ircobi short paper-final3 microsoft word - ircobi short paper-final3.docx author binhui jiang,...

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A b s t r a c t T h o r a c i c i n j u r y in t h e p e d i a t r i c p o p u l a t i o n is a r e l a t i v e l y c o m m o n c a u s e o f s e v e r e i n j u r y a n d a m a r k e r o f i n j u r y s e v e r i t y accompani ed b y a h i g h m o r t a l i t y r a t e . H o w e v e r , n o a n a t o m i c a l l y a c c u r a t e , c o m p l e x p e d i a t r i c c h e s t f i n i t e e l e m e n t ( F E ) c o m p o n e n t mode l is a v a i l a b l e f o r a 1 0 y e a r r o l d ( Y O ) in t h e l i t e r a t u r e . I n t h e c u r r e n t s t u d y , a 1 0 Y O t h o r a x F E m o d e l w a s d e v e l o p e d b a s e d o n scanned g e o m e t r i e s . T h e m o d e l w a s t h e n v a l i d a t e d a g a i n s t p u b l i s h e d d a t a m e a s u r e d d u r i n g c a r d i o p u l m o n a r y r e s u s c i t a t i o n ( C P R ) p e r f o r m e d o n p e d i a t r i c subjects. K e y w o r d s C h i l d t h o r a x f i n i t e e l e m e n t m o d e l , c a r d i o p u l m o n a r y r e s u s c i t a t i o n . I . I N T R O D U C T I O N T h o r a c i c i n j u r y in p e d i a t r i c p o p u l a t i o n is a m a r k e r o f i n j u r y s e v e r i t y a n d s i g n i f i e s a h i g h m o r t a l i t y r a t e [ 1 ] . T o i n v e s t i g a t e p e d i a t r i c i n j u r y m e c h a n i s m s a n d t o l e r a n c e s , p h y s i c a l a n d n u m er i c a l s u r r o g a t e s f o r c h i l d r e n h a v e b e e n d e v e l o p e d b y s c a l i n g f r o m a d u l t d a t a [ 2 ] . H o w e v e r , c h i l d r e n a r e n o t s m a l l adul ts, because a n a t o m i c a l s t r u c t u r e s , m a t e r i a l p r o p e r t i e s , i n j u r y m e c h a n i s m s , a n d t o l e r a n c e s a s s o c i a t e d w i t h p e d i a t r i c p o p u l a t i o n m a y v a r y g r e a t l y f r o m t h o s e f o r a d u l t s . F o r e x a m p l e , t h e c r o s s r s e c t i o n o f a n i n f a n t s c h e s t is circu lar, b u t a s t h e c h i l d g r o w s , t h e t r a n s v e r s e d i a m e t e r i n c r e a s e s w h i c h m a k e s t h e c h e s t m o r e e l l i p t i c a l [ 3 ] . T h e m a t e r i a l prope r ties o f p e d i a t r i c r i b s a r e m u c h s o f t e r t h a n t h o s e o f a n a d u l t [ 4 ] . A s s u c h , t h e c h i l d t h o r a x c a n s u s t a i n a r e l a t i v e l y h i g h e r p e r c e n t a g e o f c h e s t c o m p r e s s i o n b e f o r e it is f r a c t u r e d . T h i s i n c r e a s e d d e f l e c t i o n m a y m a k e s e v e r e i n j u r i e s t o i n t e r n a l o r g a n s m o r e l i k e l y w h e n r i b fr actures o c c u r in t h e p e d i a t r i c p o p u l a t i o n [ 5 ] r [ 7 ] . D u e t o l a c k o f a v a i l a b l e m a t e r i a l p r o p e r t y d a t a , q u a n t i t a t i v e a g e r d e p e n d e n t a n a t o m i c a l d a t a , a n d p e d i a t r i c i m p a c t r e s p o n s e d a t a , n o c o m p l e x p e d i a t r i c c h e s t componen t F E m o d e l h a s b e e n d e v e l o p e d d i r e c t l y f r o m p e d i a t r i c d a t a . T h e o b j e c t i v e s o f t h i s s t u d y w e r e t o d e v e l o p a 1 0 Y O t h o r a x F E m o d e l b a s e d o n s c a n n e d g e o m e t r i e s a n d v a l i d a t e t h e mode l a g a i n s t f o r c e r d e f l e c t i o n d a t a m e a s u r e d f r o m c a r d i o p u l m o n a r y r e s u s c i t a