an experimental investigation of the biokinetic principles

AN EXPERIMENTAL INVESTIGATION OF THE BIOKINETIC PRINCIPLES GOVERNING
NON-PENETRATING IMPACT TO THE CHEST AND THE INFLUENCE OF THE RATE OF BODY
WALL D ISTORTION UPON THE SEVERITY OF LUNG INJURY
G J Cooper and R L Maynard
Minis try of Defenee , Proeurement Exeeut iv e , Chemieal Defenee E s tab l i shment ,
Porten Down , Salisbury, W i l t shire , UK, SP4 OJQ.
ABSTRACT
Experimental impae t s to the lateral thoraeie wal l o f anaes thetised p igs by non­
penetrat ing proj eetiles of mass range 0 . 06 9 kg to 3 . 0 kg within an overall
velo e i ty range 5 . 8 m/s to 8 1 . 2 m/s have a l lowed emp irieal models to be derived
to prediet the magnitude of the peak d i s tor tion of the ehest wal l under loading
by the free-f lying proj e c t i l e (Pmax) anä the time taken for Pmax to be attained
after ini t ia l eontaet of the proj ee t i l e upon the thoracic wall (Time-9 5 ) . Pmax
ean be deseribed as a function of proj eetile momenturu , body weight and
e f f e e t ive contact diameter; Time-95 is dependent upon proj eetile mass and body
weight and is independent of proj ec t i l e veloc i t y . The severity of pulmonary
eontus ion is dependent not only upon the peak rela tive thorae ic wall d i stortion,
but a l so upon the time taken to reach the peak d i s tortion, Time-95 . The
par t ieular proj e e t i l e s used in this study resul ted in peak ehest wal l
d i s t o r t ions being attained within the time range 1 ms to 2 2 ms after contae t .
The short duration impac t s could result i n serious pulmonary inj uries a t very
sma l l thoraeie eompr e s s ion s , eonver s e l y , very large ehest eompressions produced
r e l a t ively minor lung injury if the t ime to peak d i stortion was of long
dur a t io n . Biophysieal phenomena that may aecount f o r these rate-dependent
effects are d i seus sed .
INTRODUCTION
The contact of a non-pene trat ing (NP) proj e c t i l e upon the torso w i l l result in
an inward d i s tor t ion of the body wal l ; the nature and severity of the internal
inj ury is dependent not only upon the peak d i s tort ion atta ined but must a l s o be
dependent upon the rate of the d i s tortion. The motion of the body wal l is
the pr imary physical phenomenon respons ib l e for inj ury and for any particular
proj e c t i l e impac t , this motion resu l t s from the interaction of the body wal l
and the NP proj ee t i l e .
I t fol lows therefore that the capacity for injury of a
NP proj ectile impact i s not solely dependent upon s a y , the kinetic energy of
the proj eet i l e , it is a funetion of the b iomechan ical toleranee o f the body
wal l and of morphometrie features of the proj e c t i l e such as impact d iameter ,
deformab i l i t y in add i t ion to the obvious factors of mass and vel o e i t y .
The
b iomeehanieal proper t i e s of the various s ites on the torso such as lateral
thorax or anterior abdomen are d ifferen t , however , the ab il ity to withs tand the
impact forces at a par t icular impact s i t e is dependent upon the body weight or
age o f the animal .
The rapid d i stort ion of the thoraeic or abdominal wal l may produce inj uries to
s o f t t i s sue that can be grouped as e i ther DIRECT or INDIRECT
DIRECT inJ uries are produeed generally adj acent to the point of impaet by
shear and d istort ion resul t ing from the d i s p l acement of the overlying body
331
wal l . Pulmonary contusions and some bowel contusions are exampl e s of this
type of inj ury .
The propagation of s tr e s s waves or even shock waves under
certain c ircumstances may a l so contribute d irectly to primary inj ury .
INDIRECT inj ur i e s are produced by the gro s s motion of the organ within the
body cav i ty , motion that is tempered by the inertia of the organ and by the
S train induced at these s i te s may
s i t e s of f ixation or attachment ( 1 ) .
lead to laceration, notable exampl e s being aor t i c / l e f t subc l avian artery
rupture fol lowing impac t to the anterior ehe s t , some splenic and bowel
inj uries and the tear ing of the insertion of the gall bladder on the l iver
by d i f f erential motion of these two bodies .
Indirect inj uries general l y
occur subsequent t o the d irect inj uries produced b y body wal l deformat ion .
The general aim of this study was to study the
impac t to the lateral thorax and the aetio logy
the lung. The pathophys iological consequences
a l so s tudied but will not be d iscus sed in this
biomechanical princ i p l e s of
of DIRECT contusion inj ury to
of the pulmonary injury were
pape r .
