close

Вход

Забыли?

вход по аккаунту

?

The embryonic heart subjected to radar.

код для вставкиСкачать
The Embryonic Heart Subjected to Radar'
GEORGE H. PAFF, ROBERT J. BOUCEK, RICHARD E. NIEMAN AND
WILLIAM B. DEICHMANN
Departments of Anatomy, Medicine and Pharmacology,
University of Miami School of Medicine,
Coral Gables. Florida
ABSTRACT
It is known that microwaves can damage tissue but the cause is
poorly understood, e.g., can tissue be damaged in the absence of undesirable heat
levels? To answer this question 106 isolated 72 hour embryonic chick hearts were
subjected to radar waves at a frequency of 24,000 megacycles, a wave length of
1.25 cm and exposures of 478, 297, 167 and 74 mw/cm2 for lengths of time varying
between a few seconds and three minutes. Electrocardiograms were taken as a continuous run before, during and after radar treatment. The hearts were planted in
blood plasma on the surface of saran sheet and microwaves were directed through
the sheet a t the heart. Where necessary a stream of cold air was used to offset
undesirable elevation of heat. At exposures of 478 and 297 mw/cm2 damage was
swift and devastating. No conclusion seemed justified. However, a t an exposure of
167 mw/cm2 it was possible to prevent elevation of temperatures above 38°C. Significantly the hearts showed damage in the ECG, i.e., shortening of the QT interval,
increased height and breadth of the T wave and the appearance of a large U wave.
Finally a t 74 mw/cm2 it was possible to control heat merely by maintaining an
ambient temperature below 25°C. Of twenty-five hearts so exposed, all showed ECG
changes mentioned in the previous paragraph. The conclusion seems justified, that
radar waves can damaee tissue at exposures which do not raise the temperature to a
harmful level.
-
It is well known that radar can damage
tissue (Deichmann, Stephens, Keplinger
and Lampe, '59; Carpenter, Biddle and
Van Ummerson, '60; Addington, Osborn,
Swartz, Fischer, Neubauer and Sarkees,
'61; Gunn, Gould and Anderson, '61; Howland, Thomson and Michaelson, '61; Michaelson, Thomson and Howland, '61; Van
Ummerson, '61 ; Linke, Lounsberry and
Goldschmidt, '62) but the cause of this
damage is poorly understood. Can radar
produce tissue damage in the absence of
undesirable heat levels? The present work
was undertaken in the hope that some
light could be shed on this question.
In preliminary observations on isolated
72 hour embryonic chick hearts it became
obvious that the temperature of the hearts
had to be maintained within the functional range during irradiation. This posed
a problem because no practical apparatus
is available for detecting temperature
changes in hearts whose greatest diameter
measures less than one mm. Fortunately
the embryonic chick heart at 72 hours is
poikilothermic. Small fluctations in temperature result in obvious changes in heart
rate. Taking advantage of this fact we
constructed a heart rate-temperature curve
which permitted us to use a heart as its
own thermometer.
A BIOLOGICAL THERMOMETER
Two hundred and eight hearts were dissected from chick embryos of 72 hours
incubation age and planted in chicken
blood plasma. Six hearts were studied at
one time. Each was put in a separate drop
of chicken blood plasma placed on the
inside wall of a 32 ml cork-stoppered tube
lying on its side. After clotting occurred
the tube was submersed and positioned in
a water bath to permit microscopic observation and to allow for systematic temperature changes between the extremes of
4 and 50°C. Before immersing the tube
a hypodermic needle was plunged through
the cork and a piece of spaghetti tubing
was attached to the needle and trailed
over the side of the bath. This served the
purpose of equalizing air pressure between
the interior of the tube and the atmosphere. Heart rates were taken at tempera1With the aid of NIH Grant no. HE03565-06 and
Grant from Rome Air Development Center, Air Research and Development Command, U.S.A.F.
