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Experimental Study of Thoracoabdominal Injuries Suffered from Caudocephalad Impacts Using Pigs

Experimental Study of Thoracoabdominal Injuries Suffered from Caudocephalad Impacts Using Pigs Hindawi Applied Bionics and Biomechanics Volume 2018, Article ID 2321053, 10 pages https://doi.org/10.1155/2018/2321053 Research Article Experimental Study of Thoracoabdominal Injuries Suffered from Caudocephalad Impacts Using Pigs 1 2 2 2 1 2 Sishu Guan, Zhikang Liao, Hongyi Xiang, Xiyan Zhu, Zhong Wang, Hui Zhao , 1 2 Peng Liu , and Xinan Lai Department of Spine Surgery, Daping Hospital, Third Military Medical University, Chongqing 400042, China State Key Laboratory of Trauma; Burns & Combined Wound, Institute for Traffic Medicine, Third Military Medical University, Chongqing 400042, China Correspondence should be addressed to Hui Zhao; box.zhaohui@163.com and Peng Liu; liupengd@163.com Received 7 December 2017; Revised 26 February 2018; Accepted 12 March 2018; Published 10 May 2018 Academic Editor: Yong Peng Copyright © 2018 Sishu Guan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. To know the caudocephalad impact- (CCI-) induced injuries more clearly, 21 adult minipigs, randomly divided into three groups: control group (n =3), group I (n =9), and group II (n =9), were used to perform the CCI experiments on a modified deceleration sled. Configured impact velocity was 0 m/s in the control group, 8 m/s in group I, and 11 m/s in group II. The kinematics and mechanical responses of the subjects were recorded and investigated. The functional change examination and the autopsies were carried out, with which the injuries were evaluated from the Abbreviated Injury Scale (AIS) and the Injury Severity Score (ISS). The subjects in group I and group II experienced the caudocephalad loading at the peak pelvic accelerations of 108.92 ± 58.87 g and 139.13 g ± 78.54 g, with the peak abdomen pressures, 41.24 ± 16.89 kPa and 63.61 ± 65.83 kPa, respectively. The injuries of the spleen, lung, heart, and spine were detected frequently among the tested subjects. The maximal AIS (MAIS) of chest injuries was 4 in group I and 5 in group II, while both the MAIS of abdomen injuries in group I and group II were 5. The ISS in group II was 52.71 ± 6.13, significantly higher than in group I, 26.67 ± 5.02 (p <0 05). The thoracoabdomen CCI injuries and the mechanical response addressed presently may be useful to conduct both the prevention studies against military or civilian injuries. 1. Introduction with potential disaster outcomes [12–16]. As compared to the thoracoabdomen injuries induced by the horizontal impacts, such as anterior-posterior or lateral, remarkable dis- The injuries induced by caudocephalad impacts (CCI) fre- quently occurred in military vehicles, for example, underbelly crepancies existed in injury mechanism, injury characteris- blasts (UBB), which have led to large numbers of injuries and tics, and injury tolerance from the injuries by the CCI. In deaths [1–3]. Some civilian accidents, such as helicopter the past decades, the reported researches with regard to crashes and falls [4–11], resulted in also so many casualties CCI-related injuries were done by retrospectively analyzing owing to the CCI. For example, helicopters are being widely the injuries or deaths involved in the military or civilian sce- used worldwide nowadays due to their excellent motoriza- narios [12–16] or performing the impact experiments with a tion, with an estimated incidence of 2.5 helicopter crashes dummy or cadaver [17–22]. The results have played key roles per 100,000 flying hours [9], and the mortality rate of the in understanding the injury mechanisms and evaluating the injuries involved in helicopter crashes was up to 59% [5]. injury response for the CCI injuries, that is, fractures for Falls contributed to approximately 35 million disabilities or the spine. However, the studies using postmortem human adjusted life years annually, showing an increase trend [11]. surrogates (PMHS) or finite element analysis (FEA) hardly Thoracoabdomen is vulnerable to the CCI, and the CCI- produced successfully the injuries by thoracoabdominal induced thoracoabdominal injuries were reported frequently, organs frequently reported in military or civilian scenarios, 2 Applied Bionics and Biomechanics (a) (b) Figure 1: The schematic diagram and photograph of the installation. (a) Schematic diagram. The setup comprises a sled with three thin steel pipes, a horizontal seat assembly fixed on the carriage, rail, rigid wall, and traction control system. When the thin steel pipes collide with the rigid wall, the sled stops and the carriage continues to move forward and impact with the rigid wall, and finally the buttock of the pig experienced a high caudocephalad acceleration loaded from the seat. (b) The setup photograph. The pig lays in a supine position on the carriage, and the setup was ready for the CCI. particularly hemorrhage, and as a result, the injuries led by Chongqing, China. The animals were housed in ventilated the CCI remained unclear. Furthermore, there still has been rooms and allowed to acclimatize to their surroundings for a paucity of experimental data concerning the thoracoab- over 4 days before the test, and good physical conditions were dominal CCI injuries until now, especially with animals. kept for all the animals. All animals were fastened but free of In order to more clearly address the thoracoabdomen water for 8 h prior to the tests. The animals were divided into CCI-induced injuries, adult minipigs, whose anatomical randomly 3 groups: control group (n =3), group I (n =9), structures of thoracoabdominal organs and physiological and group II (n =9). changes of the impact injury are similar to human body to After premedication with an intramuscular injection of some extent [23], were employed as a surrogate model of ketamine (30 mg/kg) and atropine (0.1 mg/kg), anesthesia human body in the present study. was induced by xylazine hydrochloride (2 