Noninvasive, In-pen Approach Test for Laboratory-housed Pigs.

Traumatic brain injury (TBI) incidences have increased in both civilian and military populations, and many researchers are adopting a porcine model for TBI. Unlike rodent models for TBI, there are few behavioral tests that have been standardized. A larger animal requires more invasive handling in test areas than rodents, which potentially adds stress and variation to the animals' responses. Here, the human approach test (HAT) is described, which was developed to be performed in front of laboratory pigs' home pen. It is noninvasive, but flexible enough that it allows for differences in housing set-ups. During the HAT, three behavioral ethograms were developed and then a formula was applied to create an approach index (AI). Results indicate that the HAT and its index, AI, are sensitive enough to detect mild and temporary alterations in pigs' behavior after a mild TBI (mTBI). In addition, although specific behavior outcomes are housing-dependent, the use of an AI reduces variation and allows for consistent measurements across laboratories. This test is reliable and valid; HAT can be used across many laboratories and for various types of porcine models of injury, sickness, and distress. This test was developed for an optimized manual timestamping method such that the observer consistently spends no more than 9 min on each sample.

Intracochlear pressure measurements during acoustic shock wave exposure.

INTRODUCTION: Injuries to the peripheral auditory system are among the most common results of high intensity impulsive acoustic exposure. Prior studies of high intensity sound transmission by the ossicular chain have relied upon measurements in animal models, measurements at more moderate sound levels (i.e. < 130 dB SPL), and/or measured responses to steady-state noise. Here, we directly measure intracochlear pressure in human cadaveric temporal bones, with fiber optic pressure sensors placed in scala vestibuli (SV) and tympani (ST), during exposure to shock waves with peak positive pressures between ∼7 and 83 kPa. METHODS: Eight full-cephalic human cadaver heads were exposed, face-on, to acoustic shock waves in a 45 cm diameter shock tube. Specimens were exposed to impulses with nominal peak overpressures of 7, 28, 55, & 83 kPa (171, 183, 189, & 192 dB pSPL), measured in the free field adjacent to the forehead. Specimens were prepared bilaterally by mastoidectomy and extended facial recess to expose the ossicular chain. Ear canal (EAC), middle ear, and intracochlear sound pressure levels were measured with fiber-optic pressure sensors. Surface-mounted sensors measured SPL and skull strain near the opening of each EAC and at the forehead. RESULTS: Measurements on the forehead showed incident peak pressures approximately twice that measured by adjacent free-field and EAC entrance sensors, as expected based on the sensor orientation (normal vs tangential to the shock wave propagation). At 7 kPa, EAC pressure showed gain, calculated from the frequency spectra, consistent with the ear canal resonance, and gain in the intracochlear pressures (normalized to the EAC pressure) were consistent with (though somewhat lower than) previously reported middle ear transfer functions. Responses to higher intensity impulses tended to show lower intracochlear gain relative to EAC, suggesting sound transmission efficiency along the ossicular chain is reduced at high intensities. Tympanic membrane (TM) rupture was observed following nearly every exposure 55 kPa or higher. CONCLUSIONS: Intracochlear pressures reveal lower middle-ear transfer function magnitudes (i.e. reduced gain relative to the ear canal) for high sound pressure levels, thus revealing lower than expected cochlear exposure based on extrapolation from cochlear pressures measured at more moderate sound levels. These results are consistent with lowered transmissivity of the ossicular chain at high intensities, and are consistent with our prior report measuring middle ear transfer functions in human cadaveric temporal bones with high intensity tone pips.

Repeated Low-Level Blast Exposure: A Descriptive Human Subjects Study.

The relationship between repeated exposure to blast overpressure and neurological function was examined in the context of breacher training at the U.S. Marine Corps Weapons Training Battalion Dynamic Entry School. During this training, Students are taught to apply explosive charges to achieve rapid ingress into secured buildings. For this study, both Students and Instructors participated in neurobehavioral testing, blood toxin screening, vestibular/auditory testing, and neuroimaging. Volunteers wore instrumentation during training to allow correlation of human response measurements and blast overpressure exposure. The key findings of this study were from high-memory demand tasks and were limited to the Instructors. Specific tests showing blast-related mean differences were California Verbal Learning Test II, Automated Neuropsychological Assessment Metrics subtests (Match-to-Sample, Code Substitution Delayed), and Delayed Matching-to-Sample 10-second delay condition. Importantly, apparent deficits were paralleled with functional magnetic resonance imaging using the n-back task. The findings of this study are suggestive, but not conclusive, owing to small sample size and effect. The observed changes yield descriptive evidence for potential neurological alterations in the subset of individuals with occupational history of repetitive blast exposure. This is the first study to integrate subject instrumentation for measurement of individual blast pressure exposure, neurocognitive testing, and neuroimaging.

Blunt impacts to the back: Biomechanical response for model development.

The development of advanced injury prediction models requires biomechanical and injury tolerance information for all regions of the body. While numerous studies have investigated injury mechanics of the thorax under frontal impact, there remains a dearth of information on the injury mechanics of the torso under blunt impact to the back. A series of hub-impact tests were performed to the back surface of the mid-thorax of four mid-size male cadavers. Repeated tests were performed to characterize the biomechanical and injury response of the thorax under various impact speeds (1.5m/s, 3m/s and 5.5m/s). Deformation of the chest was recorded with a 59-gage chestband. Subject kinematics were also recorded with a high-speed optoelectronic 3D motion capture system. In the highest-severity tests, peak impact forces ranged from 6.9 to 10.5 kN. The peak change in extension angle measured between the 1st thoracic vertebra and the lumbar spine ranged from 39 to 62°. The most commonly observed injuries were strains of the costovertebral/costotransverse joint complexes, rib fractures, and strains of the interspinous and supraspinous ligaments. The majority of the rib fractures occurred in the rib neck between the costovertebral and costotransverse joints. The prevalence of rib-neck fractures suggests a novel, indirect loading mechanism resulting from bending moments generated in the rib necks caused by motion of the spine. In addition to the injury information, the biomechanical responses quantified here will facilitate the future development and validation of human body models for predicting injury risk during impact to the back.

