abdomen flattens against the edge of the seat
pan, and the chest continues moving downward
until it hits the lower portion of the seat between
the legs. The upper torso then rebounds upwards
and backwards until it strikes the back of the
seat, after which it falls off to one side and comes
to rest. The entire sequence takes 0.5 to 0.75
seconds.

When restrained by the 3-point system, the
chest impinges upon the diagonal strap and the
shoulders move approximately 12’ from the
back of the chair and then rebound back. In
one animal (#8310) the diagonal strap was im-
properly placed across the right shoulder and
upper left chest, without extending down across
the abdomen. At impact, the upper torso under-
went 180° rotation around the diagonal belt be-
fore returning to the normal seated position.
Rearward facing impact with 3-point restraint
does not allow body flewion. There is some mo-
tion however, with extension of the neck.

A. Physical Data: Intrauterine pressure begins
to rise as the body compresses into the seat, pro-
ducing an average initial peak of 500 mm Hg.
Forward facing impact at 33 G with lap-belt
restraint failed to exceed this maximum. In
those animals impacted with a seat back angle
of 20°, the initial peak of intrauterine pressure
occurred at about the same time, but was lower
and more prolonged. Regardless of seat angle,
a second peak in intrauterine pressure occurred
as the abdomen was compressed against the seat
pan when the body was fully flexed. Average
maximum pressure achieved during the second
peak was 350 mm Hg. With 3-point restraint
or rearward facing impact, intrauterine pressure
reached similar levels, corresponding in time to
compression of the body against the shoulder
harness or the back of the seat. Intra-abdominal
pressure reached a single maximum peak that
occurred at full body flexion and approximated
50% of maximum intrauterine pressure.
Lap-belt tension rose to an average of 1050
Ibs. following impact. Shoulder harness tension
in those animals impacted facing forward with
8-point restraint rose to an average maximum
of 800 lbs. With rearward facing impact, belt
tension did not rise appreciably.
B. Physiological Data: Significant post-impact
hypotension was observed in two animals, one
related to pentobarbital anesthesia (#3062) and

the other to a broad ligament hematoma (33311).
The maternal heart rate slowed an average of
50% immediately following impact in each ani-
mal in which the body underwent violent motion
(Table I). Normal pre-impact heart rate was
restored within 60 seconds. When forward
flexion was prevented by 3-point restraint or
rearward facing impact, maternal bradycardia
did not occur (Table IT).

The fetus invariably underwent post-impact
bradycardia. In those animals in which there
was flexion or torsion of the mother’s body, there
was a 50% decrease in the fetal heart rate (Table
I), while in animals without body flexion, the
decrease in the fetal heart rate was 21% (Table
II). Two fetuses died during or immediately
following impact (#3364, #3596), and two
fetuses died prior to impact (33317, 313592).

Serum electrolyte concentrations were meas-
ured in three animals (Table III). Blood was
obtained from the femoral arterial catheter after
surgery but before impact, and at intervals fol-
lowing impact. No severe alterations occurred.
There was a moderate increase over pre-run
values in hypogastric arterial flow in the one
animal in which it could be calculated (#3592).
Increased flow lasted for 20 minutes after impact
and then returned to baseline. As yet, aortic
flow measurements have not been calculated.

C. Autopsy Findings (Tables IV, V, VI):
None of the adult animals died as a direct result
of impact, but three had significant traumatic
injuries. One had an extensive broad ligament
hematoma, one had placental separation, and one
had a subdural hemorrhage and placental sepa-
ration. In another animal (#3592), partial
separation. of the placenta resulted in fetal death
prior to impact. This was probably related to
surgical implantation of a flow transducer on
the hypogastric artery. Uterine rupture was not
observed in these experiments.

None of the fetuses survived the experiment,
and 8 of 11 sustained impact injuries. Two had
cerebral hemorrhage and one had a depressed
skull fracture with laceration of the underlying
brain. One fetus was delivered alive by Cae-
sarean section 1 hour after impact, but died 10
hours later of immaturity and atelectasis. Fetal
death also occurred in the three control animals.

