Central objectives: to date, 19 out of 25 long-duration crew members (76%) have experienced in-flight and/or post-flight vision changes. These changes define the visual impairment/intracranial…

Central objectives: to date, 19 out of 25 long-duration crew members (76%) have experienced in-flight and/or post-flight vision changes. These changes define the visual impairment/intracranial pressure (viip) syndrome. Although the exact cause of viip is unknown at this time, IT is suspected that the microgravity-induced shift in fluids from the lower body to the upper body (cephalad fluid shift) plays a significant role. This fluid shift, in turn, may cause an elevation in intracranial pressure (ICP) and intraocular pressure (IOP). Another factor that has been proposed to contribute to viip is exercise. Although moderate and high intensity aerobic or resistance exercise have clearly identified benefits for cardiac, muscle and bone health, whether such exercise contributes to the development of viip is unknown. Methods: our overall goal is to characterize the impact of 3 exercise modalities used by astronauts on cerebral blood flow, ICP, and IOP. We propose to use head down tilt (HDT), a ground based analog that is well established to elicit similar cephalad fluid shifts as spaceflight. Subjects will undergo 3 HDT sessions: 1) HDT + resistance exercise, 2) HDT + moderate intensity aerobic exercise, and 3) HDT + high intensity aerobic exercise. During and following each HDT session cerebral blood flow, IOP, and ICP will be measured. Significance: information characterizing factors contributing to the viip syndrome is of fundamental importance for sustaining human presence in space and extending the exploration of our solar system. NASA s human research program (HRP) has therefore established risks and gaps related to determining the etiology of visual acuity and ocular structural and functional changes observed in- and post-flight, and identifying safe and effective countermeasure to mitigate changes in ocular structure and intracranial hypertension. This proposal addresses the NASA request for short-term proposals that could lead to novel breakthroughs addressing one or more risks and gaps. Our proposal is specifically relevant for: risk of spaceflight-induced intracranial hypertension/vision alterations and the following gaps: GAP VIIP1: what are the etiological mechanisms and contributing risk factors for ocular structural and functional changes seen in-flight and post-flight? GAP VIIP13: identify preventative and treatment countermeasures to mitigate changes in ocular structure and function and intracranial pressure during spaceflight. IT is expected that results from the proposed investigation will provide important information that could ultimately not only improve the well being of astronauts in microgravity and upon return to earth, but could also enhance the well-being of numerous populations such as individuals with intracranial hypertension and glaucoma.