Lower body negative pressure counters headward fluid shifts in the brain and eye (1103.3)

Abstract

Recent ophthalmic evaluations of 7 astronauts after 6‐month missions to International Space Station show unexpected vision impairment. In addition, lumbar punctures in 4 astronauts with optic disc edema showed moderate elevations of cerebral spinal fluid pressure after returning to Earth. This Visual Impairment Intracranial Pressure (VIIP) syndrome is likely due to a head‐ward body fluid shift that elevates intracranial pressure (ICP). We hypothesized that a moderate level of lower body negative pressure (LBNP) would counteract headdown, body‐tilt, induced elevations in intraocular pressure (IOP) and ICP. Seven healthy non‐smoking volunteers participated in this study (mean age: 36 years). Right and left IOP, ICP (ultrasound pulse phase lock loop), arm blood pressure, and heart rate were measured during the last minute of each testing condition. Subjects were positioned supine (5 mins), sitting (5 mins), 15‐degrees head‐down tilt (HDT) (5 mins) and ten minutes of HDT with LBNP (25 mmHg). The order of HDT and HDT+LBNP tests were balanced. The right and left IOP values were averaged and used for statistical analysis (p<0.05). Data are presented as mean ± standard deviation. The change from supine was calculated for IOP values. IOP significantly decreased from supine to sitting posture by 2.4 ± 0.7 mmHg, and increased by 1.3 ± 2.4 mmHg from supine to the HDT position. LBNP during head‐down‐tilt significantly lowered IOP to supine levels (difference from supine, 0.1 ± 0.8 mmHg). In addition, added LBNP during HDT significantly decreased ICP pulse amplitudes by 2.8±4.3 microns. Mean blood pressure and heart rate did not change significantly across all conditions. These data demonstrate that short duration exposures to HDT increase IOP and ICP significantly and further, that LBNP counteracts these elevations of IOP and ICP. Therefore, LBNP may help counteract vision impairments in space. Supported by NSBRI postdoctoral fellowship (BRM), la Caixa fellowship (NNG), and NASA grant NNX13AJ12G (ARH).