IV. Discussion
These experiments were designed to produce



APPENDIX B

TABLE 1, HEART RATE AND BLOOD PRESSURE FOLLOWING VIOLENT MOTION DURING FORWARD FACING IMPACT AT 20 G

MATERNAL HEART RATE MATERNAL BLOOD PRESSURE FETAL HEART RATE

NUMBER RESTRAINT Pre-Run Post Impact Pre-Run Post Impact Pre-Run Post _Impact

2888 Lap Beit 130 36 - - 135, 60

3013 Lap Belt 170 85 - - 150 40

3062 Lap Belt 150 90 135/95 90/60 160 80

3310 3-Point® 175 90 165/100 140/100 180 no

3311 Lap Belt 140 55 165/110 100/65 124 70

3313 Lap Belt 170 105 160/105 160/100 170 92

3592 Lap Belt 220 98 90/80 100/60 - -

(arm) (arm)
3596 Lap Belt 234 180 110/80 90/70 170 0 (Died)

*Animal underwent violent rotation around improperly placed diagonal shoulder strap.

TABLE II. HEART RATE AND BLOOD PRESSURE FOLLOWING IMPACT WITHOUT VIOLENT MOTION

MATERNAL HEART RATE

MATERNAL BLOOD PRESSURE FETAL HEART RATE

NUMBER: G Pre-Run Post Impact. Pre-Run Post Impact. Pre-Run Post Impact
3314 20 160 160 165/110 225/110 170 140
3364 40 230 210 150/100 160/110 10 0 (died)
3365 20 160 160 135/65 130/75 160 124
TABLE III, SERUM CHEMISTRY
NUMBER TIME Na(MEQ/L) K(MEQ/L) C1( MEQ/L) CO. (Vol %)
3364 Pre-Run 159 3.8 130 45.9
+60 min 159 3.8 126 38.3
+90 min 157 (hemolysed) 127 43.8
3365 Pre-Run 150 3.6 121 39.0
+20 min 146 3.9 V7 37.8
3596 Pre-Run 147 4.5 112.5 44.5
+40 min 143 4.8 110.5 41.9
+120 min 143 4.8 110.8 44.0
+150 min 151 5.7 110.3 43.5



tributed to the lap belt. These experiments
show that fetal and placental injury may be
produced when the victim is pregnant. Reports
concerning injuries to pregnant automobile acci-
dent victims now are being collected by the
authors. ‘Twenty-one reports have been received
and will be published subsequently. Such in-
juries have been infrequently reported ;* their
true incidence is unknown.

Studies of automobile accidents have shown
that the major single cause of fatal injury is
ejection from the vehicle? When the body is
ejected, injury occurs as it strikes the ground
or is crushed by the vehicle. Restraining the
occupant to prevent ejection should reduce fatal
injuries. Tourin and Garrett state that, “seat
belt restraint could save at least 5,000 lives a
year and reduce injuries by 14”.* Huelke and
Gikas estimated that 80% of fatally injured
automobile accident victims would have survived
had they been wearing lap belts. As a result
of such studies, lap-type seat belts are now stand-
ard equipment on all new automobiles.?? Reduc-
tion of fatal injuries has clearly justified their
use,%820,2214 24 Since ejection will occur whether
or not the victim is pregnant, we believe that

pregnant women should use Jap belts for their
own safety. The belt should be securely placed
across the pelvis, It should not be worn over
the fundus as this position may tend to increase
abdominal compression during impact. It re-
mains to be seen whether the fetus will be pro-
tected to a similar degree. The high rate of
fetal and placental injury in these experimental
studies indicates that additional restraint may
be necessary to reduce the snubbing action of
the lap belt.

