Task Progress:
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INTRODUCTION Spaceflight-associated neuro-ocular syndrome (SANS) describes structural and functional alterations of the eye that develop in many astronauts during long-duration spaceflight missions (>1 month). The chronic headward fluid shift that occurs in weightlessness is hypothesized to be the primary factor underlying this condition. However, the specific mechanisms are unknown, and it remains uncertain whether the incidence and severity of SANS findings correlate with mission duration.
PURPOSE The purpose of this study is to evaluate whether spaceflight mission duration influences SANS incidence and severity and whether vascular changes during weightlessness relate to SANS findings. Specifically, we will test the hypotheses that ocular tissue structure, ocular vascular structure, and ocular function are altered in spaceflight. Cervicothoracic vasculature will be evaluated for volume increase in both incidence and magnitude with mission duration, as well as the magnitude of vascular adaptation and its correlation with ocular findings. Moreover, we will test the hypothesis that a genetic predisposition to SANS is conferred by 1-carbon metabolism pathway-associated gene variants that compromise vascular structure and function by perturbing of B-vitamin and related metabolite levels.
METHODS Advanced techniques will be used to study the eyes, cervicothoracic vasculature, and 1-carbon pathway genetics and biochemistry in 30 astronauts scheduled to participate in missions on the International Space Station (ISS). Subjects will be divided into 3 cohorts (n=10/cohort) based on mission duration, specified as Short (~2 months), Standard (~6 months), or Extended (~1 year). Ocular structure and function will be evaluated using magnetic resonance imaging (MRI) and 3D structural analysis, optical coherence tomography (OCT), OCT angiography (OCTA), electroretinography (ERG), visual field analysis, pneumotonometry (PTM, intraocular pressure/IOP), visual field analysis, optical biometry, and dynamic vessel analysis (DVA). Ultrasound will be used to investigate variables associated with the cervicothoracic vasculature, including stroke volume, cardiac output, and internal jugular vein morphology/pressure and carotid intima-media thickness. In addition, MRI will be used to assess brain structural changes. Many of the experiments will be performed before, during, and after flight (Table 1). Some of the data collected on the ground (i.e., before and after flight) will be acquired in the seated and supine postures to simulate the fluid shift experienced upon transition from 1 g to weightlessness. To complement the research measures, medically relevant test results already collected by the Space Medicine Operations Division will be requested.
Mission Impact The Investigating Structure and Function of the Eye (iSAFE) research study will advance NASA’s understanding of SANS, an important human health and performance risk through the following specific aims: 1) The relationships between mission duration and SANS development, progression, and recovery will be defined. 2) Experiments will identify whether optic disc edema is accompanied by leakage of the retinal vasculature. 3) With the implementation of ERG, visual function will be measured during spaceflight for the first time and will be related to the development of optic disc edema. 4) Possible mechanisms underlying SANS will be evaluated, including vascular adaptations in weightlessness and 1-carbon pathway genetics.
This research will narrow the SANS101 and SANS102 knowledge gaps described in the Human Research Roadmap and, in turn, will help NASA to evaluate this spaceflight-associated risk more accurately and refine its approach to SANS countermeasure development.
Study Progress in this reporting period includes a total of 8 of 10 crew assigned to standard duration missions (4-6 months) who have consented to participate. Forward work includes continuing to support all phases of preflight, inflight, and postflight data collection and training of crew members.
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Abstracts for Journals and Proceedings
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Macias BR, Laurie SS, Brunstetter T, Young M, Huang A, Karanjia R, Lee SMC, Martin BA, Kramer LA, Sadda S, Smith SM, Zwart SR, Martin DS, Miller A, Melvin SA. "CIPHER: Investigating structure and function of the eye (isafe)." 2024 NASA Human Research Program Investigators' Workshop, Galveston, Texas, February 13-16, 2024. Abstracts. 2024 NASA Human Research Program Investigators' Workshop, Galveston, Texas, February 13-16, 2024. , Feb-2024
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