Effects of short-term exposure to head-down tilt on cerebral hemodynamics: a prospective evaluation of a spaceflight analog using phase-contrast MRI

• Published in: Journal of applied physiology (1985) 2016-06, Vol.120 (12), p.1466-1473
• Main Authors: Marshall-Goebel, Karina, Ambarki, Khalid, Eklund, Anders, Malm, Jan, Mulder, Edwin, Gerlach, Darius, Bershad, Eric, Rittweger, Jörn
• Format: Article
• Language: English
• Subjects: Adult; Blood pressure; Cerebellum - blood supply; Cerebellum - physiology; Cerebral Arteries - physiology; cerebral blood flow; Cerebral Veins - physiology; Cerebrovascular Circulation - physiology; Flow velocity; Fluid dynamics; head-down tilt; Head-Down Tilt - physiology; Hemodynamics - physiology; Highlighted Topic; Humans; Intracranial Pressure - physiology; Jugular Veins - physiology; Magnetic Resonance Imaging - methods; Male; microgravity; MRI; NMR; Nuclear magnetic resonance; Physiology; Prospective Studies; Space Flight - methods; Veins & arteries; visual impairment and intracranial pressure; Weightlessness; Weightlessness Simulation - methods
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00841.2015

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.