拦阻着舰过程中飞行员头颈部的动力学响应

目的分析航母舰载机拦阻着舰过程中飞行员在佩戴和不佩戴头盔时的头颈部动力学响应以及主要肌肉应变量。方法建立包括头部、7个颈椎和2个胸椎共10个刚体的人体头颈部的多体动力学模型;采用集总参数法描述韧带、椎间盘等软组织的力学特性;应用非线性应力-应变关系描述人体头颈部15组肌肉的力学特性。采用多组汽车碰撞过程人体头颈部动力学响应实验数据对模型进行验证。结果获取了拦阻着舰过程飞行员头部的过载曲线和15组肌肉的应变,结果表明颈夹肌拉伸程度最大,在不佩戴头盔时其应变可达50%,佩戴2.7 kg头盔时其应变可达56%。结论佩戴防护头盔会增加飞行员在拦阻着舰过程的颈部肌肉拉伸,仿真结果可用于进一步的损伤评估。     

气囊式头盔防护下的两轮车骑车人头部损伤风险分析

目的 提出一种气囊式头盔缓冲内衬结构,并分析其对两轮车骑车人头部损伤的防护效果。方法 将气囊式内衬应用于自行车（半盔）和摩托车（全盔）两款典型的两轮车骑车人头盔,通过标准GB 24429-2009和法规ECE R22.05测试工况下的有限元碰撞仿真,获得人体头部模型运动学和生物力学响应,从颅骨骨折和颅脑损伤风险角度对比常规聚苯乙烯泡沫塑料（expanded polystyrene, EPS）头盔,综合评价气囊式头盔的防护性能。结果 当气囊压力为0.06 MPa时,气囊式头盔（半盔/全盔）防护下的人体头部颅骨骨折相关量分别小于120 g和150 g,颅骨骨折风险基本低于40%;颅脑最大主应变均小于0.3,轻度脑损伤风险均低于25%;气囊式头盔防护下的人体颅骨骨折和颅脑损伤风险均低于EPS头盔。结论 本文设计的气囊式头盔具有较好的防护效果,能兼顾颅骨骨折和颅脑损伤防护,可以为新型头盔的设计提供基础示例。损伤风险分析也可为骑车人头部损伤应急诊断提供初步参考。     

肾脏钝性撞击损伤影响因素的有限元方法研究

目的 采用有限元方法研究肾脏钝性撞击损伤的影响因素。方法 基于肾脏CT图像构建不同年龄人群肾脏有限元模型,重构肾脏钝性撞击实验,分析肾脏材料本构参数、肾脏组织结构、肾脏大小、撞击位置和撞击速度等参数对肾脏损伤的影响。结果 相同撞击工况下,肾皮质应力随肾脏质量的增加有所减少,随撞锤撞击速度的增加而增加;肾包膜具有一定的吸能效果,从而降低肾脏的应力;肾脏受到撞击时,侧面撞击的肾皮质应力明显高于正面撞击。结论 相比黏弹性本构模型,Mooney Rivlin材料本构模型更适合用于肾脏损伤的有限元评价;肾脏损伤随肾脏质量的增加有所减少;撞锤撞击速度的增加会加剧肾脏损伤;肾包膜会一定程度上减轻肾脏损伤,故在进行肾脏有限元建模时,必须考虑肾包膜结构的存在;相比正面和背面撞击,肾脏侧面受到撞击时损伤相对更严重。     

安全气囊点爆展开时儿童颈部约束对颅脑损伤的影响

目的探讨在交通事故中安全气囊点爆展开时儿童颈部约束对颅脑损伤的影响。方法基于已构建并经过有效性验证的3岁儿童头部有限元(finite element, FE)模型,采用FE方法模拟气囊点爆展开对离位(out-of-position, OOP)状态儿童乘员头部的冲击过程,研究颈部约束对交通事故中儿童颅脑响应及其损伤机制的影响。结果颈部约束的头部在受到安全气囊点爆展开的冲击之后,其运动状态与无颈部约束有很大差异,会导致儿童脑组织最大Von Mises应力明显减小,儿童颅脑损伤程度减弱。儿童头部与安全气囊距离为20、25 cm时,有颈部约束的头部脑组织最大颅内压小于没有颈部约束的头部。结论颈部约束对儿童颅脑损伤响应有较大的影响,用FE方法预测儿童颅脑损伤时应考虑颈部约束的影响。     

