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      Proposed mechanism for reduced jugular vein flow in microgravity

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          Abstract

          Internal jugular flow is reduced in space compared with supine values, which can be associated with internal jugular vein (IJV) thrombosis. The mechanism is unknown but important to understand to prevent potentially serious vein thromboses on long duration flights. We used a novel, microgravity‐focused numerical model of the cranial vascular circulation to develop hypotheses for the reduced flow. This model includes the effects of removing hydrostatic gradients and tissue compressive forces – unique effects of weightlessness. The IJV in the model incorporates sensitivity to transmural pressure across the vein, which can dramatically affect resistance and flow in the vein. The model predicts reduced IJV flow in space. Although tissue weight in the neck is reduced in weightlessness, increasing transmural pressure, this is more than offset by the reduction in venous pressure produced by the loss of hydrostatic gradients and tissue pressures throughout the body. This results in a negative transmural pressure and increased IJV resistance. Unlike the IJV, the walls of the vertebral plexus are rigid; transmural pressure does not affect its resistance and so its flow increases in microgravity. This overall result is supported by spaceflight measurements, showing reduced IJV area inflight compared with supine values preflight. Significantly, this hypothesis suggests that interventions that further decrease internal IJV pressure (such as lower body negative pressure), which are not assisted by other drainage mechanisms (e.g. gravity), might lead to stagnant flow or IJV collapse with reduced flow, which could increase rather than decrease the risk of venous thrombosis.

          Abstract

          Internal jugular flow is reduced in space, which can be associated with internal jugular vein (IJV) thrombosis. We used a novel, microgravity‐focused numerical model of the cranial vascular circulation to develop hypotheses for the reduced flow. Weightlessness reduces venous pressures throughout the body which reduces internal jugular vein diameter and thus internal jugular venous flow.

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          Most cited references25

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          Anatomy and physiology of cerebrospinal fluid.

          The cerebrospinal fluid (CSF) is contained in the brain ventricles and the cranial and spinal subarachnoid spaces. The mean CSF volume is 150 ml, with 25 ml in the ventricles and 125 ml in subarachnoid spaces. CSF is predominantly, but not exclusively, secreted by the choroid plexuses. Brain interstitial fluid, ependyma and capillaries may also play a poorly defined role in CSF secretion. CSF circulation from sites of secretion to sites of absorption largely depends on the arterial pulse wave. Additional factors such as respiratory waves, the subject's posture, jugular venous pressure and physical effort also modulate CSF flow dynamics and pressure. Cranial and spinal arachnoid villi have been considered for a long time to be the predominant sites of CSF absorption into the venous outflow system. Experimental data suggest that cranial and spinal nerve sheaths, the cribriform plate and the adventitia of cerebral arteries constitute substantial pathways of CSF drainage into the lymphatic outflow system. CSF is renewed about four times every 24 hours. Reduction of the CSF turnover rate during ageing leads to accumulation of catabolites in the brain and CSF that are also observed in certain neurodegenerative diseases. The CSF space is a dynamic pressure system. CSF pressure determines intracranial pressure with physiological values ranging between 3 and 4 mmHg before the age of one year, and between 10 and 15 mmHg in adults. Apart from its function of hydromechanical protection of the central nervous system, CSF also plays a prominent role in brain development and regulation of brain interstitial fluid homeostasis, which influences neuronal functioning. Copyright © 2011 Elsevier Masson SAS. All rights reserved.
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            Effect of gravity and microgravity on intracranial pressure.

            Astronauts have recently been discovered to have impaired vision, with a presentation that resembles syndromes of elevated intracranial pressure on Earth. Gravity has a profound effect on fluid distribution and pressure within the human circulation. In contrast to prevailing theory, we observed that microgravity reduces central venous and intracranial pressure. This being said, intracranial pressure is not reduced to the levels observed in the 90 deg seated upright posture on Earth. Thus, over 24 h in zero gravity, pressure in the brain is slightly above that observed on Earth, which may explain remodelling of the eye in astronauts.
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              Assessment of Jugular Venous Blood Flow Stasis and Thrombosis During Spaceflight

              This cohort study examines the internal jugular vein flow and morphology of crew members of the International Space Station and the use of lower body negative pressure as a countermeasure to the headward fluid shift experienced during space flight.
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                Author and article information

                Contributors
                Jay.C.Buckey.Jr@dartmouth.edu
                Journal
                Physiol Rep
                Physiol Rep
                10.1002/(ISSN)2051-817X
                PHY2
                physreports
                Physiological Reports
                John Wiley and Sons Inc. (Hoboken )
                2051-817X
                01 May 2021
                April 2021
                : 9
                : 8 ( doiID: 10.1002/phy2.v9.8 )
                : e14782
                Affiliations
                [ 1 ] Thayer School of Engineering at Dartmouth Hanover NH USA
                [ 2 ] Creare LLC Hanover NH USA
                [ 3 ] Stanford University Palo Alto CA USA
                [ 4 ] University of Colorado Boulder Boulder CO USA
                [ 5 ] University of Texas Medical Branch Galveston TX USA
                [ 6 ] Geisel School of Medicine at Dartmouth College Lebanon NH USA
                Author notes
                [*] [* ] Correspondence

                Jay C. Buckey, M.D. Department of Medicine, Dartmouth‐Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756, USA.

                Email: Jay.C.Buckey.Jr@ 123456dartmouth.edu

                Author information
                https://orcid.org/0000-0003-4591-4431
                Article
                PHY214782
                10.14814/phy2.14782
                8087922
                33931957
                880206e2-a08b-4233-96e2-bb9f9e75862a
                © 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 22 January 2021
                : 07 December 2020
                : 31 January 2021
                Page count
                Figures: 5, Tables: 5, Pages: 17, Words: 9719
                Funding
                Funded by: NASA‐Epscor
                Award ID: NNX13AD35A
                Funded by: National Space Biomedical Research Institute , open-funder-registry 10.13039/100008898;
                Award ID: CA03401
                Categories
                Original Article
                Original Articles
                Custom metadata
                2.0
                April 2021
                Converter:WILEY_ML3GV2_TO_JATSPMC version:6.0.2 mode:remove_FC converted:01.05.2021

                jugular venous blood flow,microgravity,numerical model,vertebral plexus

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