mg/kg, intramus- cular injection) and maintained by pentobarbital (10 mg/ kg/h, injecting through ear vein). The animals were tracheo- 2. Material and Methods tomised with a tracheotomy cannula where respiratory rate was adjusted to obtain arterial PCO between 35 and This study was carried out strictly following the recommen- dations in the Guide for the Care and Use of Laboratory Ani- 45 mmHg. Body temperature was maintained between 37 C and 39 C with a blanket. Cardiocirculatory and respiratory mals of the National Institutes of Health. The protocol was approved by the Animal Ethics Committee of the Third Mil- parameters were monitored continuously. Before the impact, all animals received an intravenous injection of 2 mg/kg car- itary Medical University (Permit number: 20150402), and great efforts were made to minimize suffering of the experi- profen to prevent pain. After stable anesthesia, artificial ven- mental animals and cut down the animal number. tilation was shopped for the whole process. Two sensors were used to record in vivo the mechanical 2.1. Experimental Setup. A modified deceleration sled was response during the test. One was an acceleration sensor used to mimic the CCI to the animals. Figure 1 illustrates (7287-1-300, Endevco, USA; acceleration range: 0–2000 g), and the other was a pressure sensor (CYG41000, Dechen, the schematic diagram and photo of the experimental instru- ments. The setup consists of a horizontally orientated seat China; pressure range 0–500 kpa). A metal block was mounted on the pelvis with several screws, and the accelera- assembly, fixed on a carriage designed to slide with respect to the sled. When beginning the test, the sled and carriage tion sensor was glued to the block to measure the acceleration were accelerated simultaneously to the configured velocity, along the caudocephalad direction. The pressure sensor was inserted into a balloon filled with the liquid and placed under and then the sled was stopped by the thin steel pipes as energy absorbers, fitted in front of the sled (with a thickness the liver to measure the abdomen pressure. The installation of the sensors is shown in Figure 2. of 1.5 mm and a section of 80 mm × 80 mm). The carriage continued to move towards the rigid wall along the two rails of “C” shape and stopped by contacting with the rigid wall 2.3. The Experimental Procedure. The anesthetized pig was fastened to seat with a 4-point hardness to avoid the throw- (Figure 1). A piece of hard rubber, mounted in the frontal of the wall, may avoid the destruction due to a high acceler- ing during experiencing the impact, in which the buttock of ation that resulted from the impact between the carriage the subject contacted the rigid seat prior to the test, and the and the rigid wall. limbs were loosely fixed in the frame, mimicking a “sitting” posture (Figure 1), so that the loading may be acted on the 2.2. Animal Preparation. A total of 21 healthy Guizhou buttock of the subject along the caudocephalad direction. Congjiang adult minipigs, weighing 25–30 kg, either male or Impact velocity of the sled was configured as 8 m/s in group female, were obtained from the Experimental Animal Center I and 11 m/s in group II, respectively. The animals in the con- of Daping Hospital, Third Military Medical University, trol group experienced the same test procedure in which the Applied Bionics and Biomechanics 3 Pressure sensor (b) Acceleration sensor (a) (c) (d) Figure 2: The installation of the sensors. (a) The operation photograph of the acceleration sensor installation. The sensor was glued to a metal block that was mounted on the pelvis via screws. (b) The operation photograph of the pressure sensor installation. The laparotomy was done, and the sensor was placed under the liver. (c) The photograph of the pressure sensor. The sensor was inserted into a balloon filled with liquid. (d) The X-ray photograph, in which the sensors were indicated with arrows. impact speed was defined as 0 m/s. When the experiment was The differences of the acquired histopathological alternations initiated, the sled was accelerated from the starting position, in tested animals were tested using one-way analysis of vari- running along the rail with a length of about 80.0 m, and ance (ANOVA). Comparison of AIS in groups I and II was stopped by the contact between the thin-wall pipes and rigid conducted using chi-square test, and the ISS comparison wall. The impact velocity of the sled was determined with a between groups I and II was done using t-test. A value of customer speed dosimeter. The whole course of the CCI p <0 05 was considered statistically significant. was recorded by a high-speed video camera (Phantom V4.3, Vision Research), at 1000 frames per second. 3. Results 2.4. Injury General Examination. Heart rate (HR), respira- The determined impact speeds of groups I and II were tory rate (RR), blood pressure (BP), and arterial blood gas 8.21 ± 0.13 m/s and 10.69 ± 0.41 m/s. The peak accelerations analyses (ABGA, portable blood gas analyzer: i-STAT, Prin- of the sled were 21.27 ± 1.70 g in group I and 34.07 ± 13.56 g ceton NJ, USA) of all the subjects were recorded within 6 h in group II. Figure 3 shows the kinematics of the subjects postinjury at an interval of 1 h, in which the phase of 0 h during crashing from a series of images derived from the referred to the immediate record after the test. high-speed camera, in which the maximal height (MH) was used to estimate the bending of the thoracolumbar 2.5. Injury Pathological Examination. Full-body CT scans spine, as shown in Figure 3(c). The MH in group II was were performed randomly for two pigs in group I and group significantly higher than that in group I (15.01 ± 0.98 cm II pre- and postinjury, to detect injury to the skeleton. The versus 11.27 ± 1.67 cm, p <0 05). animals were sacrificed 6 h postinjury, and then considerable The peak acceleration recorded on the subject pelvis autopsies were carried out. The tissue at the injured location in group II was 139.13 ± 78.54 g, significantly