Vv. Summary

Eleven pregnant baboons were subjected to 12
experimental impacts. At the 20-G level of de-
celeration force, maternal injuries were minimal.
Fetal death occurred in association with trau-
matic head injury, placental separation, and
maternal shock. Although prevention of body
flexion during impact did not prevent elevation
of intrauterine pressure, fetal injury or placental
separation; the number of animals is too small to
draw conclusions regarding the superiority of
one restraint system over another. The lap belt
should be worn by pregnant women, and it should
be securely placed across the pelvis and not over
the fundus.

REFERENCES

1, AIKEN, D. W. J. Louisiana St. Med. Soc., 115: 235,
1963.

2. Cocke, W. M., Jr. and Muyer, K, K, JAMA, 183: 693,
1963.

3. Dyer, I. and McCavcney, E. V. Am. J. Obst. €

Gynec., 77: 1176, 1959,

Dyer, I. and Barcray, D. L. Am. J. Obstet. €

Gynec., 88: 907, 1962.

. DuBors, BE. F. Brit. Med. J., 2: 685, 1952.

Fisn, J. and Wxicut, R. H. J. Trauma, 5: 746, 1965.

. Exuior, M. Aust. N.Z. J. Obstet. Gynaec., 6: 279,

1966.

Ganrerr, J. W. and Braunstern, P. W. J. Trauma,

2: 220, 1962.

9. Gerrrrson, R., Fropese, A. A., and Pzzzr, P. J. J.
Albert Einstein Med. Center, 14: 63, 1966.

10, Herserr, D. C. Med. J. Aust., 1: 61, 1964,

11. Hiron, B. C. Proceedings, 10th Stapp Car Crash
Conference, p.124, Hollomon AFB, New Mexico, 1966.

12. Huerxe, D. F. and Greas, P. W. Proceedings, 10th
Stapp Car Crash Conference, p.156, Holloman AFB,
New Mexico, 1966,

18. Kimproven, R. A. Am. J. Obst. & Gnyee., 78: 1161,
1959.

Nea fs

2

14, Laster, R. D. and Mizson, B. M. Practitioner, 191:
332, 1963.

15, Pace, BE. W., Kine, E, B., and Merrit, J. A. Obst.
& Gynec., 3: 385, 1954.

16. Parkinson, E. B. Am. J. Obst. & Gynec., 90: 30,
1964.

17. Reis, R. A. (discussion) Am. J. Obst. & Gynec.
57: 82, 1949,

18. Runovirs, F. E. Am. J. Obst. & Gynec., 90: 828, 1964,

19. Smrra, R. N. and Crospy, W. M. Unpublished ob-
servations on labor in the baboon.

20, Snyper, R. G., et al. Proceedings, Sesquicentennial
Symposium on the Prevention of Highway Injury,
Highway Safety Institute, Ann Arbor, Michigan,
1967, (In press).

21, Swyver, R. G., et al. Proceedings, 10th Stapp Car
Conference, p.249, Holloman, AFB, New Mexico, 1966.

22, Srape, J. P. and Tayxor, E. R. Aerospace Med.,
85: 1117, 1964.

28. Torins, S. H. J. Trauma, 4: 397, 1964.

24, Tourn, B, and Garrerr, J. Automobile Orash Re-
search of Cornell Univ., Ithaca, New York, 1960.

25, Wittams, J. S., Lies, B. A. and Haws, H. W. J.
Trauma, 6: 803, 1966.



an impact configuration comparable to an auto-
mobile accident, except for 3 in which the 45°
seat angle simulated an airplane crash. Three-
point restraint and rearward facing impact were
added to provide comparative data in the ab-
sence of forward flexion. The 20-G configuration
simulates a head-on collision at an impact of 40
miles per hour, Physical characteristics of many
automobile accidents closely agree with those
used in this study. The injuries observed are
similar to those reported in automobile accidents
involving pregnant women.’ No attempt was
made to compare fetal survival between restraint
systems because the number of available animals
was small and because the surgical procedures
resulted in fetal death in the absence of deceler-
ation,