The severity o f injury a t a particular impact s i te such a s the lat eral thorax
is dependent upon the magnitude of the d i stort ion of the thoracic wall and the
rate of the d i s tort ion . The influence of the rate of d i stort ion upon the
Jonsson
severity of pu lmonary injury has been a principal topic in th i s s tudy .
et al ( 2 ) s tudied the response of the thoracic wal l of the rabb i t to b l a s t and
impact exposure and were able to demonstrate the c r i t ical inter-r e l a t ionship of
thoracic def orma tion and the rate of deformat ion ( the index of the rate of
d i s t o r t ion was the peak velocity attained by the ehe s t wal l ) . The range of
peak ehe s t wa l l velo c i t i e s studie� was 2
20 m/ s with r e l a t ive ehe s t wal l
deformations within the range 0 . 05 - 0 . 60 . They def ined a tran s i t ion zone
be tween 5 m/ s and 10 m/s within which the lung inj ur i e s changed charac ter . At
peak ehest wall veloc i t ies <5 m/s the lung was not s ignificantly contused even
If
with relative deformations up to 0 . 5 , however , the lung could be lacerated .
the ehest wall velocity exceeded 1 5 m/s then r e l a t ive deformations o f only 0 . 1 5
- 0 . 20 could produce severe contus ions and l ethal inj u r ie s .
-
Lau and Viano ( 3 ) stud ied the relative sever i t i e s o f bronchiolar and alveolar
lung injury at fixed impact veloc ities of 5 , 10 and 18 m/s and ab solute body
wa l l d i spl acements between 0 . 2 cm and 4 . 5 cm in rabbi t s . Bronchialar contus ion
was prevalent at impac t veloc i t ie s l e s s than 6 m/ s ; alveolar inj uries were
predominant at veloc i t i e s greater than 15 m/ s . More recently , Viano and Lau
( 4 ) have proposed a ' v iscous tol erance cri ter ion ' as a predictor of the r i sk of
thoracic injury. Ana l y s i s o f impact experiments on rabb i t s with peak ehe st
wa l l velo c i t i e s within the range 5 - 2 2 m/ s and r e l a t ive ehest wal l
compress ions within the range 0 . 04 - 0 . 55 led them to propose the maximum of
the product of the ehe s t wall ve locity and the r e l at ive deformation as an index
of inj ury. This c r i t e r ion has been extended to abdominal injury ( 5 ) .
The spec ific aims of our study on thoracic impac t s were to :
1)
Iden t i fy the kine t i c charac t e r i s t i c s o f free-f lying proj e c t i l e s and
the morphomet r i c features of the body and ehest that det ermine the
magnitude of the d i s tort ion of the ehest wal l and the rate of the
ehe s t wall dis tor t ion.
2) Determine the sensi tivity of the seve r i t y of pulmonary inj ury to the
relative d i s tort ion and to the t ime to peak d i s to r t ion .
332
3 ) Describe qua l i tat ive changes in the type of thoracic pathology resul t ing
from broadly equivalent thoracic d i s t or t ions occuring at d i f f erent rates .
l t w i l l b e demons tated later that the t ime to peak thoracic d i stort ion is a
func t ion of the mass of the proj ec t i l e . Proj e c t i l e s o f markedly d if f erent mass
have been used to vary this t ime int erval to a s s e s s the influence of ehest
d is tort ion rate upon the severity of pulmonary inj ury.
To achieve the aims outl ined above, anaestheti sed p i gs within the weight range
22 - 74 kg were suoj ected to NP impac t s over the r ight l ateral thorax by 3 . 7 cm
d iame ter pro j e c t i l e s with a mass range of 0 . 069 - 3 . 0 kg at veloc i t i e s within
the overall range 5 . 8 - 8 1 . 2 m/ s . This mass range r e su l ted in t ime to peak
thoracic d i stortions within the range 1 ms to 22 ms .
The severity of the
pulmonary pathology was a s s e s sed 3 hours after impac t .
METHODS
A l i s t o f abbreviat ions is presented in TABLE 1 and the range of biokinetic
cond i t ions used in the experiment s i s surrnna ri sed in TABLE 2 .
TABLE 1 :
L i s t of abbreviations .
Abbreviation
M
1)
V
Pmax
Time-95
w
LAT and AP
Uni t s
Descript ion
ma s s of the pro j e c t i l e
impact d iameter o f the proj e c t i l e
pre-impact veloc ity of the proj e c t i l e
maximum transient inward deformation of the body wall
t ime taken for the pro j ec t i l e to at tain a 95%
reduct ion in i t s pre-impact vel o c i ty after contact
body weight of the pig
l a teral and anteropo s terior torso depth respectively
at the impact s i t e
quotient of lung injury
(actual lung weight /predicted normal lung weight)
kg
cm
m/ s
cm
ms
kg
cm
Qi
TAßLE 2 :
RANGE of pro j e c t i l e kine t i c charac t er i s t i c s , pig weight and response
of the l a t eral thoracic wa l l to the non-penetrating impact loading
All proj e c t i l e s had a d iame ter of 3 . 7 cm.
PROJECTILE
MASS
M , kg
3.0
1.0
0 . 38
0 . 14
0 . 12
0 . 06 9
VELOCITY
V , m/ s
5 . 8-12 . 0
1 3 . 8-24 . 1
1 5 . 6-38 . 6
2 3 . 7-65 . 3
43 . 0-6 9 . 7
4 3 . 6-81 . 2
PIG
WEIGHT
w,
kg
37-59
3 7-54
32-53
22-74
37-54
28-52
' n ' is the number of experimen t s .
