title: Quantitative MRI volumetry, diffusivity, cerebrovascular flow, and cranial hydrodynamics during head-down tilt and hypercapnia: the SPACECOT study.
abstract: To improve the pathophysiological understanding of visual changes observed in astronauts, we aimed to use quantitative MRI to measure anatomic and physiological responses during a ground-based spaceflight analog (head-down tilt, HDT) combined with increased ambient carbon dioxide (CO2). Six healthy, male subjects participated in the double-blinded, randomized crossover design study with two conditions: 26.5 h of -12° HDT with ambient air and with 0.5% CO2, both followed by 2.5-h exposure to 3% CO2Volume and mean diffusivity quantification of the lateral ventricle and phase-contrast flow sequences of the internal carotid arteries and cerebral aqueduct were acquired at 3 T. Compared with supine baseline, HDT (ambient air) resulted in an increase in lateral ventricular volume (P= 0.03). Cerebral blood flow, however, decreased with HDT in the presence of either ambient air or 0.5% CO2(P= 0.002 andP= 0.01, respectively); this was partially reversed by acute 3% CO2exposure. Following HDT (ambient air), exposure to 3% CO2increased aqueductal cerebral spinal fluid velocity amplitude (P= 0.01) and lateral ventricle cerebrospinal fluid (CSF) mean diffusivity (P= 0.001). We concluded that HDT causes alterations in cranial anatomy and physiology that are associated with decreased craniospinal compliance. Brief exposure to 3% CO2augments CSF pulsatility within the cerebral aqueduct and lateral ventricles.NEW & NOTEWORTHYHead-down tilt causes increased lateral ventricular volume and decreased cerebrovascular flow after 26.5 h. Additional short exposure to 3% ambient carbon dioxide levels causes increased cerebrovascular flow associated with increased cerebrospinal fluid pulsatility at the cerebral aqueduct. Head-down tilt with chronically elevated 0.5% ambient carbon dioxide and acutely elevated 3% ambient carbon dioxide causes increased mean diffusivity of cerebral spinal fluid within the lateral ventricles.
authors.affiliation: Department of Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas; larry.a.kramer@uth.tmc.edu.
authors.forename: Larry A
authors.initials: LA
authors.lastname: Kramer
authors.affiliation: Department of Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas.
authors.forename: Khader M
authors.initials: KM
authors.lastname: Hasan
authors.affiliation: Wyle Integrated Science and Engineering, Houston, Texas.
authors.forename: Ashot E
authors.initials: AE
authors.lastname: Sargsyan
authors.affiliation: Division of Space Physiology, Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.|Department of Medicine, University of Cologne, Cologne, Germany.
authors.forename: Karina
authors.identifier: http://orcid.org/0000-0002-5240-7625
authors.initials: K
authors.lastname: Marshall-Goebel
authors.affiliation: Division of Space Physiology, Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.|Department of Neurology, University of Cologne, Cologne, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Rittweger
authors.affiliation: Department of Pharmacology and Space Medicine, Baylor College of Medicine, Houston, Texas.
authors.forename: Dorit
authors.initials: D
authors.lastname: Donoviel
authors.affiliation: Tokushima University Medical School, Tokushima, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Higashi
authors.affiliation: Department of Behavioral Sciences, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas; and.
authors.forename: Benson
authors.initials: B
authors.lastname: Mwangi
authors.affiliation: Division of Space Physiology, Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.
authors.forename: Darius A
authors.initials: DA
authors.lastname: Gerlach
authors.affiliation: Neurology and Space Medicine, Baylor College of Medicine, Houston, Texas.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Bershad
mesh_terms: D000328:Adult; D002245:Carbon Dioxide; D002339:Carotid Arteries / Q000502:physiology; D002555:Cerebrospinal Fluid / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D018475:Head-Down Tilt / Q000502:physiology*; D006801:Humans; D057446:Hydrodynamics; D006935:Hypercapnia / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D013026:Space Flight / Q000379:methods
chemical_list: D002245:Carbon Dioxide
keywords: dMRI; head-down tilt; hypercapnia; intracranial hypertension; microgravity; space analog