379
380
G . H. P A F F , R. J. BOUCEK, R. E. NIEMAN AND W . B. DEICHMANN
50
46
42
W
n
4
c
-
-
38-
-
a
E
34-
v,
30-
2
W
V
W
-
-
W
a
w
w
26
D
'
w
a
2
18 -
a
S
w
I-
-
22
W
n
-
14
-
lsoloied heorts in Blood Plosmo
10 6 -
0
20
40
60
80
100
120
140
160
180
200
220 240
HEART RATE - BEATS PER MINUTE
Fia. 1 Rates of beat per minute of isolated 72 hour embryonic chick hearts plotted
against temperature in degrees centrigrade.
ture intervals of not more than 2 ° C . From
the 20 or more values obtained for each
heart a rate-temperature curve was made
(for each heart) and by interpolation a
rate value for each degree of temperature
rise was determined. From these values
the average rates of beat of 208 hearts
were determined and plotted in a single
curve (fig. 1 ) .
APPARATUS FOR OBTAINING
ELECTROCARDIOGRAMS (ECG'S)
In previous reports we described apparatus for obtaining electrocardiograms
on isolated embryonic hearts (Boucek,
Murphy and Paff, '59; Paff and Boucek,
'62). We have discarded this apparatus
in favor of relatively inexpensive and more
reliable equipment. Figure 2 is almost
self-explanatory. The magnetic armature
core of a transducer is fixed to one end
of a freely movable lever. The core is
counterbalanced by a small lead weight
positioned so that the free end of the lever
is one mgm nose heavy. The cross-bar
fulcrum of this lever rests on two arms of
a strip of bakelite which supports not only
the lever but the jacket of the transducer
which is cemented to it. By turning the
adjusting screw the lever which serves as
the exploring electrode can be lowered or
raised and thus placed on or taken off
the heart. The indifferent electrode is
adjusted so that it makes contact with the
medium surrounding the heart when the
exploring electrode is placed on the heart.
As indicated in figure 2, leads from the
electrodes pass to amplifiers and thence
to a recorder.
381
THE EMBRYONIC HEART AND RADAR
fronsducer.
wt
fulcrum
'\
\\
0 djl
screw,
a
ele frode s
elec
C
J
I
c x p lor1-ng
i
t
b
1
1I
I ' n d i f f c r enf
I
I
myogrom..."
e cg .-..'
amp/ifl'er s
omp/ifi e r s
recorder
Fig. 2 Two views of the electrode carriage and electrode: A, from side; B, from above.
Inset, C, shows position of exploring electrode on the heart. Please see text for explanation.
Although we did not record myograms
in our microwave studies it should be
noted parenthetically that the apparatus is
ideal for this purpose. Movement of the
magnetic armature core within the jacket
of the transducer is converted to electrical
impulses which can be led from the jacket,
amplified and recorded as the myogram.
TECHNIQUE FOR OBTAINING ELECTROCARDIOGRAMS BEFORE, DURING
AND AFTER EXPOSURE OF
ISOLATED EMBRYONIC
HEARTS TO RADAR
A 72 hour embryonic chick heart is
excised, washed in Tyrode solution and
placed in 0.02 ml of chicken blood plasma
lying on saran sheet stretched over embroidery hoops 4 inches in diameter. The
exploring electrode is placed on the center
of the ventricle (see insert fig. 2 and
fig. 3 ) ; the indifferent electrode in the
blood plasma adjacent to the heart (fig. 3).
The recorder is then turned on and a continuous run of ECGs is begun. The first
objective is to obtain tracings to be used
as controls. Routinely we recorded for
three minutes before subjecting the heart
to microwaves.
While the ECG is being recorded the
radar apparatus is turned on and the microwaves are directed at the heart from
below through the saron sheet (fig. 3).
