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DRDC-RDDC-2014-P113
Direct comparison of the primary blast response of a physical head model with post-mortem human subjects
Simon Ouellet1, Cynthia Bir2 and Amal Bouamoul1
1Defence Research and Development Canada-Valcartier Research Center, 2459 Bravoure road, Québec, QC, Canada, [email protected]
2Keck School of Medicine, University of Southern California, Los Angeles, CA, USA ABSTRACT As the gathering of information on the prevalence of blast-induced traumatic brain injuries (bTBI) continues, there is a need for the development and validation of a physical model (headform) reproducing the mechanical response of the human head to the direct loading from a blast wave. The chain of events leading to an injuries following direct exposure to a blast wave is very complex and its full determination is still the topic of several research efforts. The first step in the injury cascade is necessarily the mechanical insult of the blast wave to the human head. With a combination of representative anatomical features, adequate material selection and careful instrumentation, a validated physical model could measure real external pressure field history and predict resulting intra-cranial pressures (ICP) for any blast loading scenario. In addition, a physical model has the unique ability to measure quantitatively the effect of protective headwear. The following article discusses the validation of the BI2PED (Blast-Induced Brain Injury Protection Evaluation Device) response against post-mortem human subjects (PMHS). Previously reported PMHS blast wave generator tests were methodically replicated in the same facility using the BI2PED. Loading conditions, instrumentation type and position as well as the head mounting technique were reproduced to ensure that the only difference between the two series of experiments was the model itself. A direct comparison of measured ICP histories is presented for two loading orientations and three loading magnitudes. It is demonstrated that the physical model response is in good agreement with that of the PMHS response. From signal analysis, additional evidences supporting skull deformation as the main contributor to ICP variations are discussed. Finally, external pressure fields from the blast wave generator experiments are compared to full scale free-field tests. 1. INTRODUCTION There is a preponderance of clinical and experimental evidences that suggest that traumatic brain injury (TBI) can occur as a result of a direct exposure to blast wave [1]. The chain of events leading to such injuries is likely very complex and its full determination is still the topic of several multi-disciplinary research efforts [1]. Highly controlled laboratory experiments on post-mortem human subject as well as the development of physical and numerical head models can certainly provide useful information on the first step in the cascade of events leading to injury, which is considered to be the mechanical insult of the blast wave to the human head. As a thorough understanding of the injury mechanism is developed, the need for physical models capable of reproducing the mechanical response of the human head under blast loading increases. A validated physical model combining representative anatomical features, adequate material selection and careful instrumentation provides three clear benefits. First, it can help to characterize the head external pressure field history (i.e. the loading) for any blast scenario. Operational blast scenarios are infinite and it is only by characterizing the real mechanical input to the head that it will be possible to distinguish between them. Second, a physical model can help estimate the magnitude of the stresses developed in the brain. This is essential to provide a link between external mechanical insult and the potential for injury. Finally, it can help evaluating the performance of protective headwear systems.
The direct exposure of the head to a blast wave creates a very short duration high amplitude loading that is very different in nature from loadings resulting from impacts seen in automotive or sport accidents. Willinger et al. [2,3] have comprehensively discussed how the duration of a loading on the head can determine the nature of the strain and stress fields in the brain. They distinguished between three lesion mechanisms, each of which is particular to a range of loading duration. For long
duration loading above 10-12 ms, distributed lesions throughout the brain are attributed to the generation of intra-cranial stresses from inertial forces. In such regime, the whole head is subjected to the same translational and rotational acceleration field. For duration between 4-10 ms, the skull motion and brain motion are decoupled. This regime has been the subject of numerous studies since the development of the rapid skull motion theory by Viano et al. [4]. Willinger stated that for such loading durations, the first resonance frequency of the head, which he cites as being between 100-150 Hz, may be excited. Skull to brain relative translational and rotational motion can cause bridge vein shearing and contusion if direct contact occurs. Finally, for impact duration below 4 ms, the loading can excite a second resonant frequency observed between 700-800 Hz [3-6]. This is a wave-dominated regime where local skull deformation occurs. In the context of blast TBI research, such mechanism has also been referred to as “skull flexure” or simply “direct stress transmission” [7-10]. Flexure happens when the loading energy is delivered rapidly enough so that the skull does not have time to reach force equilibrium throughout its structure. The skull doesn’t move as a rigid body but rather sustain local deformation, which then propagates in the structure as waves. Local deformations in the skull may generate compressive and tensile intra-cranial stresses and lesions in nearby brain regions.
