Efficacy of Body Armor in Protection Against Blast Injuries Using a Swine Model in a Confined Space with a Blast Tube

Shock wave damage from the ventral side in primary blast injury: An experimental study in pigs

AIM/PURPOSE

This study aimed to apply a shock wave from the ventral side of a pig and examine its effect to use the results for new body armor production for humans.

METHODS

Seven male hybrid pigs were used. Each pig was placed under general anesthesia on the experimental table in a blast tube in the left lateral position to expose the front chest area, and shock waves generated by compressed air at 3.0 MPa were applied. We examined changes in vital signs and arterial blood gas in the hyper-acute phase and computed tomography (CT) images, and autopsies were performed for organ damage after 3 h of observation. Pathological examination was performed for lung damage, which is considered a characteristic of shock wave injury.

RESULTS

All seven pigs survived. Respiratory arrest occurred in two pigs; however, spontaneous breathing resumed promptly afterward. Hypotension occurred at a frequency of 4. No bradycardia or cardiac arrest was observed in any pig. In the arterial blood gas analysis before and immediately after shock wave exposure and 1 h later, PaO2 decreased immediately but tended to improve thereafter. CT revealed pulmonary contusions and multiple bulla-like lesions on the surface of the lungs. An autopsy showed lung injury in all pigs, particularly in five cases with bulla-like lesions of various sizes on the lung surface across all lobes. Pathological findings showed visceral pleural detachment with elastic fibers from the lung parenchyma, and the cavity lesion on the lung surface comprised bullae. The degree of intra-abdominal hemorrhage varied; however, all but one case showed splenic injury.

CONCLUSION

None of the pigs exposed to shock waves from the ventral side died; however, most showed multiple bullae on the lung surface with lung contusion and splenic injury, which may have been greater than those exposed from the dorsal side. This may be due to the direct impact of the shock wave proceeding from the epigastrium and subcostal region, which are not protected by the skeletal structure of the thorax. These characteristics should be considered when producing new body armor for humans to protect the body from shock waves.

Effectiveness of Body Armor Against Shock Waves: Preventing Blast Injury in a Confined Space

Introduction Blast injuries in modern society often occur owing to terrorist attacks in confined spaces, particularly in urban settings, indoors, and in vehicles, leading to significant damage. Therefore, it is important to focus on blast injuries in confined spaces rather than in conventional open-field experiments. Materials and methods We used an air-driven shock wave generator (blast tube) established indoors in 2017 and conducted basic research to potentially save the lives of patients with blast injuries. Under general anesthesia, pigs were divided into with body armor (BA) and without BA groups. The pigs were fixed in the measurement chamber with their dorsal chest directly exposed to the shock wave. The driving pressure was set at 3.0 MPa to achieve a mortality rate of approximately 50%. A generated shock wave was directly applied to the pigs. Comparisons were made between the groups with respect to cardiac arrest and survival, as well as apnea, bradycardia, and hypotension, which are the triad of blast lung. Autopsies were performed to confirm the extent of the organ damage. Statistical analysis was performed using Fisher's exact test, and statistical significance was set at p<0.05. The animal experimentation was conducted according to the protocol reviewed and approved by the Animal Ethics Committee of the National Defense Medical College Hospital (approval number 19041). Results Eight pigs were assigned to the BA group and seven pigs to the non-BA group. In the non-BA group, apnea was observed in four of seven cases, three of which resulted in death. None of the eight pigs in the BA group had respiratory arrest; notably, all survived. Hypotension was observed in some pigs in each group; however, there were no cases of bradycardia in either group. Statistical analysis showed that wearing BA significantly reduced the occurrence of respiratory and cardiac arrest (p=0.026) but not survival (p=0.077). No significant differences were found in other vital signs. Conclusions Wearing BA with adequate neck and chest protection reduced mortality and it was effective to reduce cardiac and respiratory arrest against shock wave exposure. Mortality from shock wave injury appears to be associated with respiratory arrest, and the avoidance of respiratory arrest may lead to survival.

Blast Injury Patterns Among Israel Defense Forces Fatalities

INTRODUCTION

The incidence of blast injuries on the battlefield has risen over the last several decades. In order to improve prevention and treatment, it is essential to understand the severity and bodily distribution of these injuries. This study aims to characterize blast injury patterns among IDF fatalities.

MATERIALS AND METHODS

This is a descriptive, retrospective study on postmortem reports of military-blast fatalities between the years 1982 and 2021. Body regions injured according to the Abbreviated Injury Scale (AIS) were described. The frequency of body region injury combinations was mapped, and the correlation between injured body regions was calculated using Pearson's coefficient. Analysis of a subgroup with a postmortem computed tomography (CT-PM) or autopsy was performed, describing severe (AIS ≥ 3) injury patterns.

RESULTS

Overall, 222 fatalities suffered from blast injury, with most injuries affecting the upper and lower extremities (63.7% and 66.5%, respectively), followed by the head (57.1%) and the thorax (56.6%). The median number of injured body regions was 4 (interquartile range, 2-5). The most frequent injury combinations were the upper and lower extremities (51%), the upper extremities and the thorax (45%), and the lower extremities and the thorax (41%). In all, 47/222 (21.2%) fatalities had a documented autopsy or CT-PM report. Among the fatalities with CT-PM or autopsy, the head (63.8%) and the thorax (57.4%) were most frequently severely injured (AIS ≥ 3).

CONCLUSIONS

Among blast fatalities in the military setting, the extremities were most commonly injured. However, data suggest that the head and thorax are more likely to sustain severe blast injuries resulting in mortality. Blast injuries in this cohort were characterized by concomitant involvement of several regions. Development of protective gear to minimize the multisystem injuries inflicted by blast injuries is warranted and should be focused on distinct types and anatomical distribution of severe blast injuries as reported in this study.

LEVEL OF EVIDENCE

Level III, Retrospective analysis.

The cause of acute lethality of mice exposed to a laser-induced shock wave to the brainstem

Air embolism is generally considered the most common cause of death within 1 h of a blast injury. Shock lung, respiratory arrest, and circulatory failure caused by vagal reflexes contribute to fatal injuries that lead to immediate death; however, informative mechanistic data are insufficient. Here we used a laser-induced shock wave (LISW) to determine the mechanism of acute fatalities associated with blast injuries. We applied the LISW to the forehead, upper neck, and thoracic dorsum of mice and examined their vital signs. Moreover, the LISW method is well suited for creating site-specific damage. Here we show that only mice with upper neck exposure, without damage elsewhere, died more frequently compared with the other injured groups. The peripheral oxygen saturation (SpO₂) of the former mice significantly decreased for < 1 min [p < 0.05] but improved within 3 min. The LISW exposure to the upper neck region was the most lethal factor, affecting the respiratory function. Protecting the upper neck region may reduce fatalities that are related to blast injuries.

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.