颅脑组织材料参数对儿童头部冲击响应的影响

目的针对目前对儿童颅脑组织材料参数的不确定性,研究直接冲击载荷条件下颅脑组织材料参数对儿童头部冲击响应的影响。方法应用已验证的3岁儿童头部有限元模型进行冲击仿真实验,采用正交实验设计和方差分析对儿童颅脑组织材料进行参数分析。结果颅骨弹性模量对儿童头部冲击响应具有显著性影响,随着颅骨弹性模量的增加,头部撞击侧颅内压力显著减小(P=0.000),对撞侧颅内压力显著增大(P=0.000),颅骨最大Von Mises应力显著增大(P=0.000)。脑组织的线性黏弹性材料参数对儿童头部冲击响应同样具有显著性影响,随着脑组织短效剪切模量的增加,脑组织最大主应变显著减小(P=0.000),脑组织最大剪应力则显著增加(P=0.000)。结论参数分析结果可为今后儿童头部有限元模型的材料选取提供参考依据,进而提升模型在预测临床上无法通过脑CT影像确诊的脑震荡等脑损伤时的准确性。     

人头部力锤冲击试验的生物力学研究

目的：探讨人头部受主动冲击的钝力作用时的力响应特点,同时测试头部各部位承受最大冲击力的限度,从冲击动力学角度去探讨颅脑损伤的生物力学机理。方法：使用配备大量程力传感器的力锤对人尸体头部各部位进行冲击试验,记录接触力响应曲线,并手工记录锤头的质地、质量、初速度、冲击面大小,以及被冲击的头部是否有破坏性反应(头皮挫裂及颅骨骨折)。结果：人头部对主动冲击的钝物的接触力响应曲线为类似正弦波的脉冲波形,其波形宽度及峰值因冲击物的质地、有无头皮等发生变化;人头部在小面积钝物的冲击作用下,造成头皮挫裂的冲击力最大值平均为5100N;使颞部、顶部、额部、枕部骨折的冲击力最大值的平均值分别为6200、8100、8300、11000N;利用试验得到的数据,验证了作用于头部的钝物与头部组成的系统相当于带有强阻尼的弹簧振子。结论：头部在受到主动冲击时,典型的接触力一时间曲线为类似正弦波的脉冲波形;大面积的钝器作用于头部造成的颅骨骨折,更多发生延伸至远处的线形骨折;本试验还得出了人头部能耐受的冲击力大小等参数,这些对于建立有限元模型进行分析和验证是必须的。     

6岁儿童行人-汽车碰撞中碰撞角度对头部损伤的影响

目的应用符合欧洲新车安全评鉴协会(the European New Car Assessment Programme,Euro NCAP)要求的6岁儿童行人有限元模型,探究不同碰撞角度对儿童头部损伤的影响。方法应用符合Euro NCAP技术公告(TB024)并且具有详细解剖学结构的6岁儿童行人有限元模型,设置4组行人-汽车碰撞仿真试验,探究不同碰撞角度下儿童头部损伤情况。人体头部质心初始位置在车的纵向中心线上,轿车初速度为40 km/h,轿车分别与人体右侧、前侧、左侧、后侧碰撞(即0°、90°、180°、270°)。比较不同碰撞角度下运动学差异和头部碰撞响应,同时分析面骨和颅骨的损伤情况。结果通过分析儿童行人头部接触力、头部质心合加速度、头部质心相对于车的合速度、头部损伤标准(head injury criterion,HIC_(15))、面骨骨折情况以及颅骨应力分布发现,背面、正面碰撞下儿童头部骨折及发生脑组织损伤的风险大于侧面碰撞,其中背面碰撞下儿童行人头部损伤风险最高,侧面碰撞下儿童行人头部损伤风险最低。结论背面碰撞下儿童行人头部损伤风险最大,研究结果对行人-汽车碰撞评估和防护装置研发具有重要的应用价值。     

