Effects of orientation and distance of goats on blast lung injury characteristics on a plateau above 4500-meter

Abstract

Purpose

High explosives are used to produce blast waves to study their biological effects. The lungs are considered as the critical target organ in blast-effect studies. The degree of lung hemorrhaging is related to both the explosive power and the increased lung weight. We studied the characteristics of the biological effects from an air explosion of a thermobaric bomb in a high-altitude environment and the lethality and lung injury severity of goats in different orientations and distances.

Methods

Goats were placed at 2.5, 3, 4, and 5 m from the explosion center and exposed them to an air blast at an altitude of 4700-meter. A group of them standing oriented to the right side and the other group seated facing the explosion center vertically. The lung injuries were quantified according to the percentage of surface area contused, and using the pathologic severity scale of lung blast injury (PSSLBI) to score the 4 injury categories (slight, moderate, serious and severe) as 1, 2, 3, and 4, respectively. The lung coefficient (lung weight [g]/body weight [kg]) was the indicator of pulmonary edema and was related to lung injury severity. Blast overpressure data were collected using blast test devices placed at matching locations to represent loadings to goats. All statistical analyses were performed using SPSS, version 26.0, statistical software (SPSS, Inc., Chicago, IL, USA).

Results

In total, 127 goats were involved in this study. Right-side-standing goats had a significantly higher mortality rate than those seated vertical-facing (p < 0.05). At the 2.5 m distance, the goat mortality was nearly 100%, whereas at 5 m, all the goats survived. Lung injuries of the right-side-standing goats were 1 – 2 grades more serious than those of seated goats at the same distances, the scores of PSSLBI were significantly higher than the seated vertical-facing goats (p < 0.05). The lung coefficient of the right-side-standing goats were significantly higher than those of seated vertical-facing (p < 0.05). Mortality, PSSLBI, and the lung coefficient results indicated that the right-side-standing goats experienced severer injuries than the seated vertical-facing goats, and the injuries were lessened as the distance increased. The blast overpressure was consistent with these results.

Conclusion

The main killing factors of the thermobaric bomb in the high-altitude environment were blast overpressure, blast wind propulsions and burn. The orientation and distances of the goats significantly affected the blast injury severity. These results may provide a research basis for diagnosing, treating and protecting against injuries from thermobaric explosions.

Introduction

Explosive weapons, such as mines, shells, aerial bombs and anti-tank missiles, can produce high-speed and high-energy explosions and are the cause of most blast injuries. Explosive weapons are used frequently in modern warfare and have high accuracy, with many injury factors and a wide killing area. Several local wars have shown that high-speed and high-explosive weapons are the most common weapons, and explosion injuries are the most common injuries. Blast injury incidences were 50.4% in the Vietnam War^1,2 and 84% in the Bosnia and Herzegovina war.^3,4 Blast lung injury is a major cause of immediate death in victims. The proximity of the person to the explosion point and the bombing being in a closed area increases the incidence and severity of primary blast lung injury.^5,6 This rate was higher in victims who died after the explosion (17% – 47%).⁷ To understand the killing power, factors, mechanisms and finalization of explosive weapons and to diagnose and treat explosion injuries, researchers must determine the biological effect characteristics of the weapons’ damage.

Plateaus are high-altitude areas with unique environmental factors such as hypoxia, low pressure and temperature, which greatly affect injury assessment and treatment. Four altitudes are internationally classified according to patients’ physiological reactions⁸: (1) At moderate altitudes (< 2500 m), people generally have no symptoms or only mild symptoms; (2) At high altitudes (2500 – 4500 m), most people experience obvious symptoms of hypoxia, such as increased respiratory and heart rates, headache, and arterial oxygen saturation < 90%; (3) At very high altitudes (4500 – 5500 m), hypoxic symptoms are further aggravated, with an arterial oxygen saturation < 80%; (4) At extremely high altitudes (5500 – 8844 m), the arterial oxygen saturation is < 60% – 70%, and physiological functions become progressively disordered.

