Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions.

Fabrizia Salerni,Giovanna Guidoboni,Christophe Prud’Homme,Sakamuri V Reddy,Marcela Szopos,Alon Harris,Peter Pinsky,Rodolfo Repetto

doi:10.1371/journal.pone.0216012

Abstract

This work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in structural and functional changes in the eyes of astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight.

Highlights

Microgravity conditions have been observed to induce structural and functional changes in the eyes of many astronauts that pose serious challenges for both astronauts and their missions in space [1,2,3]
This discrepancy in the results might be due to different protocols adopted for the study, such as the extent to which head tilt was enforced, and the fact that many factors may influence ocular structural and functional changes, including blood pressure, intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFp), which may vary among individuals and are difficult to isolate in an experimental setting
Changes in the blood oncotic pressure modify both ΔπCB and Δπp, leading to changes in the filtration across the blood-brain barrier and the ciliary body, respectively, and, Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions to changes in intracranial pressure (ICP), CSFp and IOP

Summary

Introduction

Microgravity conditions have been observed to induce structural and functional changes in the eyes of many astronauts that pose serious challenges for both astronauts and their missions in space [1,2,3] This syndrome, known as spaceflight associated neuro-ocular syndrome (SANS), is characterized by a large number of apparently unrelated and often not concurrent symptoms. Optic disc edema, which is one of the ocular findings associated with SANS, was not observed in the LHDT study conducted by Taibbi et al [7], whereas it was observed in the study conducted by Laurie et al [8] This discrepancy in the results might be due to different protocols adopted for the study, such as the extent to which head tilt was enforced, and the fact that many factors may influence ocular structural and functional changes, including blood pressure, intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFp), which may vary among individuals and are difficult to isolate in an experimental setting

Objectives

Methods

Results

Conclusion