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Oxygen and carbon dioxide transfer across the rhesus monkey placenta (Macaca mulatta)
Oxygen and carbon dioxide transfer across the rhesus monkey placenta (Macaca mulatta) ANDRfi
E.
HELLEGERS,
CHRISTOPHER RICHARD
E.
FREDERICK Baltimore,
J.
M.D.* HELLER,
BEHRMAN, C.
A.B. M.D.**
BATTAGLIA,
M.D.**
Maryland
N u M E R o u s studies on the transfer of oxygen and carbon dioxide across the placenta have appeared in recent years, particularly across the human placenta and across that of the sheep and the goat. Since the similarity between the anatomical characteristics of the human and the monkey placenta is marked, the present study was undertaken to determine the biochemical and physiological similarities. Determinations of the concentration gradients for physically dissolved oxygen and carbon dioxide not only provide information on the permeability characteristics of that placental type, but also yield information on the oxygen tension in which the fetus develops in utero. Since estimations of oxygen tension were made indirectIy by relating the oxygen saturation and pH in the bloods of the vessels sampled, the data also yielded informa-
tion for the study of acid-base balance across the monkey pIacenta. The present report describes the following: 1. A test of the applicability of the Van Slyke-Sendroy nomogram’ to both maternal and fetal monkey blood. 2. A comparison of maternal and fetal oxygen capacities. 3. The concentration gradient for physically dissolved oxygen. 4. The concentration gradient for physically dissolved carbon dioxide, bicarbonate ions, and hydrogen ions. 5. The arteriovenous differences for total oxygen and total carbon dioxide concentrations on the maternal side of the placenta. Finally, the data in this report are compared with similar data from other species. Materials
From the Departments of GynecologyObstetrics, and Pediatrics, The Johns Hopkins University, Baltimore, Maryland, and the Department of ObstetricsGynecology, University of Puerto Rico. This study was supported in part Research Grant HE-04231 of The National Institutes of Health.
and
methods
All experimental animals were Macaca mulatta monkeys maintained by the National Institutes of Health, Laboratory of Perinatal Physiology, San Juan, Puerto Rico. The animals were mated for a single 24 to 48 hour period during a menstrual cycle and were not remated unless it was determined that mating had not resulted in a pregnancy. Although the natural gestation of Mucaca mulafta has been reported to last about 164 days, the period from the one hundred and fifty-third to the one hundred and fiftyseventh day was arbitrarily chosen for elec-
by
“Senior Research Scholar, ,Joseph P. Kennedy, Jr., Memorial Foundation. **Member of Laboratory of Perinatal Physiology, National Institutes of Neurological Diseases and Blindness, National Institutes of Health, San Juan. Puerto Rico. 22
Volume Number
88 1
tive cesarean section, for fetuses delivered at this age survive and the substantial risk of early vaginal delivery is avoided. Hence, all fetal samples were obtained at cesarean section prior to the onset of labor. Operative procedure was as follows: the pregnant animals, caught with minimum handling, were placed in the dorsal supine position on the operating table, the head end of which was elevated 30 degrees to help obviate pressure of the pregnant uterus on the inferior vena cava. The animals were not starved prior to operation. The upper extremities were tied at a 30 degree angle from the body. It had been previously observed that when the upper extremities were tied in extension above the head, the upper pulmonary lobes were incompletely ventilated. Preoperatively, in those animals, arterial pH’s as low as 7.10 were found, presumably, secondary to the respiratory acidosis. Such animals were not used in these experiments. The left groin and left paramedian area were infiltrated with 2 per cent procaine without epinephrine, a total of about 10 cc. being required. A branch of the left femoral artery was catheterized under direct vision. All maternal arterial samples were drawn from this vessel. The peritoneum was entered through a left paramedian incision. Since most uteri were dextrorotated this incision provided easier access to the left uterine vein without handling the uterus to expose the vessel. The uterus remained in the abdominal cavity throughout the procedure and the placental site was identified by palpation. Amniotic fluid was obtained by transuterine puncture. The choice of the vessel to be sampled as representative of a vein draining the maternal surface of the placenta posed a distinct problem. Repeated attempts to sample the intervillous space yielded only very small aliquots of blood of dubious origin. This may have been due to the fact that, since the monkey placenta is diffuse and the volume of the intervillous space, presumably, is considerably smaller than in the human, the depth of the intervillous pool may make
Transplacental
transfer
of 0,
and
CO*
23
intervillous sampling difficult. For this reason we decided to sample the uteroovarian vein, so that any arteriovenous difference obtained would reflect consumption or production of substances by the entire uterus and its contents. In each animal the uteroovarian vein was sampled only once, by venipuncture. Fig. 1 presents a scheme of the gross anatomy of the venous drainage of the monkey placenta showing the site of sampling. The principal drainage into the uteroovarian vein takes place through an ascending uterine vein coursing along the left anterolateral aspect of the uterus, and a descending uterine vein coursing downward along the left anterolateral margin of the fundus. These lesser vessels were not used in the experiments reported here since sampling either of these vessels entailed the possibility of obtaining blood samples representing varying ratios of myometrial and placental venous blood. Blood gas determinations were performed by the method of Van Slyke and Neill’; pH determinations were done at 38’ C. on the radiometer, Model No. 4 pH meter. Oxygen tensions were obtained from the percentage oxygen saturation and pH using the nomogram of Behrman and co-workers.3 Carbon dioxide tensions were calculated from the Henderson-Hasselbalch equation, assuming a pK of 6.10. All fetal samples were obtained by single venipuncture from a segment of umbilical cord doubly clamped immediately upon delivery. When insufficient fetal blood was available to obtain plasma, the plasma carbon dioxide contents were derived from blood carbon dioxide contents using the Van Slyke and Sendroyl nomogram. The applicability of this nomogram to both adult and fetal monkey blood was tested and the data derived form part of the substance of this report. Inasmuch as no umbilical vein samples were obtained, gas pressure gradients across the placenta were calculated as follows: the carbon dioxide pressure gradient was estimated as the difference between tensions in the umbilical artery and the uterine vein.
24
Hellegers
Jama‘).
et al.
Am. J. Obsr.
