Optic nerve sheath ultrasound in short-duration human spaceflight

Bader Shirah, Andrew G. Lee, Christopher E. Mason, Shawna Pandya, Yvette Gonzalez, Aaron H. Persad, Mohammed M. Ahmed, Mishaal N. Ashemimry, Jon Sen

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Introduction: The pathophysiological mechanisms underlying Spaceflight Associated Neuro-ocular Syndrome (SANS) are not fully understood. Various degrees of structural and functional alterations of the visual system are well-described as key features of the syndrome. However, challenges remain in its prediction, prevention, and clinical management. Short-duration space missions offer valuable opportunities to study potentially quantifiable features of SANS in the earliest time frame of microgravity exposure. Point-of-care optic nerve sheath ultrasound, a terrestrial bedside practice for real-time inference of intracranial pressure (ICP) elevation, is used in this study to quantify the early behavior of optic nerve sheath diameter (ONSD), a measure conceivably relevant to the subsequent development of SANS-induced optic nerve edema in some astronauts. Methods: This experiment involved collecting data from the four astronauts of the Axiom Mission 2 prior to, during, and directly after a short-duration mission (10 days) to the International Space Station. All optic nerve imaging was performed with a multipurpose ultrasound device (Vivid q and 12L-RS linear array probe, GE HealthCare, Chicago, United States) through closed eyelids. ICP was calculated from the obtained ONSD values using the following empirical formula: 5.00 × ONSD in mm—13.92mmHg. Results: The ONSD values and calculated ICP were higher in-flight in comparison to preflight and postflight measurements. The ONSD values were higher in the left eye compared to the right eye, resulting in higher calculated ICP. The in-flight data showed gradually decreasing values of the ONSD and calculated ICP of the left eye as the days of the mission progressed. Subgroup analysis between age groups (mean age of 65 years vs. 32.5 years) demonstrated more pronounced changes in the ONSD and calculated ICP of both eyes in the older group. Further analysis indicated that the ONSD and calculated ICP of both eyes appear more affected in female astronauts compared to male astronauts. Conclusion: Optic nerve sheath ultrasound can provide dynamic information about the effects of short-duration spaceflight on ONSD and ICP. Our study is unique in suggesting early expansion of the optic nerve sheaths as a local effect of the cephalad fluid shifts—the probable trigger factor in the development of SANS that appears to lead to higher in-flight ONSD and calculated ICP compared to preflight and postflight measurements, as well as higher ONSD and calculated ICP in the left eye compared to the right side. We believe that this work will contribute to the understanding of SANS pathophysiology, which, in turn, may lead to the development of countermeasures and mitigation strategies in the future.

Original languageEnglish (US)
Title of host publicationNeuroscience Research in Short-Duration Human Spaceflight
PublisherElsevier
Pages43-64
Number of pages22
ISBN (Electronic)9780443339189
ISBN (Print)9780443339196
DOIs
StatePublished - Jan 1 2024

Keywords

  • brain
  • cerebrospinal fluid pressures
  • human spaceflight
  • neuroscience
  • Optic nerve sheath ultrasound

ASJC Scopus subject areas

  • General Medicine
  • General Neuroscience

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