title: Effects of short-term exposure to head-down tilt on cerebral hemodynamics: a prospective evaluation of a spaceflight analog using phase-contrast MRI.
abstract: Alterations in cerebral hemodynamics in microgravity are hypothesized to occur during spaceflight and could be linked to the Visual Impairment and Intracranial Pressure syndrome. Head-down tilt (HDT) is frequently used as a ground-based analog to simulate cephalad fluid shifts in microgravity; however, its effects on cerebral hemodynamics have not been well studied with MRI techniques. Here, we evaluate the effects of 1) various HDT angles on cerebral arterial and venous hemodynamics; and 2) exposure to 1% CO2 during an intermediate HDT angle (-12°) as an additional space-related environmental factor. Blood flow, cross-sectional area (CSA), and blood flow velocity were measured with phase-contrast MRI in the internal jugular veins, as well as the vertebral and internal carotid arteries. Nine healthy male subjects were measured at baseline (supine, 0°) and after 4.5 h of HDT at -6°, -12° (with and without 1% CO2), and -18°. We found a decrease in total arterial blood flow from baseline during all angles of HDT. On the venous side, CSA increased with HDT, and outflow decreased during -12° HDT (P = 0.039). Moreover, the addition of 1% CO2 to -12° HDT caused an increase in total arterial blood flow (P = 0.016) and jugular venous outflow (P < 0.001) compared with -12° HDT with ambient atmosphere. Overall, the results indicate decreased cerebral blood flow during HDT, which may have implications for microgravity-induced cerebral hemodynamic changes.
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany; Faculty of Medicine, University of Cologne, Cologne, Germany; Karina.Marshall-Bowman@dlr.de.
authors.forename: Karina
authors.identifier: 0000-0002-5240-7625
authors.initials: K
authors.lastname: Marshall-Goebel
authors.affiliation: Department of Radiation Sciences, Umeå University, Umeå, Sweden;
authors.forename: Khalid
authors.initials: K
authors.lastname: Ambarki
authors.affiliation: Department of Radiation Sciences, Umeå University, Umeå, Sweden; Centre of Biomedical Engineering and Physics, Umeå University, Umeå, Sweden;
authors.forename: Anders
authors.initials: A
authors.lastname: Eklund
authors.affiliation: Department of Pharmacology and Clinical Neuroscience, Umeå University, Umeå, Sweden;
authors.forename: Jan
authors.initials: J
authors.lastname: Malm
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany;
authors.forename: Edwin
authors.initials: E
authors.lastname: Mulder
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany;
authors.forename: Darius
authors.initials: D
authors.lastname: Gerlach
authors.affiliation: Department of Neurology, Baylor College of Medicine, Houston, Texas; and.
authors.forename: Eric
authors.identifier: 0000-0003-4091-2031
authors.initials: E
authors.lastname: Bershad
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany; Department of Pediatric and Adolescent Medicine, University of Cologne, Cologne, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
mesh_terms: D000328:Adult; D002531:Cerebellum / Q000098:blood supply / Q000502:physiology*; D002536:Cerebral Arteries / Q000502:physiology; D002550:Cerebral Veins / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology; D018475:Head-Down Tilt / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D007601:Jugular Veins / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D011446:Prospective Studies; D013026:Space Flight / Q000379:methods; D014893:Weightlessness; D018474:Weightlessness Simulation / Q000379:methods
keywords: MRI; cerebral blood flow; head-down tilt; microgravity; visual impairment and intracranial pressure