t i o n ( C P R ) . I I . M E T H O D S S u m m a r y o f t h e D a t a T h e g e o m e t r y d a t a f o r t h e F E t h o r a x m o d e l w e r e t a k e n f r o m c l i n i c a l C T a n d M R I s c a n s o f c h i l d r e n (approxi m ate ly 1 0 y e a r s o f a g e ) t r e a t e d a t C h i l d r en s H o s p i t a l o f M i c h i g a n . T h e p r o t o c o l u s e d t o s e c u r e t h e s e d a t a w a s a p p r o v e d b y t h e H u m a n I n v e s t i g a t i o n C o m m i t t e e a t W a y n e S t a t e U n i v e r s i t y . T h e g e o m e t r y d a t a i n c l u d e a l l m a j o r a n a t o m i c a l s t r u c t u r e s : t h e b o n y s k e l e t o n , t h e c h e s t o r g a n s a n d a b d o m i n a l o r g a n s e x c e p t t h e s m a l l a n d l a r g e i n t e s t i n e s . P e d i a t r i c c a d a v e r i c t e s t s h a v e b e e n q u i t e l i m i t e d d u e , in p a r t , t o e t h i c a l i s s u e s . M a l t e s e e t a l . [ 7 ] ( 2 0 0 8 ) r e p o r t e d f o r c e r d e f l e c t i o n d a t a m e a s u r e d f r o m s i x c h i l d r e n ( 1 0 . 5 r 1 . 7 5 Y O ) d u r i n g C P R , w h i c h w e r e u s e d f o r m o d e l v a l i d a t i o n in t h e c u r r e n t s t u d y . T o m e a s u r e t h e s e d a t a , a F o r c e r D e f l e c t i o n S e n s o r ( F D S ) w a s i n t e g r a t e d i n t o a p a t i e n t m o n i t o r r d e f i b r i l l a t o r u s e d d u r i n g C P R . D u r i n g C P R c o m p r e s s i o n s , t h e s e n s o r w a s i n t e r p o s e d b e t w e e n t h e c h e s t o f t h e p a t i e n t a n d h a n d s o f t h e r e s c u e r . A f t e r a C P R e v e n t , t h e t h o r a c i c f o r c e a n d d e f l e c t i o n d a t a w e r e c o l l e c t e d f r o m t h e m o n i t o r r d e f i b r i l l a t o r . A v e r a g e l i n e a r s t i f f n e s s v a l u e s c a l c u l a t e d f r o m t h i s s t u d y w e r e u s e d t o v a l i d a t e t h e 1 0 Y O t h o r a x F E m o d e l . P a r a m e t r i c s t u d i e s w e r e p e r f o r m e d t o s t u d y t h e e f f e c t o f C P R l o a d i n g d i r e c t i o n s o n p e a k f o r c e . M e s h g e n e r a t i o n T h e A N S Y S I C E M C F D / H E X A ( A N S Y S , C a n o n s b u r g , P e n n s y l v a n i a , U . S . A ) w a s u s e d t o m e s h s o l i d e l e m e n t s f o r t h e b o n y s k e l e t o n a n d o r g a n s . T h e m e s h s i z e c a n b e e a s i l y c h a n g e d b y c o n t r o l l i n g t h e b l o c k p a r a m e t e r s . A t y p i c a l B i n h u i J i a n g 1 , H a o j i e M a o 2 , C h r i s t i n a W a g n e r 2 , L i b o C a o 1 , a n d K i n g H . Y a n g 2 1 T h e S t a t e K e y L a b o r a t o r y o f A d v a n c e d D e s i g n a n d M a n u f a c t u r i n g f o r V e h i c l e B o d y , H u n a n U n i v e r s i t y , China 2 B i o e n g i n e e r i n g C e n t e r , Wayne S t a t e U n i v e r s i t y , U S A D e v e l o p m e n t o f a 1 0 r Y e a r r O l d P e d i a t r i c T h o r a x F i n i t e E l e m e n t M o d e l V a l i d a t e d a g a i n s t C a r d i o p u l m o n a r y R e s u s c i t a t i o n D a t a IRC-11-55 Ircobi Conference 2011 - 206 -

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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

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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����

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IRC-11-55 Ircobi Conference 2011

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