Quantification of arterial, venous, and cerebrospinal fluid flow dynamics by magnetic resonance imaging under simulated micro-gravity conditions: a prospective cohort study

Arslan M Zahid,Bryn Martin,Stephanie Collins,John N Oshinski,C Ross Ethier

doi:10.1186/s12987-021-00238-3

Abstract

BackgroundAstronauts undergoing long-duration spaceflight are exposed to numerous health risks, including Spaceflight-Associated Neuro-Ocular Syndrome (SANS), a spectrum of ophthalmic changes that can result in permanent loss of visual acuity. The etiology of SANS is not well understood but is thought to involve changes in cerebrovascular flow dynamics in response to microgravity. There is a paucity of knowledge in this area; in particular, cerebrospinal fluid (CSF) flow dynamics have not been well characterized under microgravity conditions. Our study was designed to determine the effect of simulated microgravity (head-down tilt [HDT]) on cerebrovascular flow dynamics. We hypothesized that microgravity conditions simulated by acute HDT would result in increases in CSF pulsatile flow.MethodsIn a prospective cohort study, we measured flow in major cerebral arteries, veins, and CSF spaces in fifteen healthy volunteers using phase contrast magnetic resonance (PCMR) before and during 15° HDT.ResultsWe found a decrease in all CSF flow variables [systolic peak flow (p = 0.009), and peak-to-peak pulse amplitude (p = 0.001)]. Cerebral arterial average flow (p = 0.04), systolic peak flow (p = 0.04), and peak-to-peak pulse amplitude (p = 0.02) all also significantly decreased. We additionally found a decrease in average cerebral arterial flow (p = 0.040). Finally, a significant increase in cerebral venous cross-sectional area under HDT (p = 0.005) was also observed.ConclusionsThese results collectively demonstrate that acute application of −15° HDT caused a reduction in CSF flow variables (systolic peak flow and peak-to-peak pulse amplitude) which, when coupled with a decrease in average cerebral arterial flow, systolic peak flow, and peak-to-peak pulse amplitude, is consistent with a decrease in cardiac-related pulsatile CSF flow. These results suggest that decreases in cerebral arterial inflow were the principal drivers of decreases in CSF pulsatile flow.

Highlights

Astronauts undergoing long-duration spaceflight are exposed to numerous health risks, including Spaceflight-Associated Neuro-Ocular Syndrome (SANS), a spectrum of ophthalmic changes that can result in permanent loss of visual acuity
A spaceflight-induced condition thought to be related to alterations in cerebrospinal fluid (CSF) flow dynamics is Spaceflight Associated Neuro-ocular Syndrome (SANS), a spectrum of poorly understood neuro-ophthalmological findings documented in a subset of astronauts returning from the International Space Station
Venous blood flow variables showed an increase in the internal jugular vein cross-sectional area from baseline to Head-down tilt (HDT) (Table 2)

Summary

Introduction

Astronauts undergoing long-duration spaceflight are exposed to numerous health risks, including Spaceflight-Associated Neuro-Ocular Syndrome (SANS), a spectrum of ophthalmic changes that can result in permanent loss of visual acuity. There is a paucity of knowledge in this area; in particular, cerebrospinal fluid (CSF) flow dynamics have not been well characterized under microgravity conditions. A spaceflight-induced condition thought to be related to alterations in CSF flow dynamics is Spaceflight Associated Neuro-ocular Syndrome (SANS), a spectrum of poorly understood neuro-ophthalmological findings documented in a subset of astronauts returning from the International Space Station. Of seven United States astronauts evaluated for SANS after long-duration spaceflight of greater than six months, six developed decreased near field vision with nerve fiber layer thickening; five exhibited optic disc edema, globe flattening, and choroidal folds; and three had nerve fiber layer thickening [2, 3]. Postflight surveys of 300 astronauts suggest that inflight loss of both near and distant visual acuity is a significant issue that increases in prevalence with duration of flight, with 29 % of short duration and 60 % of long duration mission participants reporting some degree of loss in visual acuity [2, 4]

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