Last Published:  07/30/21 01:05:31 PM (Central)
Responsible Element: Human Health Countermeasures (HHC)
Status: Open
Present state of knowledge: Weightlessness during spaceflight causes a headward fluid shift in multiple compartments, including arterial, venous, and cerebrospinal fluid and is hypothesized to underlie the development of SANS signs and symptoms. It is proposed that arterial, venous, and capillary pressures at the level of the eye are elevated and may directly lead to SANS. This could act through venous congestion and/or enhanced capillary filtration that is not adequately cleared from local tissue. This hypothesis could explain the lack of a dilated optic nerve sheath diameter and localized development of edema in tissue lacking a blood-brain or blood-retinal barrier. The observed flow reductions in the left internal Jugular Vein in some astronauts with thrombi formation in a few could also be related to the venous congestion and to SANS. The possible role of chronically elevated intracranial pressure in the pathophysiology of SANS and evaluations of fluid-shift related changes to brain structure and function are covered in gap SANS-102.

Research approach: Research that has been and that will be continue to be pursued by HRP includes investigating measures of vascular fluid shifts, measures of ocular structural and functional changes, and how these are affected by varying lengths of spaceflight. Correlation between degree of fluid shift and ocular changes will be studied, as will evaluation of inter-individual variations in space-flown astronauts, and long-term health impacts. Understanding the magnitude of fluid shifts in the various fluid compartments (intravascular, interstitial, lymphatic, CSF, etc.) will identify which one might be the best target for intervention. The causes for possible mechanical/anatomical induced venous flow reduction in neck and head veins will be explored both on ISS and during parabolic flights. By using partial-G exposures (0-1) during parabolic flights and during Lunar landings, G-thresholds of fluid shifts for SANS manifestations can be explored.
Target for Closure
An understanding as to the importance of spaceflight-induced head-ward fluid shifts on ocular structure and function and SANS manifestations. With this understanding, the fluid shifts hypothesis will be confirmed or rejected, and the knowledge will support the development of integrated mechanical countermeasures for mitigation of the fluid shift.
Risk Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)
You are here! Gap SANS-101: Determine the relationship between fluid shifts (intravascular, interstitial, CSF) and ocular manifestations in astronauts during spaceflight.

Multi-Disciplinary Research Plans

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