Neuropathology and Pressure in the Pig Brain Resulting from Low-Impulse Noise Exposure

Abstract

Military personnel are exposed to occupational levels of blast overpressure during training. This study characterizes the pressure-time histories of air, underwater, and localized blast, and correlates blast parameters with neuropathology. Blast overpressure was produced by a howitzer, a bazooka, an automatic rifle, underwater explosives, or a shock tube. Anesthetized pigs were exposed in positions that simulated real training scenarios. Underwater exposures were performed using explosives at distances recommended by safety requirements. In other experiments, rats were exposed via a shock tube. The pressure changes were recorded with a hydrophone sensor in the brain of the pig and in rats with an optical fiber sensor. Histological examination of porcine brains revealed small parenchymal and subarachnoid hemorrhages, predominately in the occipital lobe, cerebellum, and medulla oblongata. Relative to the peak pressure in air, that in porcine brain (Pmax brain/air) was 0.7 for the bazooka and 0.5 and 0.7, respectively, for the 9- and 30-kPa howitzer. The attenuation was stronger in water: the detonation pulse had a brain/water ratio of 0.1, and the secondary pulses had ratios of 0.3-0.4. The results indicate that low-frequency spectra penetrate easily from air or water into the brain, but high-frequency spectra appear to be filtered by body structures. In addition, blast waves were recorded in the brain and abdomen of pigs after local exposure via shock tube to either the abdomen or the top of the skull. When the abdomen was exposed, the maximal peak value in the brain was only 3% of that in the abdomen. Moreover, part of this pressure could have been derived from the air outside the head. The results gave little support to significant transmission of pressure within the body.

Neural Activation during Response Inhibition Differentiates Blast from Mechanical Causes of Mild to Moderate Traumatic Brain Injury

“…For the milTBI group, five participants (24% of the sample) had been exposed to a single blast event, 8 (38%) reported two blast exposures, and the remaining eight (38%) reported multiple blast exposures (range [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For the civTBI group, six (29%) participants had a history of a single concussion, five (24%) reported two concussions, and eight (38%) reported multiple concussions (range 3-10; data on additional concussions were not available for two participants in this group).…”

“…11 Animal models have revealed numerous pathological, biochemical, and behavioral changes as a result of blast exposure. 3 Among the blast sequellae noted in animals are diffuse axonal injury, 12 sub-arachnoid and parenchymal bleeding, 13 increases in intracranial pressure, 14 evidence of hippocampal neurodegeneration, phosphorylated tau protein and astrocytosis, 15 vasospasm and white matter (WM) degeneration, 16 increased levels of mortality, brain edema, 17 and downregulation of genes associated with hippocampal neurogenesis. 18 Despite these advances in knowledge from animal models, there remains controversy as to whether the clinical and neuropathological features of blast and mechanical TBI are the result of a unitary mechanism of injury 15 or the result of unique and distinguishable injury parameters.…”

Using a gel/plastic surrogate to study the biomechanical response of the head under air shock loading: a combined experimental and numerical investigation

“…However, the physiological connection between mTBI induced by blast or by blunt impact in a conventional setting will require a thorough epidemiological study which is beyond the scope of current study. Based on the findings in the literature Cernak 2005;Cernak et al 2001;Chavko et al 2007;DePalma et al 2005;Long et al 2009;Mayorga 1997;Säljö et al 2000Säljö et al , 2008Taber et al 2006;Wightman and Gladish 2001), it is believed that the occurrence of primary blastinduced TBI is strongly related to the overpressures produced by the explosion. In recent years, several research efforts have been devoted to the study of primary blast-induced TBI using animal and numerical models Cernak 2005;Cernak et al 2001;Chafi et al 2007a,b;Chavko et al 2007;DePalma et al 2005;Long et al 2009;Mayorga 1997;Moss et al 2009;Moore et al 2009;Taylor and Ford 2009;Teland et al 2010a,b;Zhu et al 2009).…”

“…Animal experimental models have been used to study biomechanical responses as well as pathophysiological, neuropathological, and neurological consequences Cernak 2005;Cernak et al 2001;Chavko et al 2007;Long et al 2009;Säljö et al 2000Säljö et al , 2008. However, conducting a large number of animal experiments is very expensive and time-consuming.…”

Characterization of natural and recoil-induced vibration of an AR-15 rifle at the cheekbone-stock interface

“…Far less is known, however, about the physiological impacts of various types of firearms. Säljö et al (2008) studied the physiological effects of sound pressure from the discharge of a series of weapons including a howitzer, bazooka, and an automatic rifle in the proximity of various small animals (e.g., pig, porcupine, and rats). Effects were measured via external sensors and histology.…”