High-Fidelity Simulation of Primary Blast: Direct Effects on the Head.

The role of primary blast in blast-induced traumatic brain injury (bTBI) is controversial in part due to the technical difficulties of generating free-field blast conditions in the laboratory. The use of traditional shock tubes often results in artifacts, particularly of dynamic pressure, whereas the forces affecting the head are dependent on where the animal is placed relative to the tube, whether the exposure is whole-body or head-only, and on how the head is actually exposed to the insult (restrained or not). An advanced blast simulator (ABS) has been developed that enables high-fidelity simulation of free-field blastwaves, including sharply defined static and dynamic overpressure rise times, underpressures, and secondary shockwaves. Rats were exposed in head-only fashion to single-pulse blastwaves of 15 to 30 psi static overpressure. Head restraints were configured so as to eliminate concussive and minimize whiplash forces exerted on the head, as shown by kinematic analysis. No overt signs of trauma were present in the animals post-exposure. However, significant changes in brain 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) and neurofilament heavy chain levels were evident by 7 days. In contrast to most studies of primary blast-induced TBI (PbTBI), no elevation of glial fibrillary acidic protein (GFAP) levels was noted when head movement was minimized. The ABS described in this article enables the generation of shockwaves highly representative of free-field blast. The use of this technology, in concert with head-only exposure, minimized head movement, and the kinematic analysis of the forces exerted on the head provide convincing evidence that primary blast directly causes changes in brain function and that GFAP may not be an appropriate biomarker of PbTBI.