Operational blast waves may excite the head structure through more than one frequency band and potentially create lesions from a combination of the aforementioned mechanisms. For example, skull deformation may occur along with relative brain-skull motion, at different times but still within a single event. An important question to answer is which of these mechanisms dominates in the generation of brain stresses following blast exposure. Clearly, simple physical models, such as automotive test devices (ATD), which only records head global accelerations, cannot provide the answer to such question. Even though they can be representative of certain shock severity level and therefore certain risk of cerebral lesions, they cannot distinguish between lesion mechanisms [3]. The study of the effect of blast on the brain requires a more direct measurement.
When a high-pressure blast wave travels across a body (head), it reflects off and diffracts around to form a transient pressure field that is unique to each individual blast scenario. This pressure field is influenced by the blast propagation direction, magnitude and duration at the location of interaction, but also by surrounding reflecting surfaces, including the ground. The stresses generated within the brain following blast exposure therefore also depend on all of these characteristics.
The BI2PED headform shown in Figure 1 has been developed by Defence Research and Development Canada (DRDC) Valcartier research center to characterize head external pressure field history following any given blast exposure, to predict resulting global head acceleration and brain intra-cranial pressure (ICP) variations. It is understood that biological material failure in a real scenario may also occur under shear loads, but it is assumed that ICP is representative of the magnitude of injurious stresses generated within the brain. Shear stresses or strain within brain or brain-like materials would be very difficult to measure experimentally. It has been shown that the BI2PED presents the necessary physiological feature and representative selection of material to estimate head response to blast [11]. Nevertheless, a critical aspect of this physical model to fully meet its purpose is the validation of its response against real human head response (post-mortem). Until this is achieved, there is no guarantee the evolution of ICP follows that from a human head.
Bir et al. [10] has recently reported blast wave generator tests where instrumented post-mortem human subjects (PMHS) heads were subjected to blast waves of 3 different intensities and in 4 different orientations. Fluctuation in intra-cranial pressures was monitored at 4 locations within the brain and skull strains were measured at 5 locations. This parametric approach rendered a dataset that is well fitted to begin the validation process of the BI2PED. It is understood that the full injury cascade cannot be assessed using PMHS, but the BI2PED model focuses on reproducing the mechanical response of the head and the stress transmission mechanism, not the injury itself. Through a collaboration agreement, DRDC Valcartier Research Center and Wayne State University (WSU) Biomedical Engineering Department teamed up to replicate the reported PMHS tests using the BI2PED headform. Loading conditions, instrumentation type and position as well as head mounting technique were reproduced to ensure that the only difference between the two series of experiments was the use of BI2PED or PMHS. Direct comparison of measured ICP histories was therefore possible.
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put on replicalobe, parietal
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Figure 2: piezo-resistive
ection Evaluat
are detailed innt version of ttructures. Thedifferent pol
rain is made embrane strucnted with five ve. They are pcers are also cal. These transing curing. Thate contact witnted on a Hybws for the calcMHS study frometers needed umentation, th
ating three of l lobe and ocve XCL-072 pdirectionnal. Tucers have a s
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Relative size e XCL-072 se
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ensors and b. F
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ng range. Intensor needs to ximum samplISO sensors t
fragility of theectric and fiblidation of pao break durinboth sensors
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Figure 3* Fiber op
Table 1, Sen
ernal DRDC be used in co
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h sensors wer
orientation of tough the skull,bviously the lis that it expIn a physical ires together,
ons in the test it was decidedntation is diffof a different last directiontress in the dss, brain tissuer shear moduominates the dent. The onlyh that the trans
n the original the back of thances were keS head dimen-ray photograp
he piezo-resisting all wires fr
3: BI2PED inteptic sensors a
nsor positions
calibration sonjunction wi250 kHz. Givehe ICP variatiobeen a problesors side by t FISO sensories. Great car
ed to each othre compared.
