Porcine Head Response to Blast

Abstract

Recent studies have shown an increase in the frequency of traumatic brain injuries related to blast exposure. However, the mechanisms that cause blast neurotrauma are unknown. Blast neurotrauma research using computational models has been one method to elucidate that response of the brain in blast, and to identify possible mechanical correlates of injury. However, model validation against experimental data is required to ensure that the model output is representative of in vivo biomechanical response. This study exposes porcine subjects to primary blast overpressures generated using a compressed-gas shock tube. Shock tube blasts were directed to the unprotected head of each animal while the lungs and thorax were protected using ballistic protective vests similar to those employed in theater. The test conditions ranged from 110 to 740 kPa peak incident overpressure with scaled durations from 1.3 to 6.9 ms and correspond approximately with a 50% injury risk for brain bleeding and apnea in a ferret model scaled to porcine exposure. Instrumentation was placed on the porcine head to measure bulk acceleration, pressure at the surface of the head, and pressure inside the cranial cavity. Immediately after the blast, 5 of the 20 animals tested were apneic. Three subjects recovered without intervention within 30 s and the remaining two recovered within 8 min following respiratory assistance and administration of the respiratory stimulant doxapram. Gross examination of the brain revealed no indication of bleeding. Intracranial pressures ranged from 80 to 390 kPa as a result of the blast and were notably lower than the shock tube reflected pressures of 300–2830 kPa, indicating pressure attenuation by the skull up to a factor of 8.4. Peak head accelerations were measured from 385 to 3845 G’s and were well correlated with peak incident overpressure (R2 = 0.90). One SD corridors for the surface pressure, intracranial pressure (ICP), and head acceleration are presented to provide experimental data for computer model validation.

Untangling the Effect of Head Acceleration on Brain Responses to Blast Waves

“…Further, the reflected pressures predicted by our model were similar to theoretical values. The model-predicted reflected pressure for a lateral impact was 271 kPa, which was close to 274.2 kPa, a theoretical calculation based on the following equation [13]:…”

“…In addition to these widely accepted mechanisms, brain tissue damage can also be caused by rapid acceleration of the head resulting from the interaction of the blast wave with the head [12,13]. In fact, experimental studies have reported extremely high head acceleration, often in the range of 3500-37,500 m/s 2 , in animals exposed to blast waves [12,13]. Goldstein et al observed that mice with head restraints had significantly less brain tissue damage when compared to those without head restraints [14].…”

An animal-to-human scaling law for blast-induced traumatic brain injury risk assessment

“…As is commonly done in blast injury biomechanics (13)(14)(15)17), the peak intracranial pressure was chosen as a characteristic metric of blast intensity transmitted to the brain tissue. Intracranial pressure can also be measured in animal tests in either in vitro or in vivo conditions (16), thus facilitating model validation. Peak intracranial pressure values furnished by our simulations are given in Table 1 and plotted in Fig.…”

“…As a consequence, past attempts to develop blast injury criteria have relied on animal studies, which have provided valuable information on the mechanisms and severity of injury resulting from blast loads for the specific species studied (e.g., refs. [13][14][15][16][17]. However, the applicability of animal injury assessments to humans is usually mired by the absence of adequate scaling criteria across species.…”

On the prospective contributions of the shock physics community to outstanding issues concerning blast-induced traumatic brain injury

“…Panzer et al [7] used the ground detonation of standard 105 and 155 mm artillery rounds as classic IED scenarios and used the CONWEP software [8] to predict peak incident overpressure and positive phase duration for standoff distances varying between 1 and 5 m, leading to peak overpressures ranging from 50 to 1000 kPa and durations between 2 and 6 ms. Wood et al [9] further stated that a majority of IED threats are made from artillery rounds equivalent to 7.5 kg of TNT explosives or less. Shridhanari et al [10] included a 50 kg of TNT equivalent at 7-10 m to be representative of a vehicle-borne IED. They simulated scenarios including blast waves with peak overpressures between 110 and 740 kPa with durations between 1.3 and 6.9 ms. Varas et al [11] reported peak overpressure and duration data from alleged IED experiments and stated that the ranges of peak overpressure between 10 and 200 kPa and positive phase durations between 4 and 10 ms are relevant to a military IED scenario.…”