不同载荷作用下头部生物力学响应仿真分析

目的建立符合解剖结构的人颅骨三维有限元模型,研究多种载荷作用下头部生物力学响应。方法通过建立具有解剖结构的高精度头部有限元模型,颅骨采用能模拟骨折的弹塑性材料本构模型,结合已发表的正面冲击颅内压实验、动态颅骨骨折实验、头部跌落实验结果,仿真再现实验过程中头部受冲击载荷作用下的生物力学响应、颅骨骨折及头部不同速度下的跌落响应。结果前碰撞表现出冲击与对冲侧正-负颅内压分布,相近载荷下枕骨变形比前额、顶骨严重,跌落中速度越快损伤越大。结论建立精确解剖结构的头部有限元模型可以较好模拟头部在冲击、跌落等载荷下的生物力学响应。通过量化接触力、颅内压力等参数来评价头部损伤风险,为防护系统的设计提供科学依据。     

头部钝器损伤实验与仿真分析

目的　为了研究头部在钝器作用下的生物力学响应及损伤机理。 方法　利用CT图像数据和MRI图像数据对头部骨骼与内部软组织进行几何重建,然后画分网格,构建颅脑有限元模型。另一方面,对连于躯干的头部标本进行10 m/s的低速冲击,测试冲击部位接触力、顶部应变及冲击的对侧（枕部）加速度。把构建的有限元模型导入MADYMO软件进行相同条件下模拟仿真,从输出模块里输出相应部位的结果。 结果　仿真结果表明模型的头部接触力、顶部应变、对撞侧加速度与头部标本冲击实验测得值能较好吻合。 结论　建立的头部有限元模型及采用的仿真方法可满足头部钝器损伤的仿真研究需要。     

头盔质量和质心对军机飞行员颈部肌力的影响

目的研究头盔质量和质心偏移对军机飞行员颈部肌肉活动特性的影响。方法基于AnyBody软件平台建立头颈部肌骨模型,包含C0、C1-7、T1和136组头颈部肌肉。采用集中载荷模拟头盔作用,对不同头盔质量、质心位置和加速度载荷下的7个主要肌群的肌力进行了仿真计算。结果当头盔质心与头部质心重合时,支配后伸的头半棘肌、肩胛提肌、头夹肌和颈夹肌处于收缩发力状态。当头盔质量增大,这些肌群肌力也随之线性增加,并且加速度载荷对肌力增大程度起放大作用。头盔质心后移,会降低后伸肌群的肌力,增大前屈肌群受力。头盔质心左右偏移引起的附加侧弯力矩则会激活支配侧弯功能的肌群的活动。结论头盔质量和质心位置对颈部肌群活动特性有明显影响,本文建立的头颈部肌骨模型可以计算不同状态下肌力的变化,头盔设计和使用过程可采用该技术进行定量分析。     

Effect of helmet liner systems and impact directions on severity of head injuries sustained in ballistic impacts: a finite element (FE) study

The current study aims to investigate the effectiveness of two different designs of helmet interior cushion, (Helmet 1: strap-netting; Helmet 2: Oregon Aero foam-padding), and the effect of the impact directions on the helmeted head during ballistic impact. Series of ballistic impact simulations (frontal, lateral, rear, and top) of a full-metal-jacketed bullet were performed on a validated finite element head model equipped with the two helmets, to assess the severity of head injuries sustained in ballistic impacts using both head kinematics and biomechanical metrics. Benchmarking with experimental ventricular and intracranial pressures showed that there is good agreement between the simulations and experiments. In terms of extracranial injuries, top impact had the highest skull stress, still without fracturing the skull. In regard to intracranial injuries, both the lateral and rear impacts generally gave the highest principal strains as well as highest shear strains, which exceed the injury thresholds. Off-cushion impacts were found to be at higher risk of intracranial injuries. The study also showed that the Oregon Aero foam pads helped to reduce impact forces. It also suggested that more padding inserts of smaller size may offer better protection. This provides some insights on future’s helmet design against ballistic threats.     