the sensors w, perpendiculaless intrusive poses the sensmodel, castinin the oppositseries and to
d to run the wfferent than in
orientation mwas maintain
direction of mes as well as slus, with a Postress state a
y effect that csducer itself im
PMHS study he head, distanept similar evnsions. Final ph of the BI2Pive sensor wirrom the back
ernal pressure
are not appare
for both PMH
showed a lineith FISO data en the lack oons adequatel
em in the origiside in the B
r measurementre was taken ther at the base
as challengingar to the skullway to positisor wires signng the sensorste direction frmake sure thires out togethn the origina
may be minimaed. A unidirec
measurement. silicone gel haoisson’s ratio
and the measucould be seen mpedes the me
was specifiednce from the
ven though thsensor positio
PED. The FISres. It can be nof the skull. T
e transducers pent under x-ray
HS and BI2PE
ear output foacquisition sy
of technical inly (e.g. bandwinal study, it w
BI2PED headfts and provideto ensure thate. Following t
g. The original surface tangeion the ICP senificantly, pars into the surrrom the blast. hat the bendingher toward theal PMHS stual if a certain ctional pressuIt is technic
ave a bulk mod approaching ure from the is when the a
easurement.
d in the three ahead mid-plane BI2PED lenons were vali
SO sensors arenoticed that mTable 1 lists a
positions, y imaging.
ED test series.
or pressures uystem (Velocnformation onwidth, accelerwas decided tform. This mee back-up readt sensing elemthe test series
al PHMS student and towarensors in a PMrticularly the
rogate brain alTo ensure tha
g limit of the e back of the h
udy. Howeverrange of angl
ure sensor castally a measudulus that is o0.5. The presensor shoul
angle of incid
axis using distne and depth
ngth and widthidated using xe invisible to
minimal bendinll sensors inte
up to e 50) n the ration o use ethod dings ments , raw
dy ran rd the MHS.
ones llows at we fiber head. r, the les of ted in
ure of orders essure ld be dence
tance from h did x-ray x-ray ng of
ended
frontrepresign
studyfrequprevlow- 2.2 T The for tsectiusedgas increabou
studyusedincid140 was threeoverduringauggenetypicduramilliexpagenebelothat repreblastcondhistochar
propdirecpres
Unfortunatetal sensor waesentative of als.
Post-process
y. All ICP suency of 7 kH
vious free-field-pass Butterw
Test conditio
blast wave gethe BI2PED vaion and a drivd to fill the drexpands and deased to increut the blast wa
Similarly toy, three mem
d to generatdent overpreskPa respection the order
e shock magrpressure histng calibrationge at the taerated from cally have ation in theiseconds. Wansion sectionerator is ablow the 10 ms m
the geneesentative of t profile fducted at DRories for the 8rge detonated
The BI2PEDpagation direcction (i.e. righsure levels.
