Opposite response of blood vessels in the retina to 6\xb0 head-down tilt and long-duration microgravity

Giovanni Taibbi,Susana B Zanello,Patricia Parsons-Wingerter,Ruchi J Vyas,Sara S Mason,Corey A Theriot,Millennia Young,Matthew C Murray,Nicole M Jacobs,Kayleigh N Askin,Marina Predovic,Shiyin Lim,Gianmarco Vizzeri

doi:10.1038/s41526-021-00165-5

Abstract

The Spaceflight Associated Neuro-ocular Syndrome (SANS), associated with the headward fluid shifts incurred in microgravity during long-duration missions, remains a high-priority health and performance risk for human space exploration. To help characterize the pathophysiology of SANS, NASA’s VESsel GENeration Analysis (VESGEN) software was used to map and quantify vascular adaptations in the retina before and after 70 days of bed rest at 6-degree Head-Down Tilt (HDT), a well-studied microgravity analog. Results were compared to the retinal vascular response of astronauts following 6-month missions to the International Space Station (ISS). By mixed effects modeling, the trends of vascular response were opposite. Vascular density decreased significantly in the 16 retinas of eight astronauts and in contrast, increased slightly in the ten retinas of five subjects after HDT (although with limited significance). The one astronaut retina diagnosed with SANS displayed the greatest vascular loss. Results suggest that microgravity is a major variable in the retinal mediation of fluid shifts that is not reproduced in this HDT bed rest model.

Highlights

Recent NASA studies have established that serious risks for ocular/ visual impairments are associated with microgravity exposure on the International Space Station (ISS), especially during longduration missions[1,2,3,4,5,6,7,8,9]
The comparison of vascular patterns within images focused on the macular region in the HDT and on the optic disc in astronauts was not ideal but was limited by the availability of relevant image sets
The macular region is almost completely captured by the field of view (FOV) in both image sets

Summary

Introduction

Recent NASA studies have established that serious risks for ocular/ visual impairments are associated with microgravity exposure on the International Space Station (ISS), especially during longduration missions[1,2,3,4,5,6,7,8,9]. We tested the hypothesis that the headward fluid shifts associated with SANS and Head-Down-Tilt (HDT) bed rest, a well-established microgravity analog, are mediated at least in part by retinal blood vessels. A well-established role of the microvasculature throughout the body is the regulation and maintenance of the intravascular and extravascular fluid balances within all tissues and organs, including the highly vascularized retina[26]. By this view, the microvascular endothelia and associated smooth muscle and pericytes are responders—and active players and mediators—of fluid balances within a tissue

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