Dynamic Response Due to Behind Helmet Blunt Trauma Measured with a Human Head Surrogate

A Human Head Surrogate has been developed for use in behind helmet blunt trauma experiments. This human head surrogate fills the void between Post-Mortem Human Subject testing (with biofidelity but handling restrictions) and commercial ballistic head forms (with no biofidelity but ease of use). This unique human head surrogate is based on refreshed human craniums and surrogate materials representing human head soft tissues such as the skin, dura, and brain. A methodology for refreshing the craniums is developed and verified through material testing. A test methodology utilizing these unique human head surrogates is also developed and then demonstrated in a series of experiments in which non-perforating ballistic impact of combat helmets is performed with and without supplemental ceramic appliques for protecting against larger caliber threats. Sensors embedded in the human head surrogates allow for direct measurement of intracranial pressure, cranial strain, and head and helmet acceleration. Over seventy (70) fully instrumented experiments have been executed using this unique surrogate. Examples of the data collected are presented. Based on these series of tests, the Southwest Research Institute (SwRI) Human Head Surrogate has demonstrated great potential for providing insights in to injury mechanics resulting from non-perforating ballistic impact on combat helmets, and directly supports behind helmet blunt trauma studies.     

Cervical spine response in frontal crash

Predicting neck response and injury resulting from motor vehicle accidents is essential to improving occupant protection. A detailed human cervical spine finite element model has been developed, with material properties and geometry determined a priori of any validation, for the evaluation of global kinematics and tissue-level response. Model validation was based on flexion/extension response at the segment level, tension response of the whole ligamentous cervical spine, head kinematic response from volunteer frontal impacts, and soft tissue response from cadaveric whole cervical spine frontal impacts. The validation responses were rated as 0.79, assessed using advanced cross-correlation analysis, indicating the model exhibits good biofidelity. The model was then used to evaluate soft tissue response in frontal impact scenarios ranging from 8G to 22G in severity. Disc strains were highest in the C4–C5–C6 segments, and ligament strains were greatest in the ISL and LF ligaments. Both ligament and disc fiber strain levels exceeded the failure tolerances in the 22G case, in agreement with existing data. This study demonstrated that a cervical spine model can be developed at the tissue level and provide accurate biofidelic kinematic and local tissue response, leading to injury prediction in automotive crash scenarios.     

Cervical Spine Motion During Football Equipment-Removal Protocols: A Challenge to the All-or-Nothing Endeavor

Context

The National Athletic Trainers'' Association position statement on acute management of the cervical spine-injured athlete recommended the all-or-nothing endeavor, which involves removing or not removing both helmet and shoulder pads, from equipment-laden American football and ice hockey athletes. However, in supporting research, investigators have not considered alternative protocols.

Objective

To measure cervical spine movement (head relative to sternum) produced when certified athletic trainers (ATs) use the all-or-nothing endeavor and to compare these findings with the movement produced using an alternative pack-and-fill protocol, which involves packing the area under and around the cervical neck and head with rolled towels.

Design

Crossover study.

Setting

Movement analysis laboratory.

Patients or Other Participants

Eight male collegiate football players (age = 21.4 ± 1.4 years; height = 1.87 ± 0.02 m; mass = 103.6 ± 12.5 kg).

Intervention(s)

Four ATs removed equipment under 4 conditions: removal of helmet only followed by placing the head on the ground (H), removal of the helmet only followed by pack-and-fill (HP), removal of the helmet and shoulder pads followed by placing the head on the ground (HS), and removal of the helmet and shoulder pads followed by pack-and-fill (HSP). Motion capture was used to track the movement of the head with respect to the sternum during equipment removal.

Main Outcome Measure(s)

We measured head movement relative to sternum movement (translations and rotations). We used 4 × 4 analyses of variance with repeated measures to compare discrete motion variables (changes in position and total excursions) among protocols and ATs.

Results

Protocol HP resulted in a 0.1 ± 0.6 cm rise in head position compared with a 1.4 ± 0.3 cm drop with protocol HS (P < .001). Protocol HP produced 4.9° less total angular excursion (P < .001) and 2.1 cm less total vertical excursion (P < .001) than protocol HS.

Conclusions

The pack-and-fill protocol was more effective than shoulder pad removal in minimizing cervical spine movement throughout the equipment-removal process. This study provides evidence for including the pack-and-fill protocol in future treatment recommendations when helmet removal is necessary for on-field care.Key Words: National Athletic Trainers'' Association position statement, pack and fill, motion analysis, helmet removal

Key Points

• The pack-and-fill protocol resulted in less overall motion than removal of the helmet and shoulder pads followed by placing the head on the ground, which is currently endorsed by the National Athletic Trainers'' Association.
• Using pack and fill, the athletic trainers could position the head at release in, on average, nearly the identical position as at initiation.
• Removal of the helmet and shoulder pads resulted in a drop in linear and angular head position, placing the cervical spine into increased extension.