Injury tolerance of the wrist and distal forearm to impact loading onto outstretched hands.

BACKGROUND: The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tolerance of the wrist is poorly understood. This study sought to quantify the injury tolerance of the adult male forearm-wrist complex under loading simulating axial impact to an outstretched hand. METHODS: Fifteen isolated cadaveric forearm/wrist specimens were tested. Loading was applied via an instrumented drop tower device designed to impact the palmar surface of the hand with the wrist extended to approximately 90 degrees. Impact severity was modulated by adjusting the boundary condition of the elbow. Elbow reaction force and deformation of the specimen (deflection of the palmar surface of the hand toward the elbow) were measured. Bone-implanted strain gauges were used to detect the time of fracture. Injury risk functions were developed using parametric survival analysis with a cumulative Weibull distribution. RESULTS: Of 14 specimens, 10 exhibited a fracture to the wrist or forearm after test (one specimen was excluded from the analysis). Injury severities varied from nondisplaced fractures of the radius to severely displaced fractures and/or fracture-dislocations of the carpal bones. Of the potential predictors studied, the specimen deflection expressed as a percentage of the initial specimen length produced the injury risk model of best fit (50% risk of fracture at 1.69% deflection; 95% confidence interval, 1.38-2.07% deflection). The value of the elbow reaction force corresponding to a 50% risk of injury was 4.34 kN (3.80-4.97 kN). CONCLUSION: These results provide information for the prediction of wrist and forearm injury in biomechanical models simulating impacts in the field and provide tolerance information for the development of injury mitigation countermeasures.

Brain injury risk from primary blast.

BACKGROUND: Military service members are often exposed to at least one explosive event, and many blast-exposed veterans present with symptoms of traumatic brain injury. However, there is little information on the intensity and duration of blast necessary to cause brain injury. METHODS: Varying intensity shock tube blasts were focused on the head of anesthetized ferrets, whose thorax and abdomen were protected. Injury evaluations included physiologic consequences, gross necropsy, and histologic diagnosis. The resulting apnea, meningeal bleeding, and fatality were analyzed using logistic regressions to determine injury risk functions. RESULTS: Increasing severity of blast exposure demonstrated increasing apnea immediately after the blast. Gross necropsy revealed hemorrhages, frequently near the brain stem, at the highest blast intensities. Apnea, bleeding, and fatality risk functions from blast exposure to the head were determined for peak overpressure and positive-phase duration. The 50% risk of apnea and moderate hemorrhage were similar, whereas the 50% risk of mild hemorrhage was independent of duration and required lower overpressures (144 kPa). Another fatality risk function was determined with existing data for scaled positive-phase durations from 1 millisecond to 20 milliseconds. CONCLUSION: The first primary blast brain injury risk assessments for mild and moderate/severe injuries in a gyrencephalic animal model were determined. The blast level needed to cause a mild/moderate brain injury may be similar to or less than that needed for pulmonary injury. The risk functions can be used in future research for blast brain injury by providing realistic injury risks to guide the design of protection or evaluate injury.

Ballistic impact to the forehead, zygoma, and mandible: comparison of human and frangible dummy face biomechanics.

BACKGROUND: Currently, there is a greater use of nonlethal force in law enforcement and military operations. Because facial injuries have been observed, there is a need to understand the human response to ballistic impacts involving various regions of the face. This study aimed to establish blunt ballistic response corridors for high-speed, low-mass facial impacts to the forehead, zygoma, and mandible, and to determine how these responses compare with those of the frangible Hybrid III headform. Correlation of the human and dummy responses allows injury risk assessment for munitions used in the field. METHODS: Facial impacts to the forehead, zygoma, and mandible of six cadavers at 42 +/- 10 m/sec were conducted using a 25- to 35-g projectile 37 mm in diameter that was instrumented with an accelerometer to determine impact force. High-speed video analysis determined penetration of the projectile, and autopsy determined the facial fractures. Force and deflection were normalized for the 50% tile response, and corridors were determined for blunt ballistic impacts. Similar tests were conducted on the frangible face of the Hybrid III dummy. RESULTS: Peak normalized force of 3.5 +/- 0.9 kN on the forehead and 3.0 +/- 1.0 kN on the mandible did not result in fractures, whereas an impact force of 2.3 +/- 0.5 kN on the zygoma caused anterior maxilla fractures. The frangible Hybrid III face developed similar force levels, but with less penetration of the projectile. Its stiffness was 43% greater than that of the cadaver. CONCLUSIONS: Higher impact force can be tolerated on the forehead and mandible than on the zygoma. Normalized force-deflection and force-time corridors were established for the human response. The frangible Hybrid III face is an effective surrogate for assessing ballistic injury risks, but greater compliance would make it more biofidelic. Initial human tolerance levels of 6.0 kN for the forehead, 1.6 kN for the zygoma, and 1.9 kN for the mandible have been established for ballistic impacts to the face.