Transthoracic echocardiography (TTE) is a feasible method to noninvasively examine cardiac anatomy during parabolic flight. However, transducer placement on the chest wall is very difficult to maintain during transition to microgravity. In addition, TTE requires the use of low frequency transponders which limit resolution. Transesophical echocardiography (TEE) is an established imaging technique which obtains echocardiographic information from the esophagus. It is a safe procedure and provides higher quality images of cardiac structure than obtained with TTE. This study is designed to determine whether TEE was feasible to perform during parabolic flight and to determine whether acute central volume responses occur in acute transition to zero gravity by direct visualization of the cardiac chambers

Fanton, John W.

Geffney, F. Andrew

Latham, Ricky D.

Vernalis, Marina N.

English

NASA Technical Reports Server

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N95- 15094
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TRANSESOPHAGEAI. ECIiOCARDIOGRAPHIC EVALUATION OF BABOONS
DURING NICROG_VITY INDUCED BY PARABOLIC FLIGHT
Harina N. Vernatis, Ricky D. Latham, John W. Fanton, F.
Andrew Gaffney
Laboratory for Aerospace CardiovascuLar Research (LACR)
Armstrong Laboratory, AL/AOCIY Brooke AF8, Texas 78234-5301,
USA
BACKGROUND
The central cardiovascular responses to transient
microgravtty are not weLL understood. TheoreticaLLy,
entrance into microgravtty results in the Loss of the
hydrostatic pressure head and an increase in central venous
pressure (CVP) as a consequence of augmented venous return.
However, controversy exists regarding the time course and
magnitude of cephatad blood volume shifts and its
relationship to central atrial fiLLing pressures. On the
June 1991 STS 40 shuttle mission, pne-taunch echocardiograms
suggested changes in cardiac dimensions occurred white the
astronauts were in the supine, feet-up position.
Furthermore, e CVP Line in an astronaut (n-l) demonstrated
an unexpected abrupt decrease in CVP during orbital
insertion. In April 1991, our Laboratory performed Doppler
echocardiography in 6 normal human volunteers during
parabolic flight. Increases in right ventricutar velocities
reflecting a central shift of blood volume Mes demonstrated
in subjects examined in the sitting position. However, test
subjects examined in the horizontal positions had no
significant rise in DoppLer velocities. In addition, Latham
et at noted variable central cardiovascular responses i_
chronicst ty instrumented baboons during early microgravity.
Transthoracic echocardiography (TTE) is s feasible
method to noninv_sivety examine cardiac anatomy during
parabolic flight. However, transducer placement on the
cheat walt is very difficult to maintain during transition
to B icrogrsvity, in addition, TTE requires the use of tow
frequency transducers (2.5 HHz) which Limits resolution.
Trsnsesophageal echocardiography (TEE) is an established
imaging technique which obtains echocardiographicc
information from the esophagus. It is a safe procedure and
provides higher quality images of cardiac structures than
obtained with TTE. _ Since there are no interposed
structures between the esophagus end the heart, higher
frequency transducers can be used and resolution is
enhanced. With TEE, a fLexibLe transducer tip permits
contact with the esophageal mucosa, allowing for consistent
imaging.
This study Mes designed to determine whether TEE was
feesibte to perform during parabolic flight and to determine
whether acute central volume responses occur in acute
transiton to zero gravity (06) by direct visualization of
the cardiac chambers.
NETRODS
In flight TEE was performed in five mature mate
baboons weighing between 20-25 kg. These test animals Mere
chronicat Ly instrumented in order to simultaneously evaluate
central he_x_p_amics. Echocardiographic examinations Mere
performed by utilizing the Hewtett-Peckard (HP) SONGS 1500
ultrasound system with Acoustic Quantification interfaced
with a 7.5 NHz biplane transducer tipped endoscope.
The study animals Mere in a fasting state end placed
in s custom designed confinement chair. The study animals
Mere intubated and anesthesia Mes maintained. An
experienced echocardiographer inserted the TEE probe into
the esophagus of the baboon.
After introduction of the probe, baseline TEE images
of the heart Mere obtained. Three standard esophageal views
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Mere obtai_te¢l using the transverse sectioning plane
transducer. _ Each study began by imaging the transgastric
short axis vieus of the heart at the Level of the papillary
muscles. The echoscope was withdrawn to the midesophageat
position to obtain the four chamber tomographic views of the
heart. This was followed by slight withdrawal of the scope
to the upper esophagus to obtain the various basal short
axis viet_. The best images Mere identified for measurement
of the cardiac chamber dimensions. The right atrial (RA),
Left atrial (I.A), right ventricle (RV), and Left ventricle
(LV) chamber cavities were outlined as the "region of
interest" with the use of the HP Acoustic Quantification
software. End-diastatic and end-systolic fractional area
changes Mere measured st baseline (1G) end during three
phases of flight: putt-up (2G), early OG and Late OG.
Images Mere recorded on .5 inch videotape for real time and
frame by frame, analysis. ECG end accelerative signals Mere
simuLtaneousLy displayed and recorded.
HASA's KC - 135 aircraft was used to perfom
parabolic flight profiles. Five deity flights occurred with
40 parabola per flight in 4 sets of 10. Each parabola
provided 25-30 seconds of near zero gravity after a brief 2G
period during the ascent. TEE was performed on one baboon
per flight and imaging continued throughout the parabolic
phases. The test animals Mere control ted for volume status.