1. 1964 R: Gynec.
equation. The final column yields the difference between the two methods of obtaining the carbon dioxide tension. It is thus seen that the Van Slyke-Sendroy nomogram can be applied to adult monkey blood with a mean error of 0.99 (kO.62) and to fetal blood with a mean error of 1.15 (kO.60) mm. Hg.
A comparison of the oxygen capacities of adult and fetal blood. Table III gives the
Fig. 1. Site experiments
of sampling, described in
X, of text.
uterine
vein
for
The oxygen pressure gradient was taken as the uterine vein oxygen tension minus the umbilical artery oxygen tension and, therefore, represents the minimum oxygen pressure gradient across the placenta.
Results Applicability of the Van Slyke-Sendroy nomogram to adult and fetal monkey blood. Table I presents the data testing the applicability of the nomogram to adult blood. Table II presents the corresponding data for fetal bIood. In both tables the first four columns present the data obtained. The figures in Column 5 were derived from the Van Slyke-Sendroy nomogram’ using the data contained in the first three columns. Column 6 presents the difference between measured (Column 4) and derived (Column 5) total plasma carbon dioxide concentrations. These plasma carbon dioxide concentrations were then used to calculate the carbon dioxide tensions given in Columns 7 and 8 by using the Henderson-Hasselbalch
oxygen capacities in simultaneous paired samples of maternal and fetal blood. All fetal samples were obtained at a gestational age of more than 150 days and, therefore, represent values close to term (164 days). The mean maternal oxygen capacity was 15.48 (k2.95) volume per cent. The mean fetal oxygen capacity was 17.77 (21.93) volume per cent. The difference between the two values is statistically significant (p < 0.05). It will also be noted that the fetal oxygen capacity is not in every case higher than the maternal. Table III also gives the hematocrits measured on the same samples as the oxygen capacities. In Columns 5 and 6 hemoglobin values are given for maternal and fetal blood. They have been derived by dividing the oxygen capacity, in volume per cent, by 1.34 and are, therefore, based on the assumption that Hufner’s coefficient is applicable to monkey blood. If this assumption is valid, the maternal and fetal mean corpuscular hemoglobin concentrations are those given in Columns 7 and 8. The difference between these values of 30.7 (&l-57), and 31.3 (k2.52) gram per cent for maternal and fetal blood, respectively, is not statistically significant. The figures closely resemble those for human blood.4
The oxygen concentration gradient across the placenta. Table IV, divided into two parts, presents the data on oxygen contents and concentrations. Group A includes those cases considered to be in good physiological condition. The judgement of the condition of the preparations was based on: 1. Absence of marked distention of the uterine vein suggestive of abnormally high uterine venous pressures.
Volume Number
88 1
Transplacental
2. Uncomplicated surgical procedure with minimal manipulation of the uterus. 3. Delivery of a healthy, vigorous infant through a uterine incision other than transplacental. 4. A pH in all vessels sampled of more than 7.30.
Table I. Data adult
used blood
monkey
Cal. I
Cal.
in testing
2
Cal.
0, Capacity (volume %)
fiH 7.480 7.479 7.454 7.439 7.431 7.390 7.388 7.360 7.324 7.315 7.306 7.424 7.414 7.364 7.439 7.331 7.290 7.236 7.227 7.211 7.104 0.99;
S.D.
3
Cal.
Blood (m%?L.)
19.54 13.81 16.48 14.24 13.31 16.31 20.54 16.71 17.24 11.35 15.29 19.54 16.48 17.60 13.81 14.24 11.35 15.29 17.24 16.31 16.71
*Mean,
applicability
monkey
Col.
PH 7.416 7.389 7.359 7.352 7.342 7.328 7.325 7.224 7.139 7.050 *Mean,
I
Cal.
~rnrn~?~~ 18.61 19.95 19.57 17.66 21.59 la.77 16.60 14.79 12.59 15.98 13.45 20.69 20.52 24.96 22.92 22.40 18.46 la.68 16.52 25.60 19.51
used in testing blood
0, I Capacity (v&m; %)
2
Cal.
3
I Blood CO, fmM./L.)
19.78 17.95 20.17 19.78 20.17 20.17 17.95 17.94 17.24 la.17 S.D.
and
CO,
25
5
Plasma CO, by
Slyke-Sendroy
nomogram
Col.
7
6
A CO, (Cal. 4 minus 5) (mM./L.) - 0.64 + 0.54 - 1.17 - 0.28 - 1.43 - 0.43 - 0.16 - 0.00 - 0.66 - 0.13 -0.11 - 0.44 - 1.02 + 0.73 + 1.01 - 0.86 - 0.26 t 0.75 - 0.47 - 0.62 - 0.22
Cal. PCO, measured (mm.Hg) 23.90 27.32 25.92 25.30 29.87 29.72 26.78 25.59 22.34 30.25 25.95 30.45 30.00 44.06 42.43 39.70 36.69 43.96 37.07 59.62 57.75
Cal.
to
8
Cal.
9*
PCO, by nomogram (mm.Hg)
A PCO, (Cal. 7 minus 8) fmm.Hd
24.75 26.60 27.56 25.70 31.98 30.42 27.04 25.59 23.58 30.50 26.17 31.11 31.57 42.81 40.64 41.33 37.22 42.26 38.15 61.10 58.41
- 0.85 + 0.72 - 1.64 - 0.40 -2.11 - 0.70 - 0.26 - 0.00 - 1.24 - 0.25 - 0.22 - 0.66 - 1.57 + 1.25 + 1.79 - 1.63 - 0.53 + 1.70 - 1.08 - 1.48 - 0.66
f 0.62.
Cal.
1.15;
of Van
17.97 20.49 la.40 17.38 20.16 la.34 16.44 14.79 11.93 15.85 13.34 20.25 19.50 25.69 23.93 21.54 la.20 19.43 16.05 24.98 19.29
15.24 17.39 16.64 15.42 19.02 16.155 13.66 12.72 10.82 14.54 11.78 17.16 17.56 21.69 20.52 20.04 17.00 16.74 14.48 22.92 17.48
of O2
Table IV and subsequent tables, therefore, include the animal number to allow identification of the experiment in this report as well as in the article immediately following it. It will be realized that in some cases sampling of the maternal vessels was performed in accordance with the above criteria
Plasma co, measured (mM./L.)
Table II. Data fetal
4
transfer
13.33 12.54 15.47 16.58 21.97 20.83 14.75 la.12 20.96 18.65 -I 0.60.