Although many medical research studies have been conducted on plateaus, most of them have focused on preventing and treating plateau-associated diseases, and research on blast injuries on plateaus has been limited to laboratory simulations. Few experimental studies have focused on explosion-induced injuries. Zhang et al.⁹ found that at 4000 m and 5000 m altitudes, injuries were 1 – 3 levels severer than those occurred on plains, and the mortality rates increased by 25% and 35%, respectively. Damon et al.¹⁰ and Li et al.¹¹ reported that the shock wave pressure that caused 50% lethality in animals decreased as the ambient pressure decreased, which may increase the mortality.

Lack of oxygen can lead to a series of pathophysiological changes, such as the compensatory heart rate acceleration, faster and deeper respiration, and deteriorated physical health. This may increase the risk of death and the difficulty of treatment. Therefore, we aimed to identify the characteristics of the biological effects of a thermobaric bomb during an air blast at a high altitude of 4700 m. This altitude can lead to obvious altitude-related reactions. We further assessed how different orientations and distances influence experimental animals in regard to injury characteristics by placing 127 goats at 2.5, 3, 4, or 5 m from the explosion center and oriented them standing to the right side or seated facing vertically. The goats were then exposed to 8 thermobaric bombs of the same type. The survival rate, gross anatomy, trauma scores (the pathologic severity scale of lung blast injury (PSSLBI)) and lung coefficients of the experimental goats were determined to evaluate the injury characteristics and analyze how orientation and distance influence the injury degree and characteristics. Our results provide a research basis for diagnosing and treating explosion injury and a scientific experimental basis for establishing criteria to evaluate the biological effects.

Methods

Experimental conditions

The experimental site was a flat open area with an altitude of 4700 m, a soil-layer surface, and a temperature range of −5 °C to 5 °C. The experiment was conducted from September 7, 2021 to September 29, 2021.

Animals

Goats were purchased from the Geermu Animal Breeding Center and were approved by the Ethics Committee of Army Medical University. The Animal Care and Facilities Committee of Army Medical University approved all animal experimental protocols (AMUWE20202140).

We placed 127 goats, weighing (30.45 ± 3.35) kg, at distances of 2.5, 3, 4, and 5 m, respectively from the explosion center. They were oriented standing to the right side or seated vertical-facing and exposed to an air blast at an altitude of 4700 m, using 8 thermobaric bombs of the same type. At 2.5 m from the explosion center, 6 goats were standing on the right side, and 5 were seated vertical-facing. At 3 m, 44 goats were standing on the right side, and 7 were seated vertical-facing. At 4 m, 4 goats were standing on the right side, and 6 were seated vertical-facing. At 5 m, 9 goats were standing on the right side, and 6 were seated vertical-facing. Fig. 1 shows the orientations of the goats.

Fig. 1.

The orientations and distances of experimental goats. (A) Goat seated vertically-facing; (B) Goats seated vertically-facing; (C) Goats standing to the right side; and (D) Goats standing to the right side.

Blast test devices

For the blast wave tests, blast test devices (BTDs) (PCB Piezotronics, Inc., Buffalo, New York, USA) were used to measure blast overpressure loadings to the thorax. Approximating the size of a goat torso, the BTD is a 30-inch long, 12-inch diameter rigid cylinder made of 0.75-inch-thick aluminum tubing with internal reinforcements. For each test configuration, BTD data were collected at matching locations with the goats. The BTDs were needed to collect thorax loading data for tests in enclosures because flow blockage effects are important. BTDs are still used today for blast testing.

Goat mortality

After the explosion, we immediately recorded the numbers of surviving and dead goats, inspected the surface injuries of the goats, and measured their respiratory rates, blood pressure, and heart rates. The dead goats were immediately necropsied to confirm the cause of death.

