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The magnitude of increase in the pulmonary blood volume of the postnatal guinea pig.

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THE MAGNITUDE O F INCREASE I N THE
PULMONARY BLOOD VOLUME O F T H E
POSTNATAL GUINEA P I G
NEWTON B. EVERETT AND BARBARA S. SIMMONS
Department of Anatomy, University of Washington, School of Medioime,
Seattle, Washington
ONE FIGURE
Through the use of improved methods combining rapid
freezing and isotopic tracer techniques, Everett ( '52) demonstrated that after 5 minutes of breathing the blood volume
of the newborn guinea pig lung had increased by 25% over
that of its nonbreathing littermates. The increase after this
time was shown to be more gradual and by 7 hours after delivery the blood volume per-unit-weight of lung had increased
by approximately 85%.
The studies reported here are a continuation of the former
study and cover the period from 7 to 36 hours postpartum,
which extends beyond the time of any further increase in the
blood volume per-unit-weight of lung.
METHODS
Sixteen litters of guinea pigs including 42 individual offspring were used for the pulmonary blood volume determinations. The methods used for labeling the blood with radioiron, for freezing the newborn and for comparing the blood
volume of the breathing and nonbreathing littermates were
the same as in the previous study, Everett ('52). The animals
of each litter which were permitted to breathe were kept at
This investigation was supported (In part) by a research grant (H-1530)
from The National Heart Institute, of the National Institutes of Health, Public
Health Service.
429
430
NEWTON B. EVERETT AND BARBARA
s.
SIMMOKS
37°C. for 16, 24 or 36 hours after delivery. They were fed
a mixture of dried milk, dextrose, and water with a medicine
dropper a t 2-4 hour intervals until sacrificed.
Hemoglobin determinations and radioiron assays of the
blood were made on several pigs a t 16, 24 and 36 hours postpartum. These were made to determine if there were any
significant changes in the blood during the period of breathing
which might influence the distribution of radioiron per unit
volume of blood.
Electrocardiograms were made on three pigs to determine
how long the heart continued to beat after immersing the animals in the freezing mixture of dry ice and ethanol at -75°C.
In addition the time required for complete freezing after immersion was determined by recording from thermocouples
implanted above the liver near the central point of the diaphragm.
RESULTS
The comparative radioactivity of lung samples between the
breathing and nonbreathing animals is shown in table 1. I n
all cases the lung samples from the breathing specimens gave
higher counts than the nonbreathing controls. This increase
in radioactivity, which is related directly to the increase in
blood volume, averaged 100% for the 16 hour group, 126%
for the 24 hour group, and 100% for the 36 hour group.
In figure 1the percentage increase of lung radioactivity is
plotted against time and included with the results of the present series are those of the former study covering the period
from 5 minutes to 7 hours postpartum. This scattergram
shows that after the initial marked increase within the first
5 minutes of breathing the increase was more gradual and
continued so through the 16 hour period. It is further revealed in figure 1 that there was considerable variation
amongst the values of the different litters which breathed 24
hours. The increase of 190% for one of the litters in this
group is some 46% above the next highest value within any
group. Except for this one value the average increase for
the 24 hour group and f o r those which breathed 36 hours are
431
POSTNATAL PULMONARY BLOOD VOLUME
of the same magnitude as those of the 16 hour series. Thus,
the magnitude of increase in the blood volume per-unit-weight
of lung was in the range of 100% and this was reached by the
16th hour of breathing.
TABLE 1
Radioactimity of lung samples
BREATHING
TIME
LITTER
NUMBER
AVE. CT.S./MIN. PER EQUAL
U N I T WEIGHT ( 5 0 MG)
Breathing
16 hr.
218
238
243
24 7
244
197
217
22i
24 hr.
P 14
246
245
36 hr.
231
193
190
196
230
(2)' 972
(2) 628
(1) 484
(1) 144
(2) 841
(1)
(2)
(1)
(1)
(1)
(2)
762
206
381
533
690
893
(1) 903
(1) 676
(2) 1223
(2) 417
(2) 209
% INCREASE
AFTER BREATHING
Nonbreathing
(1)' 592
(1) 33'4
(1) 209
ave.
64
88
131
96
120
100
( 1 ) 476
60
(1) 71
ave.
190
144
130
129
102
126
ave.
95
103
101
106
95
100
( 1 ) 73
( 1 ) 382
(1)
(1)
(1)
(2)
(1)
(1)
(2)
(1)
(1)
156
232
301
443
462
333
607
202
ioa
Number of animals.
There were no significant differences in the hemoglobin
values for the same animals at 16,24 and 36 hours postpartum,
table 2. The greatest difference was 4% in one animal between 16 and 36 hours. A decrease of up to 2% in hemoglobin values could be expected in the second determination
due to the withdrawal of 0.1ml of blood used for the first
determination. It is noted that where a difference is revealed
between the two determinations that the second value was the
432
NEWTON B. EVERETT AND BARBARA S. SIMMONS
lower one. There was less than 1%difference in the radioiron assays of blood from the same animals a t 24 and at 36
hours postpartum, table 2.