We used a frequency of 24,000 megacycles, a wave length of 1.25 cm and exposures of 478, 297, 167, and 74 mw/cm2
for lengths of time varying between a few
seconds and three minutes. If the temperature threatened to reach an undesirable level as indicated by heart rate (fig. 1)
a stream of dry air, chilled by running
through a copper coil submersed in dry
ice-alcohol was directed toward the under
surface of the saran sheet. The necessary
amount of air was manually controlled by
a petcock. Arbitrarily the hearts were subjected to radar for no longer than three
minutes. The radar was then turned off
but ECGs were taken until the record stabilized plus three minutes. In the final
series of experiments a total of 106 hearts,
approximately 25 at each exposure, was
used.
OBSERVATIONS
Before subjecting hearts to radar it was
first determined that the technique used
in studying the hearts was not in itself
damaging. Eleven control experiments
382
G . H. PAFF, R. J. BOUCEK, R. E. NIEMAN AND W. B. DEICHMANN
exploring
electrode-
......---......,
-..
R
Fig. 3 Diagrammatic section through ventricle of 72 hour embryonic chick heart in
blood plasma. Note exploring electrode on the heart, indifferent electrode i n the plasma,
the saran sheet and arrows indicating the direction of radar waves and cold air.
were run. The result is illustrated in
figures 4 and 5. Figure 4 is an ECG of
an untreated heart taken three minutes
after removal from the embryo. Figure 5
is an ECG from the same untreated heart
taken 15 minutes after removal from the
embryo. No changes in the ECG occurred
during the period.
Turning now to hearts treated with radar. At 478 mw/cm2 damage to the heart
was practically instantaneous as revealed
by the ECG. In 16 hearts in which no
effort was made to control heat the heart
rate soared from 50 to 220 beats per
minute, became erratic and stopped within
10 seconds. However, when cold air was
used to offset heat it was possible to maintain activity during periods of four to five
hours of continuous irradiation. We hasten
to add, however, that it was impossible to
maintain even visual semblance of normal
activity. The rate of beat was irregular;
periods of activity alternated with periods
of quiescence; dissociation of activity between atrium and ventricle was often seen;
sometimes only small areas of a chamber
contracted. There was no point to recording ECGs from these grossly abnormal
hearts.
At 297 mw/cmz heat was less intense
but damage was unavoidable whether or
not cold air was used to offset the heat.
This is demonstrated in figures 6 and 7.
Figure 6 shows the ECG of a heart three
minutes after it was removed from the
embryo but before it had been exposed to
radar. Figure 7 is the ECG of the same
heart taken 4 minutes after it had been
exposed to radar (297 mw/cm2) for three
minutes. The atrium was damaged to the
extent that all mechanical and electrical
activity had ceased. (Note the absence of
the P wave.) Only a QRS complex of decreased amplitude and bizarre T U waves
remain. At no time during the experiment
did the heart beat faster than 166 times
per minute. Presumably at no time did the
temperature of the isolated heart exceed
38.5"C (see curve fig. 1 ) .
When the dosage is reduced to 167 mw/
cm2 and maintained for a period of three
minutes damage is less pronounced but
still obvious. This is shown in figures 8,
9, 10 and 11. These are records from a
single heart taken before (fig. 8 ) , during
(figs. 9 and 10) and 5 minutes after radar
was turned off (fig. 11). We used a slow
stream of cool air to maintain the presumed temperature within the physiological range. The control record (fig. 8) was
taken at a n ambient temperature of 25°C
and the heart rate was 60 per minute.
One minute after radar was turned on
(fig. 9 ) and while cool air was used the
THE EMBRYONIC HEART AND RADAR
heart rate was 125 per minute (temperature 34°C from the curve). At the end of
three minutes of irradiation (fig. 10) the
heart rate was 107 per minute (temperature 32°C) and five minutes after radar
was turned off the ECG had settled into a
fixed pattern (fig. 11). At this time the
ambient temperature was still 25°C but
the heart rate had increased to 65 per
minute. This slight increase in rate over
that at the start of the experiment may be
of little or no importance but the changes
in the ECG, i.e., shortening of the QT
interval, increased height and breadth of
the T wave and the large broad U wave
denote damage to the heart.