Anatomical protocol and determination of lung injury severity

All goats were dissected after the explosion. The dead and seriously injured goats were dissected within 6 h. The surviving goats were observed overnight, then killed by bleeding through the abdominal aorta to check the degree and scope of the tissue injury. The gross anatomical procedures included checking the following: body surface, limb soft tissue and bone, spine, auditory apparatus (tympanic membrane perforation area and auditory ossicle integrity), eyes (cornea, anterior chamber, iris, vitreous, retina), location and area of craniocerebral hemorrhaging and degree of pia mater congestion, integrity of the chest wall and ribs, hemothorax and effusion, area and location of hemorrhaging, dust and foreign body adhesion in the throat, trachea and lungs, epicardial and intimal hemorrhage area, whether the abdominal parenchymal organs, liver, spleen and kidney were ruptured, the scope and amount of subcapsular hemorrhaging, abdominal cavity viscera, gastric and intestinal (small intestine, colon) plasma, mucosal bleeding, perforation size and scope. The skull was sawed open, and the auditory vesicle of the inner ear was opened to observe the rupture and bleeding of the eardrum and integrity of the ossicular chain. Lung injuries were quantified as the percentage of surface area contused. The PSSLBI¹² was used to score the 4 injury categories (i.e., slight, moderate, serious or severe) as 1, 2, 3, or 4, respectively. The excised lungs were weighed to calculate the lung coefficient.

Lung coefficient and lung wet-dry ratio

The lung coefficient or lung weight ratio was defined as the weight of the lung normalized to the goat's body weight. It is an indicator of pulmonary edema and is related to lung injury severity. After examining and photographing the gross anatomy of the experimental goats, the trachea was cut from the branch, and the excised lungs were weighed to calculate the lung coefficient. A severely damaged section of lung tissue was cut, wrapped in tin foil paper, and baked in a 60 °C constant-temperature oven pre-dried to a constant weight. The lung coefficient and lung wet-dry ratio were calculated as lung coefficient = whole lung weight (g)/body weight (kg) × 100% and lung wet-dry ratio = lung wet weight (g)/dry constant weight (g).

Statistical analysis

Measurement data are expressed as the mean ± SD, with “n” representing the experiment frequency. Differences between groups were examined for statistical significance using the Kruskal-Wallis H test for K independent samples in nonparametric tests. Countable data were analyzed using contingency tables and χ² tests. Correlations were analyzed using Spearman's coefficient for bivariate correlations. A p < 0.05 was defined as statistically significant after Bonferroni correction for multiple comparisons. All statistical analyses were performed using SPSS, version 26.0, statistical software (SPSS, Inc., Chicago, IL, USA).

Results

Overpressure values

The blast overpressure loadings to the thorax were measured using BTDs at distances of 2.5, 3, 4, and 5 m. Each distance was measured 3 – 5 times, and the mean overpressure was calculated (Table 1).

Table 1.

Mean overpressure at different distances.

Serial number	Distances (m)	Mean overpressure (kPa)
1	2.5	470.67
2	3	307.80
3	4	187.00
4	5	119.67

Goat mortality

Table 2 shows the goat mortality. At 2.5 m, all 6 (100.0%) right-side-standing goats and 4 of 5 (80.0%) seated vertical-facing goats died. At 3 m, 29 of 44 (65.9%) right-side-standing goats and 2 of 7 (28.6%) seated vertical-facing goats died. At 4 m, 9 of 44 (20.5%) right-side-standing goats and 1 of 6 (16.7%) seated vertical-facing goats died. At 5 m, all goats survived (mortality 0%). χ² results showed that the mortality rates differed very significantly among the different orientations and distances (χ² = 48.15, p < 0.001, Table 2, Fig. 2).

Table 2.

Numbers of dead and surviving goats at different orientations and distances, n (%).