2
$
190180170160150140130120110100-
INCREASE OF LUNG RADIOACTIVITY WITH BREATHING
X
X
X
X
X
.
X
X
90-
g4
X
X
X
X
x
x
X
X
:."Ixi 1 ;
40
K
K
,
,
,
,
;
,
,
,
,,,,
,
,,,,
,
10
1 2 3 4 5 6 7
16
BREATHING TIME
24
(HOURS)
36
Fig. 1 Increase of lung radiwctivity with breathing
TABLE 2
Comparative hemoglobin and radioiron values
ANIMAL
NUMBER
16 HRS.
B-1
B-2
B-3
A-1
A-2
17.3
24 HRS.
36 HRS.
% VARIATION
Percent Hemoglobin
18.3
19.2
15.6
15.9
17.3
17.8
18.4
15.4
15.6
0
3
4
1.3
1.5
Radioactivity in Counts/min/B~Omm * blood
c-1
c-2
243
245
241
246
>I
>I
POSTNATAL PULMONARY BLOOD VOLUME
433
An electrocardiographic record was obtainable for a variable time after immersion, ranging from 34 to 60 seconds.
The average time required for complete freezing was 3*
minutes.
DISCUSSION
The observations presented here show that in the postnatal
guinea pig the magnitude of increase in the pulmonary blood
volume per-unit-weight of lung is approximately 100%. This
increase of 100% over that of the nonbreathing littermate
controls is reached by the 16th hour of breathing. It was reported earlier, Everett ('52) that the increase was 85% following 7 hours of breathing.
Although the average increase in the pulmonary blood volume for the pigs breathing 24 hours was 126% it is believed
that this value is out of line due to the variation within this
group. The explanation for the greater variation within this
24 hour group is unknown. The increase of 190% for one of
the litters is considerably beyond the individual variations
obtained in the other groups after a particular interval of
breathing. I n fact, the values obtained for the animals of
different litters breathing 36 hours are remarkably uniform.
It would appear then that by the 36th hour the blood volume
of the lung has become stabilized.
The uniform hemoglobin values as well as uniform radioiron values of blood from the same animals at the different
time intervals would indicate that no hemal changes have occurred within the experimental period which would influence
the results.
The 33 minutes required for complete freezing of the newborn pigs was determined by a more accurate method than
that used previously, Everett ('52), which indicated that
freezing was complete in three minutes. The data obtained
from the electrocardiograms would suggest however that
there ceases to be a further circulation of blood 30 to 60
seconds after dropping the pigs into the freezing mixtures.
The observation that there is an abrupt increase of some
25% in the pulmonary blood volume of the guinea pig by 5
434
NEWTON R. EVERETT AND BARBARA
s.
SIMMONS
minutes postpartum, Everett ( '52), and a more gradual increase thereafter, reaching 100% by 16 hours, is in accord
with the recent studies of Ardran et al. ( '52). These investigators observed that in the newborn lamb with the onset of
breathing there is a considerable fall in both pulmonary
arterial and aortic pressure and that the pulmonary circulation becomes more rapid. It was proposed that the decrease
in pulmonary vascular resistance with the onset of ventilation
is responsible for these changes. This proposal was later
substantiated when it was shown that with ventilation the
pulmonary resistance to blood flow decreased from 50 to 90%,
Dawes, et al. ('52). Thus it would appear that the initial
marked increase in pulmonary blood volume and the subsequent gradual increase is due to the reduction in pulmonary
vascular resistance.
SUMMARY
Comparative blood volumes per-unit-weight of lung have
been made between non-breathing and postnatal guinea pigs
after 16 to 36 hours of breathing. This has been done by the
methods reported previously, Everett ( '52).
The increase in blood volume averaged 100% by the 16th
hour of breathing. There appears to be no further increase
after this time.
There were no significant differences in the hemoglobin
values or in the radioiron assays of blood from guinea pigs
obtained at 16, 24 and 36 hours after birth.
LITERATURE CITED
ARDRAN,
G. M., G . S. DAWES,M. M. L. PRI('IIARD,
S. R. M. REYNOLDS A N D D. G.
WYATT 1952 The effect of rentilation of the foetal lungs upon the
pulmonary circulation. J. Physiol., 218: 12-22.
DAWES,G . S.,J. C. Mom, J. G. WIDDICOMBE
AND D. G . WYATT 1952 The effect
of ventilation on pulmonary blood flow in the newborn lamb. J.
Physiol, 118: 45 P.
EVERETT,
N. B. 1952 Xarly postnatal changes i n pulmonary blood volume of
the guinca pig. Am. J. Pliysiol., 1 6 9 : 54-39.
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