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Page 1: Ircobi short paper-final3 Microsoft Word - Ircobi short paper-final3.docx Author Binhui Jiang, Haojie Mao, Christina Wagner, Libo Cao, and King H. Yang Subject IRCOBI 2011: Session

Abstract�� Thoracic��injury��in��the��pediatric��population��is��a��relatively��common��cause��of��severe��injury��and��a��marker��of��injury��severity��accompanied��by��a��high��mortality��rate.��However,��no��anatomically��accurate,��complex��pediatric��chest��finite��element��(FE)��component��model��is��available��for��a��10��year�rold��(YO)��in��the��literature.��In��the��current��study,��a��10��YO��thorax��FE��model��was��developed��based��on��scanned��geometries.��The��model��was��then��validated��against��published��data��measured��during��cardiopulmonary��resuscitation��(CPR)��performed��on��pediatric��subjects.������Keywords��Child��thorax��finite��element��model,��cardiopulmonary��resuscitation.��

I. INTRODUCTION��

Thoracic��injury��in��pediatric��population��is��a��marker��of��injury��severity��and��signifies��a��high��mortality��rate��[1].��To��investigate��pediatric��injury��mechanisms��and��tolerances,��physical��and��numerical��surrogates��for��children��have��been��developed��by��scaling��from��adult��data��[2].��However,��children��are��not��small��adults,��because��anatomical��structures,��material��properties,��injury��mechanisms,��and��tolerances��associated��with��pediatric��population��may��vary��greatly��from��those��for��adults.��For��example,��the��cross�rsection��of��an��infant’s��chest��is��circular,��but��as��the��child��grows,��the��transverse��diameter��increases��which��makes��the��chest��more��elliptical��[3].��The��material��properties��of��pediatric��ribs��are��much��softer��than��those��of��an��adult��[4].��As��such,��the��child��thorax��can��sustain��a��relatively��higher��percentage��of��chest��compression��before��it��is��fractured.��This��increased��deflection��may��make��severe��injuries��to��internal��organs��more��likely��when��rib��fractures��occur��in��the��pediatric��population��[5]�r[7].��Due��to��lack��of��available��material��property��data,��quantitative��age�rdependent��anatomical��data,��and��pediatric��impact��response��data,��no��complex��pediatric��chest��component��FE��model��has��been��developed��directly��from��pediatric��data.��The��objectives��of��this��study��were��to��develop��a��10��YO��thorax��FE��model��based��on��scanned��geometries��and��validate��the��model��against��force�rdeflection��data��measured��from��cardiopulmonary��resuscitation��(CPR).��

II. METHODS��

Summary��of��the��Data��

The��geometry��data��for��the��FE��thorax��model��were��taken��from��clinical��CT��and��MRI��scans��of��children��(approximately��10��years��of��age)��treated��at��Children’s��Hospital��of��Michigan.��The��protocol��used��to��secure��these��data��was��approved��by��the��Human��Investigation��Committee��at��Wayne��State��University.��The��geometry��data��include��all��major��anatomical��structures:��the��bony��skeleton,��the��chest��organs��and��abdominal��organs��except��the��small��and��large��intestines.��

Pediatric��cadaveric��tests��have��been��quite��limited��due,��in��part,��to��ethical��issues.��Maltese��et��al.��[7]��(2008)��reported��force�rdeflection��data��measured��from��six��children��(10.5�r1.75��YO)��during��CPR,��which��were��used��for��model��validation��in��the��current��study.��To��measure��these��data,��a��Force�rDeflection��Sensor��(FDS)��was��integrated��into��a��patient��monitor�rdefibrillator��used��during��CPR.��During��CPR��compressions,��the��sensor��was��interposed��between��the��chest��of��the��patient��and��hands��of��the��rescuer.��After��a��CPR��event,��the��thoracic��force��and��deflection��data��were��collected��from��the��monitor�rdefibrillator.��Average��linear��stiffness��values��calculated��from��this��study��were��used��to��validate��the��10��YO��thorax��FE��model.��Parametric��studies��were��performed��to��study��the��effect��of��CPR��loading��directions��on��peak��force.��

Mesh��generation��

The��ANSYS��ICEM��CFD/HEXA��(ANSYS,��Canonsburg,��Pennsylvania,��U.S.A)��was��used��to��mesh��solid��elements��for��the��bony��skeleton��and��organs.��The��mesh��size��can��be��easily��changed��by��controlling��the��block��parameters.��A��typical��

Binhui��Jiang1,��Haojie��Mao2,��Christina��Wagner2,��Libo��Cao1,��and��King��H.��Yang2������

1The��State��Key��Laboratory��of��Advanced��Design��and��Manufacturing��for��Vehicle��Body,��Hunan��University,��China��2��Bioengineering��Center,��Wayne��State��University,��USA

Development��of��a��10�rYear�rOld��Pediatric��Thorax��Finite��Element��Model��Validated��against��Cardiopulmonary��Resuscitation��Data��

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spatial��resolution��of��1��to��2��mm��was��chosen��to��capture��detailed��anatomical��structures��within��current��computational��capabilities.��Abdominal��organs��were��also��developed��for��providing��proper��boundary��conditions��during��chest��compression.��Shell��elements��were��used��to��model��cortical��bone,��and��membrane��elements��were��used��to��model��muscle.��In��total,��242,266��hexahedral,��1,524��pentahedral,��and��188,318��shell��and��membrane��elements��were��used.��For��solid��elements,��98%��have��Jacobian��values��above��0.5,��with��a��minimum��Jacobian��of��0.31.��For��shell��and��membrane��elements,��97%��have��Jacobians��above��0.7,��with��a��minimum��value��of��0.34.��The��final��model��is��shown��in��Figure��1.��

��

Model��Material��Properties��and��Cortical��Thickness��

The��ribs,��costal��cartilage,��and��sternum��are��the��major��components��of��the��rib��cage.��In��reported��numerical��child��models,��material��properties��have��been��scaled��from��the��adult’s.��For��example,��Mizuno��et��al.��[8]��(2008)��used��scale��factors��to��calculate��material��properties��for��the��3��YO��child��model.��Kim��et��al.��[9]��(2009)��utilized��an��optimization��method��to��calculate��scale��factors��for��material��properties��and��cortical��thickness��for��a��10��YO��child��pelvis��model.��In��the��current��study,��these��same��scale��factors��were��used��to��obtain��the��material��properties��and��cortical��thickness��of��ribs��and��sternum��for��the��10��YO��child��thorax��model.��The��material��properties��for��cartilage��were��calculated��from��Yamada’s��(1970)��study��by��dividing��ultimate��stress��over��ultimate��strain��[4].��RIB��Rib��cortical��thickness:��Li��et��al.��[10]��(2010)��reported��that��adult��ribs’��cortical��thickness��ranged��from��0.23��to��2.96��mm,��with��an��average��value��of��0.84��mm.��Ito��et��al.��[11]��(2009)��reported��the��thickness��of��the��rib��cortical��layer��was��0.72��mm��in��their��adult��model.��These��values��indicate��clinical��CT��scan��resolution��would��be��insufficient��to��visualize��the��cortical��thickness��accurately��in��the��child.��Therefore,��in��the��current��10��YO��thorax��model,��the��rib��cortical��thickness��was��defined��as��0.6��mm��based��on��the��scaling��factor��cited��above.��Rib��material��properties:��Cortical��and��spongy��bones��are��generally��simulated��using��the��elastic��plasticity��material��model��in��LS�rDYNA.��Li��et��al.��[10]��(2010)��used��an��elastic�rplastic��material��(*MAT3)��model��to��simulate��the��rib��cortical��layer��and��spongy��bone.��In��their��study,��for��the��rib��cortical��layer,��the��Young’s��modulus��was��11.5��GPa,��yield��stress��was��88��MPa,��and��tangent��modulus��was��1.15��MPa.��For��rib��spongy��bone,��the��Young’s��modulus��was��0.04��GPa,��yield��stress��was��2.2��MPa,��and��tangent��modulus��was��1.0��MPa.��In��this��study,��the��piecewise�rlinear�rplasticity��material��model��(*MAT24)��was��used��to��simulate��the��cortical��and��spongy��bones.��Using��the��cited��scale��factor,��the��Young’s��modulus��of��the��rib��cortical��bone��was��8.28��GPa,��the��yield��stress��was��63.36��MPa,��and��the��tangent��modulus��was��1.15��MPa.��For��the��spongy��bone,��the��Young’s��modulus��was��25.6��MPa,��the��yield��stress��was��1.408��MPa,��and��the��tangent��modulus��was��1.0��MPa.��Sternum��To��the��best��of��the��authors’��knowledge,��no��study��on��the��sternum’s��cortical��thickness��and��material��properties��has��been��reported��in��the��literature.��Usually,��the��sternum’s��material��properties��were��assumed��to��be��equivalent��to��those��of��the��rib��for��both��cortical��and��spongy��bone��[11].��The��sternum’s��cortical��thickness��was��geometrically��scaled��to��1.4��mm��in��this��study.��Costal��cartilage��Yamada��(1970)��reported��that��the��ultimate��tensile��strength��of��costal��cartilage��was��0.46��MPa��for��both��the��0�r��to��9�r��and��10�r��to��19�ryear�rold��groups,��and��their��ultimate��percentage��elongation��was��0.312��and��0.282,��respectively��[4].��Using��these��data,��the��elastic��modulus��of��costal��cartilage��can��be��calculated��from��Yamada’s��report.��The��elastic��material��model��(*MAT1)��was��used��to��model��the��costal��cartilage��in��the��10��YO��thorax��model.����

Fig.1. 10 YO thorax FE model with simplified abdominal organs

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Skin,��organs,��and��soft��tissue��For��organ��and��soft��tissues,��the��adult��properties��from��validated��WSU��human��body��model��[12]��were��used��for��the��10��YO��thorax��model,��with��the��assumption��that��the��tissue��response��is��not��greatly��related��to��age.��The��child��skin’s��stiffness��is��softer��than��that��of��adult��according��to��studies��reported��by��Mizuno��et��al.��[8]��(2009)��and��Yamada��[4]��(1970),��so��a��value��of��60��kPa��was��chosen��for��the��shear��modulus.����

III. RESULTS��

The��force�rdeflection��curve��predicted��by��the��10��YO��thorax��FE��model��(Figure��2a)��was��similar��in��shape��to��the��characteristic�� force�rdeflection��data�� recorded��during��CPR�� for��children��of��various��ages�� (Figure��2b).��The��model�rpredicted��thorax��stiffness��falls��within��the��range��of��CPR��data��for��the��10.5�r1.75��YO��children��(Figure��2c).��High��von��Mises��stresses��occurred��at��ribs��1��to��7��during��CPR��simulation.��The��locations��of��the��highest��stresses��within��each��rib��are��shaded��red��in��Figure��3.��Stresses��were��much��smaller��for��ribs��8��to��12��(Figure��3).��The��maximum��principal��strain��patterns��were��similar��to��those��of��von��Mises��stresses��(Figure��3).��The��highest��maximum��principal��strain��value��was��0.94%,��which��is��much��less��than��the��ultimate��tensile��strain��for��adult��ribs��reported��by��Kemper��et��al.��(2005)��[13].��

� � � �

��Fig.��2.��Simulation��and��CPR��results��(a)��FE��model��predicted��force�rdeflection��response,��(b)��Result��from��one��CPR��

case��showing��viscous��relationship.[7],��(c)��Comparison��of��the��linear��stiffness��obtained��from��simulation��and��CPR

��Fig.��3.��Contour��plot��of��Von�rMises��stress��and��maximum��principal��strain��for��rib��cortical��bone��

Since��CPR��was��manually��performed,��a��parametric��study��on��simulated��CPR��loading��directions��were��undertaken��to��study��the��potential��effect��of��loading��angle��change��about��the��mediolateral��axis.��Results��demonstrated��that��the��peak��reaction��force��during��CPR��was��only��slightly��affected��by��changing��loading��direction.��In��a��range��of���r10�q��to��10�q��changes��from��the��baseline��model��loading��orientation,��changes��in��the��peak��reaction��force��were��less��than��4%.����

IV. DISCUSSION��

In��this��study,��a��10��YO��thorax��FE��model��was��developed��and��validated��against��CPR��data.��The��model�rpredicted��force�rdeflection��curve��was��qualitatively��similar��to��the��adult��curves��reported��by��Melvin��et��al.��(1975)��[14],��where��

�������������������� ��a.��Von�rMises��stress��(��MPa) ��������������������������������������������������������������������b.��Maximum��principal��strain��

��c.��

0

4000

8000

12000

Line

ar��s

tiffn

ess(

N/m

)��

Mean

Average

��b.�� a.

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the��curves��were��quasi�rlinear��during��moderate��peak��deflection.��The��model��also��demonstrated��viscous��responses��during��CPR��unloading��stage,��as��seen��in��real��world��CPR.����Peak��maximum��principal��strain��predicted��by��the��model��is��significantly��lower��than��ultimate��tensile��strain��thresholds��reported��for��adult��ribs��[13].��Such��results��indicate��that��CPR��usually��does��not��cause��rib��fractures��of��children.��This��finding��is��consistent��with��the��literature��[15]�r[16].��Furthermore,��the��FE��model�rpredicted��peak��force��is��not��sensitive��to��variance��in��loading��orientation��possible��in��manual��CPR��application.��

V. CONCLUSIONS����

An��anatomically��detailed,��high��resolution��10��YO��FE��thorax��model��was��developed��and��validated��against��data��obtained��from��real�rworld��CPR.��The��validation��data��of��this��study��was��obtained��from��CPR��which��was��performed��at��a��relatively��low��speed,��with��maximum��loading��rate��of��250��mm/s��[7].��Although��this��model��uses��adult��values��for��density,��it��was��validated��during��a��loading��event��for��which��inertial��effects��are��minimal.��In��future��studies,��the��model��will��be��refined��for��more��dynamic��impact��events.��More��advanced��modeling��efforts��together��with��material��property��studies��and��dynamic��tests��on��pediatric��subjects��are��needed��for��better��understanding��of��pediatric��injury��mechanisms�� and�� injury�� tolerances�� during�� high�rspeed�� impact�� and�� development�� of�� injury�� protection��countermeasures.��

VI. ACKNOWLEDGEMENTS��

Geometry��data��of��FDS��were��provided��by��Matthew��R.��Maltese��from��Children's��Hospital��of��Philadelphia.��MRI��and��CT��images��were��taken��from��Children’s��Hospital��of��Michigan,��Detroit,��MI��using��protocol��approved��by��Wayne��State��University.��Particular��thanks��to��Aparna��Joshi,��MD��and��Wilbur��Smith,��MD��of��the��Wayne��State��University��College��of��Medicine��Radiology��department.��The��first��author��of��this��paper��is��supported��by��a��scholarship��provided��by��China��Scholarship��Council.��

VII. REFERENCES����

[1] Black��T.��L.,��Snyder��C.��L.,��Miller��J.��P.,��Mann��C.��M.,��A.��Christin��Copetas,Dick��G.��Ellis,��Significance��of��chest��trauma��in��children,��Southern��Medical��Journal,89,5,494�r496,1996��

[2] Parent��D.P.,��Crandall��J.R.,��Bolton��J.R.,��Bass��C.R.,��Ouyang��J.,��Lau��S.H.,��Comparison��of��Hybrid��III��child��test��dummies��to��pediatric��PMHS��in��blunt��thoracic��impact��response,��Traffic��Injury��Prevention,11,339�r410,2010��

[3] Burdi��A.R.,��Huelke��D.F.,��Snyder��R.G.,��Lowerey��G.H.,��Infants��and��children��in��the��adult��world��of��automobile��safety�� design:�� pediatric�� and�� anatomical�� considerations�� for�� design�� of�� child�� restraints,��J.Biomechanics,2,267�r280,1969����

[4] Yamada��H.��Strength��of��biological��materials.��Baltimore:��Williams��&��Wilkins,��1970.��[5] Holmes��J.F.,��Sokolove,��Brant��W.E.,��Kuppermann,��A��clinical��desision��rule��for��identifying��children��with��thoracic��

injuries��after��blunt��torso��trauma,��Annals��of��Emergency��Medicine,39,5,492�r499,2002��[6] Gruben�� K.G.,�� Romlein�� J.,�� Halperin�� H.R.,�� Tsitlik�� J.E.,�� System�� for�� Mechanical�� Measurements�� during��

cardiopulmonary��resuscitation��in��humans,��IEEE��Transactions��on��Biomedical��Engineering,37,2,204�r210,1990��[7] Maltese��M.R.,��Castner��T.,��Niles��D.,��Nishisaki��A.,��Balasubramanian��S.,��Methods��for��determining��pediatric��

thoracic�� force�rdeflection�� characteristics�� from�� cardiopulmonary�� resuscitation,�� Stapp�� Car�� Crash��Journal,52,83�r105,2008��

[8] Mizuno��K,��Deguchi��T,��Ikami��T,��Kubota��M,��Development��of��a��three�ryear�rold��child��FE��model,��Traffic��Injury��Prevention,6,4,361�r71,2005��

[9] Kim��J.E.,��Li��Z.,��Ito��Y.,��Huber��C.��D.,��Shih��A.��M.,��Eberhardt��A.��W.,��et��al.,��Finite��element��model��development��of��a��child��pelvis��with��optimization�rbased��material��identification,��Journal��of��Biomechanics,42,2191�r2195,2009��

[10] Li��Z.,��Kindig��M.��W.,��Subit��D.,��Kent��R.��W.,��Influence��of��mesh��density,��cortical��thickness��and��material��properties��on��human��rib��fracture��prediction,��Medical��Engineering��&��Physics,In��press,In��press,In��press,2010����

[11] Ito��O.,��Dokko��Y.,��Ohashi��K.,��Development��of��adult��and��elderly��FE��thorax��skeletal��models,��0148�r7191,paper��no.2009�r01�r0381,2009��

[12] Shah��C.S.,��Yang��K.��H.,��Hardy��W.,��Wang��H.K.,��King��A.��I.,��Development��of��a��computer��model��to��predict��aortic��rupture��due��to��impact��loading,��Stapp��Car��Crash��Journal,45,2001��

[13] Kemper��A.��R.,��Mcnally��C.,��Kennedy��E.��A.,��Manoogian��S.��J.,��Rath��A.��L.,��Ng��T.��P.,��et��al.,��Material��properties��of��human��rib��cortical��bone��from��dynamic��tension��coupon��testing,��Stapp��car��Crash��Journal,49,199�r230,2005��

[14] Melvin��J.W.,��Mohan��D.,��Stalnaker��R.L.,��Occupant��injury��assessment��criteria,��paper��no.��sae��750914,��1975��[15] Maguire��S.,��Mann��M.,��John��N.,��Ellaway��B.,��Sibert��J.��R.,��Kemp��A.��M.,��Does��cardiopulmonary��resuscitation��

cause��rib��fractures��in��children?��A��systematic��review,��Child��Abuse��&��Neglect,30,739�r751,2006��[16] Bush��C.��M,��Jones��J.��S,��Cohle��S.��D,��Johnson��H.,��Pediatric��injuries��from��cardiopulmonary��resuscitation,��Annals��

of��Emergency��Medicine,28,1,40�r44,1996��

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