Orientation and distance	Death	Survival	Total (n)
Right-side-standing
2.5 m	6 (100.0)	0 (0)	6
3 m	29 (65.9)	15 (34.1)	44
4 m	9 (20.5)	35 (79.5)	44
5 m	0 (0)	9 (100.0)	9
Seated vertical-facing
2.5 m	4 (80.0)	1 (20.0)	5
3 m	2 (28.6)	5 (71.4)	7
4 m	1 (16.7)	5 (83.3)	6
5 m	0 (0)	6 (100.0)	6

Fig. 2.

χ² test for goats at different orientations and distances.

Correlation analysis between mortality and overpressure at different distances

Correlations between the mortalities of right-side-standing and seated facing vertically goats and the correlation of overpressure at different distances were analyzed using the Spearman coefficient for bivariate correlations. Spearman's rho for the correlation between mortality of the right-side-standing goats and overpressure at different distances was 0.992 (p = 0.001). Spearman's rho for the correlation between mortality of the seated vertical-facing goats and overpressure at different distances was 0.975 (p = 0.005). These results suggest a strong positive correlation between mortality and overpressure at different distances.

According to the criteria of relationship between short pulse overpressure peak and shock wave damage to humans at standard atmospheric pressure,¹³ the mortality rate on a plateau > 4500 m should be higher than that at a standard atmospheric pressure. In our study, the overpressure peak at 2.5 m on the plateau > 4500 m was 470.67 kPa, resulting in nearly 100% mortality; however, the mortality at 346 – 471 kPa at a standard atmospheric pressure is only 50%.¹³ It suggests that a main cause of fatalities in free fields at high altitudes is blast overpressure, which may cause severer injuries than those on plains.

Injury characteristics of seated vertical-facing goats

For the seated vertical-facing goats, 4 of 5 (80.0%) died at the 2.5 m distance, 2 of 7 (28.6%) died at the 3 m distance, 1 of 6 (16.7%) died at the 4 m distance, and 0 of 6 (0%) died at the 5 m distance. The χ² value was 9.18 (p = 0.027), indicating significant differences in mortality rates at the different distances (Table 2, Fig. 1). Injury characteristics for the seated vertical-facing goats were as follows: (1) The incidence of lung collapse (pneumothorax) was very high, especially at closer distances. All 7 dead goats had collapsed lungs, suggesting that lung collapse was the main cause of death among the seated vertical-facing goats; however, the mechanism for this requires further study. (2) Gross anatomy showed that except in the dead goats, the lung injuries were 1 – 2 grades lighter in the seated vertical-facing goats than in the right-side-standing goats at the same distance.

Injuries to the right-side-standing goats

Of the 103 right-side-standing goats, 6 were at 2.5 m, 44 were at 3 m, 44 were at 4 m, and 9 were at 5 m. Table 2 and Fig. 1 show the number of deaths. The mortality rates for the different distances yielded a χ² value of 37.59 (p = 0.000), indicating a very significant difference among the distances. Blast overpressure, dynamic pressure and burn were the main causes of death. The injury severity was obvious between the different distances, and the injury gradually decreased as the distance increased (Table 2). According to the PSSLBI classification standard (severe: 4, serious: 3, moderate: 2, minor: 1, no injury: 0), the lung injuries at 2.5 and 3 m were severe, and the scores were 4. However, the fatal whole-lung hemorrhage was consolidated at 2.5 m, and the lung injury at 3 m was a proportion of the consolidated hemorrhage. At 4 m, the proportion of severe injury was 34.48%, the proportion of serious injury was 58.62%, and the proportion of moderate injury was 6.90%. At 5 m, the proportion of severe injury was 0%, the proportion of serious injury was 0%, the proportion of moderate injury was 88.89%, and the proportion of mild injury was 11.11% (Table 3, Fig. 3).

Table 3.

Proportions of injury severity among right-side-standing goats at different distances.