higher than was obtained and prepared for microscopic observation, that in group I, 108.92 ± 58.87 g (p <0 01), while the peak and the histopathological alternations were recorded. The pressure of the abdomen in group II, 63.61 ± 65.83 kPa, autopsies were done immediately once the animals died. was significantly higher than that in group I, 41.24 ± The injuries of the subjects were evaluated according to the 16.89 kPa (p <0 05). Figure 4 shows the corridor curves Abbreviated Injury Scale 2005 (AIS-2005) [24], and the of the caudocephalad accelerations and the abdomen maximal AIS (MAIS) of each anatomical region was used internal pressure. to calculate the Injury Severity Score (ISS). All the animals in group I survived, while in group II, 5 died of the mass bleeding within 2 h posttest, and 1 died 2.6. Statistical Analysis. ABGA and ISS were presented as immediately after the impact. Among all the subjects, HR mean ± SD and were analyzed using SPSS® 19.0 software. and RR speeded up immediately after the impact and lasted 4 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 3: The kinematics of the pig during the CCI. (a) T0: the sled is hitting against the wall but the pig was motionless to the carriage. (b) T1: the pig showed maximal deformation of the abdomen due to severe compression of the torso along the caudocephalad direction. (c) T2: peak point of the spine bending. The maximal height (MH) indicated with the arrows refers to the distance between the peak point of the spine bending and the deck of carriage. (d) T3: the spine returned to normal form. Chart title −50 −100 −150 −200 −20 Series1 Series1 Series2 Series2 (a) (b) Figure 4: The corridor curves of the acceleration and pressure. The corridor of the acceleration (a) and the pressure (b) was showed, in which the acceleration and the pressure were indicated with different colors, with black referring to the data in group I and red in group II. for a few minutes. Subsequently, HR and RR in group I remained stable at 40% of normal levels, in which BP in recovered to normal level, as compared to those in the con- group II dropped to 10–20% of normal levels. Oxygenation trol group, while HR and RR in group II kept at higher levels. parameters did not shift in the control group. The PCO , BP in group I decreased rapidly after the impact and then PO , pH, and HCO in group I indicated a decreasing trend, 2 3− 0.0015 0.003 0.0045 0.006 0.0075 0.009 0.0105 0.012 0.0135 0.015 0.0165 0.017999999 0.0195 0.021 0.022500001 0.024 0.0255 0.027000001 0.0285 0.029999999 0.031500001 0.033 0.034499999 0.035999998 0.037500001 0.039000001 3.85 7.7 11.55 15.4 19.25 23.1 26.95 30.8 34.65 38.5 42.35 46.2 50.05 53.9 57.75 61.6 65.45 69.3 73.15 80.85 84.7 88.55 92.4 96.25 Applied Bionics and Biomechanics 5 140 50 80 40 20 30 0 123456 0 123456 After the injury After the injury Control group Control group Group I Group I Group II Group II (a) (b) 8.5 40 7.5 6.5 6 10 0 123456 0 123456 After the injury After the injury Control group Control group Group I Group I Group II Group II (c) (d) Figure 5: Arterial blood gas analysis. (a) PO , (b) PCO , (c) pH, and (d) HCO are detected in all three groups. Deterioration of ABGA 2 2 3 (PCO ,PO , pH, and HCO ) at 1 h compared with baseline and control group, p <0 05. 2 2 3− as compared to those in the control group. In group II, the The MAIS of chest injuries was 4 in group I and 5 in value of ABGA showed a deterioration at 1 h, as compared group II, while 8 in group I and 9 in group II experienced to that in the control group, but did not reach the criteria the MAIS 5 abdomen injuries. There was a significant distri- bution discrepancy in MAIS between both groups (p <0 of respiratory failure (Figure 5). 05), The common thoracoabdomen injuries from the autop- as shown in Table 1. The ISS of group II, 52.71 ± 6.13, sies included fractures, contusion, laceration, bleeding, and was significantly higher than that of group I, 26.67 ± 5.02 hemorrhage. The injured thoracoabdominal organs, that is, (p <0 05). the spleen, lung, heart, and kidney, were observed com- monly; however, the rate of subendocardial hemorrhage 4. Discussion (SEH) in group I (4/9) was higher, as compared to that in group II (1/9). Furthermore, rib fractures and liver injuries For the CCI-induced thoracoabdomen injuries, especially at have never been detected from the tested pigs. Figure 6 shows a high loading rate, which frequently occurred in the military the typical injuries to the thoracoabdomen organs, Figure 7 or civilian scenarios, the authors presumed that there may be exhibits the fractures in the thoracolumbar spine and pelvis, two ways to transmit the vertical loading: one is the bone, and and Figure 8 illustrates the heart injuries in gross and micro- the other is the soft tissues, that is, thoracoabdomen muscles scopic observation. and organs, and the energy transmission may result in the PO (mmHg) pH 2 HCO (mmol/L) PCO (mmHg) 3− 2 6 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 6: Typical injuries of the thoracoabdominal organs of the pigs that sustained CCI. (a) Ruptures of the spleen in group I, with 2-3 small wounds in the spleen indicated; (b) multiple wounds of the spleen in group II in which the wounds were more wider and deeper than those of group I; (c) there was no obvious damage to the lung of the pigs in group I after the impact; (d) diffuse hemorrhage of the lung of the pig in group II, in which the lamellar hemorrhage was observed. Figure 7: 3D CT reconstruction of the spine and pelvic fractures. injuries to the torso. Among the previously reported litera- fractures have been validated from the published studies, ture, most studies were done by carrying out experiments while the response of the transmission along the soft tissue with a dummy or cadaver [16, 17, 20–22], in which the spine seldom was reported. In the present study, the CCI Applied Bionics and Biomechanics 7 (a) (b) Figure 8: Subendocardial hemorrhage in gross and microscopic observation. (a) Subendocardial hemorrhage in gross