The lowest radar intensity at which we
worked was 74 mw/cm2 during a continuous exposure for three minutes. At this
dosage it was not necessary to use cool air
to keep the heart rate within the physiological range if the ambient temperature
is kept below 25°C. Figures 12, 13 and 14
are ECGs from the same heart taken before (fig. 12), during (fig. 13) and 5
minutes after irradiation (fig. 14). At the
start of the experiment the ambient temperature was 24°C and the heart rate was
38 per minute (fig. 12). After 3 minutes
of radar treatment (fig. 13) the P wave
inverted, the QT segment was shortened,
the T wave was deformed and the heart
rate had increased to 115 per minute.
Finally five minutes after radar was turned
off (fig. 14) the P wave returned to the
control configuration (compare figs. 12
and 14) but the QT interval remained
somewhat shortened.
DISCUSSION
The devastating effects of the higher
concentrations of radar, i.e., 478 and 297
mw/cm2 on the embryonic heart were expected e.g. the heat was unbearable to even
a finger placed in the radar beam. However, as the dosage was reduced the effects
passed from the obvious to the subtle. In
preliminary experiments in which the
study of effects were based solely on visual
observation through the microscope, the
conclusion was drawn that at 74 mw/cm2
radar is innocuous. This developed into
the conviction that heat alone was responsible for radar damage and that if one
could control the heat factor an embryonic
383
heart would beat indefinitely in a radar
beam of any intensity.
This proved to be erroneous when electrocardiographic records were taken. From
the ECG evidence it can be said without
equivocation that the embryonic heart can
be injured by radar at dosages which do
not raise the temperature to a damaging
level. This was demonstrated in experiments in which hearts were subjected to
radar at exposures of 74 mw/cm2 for one
to three minutes at ambient temperatures
below 25°C. Of 25 hearts upon which
ECGs were obtained at this exposure, all
showed damage.
The nature of radar damage is interesting. At higher exposures both the atrium
and ventricle are injured but the more
drastic effects occur in the atrium e.g., the
P wave may be eliminated completely. At
lower exposures, those at which heat is
not sufficiently great to require cooling,
the changes in the ECG involve the ST
segments of both the atria and the ventricles and the TU waves. These latter
effects indicate an alteration in the repolarization process and point to the conclusion
that some metabolic activity influencing
the cell membrane potential of the heart
has been disturbed.
SUMMARY AND CONCLUSION
In an effort to determine if radar damages tissue by heat alone or by heat plus
an intrinsic factor, isolated 72 hour embryonic chick hearts were exposed to
radar at 478, 297, 167 and 74 mw/cm2
for a period not exceeding three minutes.
At exposures of 478 and 297 mw/cm2 active efforts were quite hopelessly made to
offset damaging heat levels. No conclusion could be drawn.
At an exposure of 167 mw/cm2 it was
possible to control the temperature so that
the heart rate remained in a physiological
range. Despite this the ECGs showed damage. This at least indicated that an intrinsic damaging factor may exist in radar.
Finally at an exposure of 74 mw/cm2 it
was unnecessary to take precautions to
cool the hearts. The heat factor was
negligible. Significantly, however, the
hearts showed damage in the electrocardiograms.
384
G . H. PAFF, R . J. BOUCEK, R. E. NIEMAN AND W . B. DEICHMANN
These experiments justify the conclusion that radar can damage tissue not only
by heating it but also because of the presence of a factor which can operate at
heat levels which are in themselves not
dangerous.
LITERATURE CITED
Addington, C. H., C. Osborn, G. Swartz, F. P.
Fischer, R. A. Neubauer and Y. T. Sarkees
1961 Biological effects of microwave energy
at 200 mc. Biological Effects of Microwave
Radiation Ed. by M. F. Peyton, Plenum Press,
New York, 177-186.