Distance	Severe (%)	Serious (%)	Moderate (%)	Minor (%)	No injury (%)
2.5 m	100.00	0	0	0	0
3 m	100.00	0	0	0	0
4 m	34.48	58.62	6.90	0	0
5 m	0	0	88.89	11.11	0

Fig. 3.

The proportion of injury severity of goats at different distances in standing-side-right.

Anatomical characteristics of the lung injuries

All goats were injured by 8 thermobaric bombs of the same type. After injury, all goats were dissected according to the protocol. The lung injuries had the following characteristics: (1) Different animals at the same distance and orientation injured by the same bomb had different injuries. Two goats were injured by the same bomb, at the same distance and orientation, but goat #232 had only moderate lung injury (PSSLBI score 2), whereas goat #233 had severe lung injury (PSSLBI score 4) and lung collapse resulting in death (Fig. 4A&B). Of 5 goats at this distance and orientation, 4 died of severe lung injury and lung collapse, whereas 1 had only moderate injury, possibly owing to individual differences or wind direction; (2) For the different orientations, even at the same distance, the injury severities were different (Fig. 4A and 4C–G). Fig. 4A&C are lungs of goats at 2.5 m from the explosion center, Fig. 4D&E are at 3 m, and Fig. 4F&G are at 4 m. Goats in Fig. 4A, D&F are seated vertical-facing; those in Fig. 4C, E&G are right-side-standing. The figures and PSSLBI scores showed that the right-side-standing goats exhibited severer lung injuries than did the seated vertical-facing goats; (3) Injury effects differed markedly among goats at the same orientation and distance (Fig. 4K, E&L showed the goats at the same orientation and distance, but with PSSLBI scores of 1, 3 and 4, respectively). The differences in injuries may be related to factors such as cartridge loading, weather, and individual differences among the goats.

Fig. 4.

The lung injury of goats in different orientations and distances. (A) Lung injury at 2.5 m in seated vertically-facing (moderate lung injury, pathologic severity scale of lung blast injury (PSSLBI) score is 2); (B) Lung injury at 2.5 m in seated vertically-facing (severe lung injury, PSSLBI score is 4); (C) Lung injury at 2.5 m right-side-standing (severe lung injury, PSSLBI score is 4); (D) Lung injury at 3 m seated vertical-facing (no lung injury, PSSLBI score is 0); (E) Lung injury at 3 m right-side-standing (serious lung injury, PSSLBI score is 3); (F) Lung injury at 4 m seated vertical-facing (no lung injury, PSSLBI score is 0); (G) Lung injury at 4 m right-side-standing (minor lung injury, PSSLBI score is 1); (H) Lung injury at 5 m seated vertical-facing (no lung injury, PSSLBI score is 0); (I) Lung injury at 5 m right-side-standing (no lung injury, PSSLBI score is 0); (J) Lung of normal goat (no lung injury, PSSLBI score is 0); (K) Lung injury at 3 m right-side-standing (minor lung injury, PSSLBI score is 1); and (L) Lung injury at 3 m right-side-standing (severe lung injury, PSSLBI score is 4).

Lung coefficients of experimental goats at different orientations and distances

Lung coefficient is indicator of pulmonary edema and is related to lung injury severity. Normal lung coefficient values differ among different species, and the lung coefficient of goats has not been reported. Pulmonary edema in experimental animals significantly increases the lung coefficient. First, the lung coefficient (degree of pulmonary edema) was differed significantly between different orientations (Fig. 5). At the same distance, pulmonary edema was severer in the right-side-standing goats than in the seated vertical-facing goats, and the anatomical lung injury was consistent with this. Second, for the same orientation, a significant dose-effect relationship occurred between the pulmonary edema severities at different distances. The pulmonary edema decreased significantly with the distance as seen in both the gross anatomy and PSSLBI grading standard (Fig. 5). However, in the seated vertical-facing goats, the cause of death was lung collapse, and the lung injury to the surviving goats was relatively light, resulting in no significant difference between them (Fig. 5). Third, the “equivalence degree” of the lung injury at different orientations was classified via gross anatomy and PSSLBI. The degree of lung injury to the right-side-standing goats at 5 m was equivalent to the degree of injury in the seated vertical-facing goats at 3 m.