There is a remarkable increase in uterine
pressure during impact. The maximum pressure
observed was approximately 10 times that ob-
served during labor? Simultaneous recordings
of abdominal pressure during impact show that
the uterus was not protected from rupture by
an equal but opposing pressure within the sur-
rounding abdominal cavity2® Nor was there a
decrease in uterine pressure during impact when
forward flexion was prevented by shoulder re-
straint or rearward facing impact. The findings
also indicate that the gravid uterus is capable
of withstanding extraordinary pressures of short
duration, and that such pressures are produced
by deceleration with or without subsequent body
flexion.

Maternal response to impact consisted of tran-
sient depression and bradycardia. The former
resembled mild cerebral concussion. Post-impact
bradycardia occurred only with violent motion
of the body. Stapp and Taylor reported this
phenomenon in deceleration experiments on hu-
man volunteers, and attributed it to increased
vagal tone secondary to acute hypertension in
the carotid sinus, This effect can be abolished
by atropine, and occurs only when there is rapid
forward motion of the head and neck.??

No fetus has yet survived an experiment. The
apparent causes of fetal death are:

A. Maternal Hypotension: Two fetuses died in
association with maternal shock (43062, #3310-
11). Elliot reported internal hemorrhage and
resultant maternal shock as a major cause of both
fetal and maternal death in unrestrained auto-
mobile accident victims.’

B. Fetal Head Injury: Two fetuses died with
cerebral hemorrhage. One occurred with breech
presentation and the fetal skull struck the ma-
ternal spine during rearward facing impact. In
the other, the fetal skull was compressed between
the seat pan and maternal spine. Fetal skull
fracture was noted in another animal impacted
after death. Many of the fetal head injuries
reported in automobile accident victims have
been associated with maternal pelvic fractures.”
These experiments show that the maternal pelvis
does not need to be fractured to produce injury
to the fetal head during impact.

C. Traumatic Separation of the Placenta:
Rapid compression and expansion of the uterus
during impact may separate the placenta, and
this may occur with or without body flexion.
The shearing force may totally separate the pla-
centa at the outset, or may initiate separation
at the placental margin. Resultant bleeding pro-
duces a retroplacental hematoma that may ulti-
mately separate the entire placenta and kill the
fetus. Premature separation of the placenta
has been observed following automobile acci-
dents,"*° but there is some controversy as to
how often it occurs. The incidence of trauma
as a contributing factor ranges from 0 to 8% in
published series.**°51" The relative frequency
of this complication in these experiments prob-
ably is more related to the superficial implanta-
tion of the baboon placenta than to the presence
of the lap belt.

D. Unknown Causes: Three fetuses died with-
out associated maternal or fetal injury. In addi-
tion, three control animals delivered stillborn
infants within 48 hours of the operation. Since
there was little change in serum electrolyte con-
centrations after surgery or impact, it is con-
cluded that maternal acidosis was not a cause of
fetal death in these experiments. Reduction of
uterine blood flow also does not appear to be a
contributing factor to post-impact fetal death
in the absence of maternal shock.

The lap belt does not reduce the amount of
force sustained in a collision, the force is merely
transmitted to the pelvic structures. The head
and chest are free to move forward or laterally,
and the body jackknifes over the belt. The re-
sultant abdominal compression could be expected
to produce strain on the abdominal and pelvic
organs. Injuries to the jejunum,"%?* spleen,?
colon, pancreas, and duodenum?’ have been at-


% sano

002°0 0210 0200 000'0 - (spuosas) 3WiL

|
1138 Y3A0 Ada ASNIVSY AGO

annogau ‘G $0104 AdOd °9 WILINI “8 LOVdWl ‘V

JuNSSIud
INIdaLN

#091 302
NOISN3L
1138 LV3S Y39L3N0N37399
aais
9 q Vv

d
"NOISN3L 1738 LV3S ONY 3UNSSJud ININaLN
‘NOILOW AGOS N33ML34 dIHSNOLLVI2Y - JONINDAS LOW



AM 68-6

IMPACT INJURIES IN PREGNANCY
I: EXPERIMENTAL STUDIES

Warren M. Crosby, M.D.
Richard G. Snyder, Ph.D.
Clyde C. Snow, Ph.D.
Peter G. Hanson, M.S.