LATERAL THORAC IC WALL D ISTORTION
ABSOLUTE
Pmax, cm
4 . 7-12 . 2
6 . 2-10 . 8
4 . 2-7 . 4
3 . 2-6.0
3 . 8- 6 . 1
2 . 5-4 . 6
RELATIVE
Pmax/LAT
0 . 2 2 3-0 . 590
0 . 295-0 . 53 7
0 . 200-0 . 400
0 . 1 68-o . 35 2
0 . 1 88-0 . 2 9 3
0 . 1 1 9-0 . 2 3 7
333
T IME TO PEAK
Time-95 , ms
1 5 . 7-22 . 0
9 .0-11 . 1
3 . 8-6 . 8
2 . 0-4 . 0
1 . 8-2 . 9
l . 0- 1 . 6
n
5
6
5
19
5
7
Animal preparation
Sedated p igs were anae s the t i sed through an ear vein with sod ium pentobarbi tone
and were then tracheo tomi s e d . A catheter was inserted into the femoral vein
In some animal s , high f requency
for subsequent admini strat ion of anae s thetic .
response tourmal ine pressure transducers were inserted by peripheral cutdown
into the thoracic aorta and vena cav a .
The impac t s i t e was chosen t o over l ie the d iaphragma t i c l o b e of the r ight lung ;
this point was def ined externally as mid-right f lank on the same t r ansver se
sect ion as the xiphisternum . Animal s were suspended hor izontally in a
spec i a l ly constructed s t ainless steel frame over a compressed-air driven
proj e c t i l e launcher . The left lateral torso was restrained to obviate motion
of the animal during the higher momentum impac t s . The par t ial p r e s s ure of
oxygen in arterial b lood of the anaesthetised p i g was mon itored for 3 hours
(results not presented) and the pig was then sacrif iced by exsanguina t ion
whi l s t s t i l l under the influence of anaes thet ic .
The pig was subj ected to a detailed post-martern examinat ion .
The sever ity of
lung injury was a s s e s s ed quant i ta t ively as an increase in lung weight (and by
The actual weight of the lungs from the
measurement of the contusion volume ) .
injured animal was compared to the pred icted normal lung weight for a pig of
that body weight (pred icted from the relat ionship b e tween body weight and lung
weight of seventeen CONTROL p igs within the body weight range 2 3- 7 9 kg) . The
rat io ( inj ured lung weight/pred i c t ed normal lung weight) was descr ibed as the
"Quo t ient of lung inj ury" , Q i .
Each set of lungs was awarded an injury
sever i ty score ranging from 1 to 4 based upon its Q i ; TABLE 3 def ines the Qi
l imi t s .
TABLE 3 : Q i l im i t s o f the four severity grades used in the quan t i t a t ive
assessment of the severit y of pulmonary contus ion .
QUOTIENT OF IHJUlff , Q i
<l.2
> l . 2 and < 1 . 5
> l . 5 and < l . 9
)' 1 . 9
GRAlJE
DE SCRIPT ION
1
2
Minor/Uninjured
Moderate
Severe
Very Severe
3
4
SYMBOL in
F igure 5
•
6
0
•
Biokine t ic techniques
Impac t s were photographed by high-speed e ine cameras at a framing rate be tween
1000 and 5000 pps depending upon the nominal veloc i ty of the free-flying
proj ec t i l e .
Computer-aided analys i s of high speed f i lm a l lowed measurement o f
impac t velocity (V)
the maximum transient deformation of the ehe s t wal l under the contact area
of the proj ec t i l e (Pmax ) . This was achieved by d i g i t i z ing the rear of the
proj e c t i l e upon contact with the ehe s t and assumes that the proj e c t i l e does
not deform upon contact and that the ehe s t wall does not overrun when the
proj e c t i l e comes to re s t .
Separate high-speed c ine-radiographic
experiments s tudying pulmonary d i stort ion f a i l ed to demonstrate overrun of
the thoracic wal l .
334
the t ime taken for the p roj e c t i l e to a t tain a 95% reduction in i t s
pre-impact v e l o c i ty a f t er contact w i t h the ehest (Time-9 5 ) .
The s i x pro j e c t i l e s had a diameter of 3 . 7 cm and were of mass (M) 0 . 069 , 0 . 1 2 ,
0 . 1 4 , 0 . 38 , 1 . 0 and 3 . 0 kg ; (reference is a l so made br iefly to data acquired
The
using a 0 . 1 4 kg proj ect i l e with an e ffe c tive contact d iameter o f 1 0 . 0 cm. )
range o f impact veloc i t i e s and the body weight of the pigs is shown in TABLE 2 .
RESULTS
Factors governing the t ime to peak thoracic deforma t ion
The motion of the l a teral thorac ic wall under impact loading is shown in F IGURE
1 for a 0 . 1 4 kg proj ec t i l e .
Pmax was 5 . 3 cm under these impac t conditions (V
58 . 8 m/ s , W
41 kg, D
3 . 7 cm) and the t ime to peak d is tort ion (Time-95) was
2 . 1 ms .