ely, due to acas significantlthe PMHS se
sing of the ICsignals were Hz. External pd experimentsorth filter with
ns
enerator facilialidation test ven expansionriver section udrives a shockease the ruptuave generator
Figure 4
o the originambrane thickne
te shocks wssures of 85,ively. Shock of 7.5 to 8.5 m
gnitudes. Fulltories were n shots usingarget locatio
classic sholong positiv
e order of With its cun, the current be to generatmark. In ordererated shockan operationa
from free-fieRDC-Valcartie85 kPa shock 0.2 m off the
D was evaluatction (i.e. fronht side exposu
ccidental pullily displaced censor position
CP signals wasfiltered usin
pressure signas with the heah a 10 kHz cu
ity of WSU useries. The sh
n section sepaup to a pressuk wave downure pressure adesign can be
4: Wayne Sta
al PHMS esses were with peak 120 and
duration ms for the l incident measured
g a pencil on. Shock ock tubes ve phase
tens of stom-built blast wave te shocks r to ensure ks were al blast, a eld tests
er research cefrom the blasground and at
ted in two orntal exposure)
ure). Three rep
ing of the wcompared to tns and was pr
s done accordig an 8-pole als were postadform [11], wut-off frequenc
sed in the orighock wave genarated by a myure causing thn the expansioand conseque
e found in [12]
te University
enter was uset wave generat a 5 m distanc
rientations; w) and with th
peats were obt
Figure 5: Cofrom shock
ires during pthe PHMS. Treferred for th
ing to the metlow-pass Bu
-processed fowhich consistecy.
ginal PMHS snerator is a twylar membran
he membraneon section. Thently the shoc].
shock wave g
ed for compaator and for ace.
with the head he head long-atained for each
omparison of k wave generat
5m (0
pouring of theThe occipital she comparativ
thod used in tutterworth filtollowing the sed of a filterin
study (Figure wo part flared ne. Compresseto rupture. U
he thickness ock wave press
generator.
arison. Figure a free-field bla
long-axis paraxis perpendih orientation a
f overpressure tor and from 5
0.2m HOB).
e silicone gelsensor is the ve analysis of
the original PMter with a cusame method ng using an 8
4) was used atube with a d
ed helium gasUpon rupturing
f the mylar casure. More d
5 shows preast from a 5 k
rallel to the scular to the sat all three inc
history gener5kg C4 charge
l, the most
f ICP
MHS ut-off as in -pole
again driver s was g, the an be etails
essure kg C4
shock shock cident
rated e at
2.3 H In thvertetop awereBI2Pmouwas the c
3. R 3.1 E The analysurroanalyaspeintradiffrat thsignof talignshocacqusampmisameaof tu2.4 aheliuoverfronttheoratioobtaforehordefieldparathe htherehead
Head mounti
he original PMebrae. They wand bottom ae centered in PED along wiunted in a sim
protected by connectors. Fi
Figure
RESULTS AN
External pres
analysis of ysis of the exounding the ysis is import
ects from the a-cranial presraction symmhe overlappingals. Synchronthe left and nment of the ck. Given tuisition, whicple every malignment cousurements. Seube boundarieand 2.6 times um, the theorerpressure is ext surface and
ory. Previous o between 2.6ained in very dhead pressure
er of 1.2 to 1.3d. The side prallel to the blaheadform. In efore, it is codform. Finally
ing
MHS study, hwere pressurizand stretched the tube as mith the acceler
milar fashion. Tbubble wrap
igure 6 shows
6: Reproduc
ND DISCUSS
ssure field
the results xternal transien
headform (Ftant to confirmtest, which casure variationetry is confirmg right and le
nicity betweenright signal
headform witthe samplingch was set at
microseconds), uld be detececond, the poes was studied
the benchmaetical reflectedxpected to be clearing effecexplosive tes
6 and 3.2 fordifferent ambie is in line w3 times the peressures are slast flow direct
general, the oncluded thaty, shock speed
heads were dzed and mounttightly by two
much as possibrometer brackThe net was cand a Kevlarboth models
cing the origin
ION
starts with tnt pressure fieFigure 7). Th
m a few differean influence tns. First, shomed by lookieft side pressun time of arrivs confirms tth the incomig rate of tt 1000 kHz
even a sligcted from theossible influend. The peak oark peak incidd to incident pbetween 2.6
cts are expectests with the hr a peak inciient conditionith what coulak incident ovlightly over thtion and the flpressure field
t the tube boud can be mea
disarticulated fted upside-doo chains that ble. The Hybrket. The headcut out aroundr™ sleeve, anmounted in th
nal PMHS stud
the eld his ent the ock ing ure val the ing the (1
ght ese nce verpressure reent overpressupressure ampland 3. Natura
ed to make theheadform in fident overpre
n (dry air at arld be expecteverpressure, whe incident ov
flow is affected is very simiundaries havesured from th
Fig
from the torsown in a soft n
were fixed torid III neck w
dform was putd the exterior d taped to the
he shock wave
dy test conditi
ecorded on thure of 85, 120lification ratioally, the headfe reflected prefree-field conessure around round 5 deg Ced. The side pwhich is similaverpressure bd by the diffrilar to what we limited effehe delay betw
gure 7: Pressupressure sh
o between thnet. The net wo the tube wa
was similarily t upside downpressure sens
e tube wall toe generator.