On flight days 1-4, the animals were euvotemic. These
animals Mere examined in the upright position. On flight
day 5, the test animal was pretreated with furosamide the
night prior to flight to result in a volume depleted (VO)
state. The VD baboon was examined in the upright and
supine, feet up positon.
RESULTS
TEE probe insertion ,as easily accomplished in
flight and theechocardiographicexaminationsMere conducted
without major complications. One baboon required treatment
for esophagitispost-ftight. The resolution of the baseLine
images obtainedbyTEE was excellent. Good visuaLization of
the RA, LA, and LV chambers was maintained even during the
rotter coaster tikeparobotic profiles. The RV chamber was
unable to be consistently viewed for accurate area
measurements.
EarLy end Late OG area changes were compared to
values during the ascent phase and at baseline in the
euvotamic animals (n=4). There was no statistical area
change bath,s=n baseline and the putt-upphese. During earLy
06, P_ end-diastoLic area significantly (p<.01) increased.
A significant (p<.05) increase in I_ end-systoLic area
during early and tale OG compared to the ascent phase Mes
recorded as welt as snares change betMeenOG and Late OG.
A trend toward end-systoLic area expansion occurred during
early06 compared to baseLine.
These results are shown in Figure 1.
5
4
3
2
1
0
Area (cm2)
BB ED Area
[] ES Area
Baseline- lg Pull-up 2g Early Og
Phase During Parabola
Late Og
https://ntrs.nasa.gov/search.jsp?R=19950008680 2020-06-16T09:01:54+00:00Z
i i i_ • •
ii Less dramatic but similar changes were seen in the
LA. There was a significant (p<.05) increase in the LA
chamber area in Late OG compared to early OG. (Figure 2)
I
EE ED Area I
I[] ES Area
4
3
2
1
0
Baseline - lg Pull-up 2g Early Og
Phase During Parabola
Area (cm2)
_ d
Late Og
There _es no statistically significant area changes noted in
the LV. However, on visual inspection all chamber areas
appeared to dilate during transition to microgravity.
DISCUSSIflli
_e successfully performed TEE in baboons during
parabolic flight. Not unexpectedly, TEE provided superior
images of the cardiac structures as welt as consistent
imaging during the parabolic profiles.
During the acute transition to zero gravity LA and
RA cha_er areas increased in the EV and VD animals when
upright. Furthermore, the echocardiographic area changes
paralleled the changes in pressures from the respective
chamber when hydrostatic forces were absent, ida believe
these results verified the hypothesi_ that sudden
microgravity results in an increase in atrial fitting
pressures as a consequence of s central shift of volume.
However, these findings were not observed in the
dehydrated test animal when examined in the supine feet up
position, in fact, the reverse was evident, that is, the RA
chamber appeared smaller and the RA pressure declined. The
tatter suggested that central atrial filling pressure
responses to microgrsvity are dependent upon initial
circulatory volume status,_u.,_ _ _'00,_
EarLy to Late changes in the LA chamber suggested
initial right heart praised increases were delayed
representing transit through the lungs.
There were Limitations in our parabolic flight
study. The study staple was small and only one primate
could be studied per flight. TEE yes performed in the
upright posture except for one VD animal subject, thus no
supine EU data was available for comparison. Furthermore,
only one VD animal was studied and therefore results were
not reproduced.
In summary, changes in chamber ares by TEE with a
concomitant parallel change in pressure appear to be a
consequence of volume rather thee primary changes in cardiac
©heater compliance. In addition, venous capacitance effects
play an important role in the acute central response to
micregravi ty.
_EREREIJCES
1. Btc_qrist, C.G. and Stone, H.L. Cardiovascular
adjustments to gravitational stress. Handbook of
The Physiologist, Vol. 36, No. 1, Suppl., 1993
Physiology. The Cerdiovescg_r System, Perioherat
Circulation and Organ BLood Flow. Bethesde, NO: AmPhystot
Sac., Sect Z, Vat 3, part 2: 1025-1063, 1983
2. LathmRD, Rubet BJ_ Sipkema P, Westerhof M, Virmatn R,
Robinovitz N, Welsh HA. Ventriculer/vascutar Coupling and
Regional Arterial Dynamics in the Chronically hypertensive
Baboon: Correlation with Cardiovascular Structural
Adaptation. Circulation Research 63:798-811, 1988.
3. HH Vernolis, JP Johns, JH Karemaker, RD Lethm. Echo-
Doppler Detemined Blood Flo_ in the Right Heart of Hon
During Nicrogrev|ty Induced by Parabolic FLight. Aerospace
Medical AsseclattonHeeting, Miami Florida, Nay 1992.
4. JBSeuerd,, BKKhandherie, dKOh, NDAbel, RWHughes_ WD
Edwards, BA Michols, _ Freeman, AJ Tajik. Transesophageel
Echocardiography: Technique, Anatomic Correlations,
Implementation, and CLinical Applications. Nays clinic
Proceedings 6.3:6_9-680, 1988.
AC_GENEMTS
The views expressed herein ere solely those of the
authors and arena[ to bacons[rued as representing those of
the Department of Defense or Departments of the Air Force or
Army. The animals in these studies were procured,
maintained and used in accordance with the Animal Welfare
Act and the"Guide for the Care and use of Laboratory
Animals" prepared by the Institute of Laboratory Animal
Resources, National Research Council. This study _es
reviewed and approved by the InstitUtional Animal Use and
Care Committee for Armstrong Laboratory, Brooks AFB, Texas.
Armstrong Laboratory has been fully accredited by the
America Association for Accreditation of LsborstoryAnimat
Care (AAALAC) since 1967. _he authors express gratitude for
the editorial essitance of Nrs. Vivian Simpson in the
preparation of this manuscript. Supported in part by AFOSR
Grant 2312_7 and NASA RTOPA2401D(SLS).
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Transesophageal echocardiographic evaluation of baboons during microgravity induced by parabolic flight

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