The range of Pmax and Time-95 measured with the various pro j e c t i l e s i s
summa r i s ed i n TABLE 2 and i t will b e shown l a t er that Time-95 had a c r it ical
influence on the sever i ty of lung injury .
Time-95 was found t o b e dependent
upon the mas s of the proj e c t i l e and inversely dependent upon the body
we ight of the p i g .
Time-95 was independent of ini t ial impact veloc i t y .
The
dependence of Time-95 upon M has a theoret ical b a s i s if the thorax i s
considered to b e a s imple l inear spring/ma s s system; the contact o f the
proj e c t i l e increases the e f f e c t ive ma s s o f the body wal l changing the natural
frequency of the mass-spr ing-ma s s sys tem crudely represent ing the thoracic
The body weight o f the p i g i s taken
wal l , lung and mediast inum respectivel y .
in t hi s context as an index of the b iomechanical proper t i e s of the body wall
and the inve r s e re l a t ionship b etween Time-95 and this index o f body wal l
s t iffness i s n o t surpr i s ing.
=
=
=
F I GURE 2 shows Time-95 a s a function o s (pro j e c t i l e mas s/pig weight) on
LOGe/LOGe axe s .
The data may be f i t ted l inearly (r
0 . 98 ) and the equation of
this l ine may be transformed to the power function
=
Time-95
1 4 1 . 3 * ( (M/W) A 0 . 7 1 1 )
. . . . .1
Abbreviations and un i t s are shown in TABLE 1 .
D i s tortions taking p l ace over
short periods of t ime with low mass pro j ec t i l e s produce much greater severity
o f injury than grea t er d i s tort ions taking place over long periods of t ime with
the high mass proj e c t i l es .
The kine t i c factors that govern the magnitude of
t he thoracic wall d i s t o r t ion w i l l b e d is c u s s ed in the next s e c t i on .
Factors relat ing the projec t i l e kinetics and the peak thoracic def orma tion
The abs olute thoracic deformation (Pmax) and the r e la tive deformation
(Pmax/LAT) mus t be a function of the mas s and velocity o f the proj e c t i l e . As
the resul tant d i s to r t ion is the resul t o f the interact ion b etween the
proj e c t i l e and the body wal l , the b iomechanical properties of the thoracic wall
mus t a l s o influence the degree o f d i s t or t ion .
Pmax will be inversely dependent
upon body weight ( i n anima l s of the same s tr a in and fat cont ent ) and a t
equivalent impact sever i t ie s , an animal o f lo w body mass wi l l undergo a greater
tho racic dis tort ion under the impact s it e than an animal of higher body weight .
Pmax (and Pmax/LAT) was found to b e a function of the momentum of the
proj e c t i l e , not i t s kinet ic energy.
The maximum ehest compress ion (Pmax) i s
shown a s a func t ion o f (momentum/ lateral ehe s t depth ) in F IGURE 3 on LOGe/LOGe
axe s .
The data i s f i t ted b y a straight l ine (r=0 . 9 6 ) and the equation o f the
l ine may be transformed to the relat ionship
335
Pmax
=
8 . 83 * ( (M*V) /LAT) A0 . 5 5 7 )
.
•
•
•
•
2
LAT in this context is an index of the biomechanical tol erance of the p ig ' s
thorax and imp l icity indicates the effective ehe s t mass and ' s t iffnes s ' o f the
thorac i c wal l . Equat ion 2 was constructed with 3 . 7 cm proj e c t i l e s of mas s
range 0 . 06 9 kg to 3 . 0 kg , velocity range 5 . 8 m/s to 8 1 . 2 m / s and pig weight
range 22 kg to 74 kg (TABLE 2) .
Previous s tudies inve s t igat ing the biomechanical p r incip l e s of NP proj e c t i l e
impac ts to the anterior ehest ( 6 ) had used an add i t ional proj ect i l e o f mas s
Increasing D to
0 . 1 4 kg with a rec tangular contact area o f 3 . 7 cm x 10 . 0 cm .
1 0 . 0 cm resulted in a lower Pmax compared to the d i s tort ion produced by 3 . 7 cm
proj e c t i l e s at broadly equivalent impac t sever i t i e s .
Th i s is not surpris ing as
the impact force was appl ied over a larger surface area . Add i t ional
experiments were performed in which the 0 . 14 kg proj ect i l e with an effec t ive
contact diameter of 1 0 . 0 cm was prope l l ed against the right lateral thorax ; the
10 . 0 cm dimension was aligned in a cranial/ caudal or ientation travers ing r ib s .
Al though the details o f these exper iment s wi l l no t b e reported now , this data
i s included in F IGUllli 4 def ining the relative ehe s t wall d i s tort ion (Pmax/LAT)
as a function of ( (M*V) / (W'�D ) ) on LOGe/LOGe axe s .
Dividing the proj e c t i l e
momentum b y the contact diameter a l l ows the 3 . 7 c m and 1 0 . 0 cm data to be
described by a connno n straight l ine of correlat ion coeff icient 0 . 96 .