.-
applicability
Cal. Plasma co, measured fmM./L.) 15.76 14.58 19.79 19.64 26.83 25.08 17.74 19.86 22.62 20.51
4
of Van
Cal.
5
Slyke-Sendroy
nomogram
Cal.
7
6
Cal.
Cal.
to
8
Plasma CO, by nomogram fmM./L.)
A CO, (Cal. 4 ~minus 5) (mM./L.J
PCO, measured (mm. HeI
PCO, by nomogram (mm. He)
16.17 14.87 18.67 19.78 25.92 24.66 17.20 20.57 23.26 20.92
- 0.41 - 0.29 + 1.12 - 0.12 + 0.51 t 0.42 f 0.54 -0.71 - 0.64 - 0.41
24.13 23.67 34.30 34.58 48.26 46.53 33.16 46.19 63.01 68.82
24.76 24.14 32.36 34.79 46.62 45.75 32.15 47.84 64.79 70.20
Cal.
9s
A PCO, (Cal. 7 minus 8) (mm. He) + + t + -
0.63 0.47 1.94 0.21 1.64 0.78 1.01 1.65 1.78 1.38
26
Hellegers
et
Table III. corpuscular
al.
Oxygen capacity, hematocrit, hemoglobin, hemoglobin values for maternal and fetal
Cd. 1
Cd.
cd.
2
3
i
cd.
and mean blood
4
Cd.
51
02 Capacity, fetal (volume %)
O2 Capacity, maternal (volume %)
Mean S.D.
14.92 18.35 19.80
15.48
17.77
39.5
_C
2.95 applicability
of
Table
Oxygen
pressure
IV. Cal.
1
1.72
1.93
*Assuming C.C. oxygen.
Hufner’s
Cal.
coefficient:
I:: -__ -__
7.7 12.5 14.6 8.6 10.9 11.4 12.3
11.0 13.4 12.9 11.9 12.4 15.0 14.8 13.4 14.0 ----_ ___ 11.1 13.7 14.8
28.6 33.0 31.6 29.7 30.8 31.2 30.7 27.6 --30.8 32.4 ----31.3 ---
34.3 33.8 27.9 ‘9.8 30.2 29.0 34.3 31.0 _ ~-_-----------
41.2
12.0
13.3
30.7
31.3
gradients
2
Cal.
i
1
8.5
4.38
1 Gm.
fully
2.20
oxynenatcd
Cal.
1.42
hemoglobin
across the monkey 3
__--Cal. 8”~~. Mean corpuscular hemoglobin concentration, fetal (gram O/0)
10.4 12.9 12.2 12.8 15.3 13.1 10.3
32.0 39.5 46.0 40.0 41.0 45.0 43.0 43.2 ___ -__ ---
36.2 39.0 38.5 43.0 49.8 42.0 33.5 30.6 _-40.5 45.0 ----36.4 ---
7*
Hemoglobin, fetal (gram To)
Hematocrit, fetal (9’0)
14.72 17.92 17.23 15.97 16.61 20.16 19.77 17.94 19.02 -----
Cal.
Hemoglobin, maternal (gram %)
Hematocrit, maternal (%)
13.89 17.23 16.31 17.09 20.56 17.5% 13.80 11.33 10.35 16.71 19.53 11.47 14.65 15.28 16.49
6”
Mean carpuscular hemoglobin concentration, maternal (gram %)
I
_----
Cal.
when
exposed
1.57 to air
combines
Cal.
6
2.52 with
1.34
placenta 4
-___Cal.
5
Col.
7
Uterine
Maternal artery oxygen .raturation /%I
Animal No. Group
Uterine vein 0, saturation f%)
pH
Umbilical artery 0, saturation f%)
veinumbilical
fiH
Uterine vein PO, (mm. Hg)
Umbilical artery PO, (mm. Hg)
artery
pressure gradient
A
v 195 X 692 x 590 Q 200
97.18 91.87 99.08 98.82
40.08 44.85 58.02 53.50
7.331 7.319 7.357 7.364
40.94 29.87 30.63 43.00
7.303 7.325 7.318 7.342
26.1 28.1 32.1 30.0
15.7 12.6 13.0 15.4
10.4 15.5 19.1 14.6
Mean Sipificant difference
96.74
49.11
7.343
36.11 6.54
7.322 0.016
29.07 2.57
14.18 1.60
14.9
v 798 Q 192 H 220 I. 242
96.43 91.81 97.60 90.90
48.54 61.64 64.49 25.80
7.349 7.227 7.329 7.067
10.70 22.89 22.96 6.90
7.258 7.224 7.050 6.842
28.5 40.1 37.0 29.3
8.5 12.8 16.1 12.5
20.0 27.3 20.9 16.8
Mean
94.19
50.12
7.243
15.86
7.094
33.73
12.48
21.25
8.32
0.191
5.72
Group
C
B
S. D.
+
3.12
0,
Volume Number
88 1
Transplacental
for a good preparation, whereas difficulty might have occurred in delivery of the fetus. In such cases the preparation is listed as good only for description of data relating to maternal blood. The uterine vein oxygen tension in all preparations was of the order of 30 mm. Hg irrespective of the oxygen saturation of the blood in these vessels. At relatively constant PO,, the oxygen saturation in the uterine vein varied directly with the pH, being lowest where the pH was lowest. This is best
Table V. Carbon Cal. I
dioxide
Cal.
Animal No.
pressure
2
Cal.
Femoral artery plasma CO, (mM./L.)
Uterine vein plasma CO, (mM./L.)
gradients
transfer
ot 0,
and
CO,
seen by comparing Animal X 590 with L 242. The PO,‘s were virtually identical (32.1 versus 29.3) and yet the oxygen saturations were strikingly different (58.0 per cent versus 25.8 per cent) due to the marked pH difference (7.357 versus 7.067). This same relationship of widely different oxygen saturations occurring at approximately the same PO, was seen most dramatically in the fetal circulation. The umbilical arterial oxygen tension, like that in the uterine vein, was fairly constant in all preparations,
across the monkey
3
Cal.
pH
Umbilical artery plasma CO, (mM./L.)
4
placenta
Cal.
5
Col.