Approved by Released by
J. Roserr Diz, M.D. P. V. Srecen, M.D.
Cuter, Crvi, AEROMEDICAL Feperat Arr SuRGEON
INSTITUTE
March 1968

DEPARTMENT OF TRANSPORTATION

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



TABLE IV. LAP BELT RESTRAINT: FORWARD FACING IMPACT AT 20 G*
DAYS SEAT SURGICAL MATERNAL FETAL
# GESTATION __ PRESENTATION ANGLE PROCEDURE AUTOPSY AUTOPSY COMMENTS
2888 160 Cephalic 45° Hysterotomy, 1/3 Placental No Trauma Autopsy 20 min.
FECG Separation post impact
3013 140 Cephalic 45° Hysterotomy, Living No Trauma
3062 n0 Breech 45° Hysterotomy, Minor Trauma No Trauma Mother died in shock
FECG 24 hes. post impact
3311 154 Cephalic 20° Laparotomy, Hematoma , No Trauma Second impact of
Arteriotomy Broad Ligament animal #3310
3313 166 Cephalic 20° Arteriotomy Minor Trauma Cerebral Fetus died 11 min.
Hemorrhage post. impact
3592 103 Cephalic 20° Thoracotomy , 1/4 Placental Died Prior Placental separation
Laparotomy Separation to Impact due to surgery, not
impact
3596 103 Breech 20° Thoracotomy, Minor Trauma No Trauma Mother died 18 hrs.
Laparotomy, (Aspiration) post impact of
Arteriotomy aspiration

*Animal #3317 not included in these tables.
dead fetus was in breech presentation and sus:

It was impacted after death, forward facing at 33 G with lap restraint. The
tained a depressed skull fracture and brain laceration.

TABLE V. 3+POINT RESTRAINT: FORWARD FACING IMPACT AT 20 G
DAYS SEAT SURGICAL MATERNAL FETAL
4 GESTATION _ PRESENTATION ANGLE PROCEDURE AUTOPSY AUTOPSY COMMENTS
3310* 154 Cephalic 20° Laparotomy, Hematoma , No Trauma Animal rotated
Arteriotomy Broad Ligament around shoulder
strap.
3314 153 Cephalic 20° Arteriotomy Minor Trauma No Trauma Fetus born alive,
died of prematurity.
*Animal impacted 2 hours later with lap restraint (#3311).
TABLE VI. REARWARD FACING IMPACT, 3-POINT RESTRAINT
DAYS SEAT SURGICAL MATERNAL FETAL
4 GESTATION _ PRESENTATION ANGLE PROCEDURE AUTOPSY AUTOPSY COMMENTS,
3364 145 Breech 20° Laparotomy, Subdural Herm. Cerebral 40 G Impact
Arteriotomy Placental Hemorrhage
Separation
3365 v0 Breech 20° Arteriotomy Minor Trauma No Trauma 20 G Impact
21064