Thi s
relationship transforms to the expression
Pmax/LAT
=
1 . 29
*
( ( (M*V) / (W'>'<D) ) A O . 529)
. . . . .3
The empir ical mode l s outl ined above (and others not described) constructed from
experiments whose biokinetic d e t a i l s provided a large range of proj e c t i l e mas s ,
velocity and pig weight permit quan t i t a t ive predict ions of the absolute
response of the lateral ehest wall under a wide var iety of NP proj e c t i l e impact
cond i t ions .
Tne results of this motion of the thoracic wall in terms of the
pulmonary injury produced by compr e s s i o n , shear and the propagation of s tr e s s
phenonemena will be considered in the next s e c t ion .
The response of the lung to the d is tor tion of the body wall
The common acute response of the lung to NP mechanical inJury is to accumulate
blood ( a pu lmonary contusion) usua l l y in the absence of gro s s parenchymal
laceration.
The presence o f b lood within alveo l i may produce a phys iological
shunt resul t ing in a reduc t ion of the partial pressur e o f oxygen in arter ial
b lood (Pa02 ) .
Haemodynamic and permeab il ity changes within lung may r e s u l t in
a s e l f reinforc ing cascade of f luid accumu l a t ion , further reduction of Pa02 ,
Sma l l contusions may b e wel l
infection and the u l t imate demise of the victim .
tolerated; the lung is ab l e to regulate (reduce) the b l ood supply to sma l l
haemorrhagic areas and maintain a normal Pa02 .
The pulmonary contusions produced in this s er ies of experiments ranged from a
Qi of approximately 1 (uninj ured lungs) to a Qi o f 2 . 7 3 showing haemorrhagic
contamination of the who l e r ight lung and a s igni f i cant proportion of the l e f t
lung.
Qual i t atively the pattern of injury seen i n these experimen t s ,
irrespec t ive of the time to peak d i s to r t io n , may be sunnna r i s ed thus :
ribs were fractured in nearly a-1 1 impac t s
contusions were conf ined t o the right lung. Recent experiments using
high-speed c ine�radiography of lateral thoracic impacts showed only minor
336
d i s tort ions o f the mediast inum and transmiss ion of s ignifieant s train to
the left lung was not evident (paper in preparation ) . Contaminat ion of the
l e f t lung in the .eurrent experiments was only seen in those animals with
very severe haemorrhagie eontaminations of the right lung; the b lood in the
l e f t lung was eon s i d ered to result from reflux of blood from the injured
r ight lung .
laeeration of the parenehyma was seen only f o l lowing impaets of the 1 . 0 kg
and 3 . 0 kg proj e e t i l e s resul t ing in large thoraeie dis tort ions over
extended t ime periods ( 10 - 20 ms) . The laeerations were quite small and
resulted from trapping of the parenehyma b etween displaeed r ib s .
Both Time-95 and Pmax/LAT had a erit ieal influenee upon the severity o f the
pulmonary eontus ions . At the extremes , high mas s / high momentum pro j e e t i l e s
produeed great d i s tortions over long periods of t ime result ing in relatively
minor lung ·inj ury whereas sma l l mass proj e e t i l e s resul t ing in qui t e small
d i s to r t ions over very short periods of t ime produeed serious inj uries .
As an examp l e of the former : a pig impae ted by a 3 . 0kg pro j e e t i l e a t 9 . 6 m/ s suffered a r e l a t ive ehest
d i s tort ion of 0 . 505 oeeuring over 2 2 . 0 ms .
In s p i t e of the faet that
loeally the ehe s t was eompressed to half i t s normal diame t er , the pulmonary
inj uries were not severe - a few seat tered pateehiae on the r ight
diaphragmat i e lobe (impaet point) and two sma l l laeerations with assoeiated
eonfirmed eontusion where fraetured / d i splaeed r ib s had injured the
parenehyma .
There was very l i t t l e haemorrhagie eontamination of the lung
(Qi
1 . 05) .
=
however ,
a pig impaeted by a 0 . 06 9 kg proj e e t i l e a t 5 3 . 5 m/ s suffered a r e l a t ive
ehe s t di s tor tion of only 0 . 184 and the peak d i s tortion was reaehed in only
1 . 6 ms . The r i ght lung was gro s s l y contused with almo s t t o tal involvement
of the right d i aphragmatie lobe and extens ive eontusions were evident on
the posterola teral surfaees of the midd l e and apieal lobe s . This was a
notable and severe haemorrhagie eontamina t ion of the lung (Qi
1 . 79) ,
equiyalent to 260 g of blood in a lung of normal predieted weight 330 g .
=
These two examp l e s are not the extremes o f injury but are presented s imply to
il l u s trate a point .
Notwiths tanding the severity of pulmonary haemorrhagie
eontamination, the only qua l i t a t ive d i f f erenee seen with high-rate and low-rate
d i s to r t ions was a larger number of fraetured r ibs in eaeh pig subj eeted to the
very large d i s tort ions , and the parenehymal trapping deseribed above .
F IGURE 5 presents the r e l a t ionship between Pmax/LAT, Time-95 and Qi for a l l the
3 . 7 cm d ia�e ter impaet data .
