Comparison of Biomechanical Outcome Measures From Characteristically Different Blast Simulators and the Influence of Exposure Location.

INTRODUCTION: Simulation of blast exposure in the laboratory has been inconsistent across laboratories. This is primarily because of adoption of the shock wave-generation techniques that are used in aerodynamic tests as opposed to application of blast exposures that are relevant to combat and training environments of a Warfighter. Because of the differences in blast signatures, characteristically different pathological consequences are observed among the preclinical studies. This is also further confounded by the varied exposure positioning of the animal subject (e.g., inside the blast simulator vs. at the mouth of the simulator). In this study, we compare biomechanical responses to blast exposures created in an advanced blast simulator (ABS) that generates "free-field"-like blast exposure with those produced by a traditionally applied cylindrical blast simulator (CBS) that generates a characteristically different blast signature. In addition, we have tested soft-armor vest protective responses with the ABS and CBS to compare the biomechanical responses to this form of personal protective equipment in each setting in a rodent model.

MATERIALS AND METHODS: Anesthetized male Sprague-Dawley rats (n = 6) were surgically probed with an intrathoracic pressure (ITP) transducer and an intracranial pressure (ICP) transducer directed into the lateral cerebral ventricle (Millar, Inc.). An ABS for short-duration blast or a CBS for long-duration blast was used to expose animals to an incident blast overpressure of 14.14 psi (impulse: 30.27 psi*msec) or 16.3 psi (impulse: 71.9 psi*msec) using a custom-made holder (n = 3-4/group). An external pitot probe located near the animal was used to measure the total pressure (tip) and static gauge (side-on) pressure. Data were recorded using a TMX-18 data acquisition system (AstroNova Inc.). MATLAB was used to analyze the recordings to identify the peak amplitudes and rise times of the pressure traces. Peak ICP, peak ITP, and their impulses were normalized by expressing them relative to the associated peak static pressure.

RESULTS: Normalized impulse (ABS: 1.02 ± 0.03 [vest] vs. 1.02 ± 0.01 [no-vest]; CBS: 1.21 ± 0.07 [vest] vs. 1.01 ± 0.01 [no-vest]) and peak pressure for ICP (ABS: 1.03 ± 0.03 [vest] vs. 0.99 ± 0.04 [no-vest]; CBS: 1.06 ± 0.08 [vest] vs. 1.13 ± 0.06 [no-vest]) remained unaltered when comparisons are made between vest and no-vest groups, and the normalized peak ITP (ABS: 1.50 ± 0.02 [vest] vs. 1.24 ± 0.16 [no-vest]; CBS: 1.71 ± 0.20 [vest] vs. 1.37 ± 0.06 [no-vest]) showed a trend of an increase in the vest group compared to the no-vest group. However, impulses in short-duration ABS (0.94 ± 0.06 [vest] vs. 0.92 ± 0.13 [no-vest]) blast remained unaltered, whereas a significant increase of ITP impulse (1.21 ± 0.07 [vest] vs. 1.17 ± 0.01 [no-vest]) in CBS was observed.

CONCLUSIONS: The differences in the biomechanical response between ABS and CBS could be potentially attributed to the higher dynamic pressures that are imparted from long-duration CBS blasts, which could lead to chest compression and rapid acceleration/deceleration. In addition, ICP and ITP responses occur independently of each other, with no evidence of thoracic surge.