28 - Neurodegeneration and inflammation profile following simulated aeromedical evacuation in a ferret traumatic brain injury and hemorrhage polytrauma model
Abstract Text: Rapid aeromedical evacuation of combat causalities to definitive care is of paramount importance to improving outcome after injury. However, the effects of long-range aeromedical evacuation in hypobaric environments on physiology and organ function remain largely unknown. The current study was conducted to evaluate the effects of hypobaria on brain histology and circulating white blood cells (WBC) in a polytrauma model combining traumatic brain injury (TBI) with hemorrhagic shock (HS). Ferrets received control cortical impact TBI and underwent a 15% blood volume hemorrhage (TBI/HS) to mimic polytrauma. Sham animals received a craniotomy only. This was followed by exposure to hypobaria for 6 hours to simulate aeromedical evacuation at 8,000ft or normobaria at sea level 24 hours after TBI/HS or sham procedures. Blood samples were collected at baseline, and 24, 48 and 72 hours post injury or sham procedures. Animals were euthanized 72 hours post TBI/HS and brains were fixed and processed for histological analysis. WBC counts were conducted using an IDEXX blood analyzer. Brain sections were stained with markers of neurodegeneration (Fluoro-Jade B) and neuroinflammation (Iba-1 and GFAP). Expectedly, Fluoro-Jade B staining showed an overall increase in neurodegeneration in TBI/HS animals compared to sham. The increase was more pronounced in animals subjected to hypobaria. Assessment of neuroinflammatory markers showed a differential response of astrocytes and microglia to TBI/HS and hypobaria, with microglia exhibiting a potential reduction in the inflammatory response and astrocytes exhibiting increased proliferation. Preliminary results from WBC analyses revealed an overall decrease in the peripheral WBC response in TBI/HS compared to sham in animals in exposed to both hypobaria and normobaria. The response to hypobaria was different in monocytes vs. lymphocytes in TBI/HS animals, with monocytes exhibiting a decrease and lymphocytes exhibiting an increase in cell count. These results indicate that hypobaria exacerbates neurodegeneration in TBI/HS hypobaria and may blunt the neuroinflammatory response. The reduction in cellular inflammatory response is also modulated by hypobaria. Further studies are indicated to elucidate the long-term impact of aeromedical evacuation on outcome after injury.