observation in group I. (b) Subendocardial hemorrhage under microscopic observation in group I (HE ×100). Table 1: The AIS distribution of the injuries of the animals. due to the vertical load transmission, while the severe and critical injuries could be reproduced by the CCI at the impact Group I AIS Group II AIS Position speed of 8 m/s and 11 m/s. Among the injuries, some remark- 01 ~23 ~45 ~601 ~23 ~45 ~ 6 able characteristics in injury distribution and pattern for the Head —— 00 —— 00 injured thoracoabdomen organs were represented. In the Neck 9 0 0 0 9 0 0 0 experiment, the injuries of the thoracoabdomen organs, that Chest 7 1 1 0 1 0 8 0 is, the spleen, lung, heart, and kidney, were detected, and the Abdomen 0 0 8 1 0 0 0 9 injury patterns included contusion, laceration, and bleeding. The injuries observed in the study were coincident with those Spine 0 9 0 0 0 0 3 6 reported upon the autopsies for the victims involved in Pelvis 0 0 9 0 0 0 0 9 some accidents [29, 30]. However, some thoracoabdomen injuries, that is, rib fractures, aortic tears, cardiac rupture, experiments were performed using adult minipigs at the dif- and liver contusion, reported in the aviation accidents and ferent impact speeds, through which the thoracoabdomen falls [29, 30], were not reproduced in the current experiment. injuries caused by the CCI and the response were studied. The authors suggest that among the autopsies for the victims, The spine plays a key role in supporting the torso and the injuries resulted from not only vertical but also horizon- transporting the loading along the vertical direction. The tal. To the authors’ viewpoint, therefore, the founding was thoracolumbar spinal curvature changes from kyphotic to valuable for the forensic worker to delineate the injury cause lordotic [25], while the thoracolumbar junction is particu- and distinguish the injuries induced by vertical, frontal, or lateral impact. larly susceptible to fracture as it is under significant biome- chanical stress due to the articulation of the relatively rigid According to the study, it was concluded that for the inju- thoracic segment, through its connections to the ribcage ries induced by the vertical loading on the buttock, the abdo- and sternum, with the more mobile lumbar region [26]. For men injuries were more severe as compared with the chest example, it was reported that in aviation accidents, very few injuries. Our study showed that the mass bleeding due to the spleen laceration attributed to the death soon without fractures occurred at the cranial and caudal levels, for exam- ple, 2% of fractures in the cervical spine, 78% of fractures in any timely treatment, which means for the CCI injuries, the the thoracic spine, and 19% of fractures in the lumbosacral injury management for the control of bleeding is necessary spine [27]. In the experiment, all subjects sustained the thor- to reduce the deaths. Kwon et al. [31] suggested that trau- acolumbar fractures, and with an increase of the impact matic pelvic fracture patient prognosis needs to be improved through early diagnosis and prompt delivery of aggressive speed, the spine fractures became worse, affecting the stabil- ity of the spine. It can be concluded that the CCI-induced treatments based on rapid identification of abdominal solid spine injuries (Figure 7) were associated with not only the organ injuries. However, previous pelvis trauma studies compression but also the bending (Figure 3). about bleeding control mostly focused on the injuries to the The review of Bailey et al. [28] suggested that among the liver rather than the spleen, whereby numerous animal models were developed using pigs [32–39]. experiments in studying pelvis and lower-extremity injuries using intact cadavers, the speed of a seat plate of a military Among the abdomen injuries from horizontal impacts, vehicle subjected to the UBB may be up to about 12 m/s, liver injuries were detected frequently. Lau and Viano [40] while for the regulation of fall tests of a helicopter, the test considered that there were two regions of biomechanical speed was configured at 8 m/s and 12 m/s. In this study, we response to blunt hepatic injury at the impact speeds of found the thoracoabdomen organs sustained severe injuries >12 m/s or ≤12 m/s. Some studies considered that the 8 Applied Bionics and Biomechanics included fractures, contusion, laceration, bleeding, and hem- abdomen pressure may be an ideal predictor of liver injuries from horizontal loading [41–44]. From the current experi- orrhage. The results presented here may be useful in forensic ment, at the impact speed of 10.69 ± 0.41 m/s, the abdomen science, emergency management, and injury prevention. internal pressure was up to 63.61 ± 65.83 kPa, while the sub- jects in group I and group II did not experience liver injury. Conflicts of Interest It may be concluded from the current study that the spleen is more vulnerable as compared to the liver for the CCI, The authors declare that they have no conflicts of interest. and as a consequence, the prevention against spleen injuries also be paid a great attention to the CCI. Authors’ Contributions The lung injuries caused in road traffic accidents were considered traditionally to be associated with the impact Sishu Guan and Zhikang Liao contributed equally to this speed and chest compression deflection, while in the present work. study, without any direct impact to the chest, lung injuries occurred frequently, so the authors presumed that the decel- Acknowledgments eration [45] and pressure changes on the chest [46] induced by the rapid diaphragmatic movement during high vertical The work was supported by the Logistics Research Project loading may contribute to diffused lung injury (Figure 6). of PLA (BWS13L019, BWS12J033) and partly sponsored Our results showed the lung injuries may rapidly cause the by the National Natural Science Foundation of China (no. deterioration of respiratory function in the critical injuries. 31470913). 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Experimental Study of Thoracoabdominal Injuries Suffered from Caudocephalad Impacts Using Pigs