APPENDIX A

KABOOM 4N2

Fal

How oo l4e

ef BRUARY Ge

Fieure 1


attached to the sled and leading to the recording
devices within the blockhouse. Physiologic data
were recorded on a Sanborn Series 350 recorder.
Physical data obtained during impact were re-
corded on a CEC Model 5-119 oscillographic
recorder, with a paper speed of 63 inches/second.
Photographic coverage was provided from an-
terior and lateral views by a high-speed camera.
Serum electrolyte determinations were performed
by a flame photometer. Total CO, content was
determined by a Natelson microgasometer.
Three animals underwent hysterotomy with
intra-amniotic placement of a pressure trans-
ducer and fetal electrocardiograph leads. Three
animals underwent laparotomy with placement
of a small pressure transducer within the uterine
wall and a femoral arteriotomy. Three animals
had femoral arteriotomy. In these 9 animals
the surgical procedures were done on the day of
impact. Two animals underwent thoracotomy
and laparotomy with placement of electromag-
netic flow transducers on the aortic arch and the
hypogastric artery one week prior to impact.
On the day of the experiment, the buried lead
wires were exposed, and an intra-abdominal
pressure transducer was placed. Following the
surgical procedures, maternal electrocardiograph
leads were attached, and the animal was carried
to the sled and placed in the seat. The lap belt,
of one inch wide 4500 Ib. test woven nylon, was
placed suprapubically at an angle of 55° from
the horizontal, and adjusted to a tension of 1.5
kg. with a scale tensiometer. The shoulder har-
ness consisted of a similar belt attached to the
back of the chair above the right shoulder and
to the seat behind the left hip.. The legs were
restrained by ankle straps attached to the under-
carriage of the sled and the forearms were taped
together to avoid interference with body motion
during impact. The animal was allowed to re-
cover from anesthesia to the point that it re-
sponded to stimuli and appeared fully awake
(Fig. 1). The blood pressure transducer was
removed from the sled and the animal decelerated.
Following impact, the animal was monitored on
the sled, on-a stretcher, or in a restraint chair.
The monitoring period varied from 20 minutes
to 4 hours. If the fetal heart tones were lost at
any time after impact, the animal was rean-
esthetized and delivered by Caesarian section (9
animals). One animal was sacrificed prior to

fetal death (#2888), and one was delivered
alive.

Anesthesia consisted of pentobarbital (1 ani-
mal), Innovar-Vet* (2 animals), or Sernyl**
(8 animals). Ether was administered by open
drop when necessary for abdominal surgery.
Atropine and diphenylhydantoin were also used
to supplement anesthesia. With the exception
of pentobarbital, the drugs used did not seem
to significantly alter physiologic responses to
impact.

Eleven pregnant animals were used in 12 de-
celeration experiments. Eight underwent impact
facing forward at 20 G with lap belt restraint.
One of these (#3310) was first impacted at 20 G
with lap belt and diagonal shoulder restraint
(“3-point restraint”), and later in the day im-
pacted at the same level with lap belt restraint
alone (#3311). One had a single impact at 20 G
with 3-point restraint (#3314). Two animals
were impacted facing rearward, one at 40 G and
the other at 20 G. These two animals were’ re-
strained by the 3-point system with additional
adhesive tape used to keep the head firmly
against the back of the seat during acceleration.
One animal that died during the surgical pro-
cedure was impacted 2 hours after death facing
forward at 33 G with lap belt restraint only,
In addition, three pregnant control animals had
similar surgical procedures without deceleration.

In nine experiments, the seat back was tilted
at 20° to approximate the usual automobile
situation, with the seat pan horizontal. In three
experiments, the seat and seat pan were tilted
backwards at an angle of 45° to simulate an
aircraft accident.

III. Results (Summarized in Tables I-VI)
Slow-motion photography shows that the up-
per torso of the animal continues moving forward
following impact of the sled (Fig. 2). In ani-
mals impacted with a seat angle of 45°, the body
initially compressed into the seat as the chest
was thrown forward. Initial body compression
did not occur when the seat pan was horizontal.
In animals with lap belt restraint alone, the
chest thrusts out and the head lags behind, pro-
ducing hyper-extension of the cervical spine.
By the time the upper torso is horizontal, the
abdomen begins to impinge on the seat pan. The

*McNeil Laboratories, Inc., Fort Washington, Pa.
**Parke, Davis and Company, Detroit, Michigan.


IMPACT INJURIES IN PREGNANCY
I: EXPERIMENTAL STUDIES

Warren M. Crosby, M.D.', Richard G. Snyder, Ph.D.TM*, Clyde C. Snow, Ph.D.’,
and Peter G. Hanson, M.S.