ions with the B
he forehead w0 and 140 kPao, for this rangform is not pe
essure history nditions gener
85 kPa. HowC). In general,peak overpresar to what wa
because they araction from thwould be seenect on the loaeen the foreh
ure field for 8hock (filtered
he third and fwas attached aall. The specimremoved from
n in a soft nesors areas. Cao avoid slappin
BI2PED.
was on averagea respectivelyge of peak incerfectly flat odeviate away
rated amplificwever, these , the measure ssures were ons observed in are not complhe front portion in free-fieldading seen by
head signal an
85 kPa incidensignals).
fourth at the mens m the t and
abling ng of
e 2.2, y. For cident on the
from cation were peak n the free-
letely on of d and y the
nd the
nt
rightwas 3.2 E The spacof raprocresomorerespsignHz bcontverypeaknois
Fig
3.3 R Repethat throuexterThisadeqorigirepre85 kconsgenesecoloweattribwavfollohisto 3.4 P Fronparaanalywas simi
t/left pressuremeasured at 0
Effect of sens
responses of cing of approxaw occipital ICcessed signal. lve pressure e high frequenonse that wasificant contenband, which dtent above 400y similar, withk. In general, e from the sig
gure 8: Examp
Repeatability
eatability of mthe instrume
ughout the ternal damage
s is critical toquately and drinal PMHSesentative exa
kPa peak insistency was erator and the ond peaks of er than 5%,butable to vae. Slightly hig
owing peaks (ories. Overall
PMHS-BI2PE
ntal, parietal allel and perpysis in the cuthe closest to
ilar in shape b
es, which are m0.22 ms, whic
sor type and p
the piezo-resiximately 4 mmCP measuremThe results influctuations incy noise, as s on par with
nt up to approxdominates the 00 Hz comparh the exceptiothe low-pass
gnals.
mple of compar
y of ICP meas
measurements entation is rest series and
to the heado be able to raw relevant c
S data. Fiample of threncident pres
achieved wheadform. Vathe ICP sign
, part of wariations in tgher variabilit(up to 10%) the repeatabil
ED ICP comp
and occipital pendicular oriurrent article wo the same senbut significan
measured on tch yields a sho
post-processi
istive and the m, were comp
ment from bothndicate that thin the brain mseen in figure
h the validatedximately 4000early time do
red to the noison of an occa filter used in
rison of intra-sensor an
surements
is verified to esponding co
d that no intedform has oc
interpret the comparison wigure 9 showee shots donessure level.
with the blastariability on finals were ge
which can althe generatedty is observedand rest of thlity was consid
parison
ICP signals ientation and was to put on nsor location ntly lower tha
the same horiock speed of 4
ing
fiber-optic separed for all teh sensors alonhe fiber-opticmaterial. The e 8a and 8b. Nd piezo-resist0 Hz, with an omain responssier fiber-optisional variation the original
-cranial pressud piezo-resist
ensure orrectly ernal or ccurred.
results with the ws a
e at the Great
t wave irst and
enerally lso be
d shock d on the he ICP dered excellen
were comparfor all threethe occipital in the PMHS
an in the PM
Fsig
izontal plane. 450 m/s.