Fig. 5.

The p value of the Kruskal-Wallis H for lung weight ratio of goats at different orientations and distances.

Lung wet-dry ratio of goats at different orientations and distances

The lung wet-dry ratio is a measurement indicator in animal experiments calculated as lung wet-dry ratio = lung wet weight (g)/constant weight after baking (g) × 100%. This indicator reflects the water content in the lung tissue. When this indicator is significantly higher than that of normal controls, the water content of the lung tissue is significantly increased. The means and standard deviations of the lung wet-dry ratio among the different orientations and distances were as follows: at 2.5 m, right-side-standing 3.22 ± 0.69, seated vertical-facing 3.32 ± 0.24; at 3 m, right-side-standing 3.70 ± 1.05, seated vertical-facing 3.39 ± 0.67; at 4 m, right-side-standing 3.29 ± 0.61, seated vertical-facing 3.54 ± 0.17; and at 5 m, right-side-standing 4.04 ± 0.43, seated vertical-facing 3.78 ± 0.39; p value between right-side-standing and seated vertical-facing at 2.5 m, 3 m, 4 m, 5 m were > 0.05. The results showed no significant differences between the groups, possibly because of the selected section of the injured lung. The sections with the most severe injuries often had heavy edema, resulting in no significant differences between the groups.

Discussion

Explosion injury is very common in times of both war and peace and is an important cause of death. The lung is the critical target organ in blast injuries. The release of air bubbles from disrupted alveoli in the lungs into the vascular system likely accounts for the rapid death.14, 15, 16 This study was conducted to research the characteristics of the biological effects of air explosions from thermobaric bombs in a high-altitude environment and the mortality and degree of lung injury to right-side-standing and seated vertical-facing goats at different distances. We placed 127 goats in different orientations and distances and exposed them to an air blast at an altitude of 4700 m, using 8 thermobaric bombs of the same type. We found that the mortality and injury severity to the goats at different orientations and distances differed significantly. Mortality, PSSLBI, and lung coefficient results showed that the lung injury of right-side-standing goats was severer than that in the seated vertical-facing goats, and the injury lessened as the distance increased. These results were consistent with those of blast overpressure and indicate that the different orientations of the goats significantly affected their mortality and injury severity.

Richmond et al.^17,18 reported that for exposure in the free-stream, orientation of the biological target significantly affects the response. They compared the 50% lethal conditions of guinea pigs in different positions in the free-stream of an open I2-in and showed that for side-on incident pressures, 17 – 18 psi accounted for 50% lethality for animals suspended vertically or prone-broadside, whereas incident pressures of 25 – 26 psi were required for the same effect as those head-on or tail-on. The incident shock pressure was the lowest (10 psi) for animals against a reflecting surface. Their results show that overpressure was higher for the side-on orientation than for those oriented end-on or suspended vertically. Our results regarding mortality, PSSLBI, lung anatomy and the lung coefficient were consistent with those of Richmond et al.^17,18 Thus, in our study of the biological effect, the goats were standing on the right side to simulate maximum injury.

Bouamoul and Williams¹⁹ studied the effects of human and sheep lung orientation on primary blast injury induced by a single blast. They used the non-linear arbitrary Lagrangian-Eulerian formulation in LS-Dyna to develop quasi two-dimensional finite element models of a human and sheep thorax to verify whether the injuries observed in the animals were truly representative of human lung injuries for simple blast loadings at different orientations to the blast. They simulated 12 blast directions for 3 blast injury levels based on Bowen curves. The sheep and human torsos were rotated according to their vertical axis in increments of 30° starting from 0 to 330°. They predicted that focusing on protecting the torso from −60° to 60° may yield the greatest reduction in lung primary blast injuries. In other words, the torso from −60° to 60° represented maximum human lung overpressure. When the blast impacts a sheep torso at 0° – 270° clockwise, the blast overpressure is the maximum loading, but all degrees are below the threshold for injury regardless of orientation. Their results for sheep were only partially consistent with ours and the study of Richmond et al.,¹⁷ which showed that the lung injury to right-side-standing experimental animals was severer than that to seated vertical-facing animals. In other words, for blast impacts to experimental animal torsos at 0° clockwise, the blast overpressure represents maximum loading, but that at 270° represents minimal loading, and the main cause may be material properties and constitutive models specifically for lung tissues.