The range of Pmax/LAT and Time-95 produeed by
eaeh pro j e e t i l e is shown in TABLE 2 .
The ordinate in FIGURE 5 i s in faet the
ree iproeal of the t ime to 95% reduetion in proj e e t i l e veloeity, l /Time-95 and
the abe issa is the peak relative body wall d i s tortion. The severity of lung
injury, Qi is summa r i s ed for eaeh animal by ass igning a symbol to represent the
inj ury grade dedueed from Qi (TABLE 3) .
The data ean be seen t o l i e broadly in three band s , Grade 1 inj ur i e s , Grade 2
lt ean b e seen from this F igure that
and 3 eomb ined and Grade 4 inj uries .
337
those anima l s suffer ing r e l a t ive ehe s t distort ions over t ime intervals greater
than approximately 1 0 ms had minor pulmonary eontusions in s p i t e of the very
severe ehe s t compressions produeed (up to 0 . 6 ) .
Sho r t ening the t ime to peak
d i s t o r t ion resul ted in a greater ineidence of ser ious and very ser ious inj uries
a l though very serious Grade 4 eontusions were only evident if the value of
Time-95 was l e s s t hau approximat e ly 4 ms ( the greatest value of Time-95 showing
Grade 4 injuries was 3 . 8 ms ) .
In the most extreme ease of Grade 4 inJ uries
produced by very short duration impae t s , a Qi=l . 94 was produeed by a Pmax/LAT
of only 0 . 1 5 7 (Pmax = 3 . 3cm) oceurr ing within 1 ms .
Physieal p henomena respon s i b l e for the rate dependenee of lung injury
Consideration of the mechan i s t i e reasons for the dependenee of the severi t y of
lung injury upon Time-95 eould impl icate the f o l l owing phenomena:
shear s train of the underlying lung parenehyma with the propensity to
tear small blood vessel s dependent upon the magnitude and rate of
d i s t or t ion of the t i s sue .
Quite large d i s t o r t ions of parenehyma would b e
expected with t h i s low-frequeney phenomenon .
s t r e s s waves result ing from the d is tortion of the ehest wal l w i th
p o s s i b l e stress eoneentration at interfaees of d i f f erent density and at
regions within the thorax that may result in mul t ip l e r e f l eet ions ( for
examp l e the medial border of the lung) . These waves ean be eonsidered to b e
compress ion waves of high-frequeney.
shoek waves generated by the acceleration of parenehyma to veloe i t i e s
i n exeess o f the ve loeity o f sound i n the t i s s u e .
These wave s would
initially possess effeet ively instantaneous pres sure wavefront s .
l t i s we l l known from studies o f the behaviour o f inanimate mater ials that
s o l ia material wi ll break when strained too grea t l y or too quiekly . Al though
this is a eonvenient explanation for the rate dependent effeets of lung inj ury
par t ieularly at the low impae t veloe ity and high Pmax eonditions where shear
s train may be a notable eomponent , the extent of lung injury found with the
high yeloe i ty impacts ( low T i:me-95) and the minor physieal d i s tortions of the
The ehest
body wall imply that other physi:eal phenomena may be invo lved .
wall under impae t loading a e t s as a p i s ton and proj eets a pressure pul se into
the thoracie content s , the pres sure being an index of the average s tr e s s f ie l d .
We (and o ther s ( 2 ) ) have measured the pressur e s within the ehest and bronchi
under impae t loading and have found it to be a f a i r l y smoothed low-frequency
s tr e s s wave .
Gauges in bronehi measure only the pres sure in the bronehi not in
the true parenehyma ; eomp r e s s ion waves in the t i s sue i t s e l f may be quite
intense result ing in high loeal forees at the cap i l l ary l evel assoeiated with
qu ite sma l l d i s to r t ions of t i s sue . These forees and small d i s tortions
( compared to quite gro s s d i s t or t ions associated with shear waves ) may be
impl ieated in the laeeration of sma l l cap i l l ar i e s .
The velocity of sound within the lung i s around 1 5 - 30 m / s ( 2 ) . Ae eelerat ion
of t i s sue partieles by an advaneing ehest wall at veloe i t i e s greater than this
could give rise to true shoek phenomena e lose at the impae t site with
propagation of the shoek wave into the parenehyma . Mo st of the initial ehest
wall v e l o e i t ies produced by the low mass pro j ec t i l e s used in this s tudy exceeded
this veloe i ty of wave propagation in the lung .
Al though the shoek is l ikely to
be damped by the lung fairly quiekl y , s ignifieant pres sure f luetuations may b e
transm i t ted widely i n t h e parenehyma with d i s s i pa t ion of energy a t boundaries
and a t regions of S tr e s s eoneentration such as pleural niehe s .
Implos ion of
338
alveo l i and spal l ing a t the alveolar level have been impl icated but the absence
of high f requency components in the pressure waves measured in bronchi have
imp l ied to other s that the spa l l ing hypotheses are unlikely ( 2 ) and are simply
speculative .