ensors, which ests. Figure 8 ng with their fr
sensor probafiber-optic s
Nevertheless, tive sensor. Bimportant con
se. The piezo-ic sensors. Onon on the ordl PMHS study
ure measuremtive sensor.
nt.
red with the incident presince the sens
S. In general, HS. This was
Figure 9, Exagnals from thr
lo
The delay for
were casted sshows a repre
frequency respably had sufficsensor signalsthe sensors sh
Both FFTs forntribution wit-resistive sens
nce filtered, boder of 10% ony only remov
ments obtained
original PMHessure levels.sor final positfrontal ICP ms expected co
ample of filterree different teoading conditi
r the 85 kPa s
side by side wesentative exaponse and the cient bandwids had considehowed a frequr this test revthin the 1000-sors show minoth responses n the first preed high frequ
d from fiber op
HS study for The focus o
tion in the BI2
measurements onsidering tha
red occipital ICests using the ions
shock
with a ample post-
dth to erably uency ealed -1200 nimal were
essure uency
ptic
both of the 2PED were
at the
CP same
BI2PICP 3.4.1 The incidwhicnega
phasstrescontattribwavtensifromPMHin ththe eobsein thvariafrequinitiareach0.4 m
Figu
was resuincrean inthe modthe dhavehighFigusignorigiThe 700 resoncont
PED frontal seshowed a lev
1 Parallel orie
direct compadent overpressch was the timative peaks we
The signals ses of compresses in the reatre-coup injurbuted to the ce at the back sile wave can b
m the front reaHS study alreahe brain [10]. external blast erved is likelyhe exterior trations due to uency phenomal tensile phahing the backms).
ure 10 , Direc
In terms of in very good
lts over the ease in blast increase in BIPMHS. The
dels was on thdamping of the a stiffer respher frequencyure 11 shows tals for the 85in of the diffePMHS show
Hz whereas nance peak tent around b
ensors were cel of correlati
entation – Occ
arison of occisure is shown meframe wherere measured.indicate that
ession and tear portion of thry) has been compressive wskull free surfbe transmittedaches the backady suggestedIt is importanwave even re
y linked to a nransient pressrelative brain
menon [2-4]. ase is of a higk of the head a
ct comparison for a pa
ICP magnitudd agreement w
three testedincident peakI2PED ICPs tmain discrep
he main oscillhat oscillation.ponse than they and for a sthe Fast Fouri5 kPa shock. Terence in the rws a diffuse
the BI2PEDaround 110
etween 50-20
considerably mon to the PMH
cipital region
ipital ICPs foin Figure 10.
re most of the the brain mat
ension at a nohe brain followreported in t
wave initiated face. Because d to the back ok. Based on sd that there want to understaneach the back
natural frequensure history, tn-skull motionIt is interestin
gher magnitudat the same tim
of intra-cranarallel exposu
de, the BI2PEDwith the origid blast severk overpressurethat was verypancy betweelation frequen. The BI2PEDe PMHS, oscishorter periodier Transform This plot con
response of boresonance pe has a simil
00-1200 Hz. 00 Hz, respon
more distant fHS that was cl
ICP
or parallel shoThe ICP histo
e ICP variation
terial is first loticeably specwing shock lothe literature at the front ostress waves
of the brain bekull strain meas a direct cornd that stressek of the head.ncy of the skuthey are the n would occung to note thde in every sime as the sku
ial pressure hures to differen
D response inal PMHS rities. The e generated y similar to en the two ncy and on appears to illating at a d of time. of the ICP
nfirmed the oth models. eak around lar diffuse Frequency
nsible for the
from the skulllose to that of
ocks of 85 kPories are plottns were obser
loaded in tenscific frequencoading of the
already [7-9of the skull wtravel faster in
efore the initiaeasurements arrelation betws in the skull The specific
ull itself. Sincresult of inte
ur on a longerhat the first coignal. This co
ull back face i
history betweent overpressu
ICP fluctuati
Figure 1occipital I
BI2PED he
l surface (seef the occipital
Pa, 120 kPa aed over the firrved and wher
sion and then cy. The develfront surface
9]. This phenwhich is reflect
n the skull thaal compressiveat various loca
ween skull stracan travel forfrequency of
ce these oscillaernal wave ar time frame ompressive phould be due ts unloaded (a
en PMHS and re level.