6
Cal.
pH
Uterine vein PCO, (mm. Hg)
Umbilical artery PCO, (mm. Hg)
A 195 692 590 200
17.38 16.88 20.43 20.16
21.54 21.45 22.91 25.69
7.331 7.319 7.357 7.364
23.72 22.45 23.85 26.83
7.303 7.325 7.318 7.342
39.70 44.36 39.91 44.06
46.51 44.90 45.26 48.26
6.81 0.54 5.35 4.20
Group v Q H X Q
B 798 192 220 706 178
20.49 11.93 16.44 13.34 18.34
23.93 16.05
7.349 7.227 7.329 7.236 7.211
25.06 19.86 20.51 21.75 22.62
7.258 7.224 7.050 7.246 7.139
40.64 37.07 37.15 43.96 59.62
54.12 46.19 70.03 48.12 63.01
13.48 9.12 32.88 4.16 3.5
Table VI. Maternal carbon
uterine contents
dioxide
arteriovenous
differences
of oxygen
*
and
Carbon Column
Oxveen
7
Umbilical artery uterine vein PCO, (mm. Hg)
Group v X x Q
19.43 24.98
27
4
dioxide Column
5
Column
.I
Column
1
Column
2
Column
3
Uterine
Maternal artery
20.04 20.42 20.29 16.86
15.42 16.33 17.80 13.66
22.92 17.48
16.16 12.72
Animal identification No. v 195 X 692 x 590 H 220 Mean
6.03 7.01 6.48 8.96
v Q x
8.46 6.59 6.93
191 178 292
7:4:9 7.424 7.415 7.388
7.480 7.390 7.360
2.49 3.42 3.67 5.92
7.65 0.68 2.17
PH 7.331 7.319 7.357 7.329
7.424 7.211 7.104
3.45 3.59 2.81 3.04 3.25 0.81 5.91 4.76
t 0.38
4.62 4.09 2.49 3.20 3.60 Macerated 6.76 4.76
t 0.95 fetus
6
28
Hellegers
Jmua,\ I. 1964 .\m. .I. Obat. & Gynec
et al.
approximately 14 mm. Hg. Yet despite the constancy of the PO,, the animals in Group B had significantly lower oxygen saturations (p< 0.05) than the animals in Group A due to the lower pH’s of the Group B animals. The major differences between animals in Groups A and B, therefore, lie in the oxygen saturations and pH’s. The lower oxygen saturations, representing a decrease in the oxygen reserves of the fetuses involved, illustrate the fact that the oxygen pressure gradient alone did not yield a satisfactory indication of the oxygenation of the fetus. The oxygen pressure gradients in the Group B animals are if anything steeper than those in Group A animals. .Yet the fetal acidosis in some animals (e.g., L 242)) was severe enough to lower the oxygen affinity of the hemoglobin to near zero at a normal fetal PO,, i.e., 14 mm. Hg. The values of the umbilical arterial oxygen tension, said to be most representative of the oxygen tension in which the fetus develops, are considerably lower than those to which adult tissues are exposed but they are in striking agreement with those reported for all other fetal species.
The carbon dioxide concentration gradient acrossthe placenta. Table V presents the carbon dioxide concentration gradient between the umbilical artery and the uterine vein. In Group A animals the plasma carbon dioxide concentration in the umbilical artery (Column 4)) closely approximates that in the uterine vein. In all cases but one the fetal carbon dioxide contents and carbon dioxide tensions were slightly higher than in the maternal values. Only in Animal Q 178 was the plasma carbon dioxide content in the umbilical artery lower than in the maternal vein. There is close agreement between the carbon dioxide concentration gradient in this species and that reported in the human by Prystowsky, Hellegers, and Bruns.6 The very high fetal PCO,‘s in Animals H 220 and Q 178 occurred as a result of difficulty encountered in the delivery of the fetus necessitating transection of the placenta. The CO, pressure gradient across
the placenta arations.
was increased
in the bad prep-
Arteriovenous differences of oxygen and carbon dioxide contents along the maternal surface of the placenta. The arteriovenous differences of oxygen and CO, are presented in Table VI. The animals in Group A had a mean artery-vein (A-V) difference in oxygen contents of 3.25 mM. and vein-artery (V-A) difference in carbon dioxide contents of 3.60 mM. per liter. In animals in Group B (Q 178 and X 292) the A-V differences were considerably larger. In both these cases the oxygen contents in the uterine vein were the lowest of the entire series, as were the pH’s. Both cases showed distention of the uterine vein, giving it the appearance of a varicosity. Hence, the values in both preparations probably represent examples of A-V differences with decreased blood flow along the maternal surface of the placenta. This is also reflected in the fact that these animals had the highest A-V glucose concentration diff erencesG In one animal an identical experiment was carried out in the presence of a fetus which had been dead for more than thirty days. The A-V oxygen difference in that preparation was 0.8 mM. per liter and represents predominantly the oxygen consumption by the uterus. If the oxygen consumption by the uteri themselves in the other preparations were of the same order of magnitude, the A-V oxygen difference due to uterine contents, alone, would be of the order of 2.4 mM. per liter. Comment
The applicability of the Van SlykeSendroy nomogram to adult and fetal monkey blood is evidence that the distribution of bicarbonate between the red cell and the plasma in human and monkey blood is similar. The minor differences found may be in part explained by the fact that the BohrHaldane effect in adult and fetal monkey blood differs from that in adult human blood.3 The magnitude of this effect in the fetal and maternal blood of the monkey is similar to that in fetal human blood.
