Last Published:  07/30/21 01:05:31 PM (Central)
Responsible Element: Human Health Countermeasures (HHC)
Status: Open
Description
Present state of knowledge: Based on invasively measured intracranial pressure (ICP) values during short periods of weightlessness in parabolic flight, and the fact that astronauts do not present with traditional symptoms observed in patients with idiopathic intracranial hypertension (IIH), it is hypothesized that the headward fluid shift during spaceflight leads to an ICP that is similar, or slightly below, that of the supine posture on Earth. However, unlike on Earth where daily posture changes into the upright posture lower ICP, ICP during weightlessness remains mildly elevated 24 hours per day. Whether this chronic mild elevation in ICP is the root cause of SANS signs is unknown. Brain structural changes, including enlargement of the lateral ventricles and an upward shift of the brain, have been observed on magnetic resonance images after spaceflight and the cause of these changes is hypothesized to be the chronic headward fluid shift experienced by astronauts during spaceflight. It is unknown if this results from differences in intracranial pressure, CSF dynamics, or a direct effect of the headward fluid shift on varying fluid compartments, including arterial inflow, venous outflow, and cerebrospinal fluid flow within the central nervous system. The magnitude of the ventricular enlargement is small and partially recovers after spaceflight, but long term structural and functional consequences are unknown. Understanding the relationship between the development of ocular changes and brain structural changes will provide further insight into the role of fluid shifts in these outcomes.

Research approach
: HRP has been and will continue to pursue studies evaluating intracranial pressure in astronauts and non-astronaut subjects, in long-duration spaceflight, under short periods of weightlessness such as afforded by parabolic flight, and in head-down tilt bed rest. Both direct (invasive) and indirect (non-invasive) determinations of ICP have been and will be pursued. In addition, studies evaluating and correlating ocular and central nervous system structure and function have been and will continue to be supported.
Target for Closure
Understanding the role of potential elevated ICP and brain edema as contributors to development of SANS, and elucidation of any relationship between ocular and brain anatomic or functional changes.
Mappings
Risk Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS)
You are here! Gap SANS-102: Determine the relationship between the fluid-shifts induced ocular changes and fluid shifts in the CNS, including whether elevated intracranial pressure or brain edema play a role.
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Multi-Disciplinary Research Plans

Documentation:
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