacts on brain homeostasis. It is not known at this point how the environmental stressors of microgravity exposure impact glymphatic function.
In the proposed study, we will investigate the individual and combined effects of simulated microgravity and hypercapnia on human glymphatic function. Using acute head-down tilt (HDT) bedrest and exposure to elevated CO2, this study will be a critical first step toward understanding the potential interactions of microgravity and elevated CO2 on perivascular glymphatic function and brain health.
Progress to Date We identified a vendor for an MRI-safe foam wedge to place participants in the head-down tilt position. We acquired it and have conducted pilot testing to ensure that it does not create signal distortion in the MRI environment. We also confirmed that it is tolerable for participants to remain head-down tilt on the wedge for the duration of the testing day (approximately eight hours). We are currently in process of recruiting participants and collecting data in the head-down tilt position with and without elevated CO2.