Design of a simplified cranial substitute with a modal behavior close to that of a human skull.

Individuals exposed to the propagation of shock waves generated by the detonation of explosive charges may suffer Traumatic Brain Injury. The mechanism of cranial deflection is one of many hypotheses that could explain the observed brain damage. To investigate this physical phenomenon in a reproducible manner, a new simplified cranial substitute was designed with a mechanical response close to that of a human skull when subjected to this type of loading. As a first step, a Finite Element Model was employed to dimension the new substitute. The objective was indeed to obtain a vibratory behavior close to that of a dry human skull over a wide range of frequencies up to 10 kHz. As a second step, the Finite Element Model was used together with Experimental Modal Analyses to identify the vibration modes of the substitute. A shaker excited the structure via a metal rod, while a laser vibrometer recorded the induced vibrations at defined measurement points. The results showed that despite differences in material properties and geometry, the newly developed substitute has 10/13 natural frequencies in common with those of dry human skulls. When filled with a simulant of cerebral matter, it could therefore be used in future studies as an approximation to assess the mechanical response of a simplified skull substitute to a blast threat.

A New Anthropomorphic Mannequin for Efficacy Evaluation of Thoracic Protective Equipment Against Blast Threats.

Exposure to blast is one of the major causes of death and disability in recent military conflicts. Therefore, it is crucial to evaluate the protective capability of the ballistic-proof equipment worn by soldiers against the effects of blast overpressure (i.e., primary blast injuries). A focus will be made on thoracic protective equipment (TPE). An anthropomorphic mannequin, called BOPMAN, and anesthetized swine both wearing soft, hard or no ballistic protection, were subjected to an open-field high-intensity blast. For swine, thoracic wall motion (acceleration and velocity) was recorded during blast exposure and severity of lung injury was evaluated postmortem. Different data were collected from BOPMAN thoracic responses, including reflected and internal pressure, as well as the force at the rear face of the instrumented part. The severity of blast-induced lung injuries (contusion extent, Axelsson Severity Scale) and the thoracic wall motion were decreased in animals protected with thoracic ceramic hard plates as compared to those wearing soft or no protection. There was a clear trend towards greater lung injury in animals protected with the soft body armor used, even when compared to unprotected animals. In line with these experimental data, the measured force as well as the force impulse measured using BOPMAN were also decreased with a ceramic hard plate protection and increased when a soft ballistic pack was used compared to no protection. Comparison of data collected on BOPMAN and swine equipped with the same protection level revealed that those two force parameters were well correlated with the level of blast-induced lung injury (force, R2 = 0.74 and force impulse, R2 = 0.77, p < 0.05). Taken together, our results suggest that the force and the force impulse data from BOPMAN may help estimate the efficiency of existing TPE regarding lung protection under blast exposure and may represent an important tool for development of future TPE.

Lung injury risk assessment during blast exposure.

Blast pulmonary trauma are common consequences of modern war and terrorism action. To better protect soldiers from that threat, the injury risk level when protected and unprotected must be assessed. Knowing from the literature that a possible amplification of the blast threat would be provided by some thoracic protective systems, the objective is to propose an original approach to correlate a measurable parameter on a manikin with a pulmonary risk level. Using a manikin whose response is correlated with the proposed tolerance limits should help in the evaluation of thoracic protective system regarding injury outcomes. A database including lung injury data from large mammals have been created, allowing the definition of iso-impulse tolerance limits from no lung injury to severe ones (∼60% of ecchymosis). As the use of this metric is not sufficient to evaluate the performance of protective systems on a manikin, the iso-impulse tolerance limits were associated with the thoracic response of post-mortem swine under blast loading. It was found that the lung injury threshold in terms of incident impulse is 58.3 kPa·ms, corresponding to a chest wall peak of acceleration/velocity/displacement of 7350 m/s2, 3.7 m/s and 6.4 mm respectively. Lung injuries are considered as severe (30-60% of ecchymosis) when the incident impulse exceed 232.8 kPa·ms, leading to a chest wall peak of acceleration/velocity/displacement of 79.7 km/s2, 14.7 m/s and 30.1 mm respectively. The defined lung tolerance limits are valid for a 50 kg swine (unprotected) exposed side-on to the blast threat and against a wall.

Chest response assessment of post-mortem swine under blast loadings.

To better protect soldiers from blast threat, that principally affect air-filled organs such a lung, it is necessary to develop an adapted injury criterion and, prior to this, to evaluate the response of a biological model against that threat. The objective of this study is to provide some robust data to quantify the chest response of post-mortem swine under blast loadings. 7 post-mortem swine (54.5 ±â€¯2.6 kg), placed side-on to the threat and against the ground, were exposed to 5 shock-waves of increasing intensities. Their thorax were instrumented with a piezo-resistive pressure sensor, an accelerometer directly exposed to the shock-wave and a target was mounted on the latter in order to track the chest wall displacement. For incident impulses ranging from 47 kPa ms±2% to 173 kPa ms ±6%, the measured maximum of linear chest wall acceleration (Γmax) goes from 5800 m/s2 ±16% to 41,000 m/s2 ±â€¯8%, with a duration of 0.8 ms. Chest wall displacements ranging from 5 mm ±â€¯20% to 20 mm ±â€¯15%, with a duration of 9 ms, are reached. These reproducible data were used to find simple relations (linear, 2nd and 3rd order polynomials) between the kinematic parameters (plus the viscous criterion) and the incident and reflected impulses. Correlating the new reproducible data with the prediction from the Bowen curves showed a lung injury threshold in terms of Γmax similar to that of Cooper (10,000 m/s2). However, the limits defined for the viscous criterion in the automobile field and for non-lethal weapons seems not adapted for the blast threat.