I. Introduction

It is estimated that thousands of pregnant
women are involved in vehicular accidents each
year. Seat belts have been available for use by
aircraft occupants for decades. With the current
emphasis on safety, automobile occupants have
also been urged to use lap-type seat belts. If
the lap belt is worn, nearly all sudden decelera-
tions will produce folding of the abdomen over
the restraining belt. In minor accidents, this is
usually of little consequence. But when the vic-
tim is pregnant, the resultant abdominal com-
pression could produce uterine and fetal injury.
These experiments were undertaken to study the
physical and physiological effects of impact on
the pregnant animal with lap belt restraint.

II, Method and Materials

The Savannah Baboon,** Papio cynocephalus,
was chosen because the uterine and placental
. anatomy is similar to that of the human. The
baboon breeds well in captivity and pregnancy
can be accurately diagnosed and dated. The
gestational period averages 167 days and the
neonate weighs 750 to 1000 grams at birth.

“Phe Department of Gynecology and Obstetrics, Uni-
versity of Oklahoma School of Medicine.

“Civil Aeromedical Institute, FAA, Oklahoma City,
Oklahoma.

%57ist Aeromedical Laboratory, Holloman AFB, New
Mexico.

*Present address: Biomechanics Department of Auto-
motive Safety Research Office, Ford Motor Company,
Dearborn, Michigan.

*#The animals used for these experiments were law-
fully acquired and treated in accordance with the Prin-
ciples of Laboratory Animal Care issued by the Animal
Facilities Standard Committee of the Animal Care
Panel, U.S. Department of Health, Education, and
Welfare, Public Health Service, March 1963.

Presented to Central Association of Obstetricians and
Gynecologists in Detroit, Michigan, Sept. 14-16, 1967.

The Daisy Decelerator, an impact apparatus
at the 6571st Aeromedical Laboratory, Holloman
AFB, New Mexico, was used to produce decelera-

tion. It consists of an air-driven piston that
propels a sled along a track. The sled has a
shaft protruding from the front that enters a
brake. The brake resembles an engine block
that is filled with water. A series of valves
allows control of the rate of egress of water that
has been displaced from the brake by entrance
of the shaft. Sled velocity and rate of water
exit from the brake control the degree and dura-
tion of decelerative force. A seat designed for
the baboon was mounted on the sled. The seat
was padded with 1’ EnsoliteTM on the floor and
back.

Intrauterine pressures were measured either
by an intra-amniotic Statham 222 pressure
transducer or by a Microsystems 1017 pressure
transducer in the wall of the uterus. Intra-
abdominal pressure was measured with a Micro-
systems 1017 pressure transducer in the peritoneal
cavity. Electrocardiograph leads of insulated
stainless steel wires were sutured into the arm
and the scalp of the fetus. Fetal heart rates
were monitored by stethoscope when not recorded
continuously by electrocardiography. The ma-
ternal electrocardiogram was obtained by Beck-
man silver-silver chloride adhesive electrodes.
Maternal blood pressures were measured before
and after impact by sphygmomanometer or
through a polyethylene catheter in the abdominal
aorta. The catheter had an internal diameter
of 1.19 mm, and was connected to a Statham
Series P23 pressure transducer. Aortic and
hypogastric artery blood flow was measured by
Biotronex Series 1000 electromagnetic flow trans-
ducers and recorded by means of Biotronex
Model 310 flowmeters. Belt tensions were re-
corded by buckle-type strain gauges, designed
and produced by the 6571st Aeromedical Labora-
tory. Instrument wires were connected to a cable



ACKNOWLEDGMENTS

The authors are indebted to Richard Chandler for his valuable assistance,
and to G. Townley Price, D.V.M., Allan A, Katzberg, Ph.D., and Joseph
Young, A.M., who performed the autopsies.

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151,