151. Quantitative MRI volumetry, diffusivity, cerebrovascular flow, and cranial hydrodynamics during head-down tilt and hypercapnia: the SPACECOT study.
- Author
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Kramer LA, Hasan KM, Sargsyan AE, Marshall-Goebel K, Rittweger J, Donoviel D, Higashi S, Mwangi B, Gerlach DA, and Bershad EM
- Subjects
- Adult, Carbon Dioxide, Carotid Arteries physiology, Cerebrospinal Fluid physiology, Cross-Over Studies, Double-Blind Method, Humans, Hydrodynamics, Magnetic Resonance Imaging methods, Male, Space Flight methods, Cerebrovascular Circulation physiology, Head-Down Tilt physiology, Hypercapnia physiopathology
- 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 (CO
2 ). 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% CO2 Volume 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 and P = 0.01, respectively); this was partially reversed by acute 3% CO2 exposure. Following HDT (ambient air), exposure to 3% CO2 increased 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% CO2 augments CSF pulsatility within the cerebral aqueduct and lateral ventricles. NEW & NOTEWORTHY Head-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., (Copyright © 2017 the American Physiological Society.)- Published
- 2017
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