U e t e c t ion o f the actual s i t e s of capillary di sruption in lungs ( impact s i t e ,
contralateral border o f the lung , interlobular septae , p l eural borders and
other s i t e s predisposing to s t r e s s concentration and energy transfer) would
a l l ow informed specula t ion of the relat ive contribution of the phenomena
o u t l ined above to the pulmonary injury witne s s ed at the var ious energy transfer
ra te s .
Ident i f ication of microvascular laceration by h i stological sampl ing of
an organ such as the lung is extremely d i f f icul t . The gro ss appearance of a
pulmonary contusion def ines s imply the presence o f blood not necessar ily the
s i t e s of mechanical injury to cap il laries or larger vesse l s .
Blood has a
remarkable ability to r e f lux throughout the lung and we bel ieve that a
significant proportion o f the volume of a pulmonary contusion is simply blood
from a s i t e of mechanical injury contaminating normal parenchyma . Quant itative
h i s tological exper imen t s are underway to a t t empt to locate these s ites .
In sunnna ry , it i s obvious that impact injury to the thorax may exc ite a
combination of wave modes who se relative s ignificance will be dependent upon
the rate of di stort ion of the body wal l ; the d i ff erent wave phenomena may
r e s u l t in d i f f ering types and sever i t i e s of inJury to lung. A theoretical
s tudy of the po s s i b l e phenomena i s underway u s ing the present empirical data as
a foundation.
CONCLUSIONS
1 ) The body wall subj e c t ed to a loading by NP impact with a free f lying
proj e c t i l e will d i s t o r t asymptotically with respect to t ime to a maximum body
wal l d i s tortion. The d i s tort ion is transient .
2 ) The time taken to achieve maximum body wa l l d i s tort ion is governed by the
mass of the proj e c t i l e and inversely dependent upon the body mass of the p i g .
3 ) The t ime t o peak d i s t o r t ion is independent of pro j ec t i l e velocity.
4) The maximum thoracic di stort ion ( e i ther absolute or r e l a t ive) i s dependent
upon the momentum of the pro j e c t i l e .
5 ) Impacts a t the same s i t e upon pigs of dif ferent b iomechanical t o l erances
resu l t ing from varying e f f e c t ive mass of the ehe s t wal l and r ib s t r ength can be
expressed s imply in terms of the mass of the animal or ehe s t dimens ions . With
the pig model , dividing by the mass of the animal can be used to normal i s e
impact seye r i t i e s t o compare impacts upon targets or d i fferent weight .
6 ) The severity of pu lmonary contusion is dependent not only upon the peak
r e l a t ive thoracic deformation but also upon the t ime taken to achieve the peak
d i s tortion .
7 ) Ser ious pulmonary inJ u r i e s may be produced by quite sma l l thoracic wall
2 ms) .
d i � t or t ions if the d i s tor tion occurs over a short period of t ime ( 1
Impacts producing severe ehest wal l d i s t o r t ions of extended duration ( 1 0
20
ms ) produce l e s s severe pulmonary inj urie s .
-
-
339
REFERENCES
1 ) COOPER G J e t al ( 1 984) .
Cardiovaseular d i s tort ion in experimental
non-penetrat ing ehe s t impae t s .
J Trauma Vol 2 4 , 188-200 .
2 ) JONSSON A ( 1 9 79 ) .
Experimental inve s t igations on the meehanisms o f lung
injury in b last and impae t expo sur e . Linkoping Univ . Medieal D i s s er t a t ion NR80
3) LAU V-K et al ( 1 9 81 ) .
Influenee of impaet v e l o e i ty and ehe s t eomp r e s s ion on
experimental pulmonary injury severity in rabbi t s . J Trauma Vol 2 1 , 1022- 1 02 8 .
4 ) V IANO D C e t a l ( 1 9 85 ) .
Thoraeie impae t : a vi seous t o l eranee e r i t erion .
Proe .
Tenth Int . Teeh .
Conf .
on Experimental Safety Vehie l e s , Oxford .
Influenee of veloeity and foreed eomp r e s s ion
5 ) ROUHANA S W e t al ( 1 9 8 5 ) .
on the severity of abdominal injury in blunt , non-pene trating lateral impae t .
J Trauma Vol 2 5 , 490-500 .
6 ) COOPER G J e t al ( 1 9 82 ) .
The b iomeehanieal response of the thorax to
non-penetrating impae t with partieular referenee to eardiae inj urie s . J Trauma
Vo l 2 2 , 994-1008 .
M
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e
.
60
12
55
11
50
45
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40
0
..J
w
>
35
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..J
IC
3:
25
1-4
u
t(1)
w
J:
u
30
20
15
10
\
e
u 10
.
tz
w
J:
w
u
IC
..J
0..
(1)
1-4
r:I
..J
..J
IC
3:
t-
(1)
w
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u
\
\
9
\
\
\
7
\
6
\
\
5
\
4
\
3
2
1
0
0
0. 1 4 kg
5 8 . 8 m/s
5 . 3 cm
2 . 1 ms
\
8
5
1 62/83
EXPERIMENT:
Projec t t l e mas s :
In t t t a 1 ve l oc t t y :
Pmax :
T t me-9 5 :
0
'
'
'
'
......