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Copyright © 2018 Sishu Guan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Hindawi Applied Bionics and Biomechanics Volume 2018, Article ID 2321053, 10 pages https://doi.org/10.1155/2018/2321053 Research Article Experimental Study of Thoracoabdominal Injuries Suffered from Caudocephalad Impacts Using Pigs 1 2 2 2 1 2 Sishu Guan, Zhikang Liao, Hongyi Xiang, Xiyan Zhu, Zhong Wang, Hui Zhao , 1 2 Peng Liu , and Xinan Lai Department of Spine Surgery, Daping Hospital, Third Military Medical University, Chongqing 400042, China State Key Laboratory of Trauma; Burns & Combined Wound, Institute for Traffic Medicine, Third Military Medical University, Chongqing 400042, China Correspondence should be addressed to Hui Zhao; box.zhaohui@163.com and Peng Liu; liupengd@163.com Received 7 December 2017; Revised 26 February 2018; Accepted 12 March 2018; Published 10 May 2018 Academic Editor: Yong Peng Copyright © 2018 Sishu Guan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. To know the caudocephalad impact- (CCI-) induced injuries more clearly, 21 adult minipigs, randomly divided into three groups: control group (n =3), group I (n =9), and group II (n =9), were used to perform the CCI experiments on a modified deceleration sled. Configured impact velocity was 0 m/s in the control group, 8 m/s in group I, and 11 m/s in group II. The kinematics and mechanical responses of the subjects were recorded and investigated. The functional change examination and the autopsies were carried out, with which the injuries were evaluated from the Abbreviated Injury Scale (AIS) and the Injury Severity Score (ISS). The subjects in group I and group II experienced the caudocephalad loading at the peak pelvic accelerations of 108.92 ± 58.87 g and 139.13 g ± 78.54 g, with the peak abdomen pressures, 41.24 ± 16.89 kPa and 63.61 ± 65.83 kPa, respectively. The injuries of the spleen, lung, heart, and spine were detected frequently among the tested subjects. The maximal AIS (MAIS) of chest injuries was 4 in group I and 5 in group II, while both the MAIS of abdomen injuries in group I and group II were 5. The ISS in group II was 52.71 ± 6.13, significantly higher than in group I, 26.67 ± 5.02 (p <0 05). The thoracoabdomen CCI injuries and the mechanical response addressed presently may be useful to conduct both the prevention studies against military or civilian injuries. 1. Introduction with potential disaster outcomes [12–16]. As compared to the thoracoabdomen injuries induced by the horizontal impacts, such as anterior-posterior or lateral, remarkable dis- The injuries induced by caudocephalad impacts (CCI) fre- quently occurred in military vehicles, for example, underbelly crepancies existed in injury mechanism, injury characteris- blasts (UBB), which have led to large numbers of injuries and tics, and injury tolerance from the injuries by the CCI. In deaths [1–3]. Some civilian accidents, such as helicopter the past decades, the reported researches with regard to crashes and falls [4–11], resulted in also so many casualties CCI-related injuries were done by retrospectively analyzing owing to the CCI. For example, helicopters are being widely the injuries or deaths involved in the military or civilian sce- used worldwide nowadays due to their excellent motoriza- narios [12–16] or performing the impact experiments with a tion, with an estimated incidence of 2.5 helicopter crashes dummy or cadaver [17–22]. The results have played key roles per 100,000 flying hours [9], and the mortality rate of the in understanding the injury mechanisms and evaluating the injuries involved in helicopter crashes was up to 59% [5]. injury response for the CCI injuries, that is, fractures for Falls contributed to approximately 35 million disabilities or the spine. However, the studies using postmortem human adjusted life years annually, showing an increase trend [11]. surrogates (PMHS) or finite element analysis (FEA) hardly Thoracoabdomen is vulnerable to the CCI, and the CCI- produced successfully the injuries by thoracoabdominal induced thoracoabdominal injuries were reported frequently, organs frequently reported in military or civilian scenarios, 2 Applied Bionics and Biomechanics (a) (b) Figure 1: The schematic diagram and photograph of the installation. (a) Schematic diagram. The setup comprises a sled with three thin steel pipes, a horizontal seat assembly fixed on the carriage, rail, rigid wall, and traction control system. When the thin steel pipes collide with the rigid wall, the sled stops and the carriage continues to move forward and impact with the rigid wall, and finally the buttock of the pig experienced a high caudocephalad acceleration loaded from the seat. (b) The setup photograph. The pig lays in a supine position on the carriage, and the setup was ready for the CCI. particularly hemorrhage, and as a result, the injuries led by Chongqing, China. The animals were housed in ventilated the CCI remained unclear. Furthermore, there still has been rooms and allowed to acclimatize to their surroundings for a paucity of experimental data concerning the thoracoab- over 4 days before the test, and good physical conditions were dominal CCI injuries until now, especially with animals. kept for all the animals. All animals were fastened but free of In order to more clearly address the thoracoabdomen water for 8 h prior to the tests. The animals were divided into CCI-induced injuries, adult minipigs, whose anatomical randomly 3 groups: control group (n =3), group I (n =9), structures of thoracoabdominal organs and physiological and group II (n =9). changes of the impact injury are similar to human body to After premedication with an intramuscular injection of some extent [23], were employed as a surrogate model of ketamine (30 mg/kg) and atropine (0.1 mg/kg), anesthesia human body in the present study. was induced by xylazine hydrochloride (2 