Boucek, R. J., W. R. Murphy, Jr. and G. H. Paff
1959 Electrical and Mechanical properties of
chick embryo heart chambers. Circulation
Res., 7: 787-793.
Carpenter, R. L., D. K. Biddle and C. A. van
Ummerson 1960 Opacities in the lens of
the eye experimentally induced by exposure to
microwave radiation. IRE Trans. Med. Electronics ME 7: 152-157.
Deichmann, W. B., F. H. Stephens, Jr., M. Keplinger and K. F. Lampe 1959 Acute effects
of microwave radiation o n experimental ani-
mals (24,000 megacyles). Jour. Occupational
Med., I: 369-381.
Gunn, S. A., T. C. Gould and W. A. D. Anderson
1961 The effect of microwave radiation on
morphology and function of rat testis. Lab. Investigation, 10: 301-314.
Howland, J. W., R. A. E. Thomson and S. M.
Michaelson 1961 Biomedical aspects of microwave irradiation of mammals. Biological
Effects of Microwave Radiation Ed. by M. F.
Peyton, Plenum Press, New York, 261-284.
Linke, C. A , , W. Lounsberry and V. Goldschmidt
1962 Effects of microwaves on normal tissues.
J. Urol., 88: 303-311.
Michaelson, S . M., R. A. E. Thomson and J. W.
Howland 1961 Physiologic aspects of microwave irradiation of mammals. Am. J. Physiol.,
201: 351-356.
Paff, G. H., and R. J. Boucek 1962 Simultaneous electrocardiograms and myograms of the
isolated atrium, ventricle and conus of the
embryonic chick heart. Anat. Rec., 142: 7380,
Van Ummerson, C. 1961 The effect of 2450 mc
radiation on the development of the chick embrvo. Biological Effects of Microwave RadiaEd. by-M. F. Peyton, Plenum Press, New
York, 201-220.
PLATE 1
EXPLANATION O F FIGURES
4
Electrocardiogram (ECG) of non-irradiated heart taken three minutes
after removal from embryo. Note P, QRS and T waves.
5
ECG of non-irradiated heart (same as used in fig. 3 ) taken 15
minutes after removal from the embryo. No essential change.
6
ECG of a second heart three minutes after removal from the embryo
and before exposed to radar. Note P, QRS and T waves.
7
ECG of same heart as used in figure 6 taken four minutes after it
had been irradiated (297 mw/cmz) for three minutes. Note absence
of P wave, decreased amplitude of QRS, elevated ST segment, bizarre
T waves.
8
ECG of a third heart three minutes after removal from the embryo
and before treatment with radar. Note P, QRS and T waves.
9
ECG of same heart (fig. 8 ) taken after one minute of exposure to
radar (167 mw/cm2). Note depressed ST segment.
10
ECG of same heart (figs. 8 and 9 ) taken at end of three minutes of
irradiation (167 mw/cmz). Note ST segment depressed and very tall
broad T wave.
11
ECG of same heart (figs. 8, 9 and 10) taken five minutes after radar
had been turned off. Note persistence of a prominent T wave and the
presence of a broad U wave.
12 ECG of a fourth heart taken three minutes after removal from the
embryo. No radar.
13 ECG of same heart (fig. 12) taken three minutes after radar treatment (74 mw/cm2). P wave is inverted. T wave is elevated.
14
ECG of same heart (figs. 12 and 13) taken five minutes after radar
was turned off. P wave now normal but T wave is deformed.
THE EMBRYONIC HEART AND RADAR
George H. Paff, Robert J. Boucek, Richard E. Nieman and William B. Deichmann
PLATE 1
385
Документ
Категория
Без категории
Просмотров
2
Размер файла
593 Кб
Теги
radar, embryonic, heart, subjected
1/--страниц
Пожаловаться на содержимое документа