Responses of the Acutely Injured Spinal Cord to Vibration that Simulates Transport in Helicopters or Mine-Resistant Ambush-Protected Vehicles

Abstract

In the military environment, injured soldiers undergoing medical evacuation via helicopter or mine-resistant ambush-protected vehicle (MRAP) are subjected to vibration and shock inherent to the transport vehicle. We conducted the present study to assess the consequences of such vibration on the acutely injured spinal cord. We used a porcine model of spinal cord injury (SCI). After a T10 contusion-compression injury, animals were subjected to 1) no vibration (n = 7-8), 2) whole body vibration at frequencies and amplitudes simulating helicopter transport (n = 8), or 3) whole body vibration simulating ground transportation in an MRAP ambulance (n = 7). Hindlimb locomotor function (using Porcine Thoracic Injury Behavior Scale [PTIBS]), Eriochrome Cyanine histochemistry and biochemical analysis of inflammatory and neural damage markers were analyzed. Cerebrospinal fluid (CSF) expression levels for monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-6, IL-8, and glial fibrillary acidic protein (GFAP) were similar between the helicopter or MRAP group and the unvibrated controls. Spared white/gray matter tended to be lower in the MRAP-vibrated animals than in the unvibrated controls, especially rostral to the epicenter. However, spared white/gray matter in the helicopter-vibrated group appeared normal. Although there was a relationship between the extent of sparing and the extent of locomotor recovery, no significant differences were found in PTIBS scores between the groups. In summary, exposures to vibration in the context of ground (MRAP) or aeromedical (helicopter) transportation did not significantly impair functional outcome in our large animal model of SCI. However, MRAP vibration was associated with increased tissue damage around the injury site, warranting caution around exposure to vehicle vibration acutely after SCI.

Review of the UBC Porcine Model of Traumatic Spinal Cord Injury

“…While we had previously shown this therapy to be effective at improving behavioral recovery in a rodent model of thoracic and cervical SCI [ 12 , 15 ], we found that the magnesium chloride therapy did not reproduce the same promising therapeutic benefits in our pig model, either for improving locomotor recovery or increasing spared tissue at the injury site [ 22 ]. We have also used the pig model to evaluate the effect of wholebody vibration, which is applicable to individuals who have sustained an SCI and are being transported via air or road [ 21 ]. It was established that such vibration was not detrimental to the acutely injured spinal cord, and in fact in some ways may have even been beneficial [ 21 ].…”

“…We have also used the pig model to evaluate the effect of wholebody vibration, which is applicable to individuals who have sustained an SCI and are being transported via air or road [ 21 ]. It was established that such vibration was not detrimental to the acutely injured spinal cord, and in fact in some ways may have even been beneficial [ 21 ].…”

“…With our pig model of SCI, we have collected up to 5 mL of CSF, as well as large volumes of blood, from the same animals over 7 days post-injury, while the animals are awake and freely moving. Using serially collected samples of CSF and blood, we have identified potential biomarkers of injury severity, which will aide in the diagnosis of SCI patients [ 20 , 21 ]. Interestingly, in a study in which we took parallel CSF and blood samples over the first week post-injury and evaluated microRNAs using next-generation sequencing, we found that the levels of miRNA were very low in the CSF but systemically elevated in the blood; these elevated serum microRNA levels were strongly correlated to poorer PTIBS scores and greater histologic damage [ 26 ].…”

“…Interestingly, in a study in which we took parallel CSF and blood samples over the first week post-injury and evaluated microRNAs using next-generation sequencing, we found that the levels of miRNA were very low in the CSF but systemically elevated in the blood; these elevated serum microRNA levels were strongly correlated to poorer PTIBS scores and greater histologic damage [ 26 ]. We have used the pig model to evaluate the effects of vibration associated with transportation in ground or aircraft settings, and have taken advantage of the ability to obtain serial CSF samples to evaluate biomarkers of injury severity and surrogate outcome measures [ 20 , 21 ]. The ability to take serial CSF samples is also valuable for testing the biodistribution of drugs, as we have shown by measuring CSF levels of magnesium in a study of a magnesium chloride neuroprotective agent in the pig model [ 22 ].…”

“…Although there are challenges with regards to experimental cost and animal housing of larger species, the pig model has a number of advantages as a preclinical model of traumatic SCI. The anatomical, physiological, and genetic similarities between pigs [ 27 ] and humans have made pigs useful as models in a variety of research settings including stroke [ 3 , 9 , 17 ], traumatic brain injury [ 2 , 25 , 28 ], and SCI [ 18 , 21 - 23 , 26 ]. We suggest that the porcine model of thoracic SCI is a useful intermediary model for preclinical SCI studies.…”