We also found that mortality was higher on the plateau at > 4500 m than at standard atmospheric pressure. The overpressure peak at 2.5 m on the plateau at > 4500 m was 470.67 kPa, leading to almost 100% mortality; however, the mortality at 346 – 471 kPa at standard atmospheric pressure is only 50%.¹³ This result was consistent with the report of Zhang et al.⁹ found that blast injury is severer on plateaus than in low-altitude areas, and the mortality rate increased with the altitude. At 4000 and 5000 m, the injuries were 1–3 levels higher than those on the plains, and the mortality rates increased by 25% and 35%, respectively. The main target organs for injury/death were still the lungs, intestines and other gas-containing organs, and injuries to substantive organs such as the liver and kidney were rare.

Oxygen partial pressure decreases on plateaus, hypoxia causes microcirculatory vascular endothelial damage and increased vascular permeability, capillaries are more likely to rupture and bleed under the action of blast waves, and cavity organ injury is aggravated. Therefore, pathological changes in the lungs at high altitudes include mainly pulmonary hemorrhaging and edema. The injured area exhibits blood spillage in the alveoli, and the alveolar walls break and fuse with each other to form a large alveolar structure, which can adversely affect the respiratory and barrier functions of the lung, leading to respiratory failure in severe cases. This is the main cause of early death in experimental animals after blast exposure.

We used thermobaric bombs to induce injury, and the blast overpressure and temperature were attenuated quickly as the distance increased. Additionally, the power for injury decreased rapidly. The overpressure was 470.67 kPa at 2.5 m and 307.80 kPa at 3 m. The temperature at the explosion center was 3900 °C. According to the fireball durations for different high-temperature regions, the temperature at 2.5 m is 200 °C – 300 °C; thus, burn may be another main cause of fatalities, and the injury was relieved as the distance increased. Our result was consistent with the report of Liu et al.¹⁶ and Yang et al.²⁰ found that the severity of lung injuries was correlated with the injury distances.

In our study, there are some limitations, for example, the sample size of the seated vertical-facing goats is small, and in our follow-up research, we may be supple it.

We confirmed that for thermobaric warhead explosions in an open area at high altitude, the main killing factors are blast wave overpressure and burn. The mortality and injury severity to the lungs at different orientations and distances differed significantly. The mortality and injury severity were worse to right-side-standing goats than to seated vertical-facing goats, and the injury was relieved significantly as the distance increased. These results may provide a research basis for early diagnosis and treatment of explosive injuries at high altitudes.

Funding

This work was supported by the Military Logistic(s) Scientific Research Program of China (ALJ18J001).

Ethical statement

The Animal Care and Facilities Committee of Army Medical University approved all animal experimental protocols (AMUWE20202140).

Declaration of competing interest

There are no potential conflicts of interests.

Author contributions

Author Zhao-Xia Duan designed the study and wrote the protocol. Author Guan-Hua Li and Liang-Chao Zhang were responsible for the clinical data collection. Author Jie-Yuan Zhang and Kui-Jun Chen managed the literature searches and analyses. Authors Meng-Sheng Deng, Jing Chen and Xiang-Yun Cheng undertook the statistical analysis and figure. Authors Guang-Ming Yang, Jian-Min Wang undertook the revision of this article.