Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 120, Issue 12, Pages 1466-1473Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00841.2015
Keywords
visual impairment and intracranial pressure; microgravity; cerebral blood flow; head-down tilt; MRI
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Funding
- German Aerospace Center [2475 115]
- SpaceLife Scholarship of the Helmholtz Space Life Sciences Research School
- Helmholtz Association (Helmholtz-Gemeinschaft) [VH-KO-300]
- DLR
- Aerospace Executive Board
- Institute of Aerospace Medicine
- Rymdstyrelsen (Swedish National Space Board)
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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 degrees) 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 degrees) and after 4.5 h of HDT at -6 degrees, -12 degrees (with and without 1% CO2), and -18 degrees. 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 degrees HDT (P = 0.039). Moreover, the addition of 1% CO2 to -12 degrees HDT caused an increase in total arterial blood flow (P = 0.016) and jugular venous outflow (P = 0.001) compared with -12 degrees HDT with ambient atmosphere. Overall, the results indicate decreased cerebral blood flow during HDT, which may have implications for microgravity-induced cerebral hemodynamic changes.
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