ions over lon
11: Direct comICP FFT betw
eadform for a pto a 85 kPa s
e Table 2). PaICPs.
and 140 kPa rst 8 ms of sigre the positive
oscillates betwlopment of teof the skull (c
nomenon has ted off as a tean in the braine wave transmations, the oriain and ICP hirth and back bf oscillation thations are notctivities. Thesince it is a lhase followinto the shock iafter approxim
BI2PED headf
nger intervals,
mparison of thween PMHS aparallel exposshock.
arietal
peak gnals, e and
ween ensile coup-been
ensile n, this mitted iginal istory
before hat is t seen e ICP lower g the in air
mately
dform
, also
he and sure
showlongapprare TherPMHThe tightis noand
Willdefoto gassemis a influsuturthis physresp 3.4.2 Occioverparaoscilphascastedefothe bby in
perpwhicresonfrequobsewiththe sthe sBI2P
Figu
wed some disger time scaleroximately 50likely attriburefore, they arHS head fromfact that this
ten in the net. ot attached to the flax and te
The diffuse linger [2,3] wormations (i.e global head rmbly is slightgood match
uences its stiffres surely affesecond reson
sical model. Tonse may fall
2 Perpendicul
ipital ICP corpressure are sallel shock, thellating betweese is expecteded in the right
ormations whibrain stress stncreasing blas
A level of copendicular oriech ICPs fluctunance arounduency (500 Herved that damh the bone on skull may respstress state in PED, which ha
ure 12: Direc
crepancies. Ine in the time
0 Hz and was utable to a mre inevitably i
m the body. Ths was not obsMore so, the any spine-likeentorium mem
700 Hz resonwhich associa
skull flexure,esponse. Thetly too stiff. Tfor skull mat
fness. Indeed, ect the local a
nance frequencThe present co within the sc
lar orientation
omparisons fshown in Figue results showen phases of ted since the right hemisphere. ich loads the btate following st severity is s
orrelation betwentation. Peakuate is again
d 1100-1200 HHz) than in thmped harmoniwhich the str
pond quasi-inthe brain und
as a uniform h
ct comparison for perpe
n particular, ae domain in tnot seen with
more global minfluenced by hese motions aserved on the BI2PED brain
e structure in tmbrane.
nant frequencyated the respo, direct stress e higher resonhe magnitudeterial. Howevthe human sk
and global strucy should be omparison is batter of a larg
n – Occipital r
for perpendicure 12. The IC
w that the rightension and coht side of the Very rapid cobrain region d exposure to a
similar to wha
ween PHMS ak ICPs are ver
higher in theHz, the PMHhe parallel oric oscillationsrain gauge wandependently oderneath [10]. homogenous s
of intra-craniendicular expo
a lower oscillthe original P
h the BI2PEDmotion of the
the head mouare most proba
BI2PED couln is not expectthe cranial cav
y observed on onse of the htransmission)nance frequen
e of the ICP bever, the homokull is not a houctural responconsidered b
based on a veer population
region ICP
cular shocks CP histories wt occipital reg
ompression at head is expos
ompressive lodirectly undera blast is senst was seen in
and BI2PED sry similar for e headform. W
HS ICPs oscilrientation (70s seen in the sas mounted. Itof each other This would e
skull compare
ial pressure hosures to diffe
atory fluctuatPMHS resultsheadform. Thhead or to
unting techniqably not repreld simply indted to move invity. Its move
the PMHS ishead to high ) rather than tncy in the Being similar, igeneous geomomogenous strnse. Neverthelefore trying t
ery limited amresponse.