.......
.....
2
-
3
TIME AFTER CONTACT HITH CHEST HALL,
4
5
ms
FIGURE 1 : The displaeement of the ehe s t wall with respeet to t ime f o r a 0 . 1 4
Kg proj e e t i l e . The f i r s t d ifferential o f the eurve f i t ted to this data i s a l so
shown .
340
M
e +3 . 5
�
x
0
+
S
H
*
,...
H
10:
0
1(1)
H
Q
1(1)
w
:r:
u
fi
�
n.
0
1-
w
J:
�
+3 . 0
+2 . 5
kg
kl
kg
kg
kg
kg
• 3
1
• B.3
• B . B69
• B. 14
• B. 12
+2 . 0
+l . 5
•
H
+l . 0
+0 . 5
-0 . 0
„
g
...J
-0 . 5
-
7
.
0
-6 . 5
-6 . 0
-5 . 5
-5 . 0
-4 . 5
-4 . 0
-
-3 . 5
LOGe C PROJECT ILE MASS / P I G MASS > ,
3
.
0
-2 . 5
kg/kg
The t ime to peak ehe s t wal l d i s to r t ion , Time-95 as a function of
F IGURE 2 :
(M/W) .
The pro j e c t i l e s varied in mass from 0 . 069 - 3 . 0 kg and are separately
iden t i f ied . All proj e c t i l e s had a contact diameter of 3 . 7 cm .
e
u
„
,...
....
z
w
J:
w
�
...J
Bi
H
Q
....
(1)
w
:r:
u
J:
:::::>
J:
H
X
a:
J:
�
<--'
0
...J
2.6
X
0
+
S
H
*
2.4
2.2
kg
kl
kg
kg
kg
kg
• 3
1
• B.3
• B . B69
• B. 14
e. 12
0
2.0
X
l .8
l .6
X
s
H
l .4
1.2
H
1.0
s
0.8
0.6
1
-2 . 2
1
1
1
1
1
-1 . 7
1
1
1
1
1
1
1
-1 . 2
1
1
1
-0 . 7
1 1
1
1
1 1
1 1
-0 . 2
LOGe C PROJECT ILE MOMENTUM / LATERAL CHEST DEPTH > ,
1
1
+0 . 3
1
1
1
+0 . 8
C k g . m/s ) /cm
The maximum absolute ehest wall d i s tort ion , Pmax as a function of
F IGURE 3:
( (M*V) /LAT) p lo tted on LOGe/LOGe axes for the impact of 3 . 7 cm proj ec t i l e s .
341
1
......
tz
w
J:
w
u
a:
-'
0..
(1)
....
�
-0 . 4
H
Z
*
•
o
X
•
-0 . 6
-0 . 0
-1 . 0
•
•
•
-
B . 1 4 kg
8 . 1 4 kg , D•18 cm
0 . 1 2 kg
8 . 38 kg
1 . 0 kg
3 . 8 kg
8 . 869 kg
•
-1 . 2
-1 . 4
t(1)
w -1 . 6
:::c
u
w
>
....
ta:
-'
w
0::
...,
„
�
0
-'
X
-1.8
$
-2 . 0
$
-2 . 2
z
-2 . 4
-2 . 6
-2 . 0
-4 . 5
-5 . 0
-4 . 0
-3 . 5
LOGe C PROJECTILE MOMENTUM /
-2 . 0
-2 . 5
-3 . 0
-1.5
[ I MPACT D I AMETER * P I G MASS J >
The maximum r e l a t ive ehe s t wal l d i s to r t ion , Pmax/LAT as a func t ion
FIGURE 4 :
of ( (M*V ) / (W*D) ) p l o tted on LOGe/LOGe axes . Thi s F igure includes proj e c t i l e s
having effective contact d iameters o f 3 . 7 cm (H, * ,4" , o , x , $ ) and 10 . 0 cm ( Z ) .
e
(.)
'
0.7
.
z
0
....
t0::
0
t(1)
....
�
0.6
e
(.)
-'
-'
a:
3:
t(1)
w
:::c
u
w
>
....
ta:
-'
w
0::
t
• A•
0.5
A
A
•
0.4
0.3
•
0.2
1
l
0
•
0
•
•
0
•
A
•
•
•
'b �OA
•
•
•t
•
t
•
•
•
0
0
0
•
•
•
A
0. 1
0.0
0.0
0. 1
1
/
0.2
0.3
0.4
0.5
C T IME TO 95� REDUCTION
0.6
0.7
0.8
0.9
IN PROJECT ILE VELOCITY,
1.0
1 . 1
ms )
F IGURE 5 :
The severity of lung injury related to Pmax/LAT and the reciprocal
of the t ime to peak d i stor t ion ( l /Time-9 5 ) . The seve r i t y of lung injury is
expressed as a symbol : minor inJury (•) , moderate (�) , severe (o) and very
severe (• ) . The Qi l imits for these grades are shown in TABLE 3 . This F igure
only plots data acquired with 3 ; 7 cm d iame ter proj ec t i l e s .
342