A critical literature review on primary blast thorax injury and their outcomes.

Since World War II, researchers have been interested in exploring the injury mechanisms involved in primary blast on the thorax by using animal model surrogates. These studies were mostly concerned with the finding of the lung injury threshold, the relationship between the physical components of the air blast wave, and the biological response. Studies have also been conducted to investigate the effect of repeated blast exposures on the injury outcome threshold. This has led to several injury criteria, such as the Bowen curves based on pressure history's characteristics or the Axelsson Chest Wall Velocity Predictor that used measurement from the mammals' chest wall. This article aims at doing a critical literature review of this specific topic.

Comprehensive evaluation of coagulation in swine subjected to isolated primary blast injury.

Blast is one of the major causes of injury and death in recent armed conflicts. With increased use of improvised explosive devices in Iraq and Afghanistan, more than 71% of combat casualties are caused by explosions. Blast injuries can range from primary (caused by shock wave) to quaternary injuries (e.g., burns), and such injuries can result in an acute coagulopathy denoted by a hypocoagulable state. It is not clear if this coagulopathy observed in victims of explosion is caused by local or general effect of the primary blast injury itself. In this study, 13 pigs were subjected to severe isolated open-field blast injury and we measured indices of coagulation impairment during the first hour after injury: ROTEM, prothrombin time, activated partial thromboplastin time, coagulation factors, thrombin generation potential, platelet count, platelet activation, platelet function, and procoagulant microparticle formation. After 1 h, the mortality was 33%. No coagulation dysfunction was observed in the survivors in this period. This study presented a highly reproducible and consistent isolated blast injury in large mammals with comprehensive coagulation testing. The data suggest that isolated primary blast injury is not responsible for acute coagulopathy of trauma in victims of explosion but seems to lead to an early hypercoagulable state.

Comparison of thoracic wall behavior in large animals and human cadavers submitted to an identical ballistic blunt thoracic trauma.

BACKGROUND: Several models of ballistic blunt thoracic trauma are available, including human cadavers and large animals. Each model has advantages and disadvantages regarding anatomy and physiology, but they have not been compared with identical ballistic aggression. METHODS: To compare thoracic wall behavior in 40-kg pigs and human cadavers, the thorax of 12 human cadavers and 19 anesthetized pigs were impacted with two different projectiles at different speeds. On the thoracic wall, the peak acceleration, peak velocity, maximal compression, viscous criterion, and injury criteria (e.g. abbreviated injury scale and number of rib fractures) were recorded. The correlations between these motion and injury parameters and the blunt criterion were compared between the two groups. The bone mineral density of each subject was also measured. RESULTS: The peak acceleration, the peak velocity and the viscous criterion were significantly higher for the pigs. The AIS and the number of rib fractures were significantly higher for human cadavers. The bone mineral density was significantly higher for cadavers, but was, for the two groups, significantly lower than for 30-year-old human. CONCLUSION: The motion of the pig's thoracic wall is greater than that of the human cadaver, and the severity of the impact is always greater for human cadavers than for pigs. In addition, pig bone is more elastic and less brittle than older human cadaver bone. Due to the bone mineral density, the thoracic wall of human adults should be more rigid and more resistant than the thoracic wall of human cadavers or pigs.

Intrathoracic pressure impulse predicts pulmonary contusion volume in ballistic blunt thoracic trauma.

BACKGROUND: Blunt thoracic trauma including behind armour blunt trauma or impact from a less lethal kinetic weapon (LLKW) projectile may cause injuries, including pulmonary contusions that can result in potentially lethal secondary complications. These lung injuries may be caused by intrathoracic pressure waves. The aim of this study was to observe dynamic changes in intrathoracic hydrostatic pressure during ballistic blunt thoracic trauma and to find correlations between these hydrostatic pressure parameters (especially the impulse parameter) and physical damages. METHODS: Thirty anesthetized pigs sustained a blunt thoracic trauma. In group 1 (n = 20), pigs were protected by a National Institute of Justice class III or IV bulletproof vest and shot with 7.62 NATO bullets. In group 2 (n = 10), pigs were shot by an LLKW. Intrathoracic pressure was recorded with an intraesophageal pressure sensor and three parameters were determined: intrathoracic maximum pressure, intrathoracic maximum pressure impulse (PI(max)), and the Pd.P/dt(max), derived from Viano's viscous criterion. Relative right lower lung lobe contusion volume was also measured. RESULTS: Different thoracic loading conditions were obtained. PI(max) best correlated with relative pulmonary contusion volume (R² = 0.64 and p < 0.0001). This result was homogenous for all experiments and was not related to the type of chest impact (LLKW-induced trauma or behind armour blunt trauma). CONCLUSIONS: The PI(max) is a good predictor of pulmonary contusion volume after ballistic blunt thoracic trauma. It is a useful criterion when the kinetic energy record or thoracic wall displacement data are unavailable, and the recording and calculation of this physical value are quite simple on animals.