Volume Number
88 1
Transplacental
transfer
of 0,
and
CO,
Unfortunately no data on this aspect are available. In the present report the oxygen saturations in the umbilical artery vary widely between the Group A and Group B animals, despite a relatively constant oxygen tension. Fig. 2 illustrates this variation. Three isobars are drawn at PO,‘s of 17, 14j and 12 mm. Hg, respectively, using the data of Behrman and associates3 for fetal monkey blood. Along each isobar one can determine the change in oxygen saturation for a given change in PH. PO,‘s of 12 to 17 mm. Hg represent the range found in fetal umbilical artery samples. A POz of 14 mm. Hg represents the mean oxygen tension of the cases. At this tension a fall in fetal pH from 7.40 to 6.80 would so decrease the oxygen affinity of fetal monkey red cells as to cause the saturation to fall from 42 per cent to 7.9 per cent. The reasons for the difference between oxygen saturations reported here for umbilical artery blood and those reported by Dawes and co-workers18 for fetal femoral artery blood cannot be determined in the absence of either simultaneous pH or PO, measurements accompanying those oxygen saturations. It will be noted from Table V that with respect to the bicarbonate and physically
The Van Slyke-Sendroy nomogram is ap plicable to monkey blood unless the buffering capacity of the red cells in this species is markedly different than in the human. The present report offers evidence that if Hufnefs coefficient is applicable to monkey blood the mean corpuscu1a.r hemoglobin concentrations in the red cells of human and monkey blood would be identical. This is, of course, consistent with the applicability of the Van Slyke-Sendroy nomogram. A comparison of the oxygen capacities of maternal and fetal monkey blood reveals significant differences from the human. The monkey’s fetal oxygen capacity is not invariably higher than the maternal, as it is in the human. In this respect the monkey more closely resembles the sheep7 and the goats than the human9 Thus, while the fetuses of many species develop in the same environment of low oxygen tension,T* 8* lo-l1 they do not all respond to this diminished oxygen tension with an elevated oxygen capacity. This elevation then, is not a universally required adaptation to the low oxygen tension. In comparing fetal blood of the monkey and the human, the similarity in the mean corpuscular hemoglobin concentration and the difference in oxygen capacities suggest that the red blood cell count in the monkey fetus would be lower than in the human.
PO, 17
. ,/
O6!8
29
I 6.9
I
10
/
PO,14
I
I
I
I
1.2
7.3
7.4
pH to percentage PO*‘s.
-
42.0%
-
1.9%
PO* 12
1.1
PH Fig. 2. Plot relating saturation at various
.
30
Hellegers
et al
dissolved carbon dioxide concentrations, the monk(,)- data closely resemble those reported for the human. The data of the table support the concept previously documented that in good preparations the pH, bicarbonate, and dissolved carbon dioxide gradients across the placenta are small.“, I73 ‘K 2ogz The data on arteriovenous oxygen differences reported here are difficult to compare with those reported in the human due to the fact that we have sampled the uterine vein, while, in the human, samples were obtained from the intervillous space. In Animal V 191, in which the fetus had been dead for several weeks, the arteriovenous oxygen difference was 0.8 mM. per liter. Assuming that this difference represents predominantly consumption of oxygen by the uterus, itself, an arteriovenous oxygen difference of 2.4 mM. per liter would be accounted for by the consumption of the fetus and placenta, alone (3.2 minus 0.8). This figure is in good agreement with those reported by Bruns and co-workers,17 who, excepting the first of their cases, found the mean arteriovenous difference between arterial blood and intervillous space blood to be 1.9 mM. per liter in their normal cases. The problem of representative intervillous space samples referred to in methods stems from the difficulty of determining the proximity of the sampling needle to spurts of arterial blood delivered into the intervillous space by arterioles. The possibility of obtain-
ing such samples is inherent in the data 01 Prystowskyt Hellegers, and Hruns,’ showing that samples taken from the intervillous space occasionally showed pH’s of 7.40 or greater, compatible with those of arterial blood. The first of the above-described cases of Bruns, Cooper, and Drosel’ demonstrates the same phenomenon. This would suggest that where intervillous space samples are obtained an arterial sample should be obtained simultaneously since this would provide a check on the intervillous space sample. In the presence of reasonable uterine blood flows, the absence of a pH difference at term seems improbable. Summary
Data are reported showing that the Van Slyke-Sendroy nomogram is applicable to adult and fetal monkey blood. The fetal oxygen capacity, while slightly higher than the maternal, was not invariably so. The data quantitating the oxygen and carbon dioxide pressure gradients across the placenta are reported. The mean arteriovenous oxygen difference along the maternal surface of the placenta was found to be 3.25 mM. per liter of which approximately 2.4 mM. per liter was ascribed to the fetus and placenta. A comparison of these data and those relating to other species is given. The importance of blood pH determinations in the evaluation of fetal oxygenation has been discussed and emphasized.
REFERENCES 1.
2. 3.
4. 5. 6.
7.
Van Slyke, D. D., and Sendroy, J., Jr.: J. Biol. Chem. 179: 781. 1928. Van Slyke, D. D., and Neill, J. M.: J. Biol. Chem. 61: 523, 1924. Behrman, R. E., Heller, C. J., Battaglia, F. C., and Hellegers, A. E.: Quart. J. Exper. Physiol.. 1963. (In press.) Turnbull, E. P. N.,. and Walker, J.: Arch. Dis. Childhood 30: 102. 1955. Prystowsky, H., Hellegeis, A. E., and Bruns, P. D.: AM. J. OBST. GYNEC. 81: 372, 1961. Battaglia, F. C., Hellegers, A. E.,. Heller, R. E.: AM. T. OBST. & c. J., and Behrman. GY&c., 1963. (In press.) ” Metcalfe, J., Meschia. G., Hellegers, A. E.,
Prystowsky, H.. Huckabee, W.> and Barron, D. H.: Quart. J. Exper. Physiol. 47: 74. 1962. 8. Prystowski, H., Meschia, G., and Barron. D. H.: Yale J. Biol. & Med. 32: 441, 1960. 9. Anselmino. L., and Hoffman, F.:. Arch. Gvnlk. 143: 477. 1930. 10. Barron, D. H., and Battaglia, F. C.: Yale J. Biol. & Med. 28: 197, 1955. 11. Beer, R., Bartels, J., and Raczkowski, H. A.: Pflug. Arch. ges. Physiol. 260: 306, 1955. 12. Prystowsky, H., Hellegen, A. E., and Bruns, P. D.: Surg. Gynec. & Obst. 110: 495, 1960. 13. Vasicka, A., Quilligan, E. J., Aznar, R.,
Volume 88 Number 1
14.
15.
16. 17.
Lipsitz, P. F., and Bloor, B. M.: AM. J. OBST. & GYNEC. 79: 1041, 1960. Quilkigan, E. J., Vasicka, A., Aznar, R., Lipsitz. P. F.. Moore. T.. and Bloor, B. M.: AM. J. ~BST. ‘& GYN&. $9: 1048, 1560. Meschia, G., Prystowsky, H, Hellegers, A. E., Huckabee, W., Metcalfe, J., and Barron, D. H.: Quart. J. Exper. Physiol. 45: 284, 1960. Sjostedt, S., Rooth, G., and Caligara, F.: Arch. Dis. Childhood 35: 529, 1960. Bruns, P. D., Cooper, W. E., and Drose,
Transplacental
18.