American football has the highest number of catastrophic cervical spine injuries of all sports in the United States.¹ Although still of major concern, the incidence of catastrophic cervical spine injuries has declined over the past 35 years, and the rate is now less than 1 per 100 000 exposures.² Much of this decline has been attributed to a 1976 rule change making it illegal to spear, or lower the head to butt or ram an opponent.² Given the force applied at the front and top of a player''s helmet, spearing has long been associated with the axial-load mechanism of injury that results in catastrophic cervical spine injury.³ However, despite a focus on player safety, researchers^4–6 have suggested that the incidence of spearing or other axial head impacts may be as prevalent in American football in the United States today as before the 1976 rule change. Instead, improved prehospital care and on-field management of equipment-laden athletes with potential spine injuries possibly also has led to a reduction in catastrophic cervical spine injuries by reducing the number of cervical spine injuries that result in catastrophic outcomes. This possibility needs to be documented, and research pertaining to prehospital care protocols and management techniques that may affect catastrophic spinal cord injury outcomes in American football needs to continue.Proper prehospital on-field medical care of the athlete with a spine injury, including equipment management, may be critical in limiting secondary cervical spine injury while also allowing access to the airway and chest compressions. The National Athletic Trainers'' Association (NATA) position statement on the acute management of the cervical spine-injured athlete⁷ includes the all-or–nothing technique, which discourages independent removal of the helmet or shoulder pads in American football or ice hockey when an athlete has a potential cervical spine injury. This specific NATA recommendation is based on several studies^8–11 in which the researchers measured vertebral positioning or spinal cord space before and after equipment removal and showed that when the football helmet is removed while the shoulder pads remain in place, cervical alignment can be compromised as the head and neck fall backward into extension.However, a gap exists in the body of evidence used to support this recommendation, as no authors of supporting studies have addressed the use of fillers (eg, rolled towels) to stabilize the head and cervical spine after removing only the helmet and leaving the shoulder pads on the athlete. This technique, termed pack and fill, would fill the void of the missing helmet by placing rolled towels around and beneath the posterior head, cervical spine, and surface of the spine board or ground to prevent the head and cervical spine from moving into extension during performance of critical-care tasks. Although the NATA position statement⁷ mentions this technique as a possibility for an athlete whose helmet is dislodged or shoulder pads are not removed easily, pack and fill could be an alternative clinical practice when removal of the helmet is necessary to provide safe access to the airway (eg, inability to remove the facemask efficiently or a poorly fitted football helmet creating instability of the head and cervical spine within the helmet). Decoster et al¹² recently demonstrated that pack and fill can effectively maintain a neutral sagittal cervical alignment after helmet removal.Another gap in these supporting studies is that they were based on static imaging and, therefore, did not account for the amount of head and neck movement that occurs during the equipment-removal process. In the case of shoulder-pad removal, this could be substantial. Therefore, the purposes of our study were to address these 2 gaps by measuring cervical spine movement (head with respect to sternum) throughout the removal process and to compare this movement among several possible removal protocols. We hypothesized that removal of the helmet combined with the pack-and-fill technique would result in less overall movement than removal of both the helmet and shoulder pads.     

手枪子弹冲击下有防护生物靶标多参数测量与分析

目的 研究枪弹对有防护生物靶标的致伤情况与原因,为揭示人体在防护条件下的致伤机理和医学治疗提供参考。方法 选择体重60 kg的活猪作为生物靶标,参照防护条件下单兵头部和胸部的易损情况确定生物靶标内的测试物理量和具体位置。在25 m射距下分别对防护条件下生物靶标的头部和胸部射击3发9 mm巴拉贝鲁姆手枪弹,综合测量手枪弹冲击对有防护生物靶标钝性损伤起重要作用的加速度、压力、载荷力等多个力学量。结果 （1） 手枪弹对生物靶标头部的钝性损伤使颅内产生负压脉冲并伴随产生远达效应,在其脊柱和颈动脉内出现脉冲压力;（2） 手枪弹对生物靶标胸部的钝性损伤使心脏承受高加速度冲击,肺部承受高压力波作用。结论 测量结果为定量认识手枪弹对防护条件下有生目标致伤机理提供依据。     

