Lower Body Negative Pressure Counters Simulated Microgravity‐Induced Elevations of Intracranial Pressure

Abstract

Ophthalmic evaluations of 7 astronauts after 6‐month missions to International Space Station show unexpected vision impairment. Lumbar punctures in 4 astronauts showed elevations of cerebrospinal fluid pressure after flight. We hypothesized that lower body negative pressure (LBNP) would counteract head down, head‐down tilt (HDT), induced elevations in intracranial pressure (ICP). Ten healthy volunteers participated in this study (mean age: 34 years) after IRB review. Cerebral and Cochlear Fluid Pressure (CCFP, noninvasive ICP surrogate) device determined relative changes in ICP. ICP, arm blood pressure, and heart rate were measured during the last minute of each condition. Subjects were positioned supine (5 mins), sitting (5 mins), 15‐degrees HDT (5 mins) and ten minutes of HDT with LBNP (25 mmHg). RMANOVA determined statistical significance (p<0.05). ICP significantly increased from the sitting to the supine posture, p=0.028. Moreover, ICP further increased when the subjects were positioned in HDT, p=0.005. However, when LBNP was activated during HDT, ICP decreased and was not significantly different from supine levels (p=0.549). Mean blood pressure and heart rate did not change significantly across all conditions. In conclusion, short duration exposures to simulated microgravity increase ICP significantly and importantly, LBNP counteracts these elevations of ICP. Therefore, spaceflight countermeasures that shift fluid to the lower body may mitigate vision problems. This project was supported by NSBRI through NASA NCC 9‐58 (to BRM), APS Undergraduate Summer Research Fellowship (to EMC), and NASA grant NNX13AJ12G (to ARH).