19.
20. 21.
transfer
of
0,
and
COr
31
V. E.: AM. J. OBST. & GYNEC. 82: 1079, 1961. Dawes, G. S., Jacobson, H. N., Mott, J. C., and Shelley, H. J.: J. Physiol. 152: 271, 1960. Sutton, J., Schruefer, J. J. P., and Hellegers, A. E.: AM. .I. OBST. & GYNEC. 82: 793, 1961. Barron, D. H.: Yale J. Biol. & Med. 26: 119, 1953. Young, M. T.: Am. J. Physiol. 170: 434, 1952.
E.
HELLEGERS,
CHRISTOPHER RICHARD
E.
FREDERICK Baltimore,
J.
M.D.* HELLER,
BEHRMAN, C.
A.B. M.D.**
BATTAGLIA,
M.D.**
Maryland
N u M E R o u s studies on the transfer of oxygen and carbon dioxide across the placenta have appeared in recent years, particularly across the human placenta and across that of the sheep and the goat. Since the similarity between the anatomical characteristics of the human and the monkey placenta is marked, the present study was undertaken to determine the biochemical and physiological similarities. Determinations of the concentration gradients for physically dissolved oxygen and carbon dioxide not only provide information on the permeability characteristics of that placental type, but also yield information on the oxygen tension in which the fetus develops in utero. Since estimations of oxygen tension were made indirectIy by relating the oxygen saturation and pH in the bloods of the vessels sampled, the data also yielded informa-
tion for the study of acid-base balance across the monkey pIacenta. The present report describes the following: 1. A test of the applicability of the Van Slyke-Sendroy nomogram’ to both maternal and fetal monkey blood. 2. A comparison of maternal and fetal oxygen capacities. 3. The concentration gradient for physically dissolved oxygen. 4. The concentration gradient for physically dissolved carbon dioxide, bicarbonate ions, and hydrogen ions. 5. The arteriovenous differences for total oxygen and total carbon dioxide concentrations on the maternal side of the placenta. Finally, the data in this report are compared with similar data from other species. Materials
From the Departments of GynecologyObstetrics, and Pediatrics, The Johns Hopkins University, Baltimore, Maryland, and the Department of ObstetricsGynecology, University of Puerto Rico. This study was supported in part Research Grant HE-04231 of The National Institutes of Health.
and
methods
All experimental animals were Macaca mulatta monkeys maintained by the National Institutes of Health, Laboratory of Perinatal Physiology, San Juan, Puerto Rico. The animals were mated for a single 24 to 48 hour period during a menstrual cycle and were not remated unless it was determined that mating had not resulted in a pregnancy. Although the natural gestation of Mucaca mulafta has been reported to last about 164 days, the period from the one hundred and fifty-third to the one hundred and fiftyseventh day was arbitrarily chosen for elec-
by
“Senior Research Scholar, ,Joseph P. Kennedy, Jr., Memorial Foundation. **Member of Laboratory of Perinatal Physiology, National Institutes of Neurological Diseases and Blindness, National Institutes of Health, San Juan. Puerto Rico. 22
Volume Number
88 1
tive cesarean section, for fetuses delivered at this age survive and the substantial risk of early vaginal delivery is avoided. Hence, all fetal samples were obtained at cesarean section prior to the onset of labor. Operative procedure was as follows: the pregnant animals, caught with minimum handling, were placed in the dorsal supine position on the operating table, the head end of which was elevated 30 degrees to help obviate pressure of the pregnant uterus on the inferior vena cava. The animals were not starved prior to operation. The upper extremities were tied at a 30 degree angle from the body. It had been previously observed that when the upper extremities were tied in extension above the head, the upper pulmonary lobes were incompletely ventilated. Preoperatively, in those animals, arterial pH’s as low as 7.10 were found, presumably, secondary to the respiratory acidosis. Such animals were not used in these experiments. The left groin and left paramedian area were infiltrated with 2 per cent procaine without epinephrine, a total of about 10 cc. being required. A branch of the left femoral artery was catheterized under direct vision. All maternal arterial samples were drawn from this vessel. The peritoneum was entered through a left paramedian incision. Since most uteri were dextrorotated this incision provided easier access to the left uterine vein without handling the uterus to expose the vessel. The uterus remained in the abdominal cavity throughout the procedure and the placental site was identified by palpation. Amniotic fluid was obtained by transuterine puncture. The choice of the vessel to be sampled as representative of a vein draining the maternal surface of the placenta posed a distinct problem. Repeated attempts to sample the intervillous space yielded only very small aliquots of blood of dubious origin. This may have been due to the fact that, since the monkey placenta is diffuse and the volume of the intervillous space, presumably, is considerably smaller than in the human, the depth of the intervillous pool may make
Transplacental
transfer
of 0,
and
CO*
23
intervillous sampling difficult. For this reason we decided to sample the uteroovarian vein, so that any arteriovenous difference obtained would reflect consumption or production of substances by the entire uterus and its contents. In each animal the uteroovarian vein was sampled only once, by venipuncture. Fig. 1 presents a scheme of the gross anatomy of the venous drainage of the monkey placenta showing the site of sampling. The principal drainage into the uteroovarian vein takes place through an ascending uterine vein coursing along the left anterolateral aspect of the uterus, and a descending uterine vein coursing downward along the left anterolateral margin of the fundus. These lesser vessels were not used in the experiments reported here since sampling either of these vessels entailed the possibility of obtaining blood samples representing varying ratios of myometrial and placental venous blood. Blood gas determinations were performed by the method of Van Slyke and Neill’; pH determinations were done at 38’ C. on the radiometer, Model No. 4 pH meter. Oxygen tensions were obtained from the percentage oxygen saturation and pH using the nomogram of Behrman and co-workers.3 Carbon dioxide tensions were calculated from the Henderson-Hasselbalch equation, assuming a pK of 6.10. All fetal samples were obtained by single venipuncture from a segment of umbilical cord doubly clamped immediately upon delivery. When insufficient fetal blood was available to obtain plasma, the plasma carbon dioxide contents were derived from blood carbon dioxide contents using the Van Slyke and Sendroyl nomogram. The applicability of this nomogram to both adult and fetal monkey blood was tested and the data derived form part of the substance of this report. Inasmuch as no umbilical vein samples were obtained, gas pressure gradients across the placenta were calculated as follows: the carbon dioxide pressure gradient was estimated as the difference between tensions in the umbilical artery and the uterine vein.