mg/kg, intramus- cular injection) and maintained by pentobarbital (10 mg/ kg/h, injecting through ear vein). The animals were tracheo- 2. Material and Methods tomised with a tracheotomy cannula where respiratory rate was adjusted to obtain arterial PCO between 35 and This study was carried out strictly following the recommen- dations in the Guide for the Care and Use of Laboratory Ani- 45 mmHg. Body temperature was maintained between 37 C and 39 C with a blanket. Cardiocirculatory and respiratory mals of the National Institutes of Health. The protocol was approved by the Animal Ethics Committee of the Third Mil- parameters were monitored continuously. Before the impact, all animals received an intravenous injection of 2 mg/kg car- itary Medical University (Permit number: 20150402), and great efforts were made to minimize suffering of the experi- profen to prevent pain. After stable anesthesia, artificial ven- mental animals and cut down the animal number. tilation was shopped for the whole process. Two sensors were used to record in vivo the mechanical 2.1. Experimental Setup. A modified deceleration sled was response during the test. One was an acceleration sensor used to mimic the CCI to the animals. Figure 1 illustrates (7287-1-300, Endevco, USA; acceleration range: 0–2000 g), and the other was a pressure sensor (CYG41000, Dechen, the schematic diagram and photo of the experimental instru- ments. The setup consists of a horizontally orientated seat China; pressure range 0–500 kpa). A metal block was mounted on the pelvis with several screws, and the accelera- assembly, fixed on a carriage designed to slide with respect to the sled. When beginning the test, the sled and carriage tion sensor was glued to the block to measure the acceleration were accelerated simultaneously to the configured velocity, along the caudocephalad direction. The pressure sensor was inserted into a balloon filled with the liquid and placed under and then the sled was stopped by the thin steel pipes as energy absorbers, fitted in front of the sled (with a thickness the liver to measure the abdomen pressure. The installation of the sensors is shown in Figure 2. of 1.5 mm and a section of 80 mm × 80 mm). The carriage continued to move towards the rigid wall along the two rails of “C” shape and stopped by contacting with the rigid wall 2.3. The Experimental Procedure. The anesthetized pig was fastened to seat with a 4-point hardness to avoid the throw- (Figure 1). A piece of hard rubber, mounted in the frontal of the wall, may avoid the destruction due to a high acceler- ing during experiencing the impact, in which the buttock of ation that resulted from the impact between the carriage the subject contacted the rigid seat prior to the test, and the and the rigid wall. limbs were loosely fixed in the frame, mimicking a “sitting” posture (Figure 1), so that the loading may be acted on the 2.2. Animal Preparation. A total of 21 healthy Guizhou buttock of the subject along the caudocephalad direction. Congjiang adult minipigs, weighing 25–30 kg, either male or Impact velocity of the sled was configured as 8 m/s in group female, were obtained from the Experimental Animal Center I and 11 m/s in group II, respectively. The animals in the con- of Daping Hospital, Third Military Medical University, trol group experienced the same test procedure in which the Applied Bionics and Biomechanics 3 Pressure sensor (b) Acceleration sensor (a) (c) (d) Figure 2: The installation of the sensors. (a) The operation photograph of the acceleration sensor installation. The sensor was glued to a metal block that was mounted on the pelvis via screws. (b) The operation photograph of the pressure sensor installation. The laparotomy was done, and the sensor was placed under the liver. (c) The photograph of the pressure sensor. The sensor was inserted into a balloon filled with liquid. (d) The X-ray photograph, in which the sensors were indicated with arrows. impact speed was defined as 0 m/s. When the experiment was The differences of the acquired histopathological alternations initiated, the sled was accelerated from the starting position, in tested animals were tested using one-way analysis of vari- running along the rail with a length of about 80.0 m, and ance (ANOVA). Comparison of AIS in groups I and II was stopped by the contact between the thin-wall pipes and rigid conducted using chi-square test, and the ISS comparison wall. The impact velocity of the sled was determined with a between groups I and II was done using t-test. A value of customer speed dosimeter. The whole course of the CCI p <0 05 was considered statistically significant. was recorded by a high-speed video camera (Phantom V4.3, Vision Research), at 1000 frames per second. 3. Results 2.4. Injury General Examination. Heart rate (HR), respira- The determined impact speeds of groups I and II were tory rate (RR), blood pressure (BP), and arterial blood gas 8.21 ± 0.13 m/s and 10.69 ± 0.41 m/s. The peak accelerations analyses (ABGA, portable blood gas analyzer: i-STAT, Prin- of the sled were 21.27 ± 1.70 g in group I and 34.07 ± 13.56 g ceton NJ, USA) of all the subjects were recorded within 6 h in group II. Figure 3 shows the kinematics of the subjects postinjury at an interval of 1 h, in which the phase of 0 h during crashing from a series of images derived from the referred to the immediate record after the test. high-speed camera, in which the maximal height (MH) was used to estimate the bending of the thoracolumbar 2.5. Injury Pathological Examination. Full-body CT scans spine, as shown in Figure 3(c). The MH in group II was were performed randomly for two pigs in group I and group significantly higher than that in group I (15.01 ± 0.98 cm II pre- and postinjury, to detect injury to the skeleton. The versus 11.27 ± 1.67 cm, p <0 05). animals were sacrificed 6 h postinjury, and then considerable The peak acceleration recorded on the subject pelvis autopsies were carried out. The tissue at the injured location in group II was 139.13 ± 78.54 g, significantly