Lessons from Spaceflight: Decreasing Intracranial Pressure by Lowering Body Negative Pressure

Introduction: Some astronauts on long duration spaceflight suffer from increased intracranial pressure (ICP), possibly related to venous stasis in zero-gravity and consequent alterations in cerebral perfusion pressure. On Earth, increased ICP is a common and potentially devastating sequelae of traumatic brain injury, brain tumors and other pathologies. Lower body negative pressure (LBNP), which pulls pooled blood away from cranial compartments, has been shown to reduce ICP in the setting of altered gravity. The aim of this study is to review published literature on the effect of LBNP on ICP in the setting of simulated microgravity using the 15° head down tilt (HDT). A better understanding of the effect of LBNP on ICP might provide new clinical opportunities for neurosurgical patients with increased ICP.

Methods: A scoping review of the literature was performed to assess the current state of LBNP devices in simulated microgravity conditions following the PRISMA guidelines for scoping review. PubMed, Scopus and OVID were searched by independent researchers using the terms: lower body negative pressure, intracranial pressure, microgravity, and neurosurgery. Articles which used healthy human volunteers, simulated microgravity using the 15° HDT, and assessed ICP via invasive and non-invasive means were included. Articles which used astronauts, spaceflight, or zero-gravity conditions, and/or other methods of microgravity simulation were excluded.

Results: Four out of seventy-six identified studies were included in this review. Included studies utilized non-invasive measures of ICP including tympanic membrane displacement, intraocular pressure and transcranial ultrasound pulse amplitude, and invasive measures including parenchymal intracranial pressure sensors and Ommaya-reservoirs in the frontal horn of the lateral ventricle. All studies reported statistically significant decreases in ICP following administration of LBNP in 15° HDT.

Conclusion : LBNP is an existing method for decreasing ICP in the setting of simulated microgravity and may be a promising tool for the same purpose in neurosurgical patients with increased ICP.