24
Hellegers
Jama‘).
et al.
Am. J. Obsr.
1. 1964 R: Gynec.
equation. The final column yields the difference between the two methods of obtaining the carbon dioxide tension. It is thus seen that the Van Slyke-Sendroy nomogram can be applied to adult monkey blood with a mean error of 0.99 (kO.62) and to fetal blood with a mean error of 1.15 (kO.60) mm. Hg.
A comparison of the oxygen capacities of adult and fetal blood. Table III gives the
Fig. 1. Site experiments
of sampling, described in
X, of text.
uterine
vein
for
The oxygen pressure gradient was taken as the uterine vein oxygen tension minus the umbilical artery oxygen tension and, therefore, represents the minimum oxygen pressure gradient across the placenta.
Results Applicability of the Van Slyke-Sendroy nomogram to adult and fetal monkey blood. Table I presents the data testing the applicability of the nomogram to adult blood. Table II presents the corresponding data for fetal bIood. In both tables the first four columns present the data obtained. The figures in Column 5 were derived from the Van Slyke-Sendroy nomogram’ using the data contained in the first three columns. Column 6 presents the difference between measured (Column 4) and derived (Column 5) total plasma carbon dioxide concentrations. These plasma carbon dioxide concentrations were then used to calculate the carbon dioxide tensions given in Columns 7 and 8 by using the Henderson-Hasselbalch
oxygen capacities in simultaneous paired samples of maternal and fetal blood. All fetal samples were obtained at a gestational age of more than 150 days and, therefore, represent values close to term (164 days). The mean maternal oxygen capacity was 15.48 (k2.95) volume per cent. The mean fetal oxygen capacity was 17.77 (21.93) volume per cent. The difference between the two values is statistically significant (p < 0.05). It will also be noted that the fetal oxygen capacity is not in every case higher than the maternal. Table III also gives the hematocrits measured on the same samples as the oxygen capacities. In Columns 5 and 6 hemoglobin values are given for maternal and fetal blood. They have been derived by dividing the oxygen capacity, in volume per cent, by 1.34 and are, therefore, based on the assumption that Hufner’s coefficient is applicable to monkey blood. If this assumption is valid, the maternal and fetal mean corpuscular hemoglobin concentrations are those given in Columns 7 and 8. The difference between these values of 30.7 (&l-57), and 31.3 (k2.52) gram per cent for maternal and fetal blood, respectively, is not statistically significant. The figures closely resemble those for human blood.4
The oxygen concentration gradient across the placenta. Table IV, divided into two parts, presents the data on oxygen contents and concentrations. Group A includes those cases considered to be in good physiological condition. The judgement of the condition of the preparations was based on: 1. Absence of marked distention of the uterine vein suggestive of abnormally high uterine venous pressures.
Volume Number
88 1
Transplacental
2. Uncomplicated surgical procedure with minimal manipulation of the uterus. 3. Delivery of a healthy, vigorous infant through a uterine incision other than transplacental. 4. A pH in all vessels sampled of more than 7.30.
Table I. Data adult
used blood
monkey
Cal. I
Cal.
in testing
2
Cal.
0, Capacity (volume %)
fiH 7.480 7.479 7.454 7.439 7.431 7.390 7.388 7.360 7.324 7.315 7.306 7.424 7.414 7.364 7.439 7.331 7.290 7.236 7.227 7.211 7.104 0.99;
S.D.
3
Cal.
Blood (m%?L.)
19.54 13.81 16.48 14.24 13.31 16.31 20.54 16.71 17.24 11.35 15.29 19.54 16.48 17.60 13.81 14.24 11.35 15.29 17.24 16.31 16.71
*Mean,
applicability
monkey
Col.
PH 7.416 7.389 7.359 7.352 7.342 7.328 7.325 7.224 7.139 7.050 *Mean,
I
Cal.
~rnrn~?~~ 18.61 19.95 19.57 17.66 21.59 la.77 16.60 14.79 12.59 15.98 13.45 20.69 20.52 24.96 22.92 22.40 18.46 la.68 16.52 25.60 19.51
used in testing blood
0, I Capacity (v&m; %)
2
Cal.
3
I Blood CO, fmM./L.)
19.78 17.95 20.17 19.78 20.17 20.17 17.95 17.94 17.24 la.17 S.D.
and
CO,
25
5
Plasma CO, by
Slyke-Sendroy
nomogram
Col.
7
6
A CO, (Cal. 4 minus 5) (mM./L.) - 0.64 + 0.54 - 1.17 - 0.28 - 1.43 - 0.43 - 0.16 - 0.00 - 0.66 - 0.13 -0.11 - 0.44 - 1.02 + 0.73 + 1.01 - 0.86 - 0.26 t 0.75 - 0.47 - 0.62 - 0.22
Cal. PCO, measured (mm.Hg) 23.90 27.32 25.92 25.30 29.87 29.72 26.78 25.59 22.34 30.25 25.95 30.45 30.00 44.06 42.43 39.70 36.69 43.96 37.07 59.62 57.75
Cal.
to
8
Cal.
9*
PCO, by nomogram (mm.Hg)
A PCO, (Cal. 7 minus 8) fmm.Hd
24.75 26.60 27.56 25.70 31.98 30.42 27.04 25.59 23.58 30.50 26.17 31.11 31.57 42.81 40.64 41.33 37.22 42.26 38.15 61.10 58.41
- 0.85 + 0.72 - 1.64 - 0.40 -2.11 - 0.70 - 0.26 - 0.00 - 1.24 - 0.25 - 0.22 - 0.66 - 1.57 + 1.25 + 1.79 - 1.63 - 0.53 + 1.70 - 1.08 - 1.48 - 0.66
f 0.62.
Cal.