Head Position and Football Equipment Influence Cervical Spinal-Cord Space During Immobilization

OBJECTIVE: To assess the effect of head position and football equipment (ie, helmet and shoulder pads) on cervical spinal cord space in individuals lying supine on a spine board. DESIGN AND SETTING: The independent variables were head position (0-cm, 2-cm, and 4-cm occiput elevation with no helmet and shoulder pads and with helmet and shoulder pads) and cervical spine level (C3, C4, C5, C6, and C7). The 3 dependent variables were sagittal space available for the cord (SAC) (mm), sagittal spinal-cord diameter (mm), and cervical-thoracic angle ( degrees ), determined via magnetic resonance imaging. SUBJECTS: Twelve men (age = 24.3 +/- 2.1 years; height = 181.1 +/- 5.7 cm; weight = 93.9 +/- 3.6 kg). MEASUREMENTS: Sagittal space available for the cord was determined by subtracting the sagittal spinal-cord diameter from the corresponding sagittal spinal-canal diameter. The spinal-canal diameter was measured as the shortest distance from the vertebral body to the spinolaminar line at each of the spinal levels. Each measurement was taken 3 times, and the 3 measurements were averaged. RESULTS: Sagittal space available for the cord was significantly greater (P <.01) for 0-cm (mean = 5.50 mm) than for 2-cm (mean = 4.86 mm) and 4-cm (mean = 5.07 mm) occiput elevation. SAC was also significantly greater (P <.01) for the equipment condition (mean = 5.34 mm) than for the 2-cm and 4-cm elevation levels. No significant difference (P =.093) in SAC existed between 0-cm elevation and the equipment condition. CONCLUSIONS: The helmet and shoulder pads should be left on during spine-board immobilization of the injured football player. Similarly, during spine-board immobilization of an individual without football helmet and shoulder pads, the head should be maintained at 0 cm of occiput elevation. Sagittal spinal-cord space is optimized in both of these conditions.     

Change in Size and Impact Performance of Football Helmets from the 1970s to 2010

Linear impactor tests were conducted on football helmets from the 1970s–1980s to complement recently reported tests on 1990s and 2010s helmets. Helmets were placed on the Hybrid III head with an array of accelerometers to determine translational and rotational acceleration. Impacts were at four sites on the helmet shell at 3.6–11.2 m/s. The four generations of helmets show a continuous improvement in response from bare head impacts in terms of Head Injury Criterion (HIC), peak head acceleration and peak rotational acceleration. Helmets of 2010s weigh 1.95 ± 0.2 kg and are 2.7 times heavier than 1970s designs. They are also 4.3 cm longer, 7.6 cm higher, and 4.9 cm wider. The extra size and weight allow the use of energy absorbing padding that lowers forces in helmet impacts. For frontal impacts at 7.4 m/s, the four best performing 2010s helmets have HIC of 148 ± 23 compared to 179 ± 42 for the 1990s baseline, 231 ± 27 for the 1980s, 253 ± 22 for the 1970s helmets, and 354 ± 3 for the bare head. The additional size and padding of the best 2010s helmets provide superior attenuation of impact forces in normal play and in conditions associated with concussion than helmets of the 1970s–1990s.     

Wearing a bike helmet leads to less cognitive control,revealed by lower frontal midline theta power and risk indifference

A recent study claims that participants wearing a bike helmet behave riskier in a computer‐based risk task compared to control participants without a bike helmet. We hypothesized that wearing a bike helmet reduces cognitive control over risky behavior. To test our hypothesis, we recorded participants' EEG brain responses while they played a risk game developed in our laboratory. Previously, we found that, in this risk game, anxious participants showed greater levels of cognitive control as revealed by greater frontal midline theta power, which was associated with less risky decisions. Here, we predicted that cognitive control would be reduced in the helmet group, indicated by reduced frontal midline theta power, and that this group would prefer riskier options in the risk game. In line with our hypothesis, we found that participants in the helmet group showed significantly lower frontal midline theta power than participants in the control group, indicating less cognitive control. We did not replicate the finding of generally riskier behavior in the helmet group. Instead, we found that participants chose the riskier option in about half of trials, no matter how risky the other option was. Our results suggest that wearing a bike helmet reduces cognitive control, as revealed by reduced frontal midline theta power, leading to risk indifference when evaluating potential behaviors.