higher than was obtained and prepared for microscopic observation, that in group I, 108.92 ± 58.87 g (p <0 01), while the peak and the histopathological alternations were recorded. The pressure of the abdomen in group II, 63.61 ± 65.83 kPa, autopsies were done immediately once the animals died. was significantly higher than that in group I, 41.24 ± The injuries of the subjects were evaluated according to the 16.89 kPa (p <0 05). Figure 4 shows the corridor curves Abbreviated Injury Scale 2005 (AIS-2005) [24], and the of the caudocephalad accelerations and the abdomen maximal AIS (MAIS) of each anatomical region was used internal pressure. to calculate the Injury Severity Score (ISS). All the animals in group I survived, while in group II, 5 died of the mass bleeding within 2 h posttest, and 1 died 2.6. Statistical Analysis. ABGA and ISS were presented as immediately after the impact. Among all the subjects, HR mean ± SD and were analyzed using SPSS® 19.0 software. and RR speeded up immediately after the impact and lasted 4 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 3: The kinematics of the pig during the CCI. (a) T0: the sled is hitting against the wall but the pig was motionless to the carriage. (b) T1: the pig showed maximal deformation of the abdomen due to severe compression of the torso along the caudocephalad direction. (c) T2: peak point of the spine bending. The maximal height (MH) indicated with the arrows refers to the distance between the peak point of the spine bending and the deck of carriage. (d) T3: the spine returned to normal form. Chart title −50 −100 −150 −200 −20 Series1 Series1 Series2 Series2 (a) (b) Figure 4: The corridor curves of the acceleration and pressure. The corridor of the acceleration (a) and the pressure (b) was showed, in which the acceleration and the pressure were indicated with different colors, with black referring to the data in group I and red in group II. for a few minutes. Subsequently, HR and RR in group I remained stable at 40% of normal levels, in which BP in recovered to normal level, as compared to those in the con- group II dropped to 10–20% of normal levels. Oxygenation trol group, while HR and RR in group II kept at higher levels. parameters did not shift in the control group. The PCO , BP in group I decreased rapidly after the impact and then PO , pH, and HCO in group I indicated a decreasing trend, 2 3− 0.0015 0.003 0.0045 0.006 0.0075 0.009 0.0105 0.012 0.0135 0.015 0.0165 0.017999999 0.0195 0.021 0.022500001 0.024 0.0255 0.027000001 0.0285 0.029999999 0.031500001 0.033 0.034499999 0.035999998 0.037500001 0.039000001 3.85 7.7 11.55 15.4 19.25 23.1 26.95 30.8 34.65 38.5 42.35 46.2 50.05 53.9 57.75 61.6 65.45 69.3 73.15 80.85 84.7 88.55 92.4 96.25 Applied Bionics and Biomechanics 5 140 50 80 40 20 30 0 123456 0 123456 After the injury After the injury Control group Control group Group I Group I Group II Group II (a) (b) 8.5 40 7.5 6.5 6 10 0 123456 0 123456 After the injury After the injury Control group Control group Group I Group I Group II Group II (c) (d) Figure 5: Arterial blood gas analysis. (a) PO , (b) PCO , (c) pH, and (d) HCO are detected in all three groups. Deterioration of ABGA 2 2 3 (PCO ,PO , pH, and HCO ) at 1 h compared with baseline and control group, p <0 05. 2 2 3− as compared to those in the control group. In group II, the The MAIS of chest injuries was 4 in group I and 5 in value of ABGA showed a deterioration at 1 h, as compared group II, while 8 in group I and 9 in group II experienced to that in the control group, but did not reach the criteria the MAIS 5 abdomen injuries. There was a significant distri- bution discrepancy in MAIS between both groups (p <0 of respiratory failure (Figure 5). 05), The common thoracoabdomen injuries from the autop- as shown in Table 1. The ISS of group II, 52.71 ± 6.13, sies included fractures, contusion, laceration, bleeding, and was significantly higher than that of group I, 26.67 ± 5.02 hemorrhage. The injured thoracoabdominal organs, that is, (p <0 05). the spleen, lung, heart, and kidney, were observed com- monly; however, the rate of subendocardial hemorrhage 4. Discussion (SEH) in group I (4/9) was higher, as compared to that in group II (1/9). Furthermore, rib fractures and liver injuries For the CCI-induced thoracoabdomen injuries, especially at have never been detected from the tested pigs. Figure 6 shows a high loading rate, which frequently occurred in the military the typical injuries to the thoracoabdomen organs, Figure 7 or civilian scenarios, the authors presumed that there may be exhibits the fractures in the thoracolumbar spine and pelvis, two ways to transmit the vertical loading: one is the bone, and and Figure 8 illustrates the heart injuries in gross and micro- the other is the soft tissues, that is, thoracoabdomen muscles scopic observation. and organs, and the energy transmission may result in the PO (mmHg) pH 2 HCO (mmol/L) PCO (mmHg) 3− 2 6 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 6: Typical injuries of the thoracoabdominal organs of the pigs that sustained CCI. (a) Ruptures of the spleen in group I, with 2-3 small wounds in the spleen indicated; (b) multiple wounds of the spleen in group II in which the wounds were more wider and deeper than those of group I; (c) there was no obvious damage to the lung of the pigs in group I after the impact; (d) diffuse hemorrhage of the lung of the pig in group II, in which the lamellar hemorrhage was observed. Figure 7: 3D CT reconstruction of the spine and pelvic fractures. injuries to the torso. Among the previously reported litera- fractures have been validated from the published studies, ture, most studies were done by carrying out experiments while the response of the transmission along the soft tissue with a dummy or cadaver [16, 17, 20–22], in which the spine seldom was reported. In the present study, the CCI Applied Bionics and Biomechanics 7 (a) (b) Figure 8: Subendocardial hemorrhage in gross and microscopic observation. (a) Subendocardial hemorrhage in gross observation