of 85, 120 were again plotgion is now fir
a specific freqsed first to the
oading on one rneath in comsitive to orienthe parallel or
similar to the pthe three blasWhile the BI2
lation appear00 Hz). In theskull strain sigt was hypotheand that the l
explain the unid to the PHM
history betweenrent overpress
tion was obses. This fluctuhese low freqrelative brain
que and the disesentative of adicate that it wn a biofidelic fement is only l
in accordancvelocity load
to relative skuBI2PED suggeit is likely thatmetry of the Bructure. The dess, a study oto match it to
mount of PMH
and 140 ktted over 8 msrst loaded in cquency. The ie shock and thside of the sk
mpression. Thintation. The ICrientation.
parallel shockst severities bu2PED ICPs aed to occur ae original PMgnals appeare
esized that theocalized defoiform frequenS.
n PMHS and Bsure level.
erved over a muation occurrequency fluctuan-skull movemsarticulation o
a realistic respwas more strofashion yet sinlimited by the
ce with the woding to local ull-brain motioests that the t the material BI2PED skulldifferent bonen the variabili
oo precisely wHS and the BI2
kPa peak incs. Contrarily t
compression binitial comprehe ICP sensor
kull generates is emphasizesCP increase ca
k is observed iut the frequen
again show a at a slightly l
MHS study, ited to be assoce bones compormation may
ncy response o
BI2PED headf
much ed at ations ment. of the onse. ongly nce it
e CSF
ork of skull on or skull itself
l also s and ity of
with a 2PED
cident to the
before ession rs are local
s how aused
in the ncy at
clear lower t was ciated osing drive
of the
dform
4. CONCLUSION Previously reported PMHS blast tests were methodically replicated using the DRDC Valcartier research center physical head model named BI2PED. The loading conditions, instrumentation type and position as well as head mounting technique were reproduced to ensure that the only difference between the two series of experiments was the use of BI2PED or PMHS. The loading obtained from the blast wave generator was compared to free-field blast loading and it was confirmed that the generator produced relevant loading magnitude and duration for the study of blast-induced TBI. Excellent reproducibility was obtained on the BI2PED intra-cranial pressure measurements. A direct comparison of measured occipital ICP revealed good agreement between the headform and PMHS for three blast intensities (80, 100 and 120 kPa) and two blast orientations (parallel and perpendicular). The ICP magnitudes were particularly close to the PMHS ones, while the frequency of the oscillations was slightly higher in the headform. The BI2PED exhibited specific ICP oscillations around 1000-1200 Hz in both orientations while the PMHS ICP oscillations were respectively around 700 Hz and 500 Hz in the parallel and perpendicular orientations. Based on previous work correlating skull local deformation to early-time ICP variations, these frequencies are linked to the skull natural resonance frequencies. The results suggest that the BI2PED skull assembly may be slightly too stiff compared with the chosen PMHS. The design of the BI2PED skull could be refined but matching its response of a very limited amount of PMHS specimen should be avoided and a survey on the variability of human skull modal response should be done first. There were a few discrepancies on the longer duration ICP variations. However, those variations are not believed to be representative of real human response since the head is no longer attached to the neck and body. The neck provides a compliance that is very different from the soft net in which the heads were mounted for the tests. Lower frequency ICP variations are associated with skull-brain relative motion and head global motion. The BI2PED brain is currently not attached to any spine-like structure in the cranial cavity and its movement is only constrained by the CSF and membranes so it is not currently designed to replicate relative brain-skull relative motion. However, the representative mass and center of gravity of the headform should ensure that a representative global motion can be obtained in an ideal test configuration. Overall, the BI2PED was in very good agreement with the PMHS on the early-time ICP variations, which is where the highest pressure peaks are observed. Assuming that blast-induced TBI may be correlated with these early peaks in ICP, the BI2PED would represent a very useful tool to assess the severity of different blast scenarios and help with the performance evaluation of protective headwear systems. 5. REFERENCES [1] Bass C.R., Panzer M.B., Rafaels K.A., Wood G., Shridharani J., Capehart B., Brain injury from
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