in group I. (b) Subendocardial hemorrhage under microscopic observation in group I (HE ×100). Table 1: The AIS distribution of the injuries of the animals. due to the vertical load transmission, while the severe and critical injuries could be reproduced by the CCI at the impact Group I AIS Group II AIS Position speed of 8 m/s and 11 m/s. Among the injuries, some remark- 01 ~23 ~45 ~601 ~23 ~45 ~ 6 able characteristics in injury distribution and pattern for the Head —— 00 —— 00 injured thoracoabdomen organs were represented. In the Neck 9 0 0 0 9 0 0 0 experiment, the injuries of the thoracoabdomen organs, that Chest 7 1 1 0 1 0 8 0 is, the spleen, lung, heart, and kidney, were detected, and the Abdomen 0 0 8 1 0 0 0 9 injury patterns included contusion, laceration, and bleeding. The injuries observed in the study were coincident with those Spine 0 9 0 0 0 0 3 6 reported upon the autopsies for the victims involved in Pelvis 0 0 9 0 0 0 0 9 some accidents [29, 30]. However, some thoracoabdomen injuries, that is, rib fractures, aortic tears, cardiac rupture, experiments were performed using adult minipigs at the dif- and liver contusion, reported in the aviation accidents and ferent impact speeds, through which the thoracoabdomen falls [29, 30], were not reproduced in the current experiment. injuries caused by the CCI and the response were studied. The authors suggest that among the autopsies for the victims, The spine plays a key role in supporting the torso and the injuries resulted from not only vertical but also horizon- transporting the loading along the vertical direction. The tal. To the authors’ viewpoint, therefore, the founding was thoracolumbar spinal curvature changes from kyphotic to valuable for the forensic worker to delineate the injury cause lordotic [25], while the thoracolumbar junction is particu- and distinguish the injuries induced by vertical, frontal, or lateral impact. larly susceptible to fracture as it is under significant biome- chanical stress due to the articulation of the relatively rigid According to the study, it was concluded that for the inju- thoracic segment, through its connections to the ribcage ries induced by the vertical loading on the buttock, the abdo- and sternum, with the more mobile lumbar region [26]. For men injuries were more severe as compared with the chest example, it was reported that in aviation accidents, very few injuries. Our study showed that the mass bleeding due to the spleen laceration attributed to the death soon without fractures occurred at the cranial and caudal levels, for exam- ple, 2% of fractures in the cervical spine, 78% of fractures in any timely treatment, which means for the CCI injuries, the the thoracic spine, and 19% of fractures in the lumbosacral injury management for the control of bleeding is necessary spine [27]. In the experiment, all subjects sustained the thor- to reduce the deaths. Kwon et al. [31] suggested that trau- acolumbar fractures, and with an increase of the impact matic pelvic fracture patient prognosis needs to be improved through early diagnosis and prompt delivery of aggressive speed, the spine fractures became worse, affecting the stabil- ity of the spine. It can be concluded that the CCI-induced treatments based on rapid identification of abdominal solid spine injuries (Figure 7) were associated with not only the organ injuries. However, previous pelvis trauma studies compression but also the bending (Figure 3). about bleeding control mostly focused on the injuries to the The review of Bailey et al. [28] suggested that among the liver rather than the spleen, whereby numerous animal models were developed using pigs [32–39]. experiments in studying pelvis and lower-extremity injuries using intact cadavers, the speed of a seat plate of a military Among the abdomen injuries from horizontal impacts, vehicle subjected to the UBB may be up to about 12 m/s, liver injuries were detected frequently. Lau and Viano [40] while for the regulation of fall tests of a helicopter, the test considered that there were two regions of biomechanical speed was configured at 8 m/s and 12 m/s. In this study, we response to blunt hepatic injury at the impact speeds of found the thoracoabdomen organs sustained severe injuries >12 m/s or ≤12 m/s. Some studies considered that the 8 Applied Bionics and Biomechanics included fractures, contusion, laceration, bleeding, and hem- abdomen pressure may be an ideal predictor of liver injuries from horizontal loading [41–44]. From the current experi- orrhage. The results presented here may be useful in forensic ment, at the impact speed of 10.69 ± 0.41 m/s, the abdomen science, emergency management, and injury prevention. internal pressure was up to 63.61 ± 65.83 kPa, while the sub- jects in group I and group II did not experience liver injury. Conflicts of Interest It may be concluded from the current study that the spleen is more vulnerable as compared to the liver for the CCI, The authors declare that they have no conflicts of interest. and as a consequence, the prevention against spleen injuries also be paid a great attention to the CCI. Authors’ Contributions The lung injuries caused in road traffic accidents were considered traditionally to be associated with the impact Sishu Guan and Zhikang Liao contributed equally to this speed and chest compression deflection, while in the present work. study, without any direct impact to the chest, lung injuries occurred frequently, so the authors presumed that the decel- Acknowledgments eration [45] and pressure changes on the chest [46] induced by the rapid diaphragmatic movement during high vertical The work was supported by the Logistics Research Project loading may contribute to diffused lung injury (Figure 6). of PLA (BWS13L019, BWS12J033) and partly sponsored Our results showed the lung injuries may rapidly cause the by the National Natural Science Foundation of China (no. deterioration of respiratory function in the critical injuries. 31470913). 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