1.15;
of Van
17.97 20.49 la.40 17.38 20.16 la.34 16.44 14.79 11.93 15.85 13.34 20.25 19.50 25.69 23.93 21.54 la.20 19.43 16.05 24.98 19.29
15.24 17.39 16.64 15.42 19.02 16.155 13.66 12.72 10.82 14.54 11.78 17.16 17.56 21.69 20.52 20.04 17.00 16.74 14.48 22.92 17.48
of O2
Table IV and subsequent tables, therefore, include the animal number to allow identification of the experiment in this report as well as in the article immediately following it. It will be realized that in some cases sampling of the maternal vessels was performed in accordance with the above criteria
Plasma co, measured (mM./L.)
Table II. Data fetal
4
transfer
13.33 12.54 15.47 16.58 21.97 20.83 14.75 la.12 20.96 18.65 -I 0.60.
.-
applicability
Cal. Plasma co, measured fmM./L.) 15.76 14.58 19.79 19.64 26.83 25.08 17.74 19.86 22.62 20.51
4
of Van
Cal.
5
Slyke-Sendroy
nomogram
Cal.
7
6
Cal.
Cal.
to
8
Plasma CO, by nomogram fmM./L.)
A CO, (Cal. 4 ~minus 5) (mM./L.J
PCO, measured (mm. HeI
PCO, by nomogram (mm. He)
16.17 14.87 18.67 19.78 25.92 24.66 17.20 20.57 23.26 20.92
- 0.41 - 0.29 + 1.12 - 0.12 + 0.51 t 0.42 f 0.54 -0.71 - 0.64 - 0.41
24.13 23.67 34.30 34.58 48.26 46.53 33.16 46.19 63.01 68.82
24.76 24.14 32.36 34.79 46.62 45.75 32.15 47.84 64.79 70.20
Cal.
9s
A PCO, (Cal. 7 minus 8) (mm. He) + + t + -
0.63 0.47 1.94 0.21 1.64 0.78 1.01 1.65 1.78 1.38
26
Hellegers
et
Table III. corpuscular
al.
Oxygen capacity, hematocrit, hemoglobin, hemoglobin values for maternal and fetal
Cd. 1
Cd.
cd.
2
3
i
cd.
and mean blood
4
Cd.
51
02 Capacity, fetal (volume %)
O2 Capacity, maternal (volume %)
Mean S.D.
14.92 18.35 19.80
15.48
17.77
39.5
_C
2.95 applicability
of
Table
Oxygen
pressure
IV. Cal.
1
1.72
1.93
*Assuming C.C. oxygen.
Hufner’s
Cal.
coefficient:
I:: -__ -__
7.7 12.5 14.6 8.6 10.9 11.4 12.3
11.0 13.4 12.9 11.9 12.4 15.0 14.8 13.4 14.0 ----_ ___ 11.1 13.7 14.8
28.6 33.0 31.6 29.7 30.8 31.2 30.7 27.6 --30.8 32.4 ----31.3 ---
34.3 33.8 27.9 ‘9.8 30.2 29.0 34.3 31.0 _ ~-_-----------
41.2
12.0
13.3
30.7
31.3
gradients
2
Cal.
i
1
8.5
4.38
1 Gm.
fully
2.20
oxynenatcd
Cal.
1.42
hemoglobin
across the monkey 3
__--Cal. 8”~~. Mean corpuscular hemoglobin concentration, fetal (gram O/0)
10.4 12.9 12.2 12.8 15.3 13.1 10.3
32.0 39.5 46.0 40.0 41.0 45.0 43.0 43.2 ___ -__ ---
36.2 39.0 38.5 43.0 49.8 42.0 33.5 30.6 _-40.5 45.0 ----36.4 ---
7*
Hemoglobin, fetal (gram To)
Hematocrit, fetal (9’0)
14.72 17.92 17.23 15.97 16.61 20.16 19.77 17.94 19.02 -----
Cal.
Hemoglobin, maternal (gram %)
Hematocrit, maternal (%)
13.89 17.23 16.31 17.09 20.56 17.5% 13.80 11.33 10.35 16.71 19.53 11.47 14.65 15.28 16.49
6”
Mean carpuscular hemoglobin concentration, maternal (gram %)
I
_----
Cal.
when
exposed
1.57 to air
combines
Cal.
6
2.52 with
1.34
placenta 4
-___Cal.
5
Col.
7
Uterine
Maternal artery oxygen .raturation /%I
Animal No. Group
Uterine vein 0, saturation f%)
pH
Umbilical artery 0, saturation f%)
veinumbilical
fiH
Uterine vein PO, (mm. Hg)
Umbilical artery PO, (mm. Hg)
artery
pressure gradient
A
v 195 X 692 x 590 Q 200
97.18 91.87 99.08 98.82
40.08 44.85 58.02 53.50
7.331 7.319 7.357 7.364
40.94 29.87 30.63 43.00
7.303 7.325 7.318 7.342
26.1 28.1 32.1 30.0
15.7 12.6 13.0 15.4
10.4 15.5 19.1 14.6
Mean Sipificant difference
96.74
49.11
7.343
36.11 6.54
7.322 0.016
29.07 2.57
14.18 1.60
14.9
v 798 Q 192 H 220 I. 242
96.43 91.81 97.60 90.90
48.54 61.64 64.49 25.80
7.349 7.227 7.329 7.067
10.70 22.89 22.96 6.90
7.258 7.224 7.050 6.842
28.5 40.1 37.0 29.3
8.5 12.8 16.1 12.5
20.0 27.3 20.9 16.8
Mean
94.19
50.12
7.243
15.86
7.094
33.73
12.48
21.25
8.32
0.191
5.72
Group
C
B
S. D.
+
3.12
0,
Volume Number
88 1
Transplacental
for a good preparation, whereas difficulty might have occurred in delivery of the fetus. In such cases the preparation is listed as good only for description of data relating to maternal blood. The uterine vein oxygen tension in all preparations was of the order of 30 mm. Hg irrespective of the oxygen saturation of the blood in these vessels. At relatively constant PO,, the oxygen saturation in the uterine vein varied directly with the pH, being lowest where the pH was lowest. This is best
Table V. Carbon Cal. I
dioxide
Cal.
Animal No.
pressure
2
Cal.
Femoral artery plasma CO, (mM./L.)
Uterine vein plasma CO, (mM./L.)
gradients
transfer
ot 0,
and
CO,
seen by comparing Animal X 590 with L 242. The PO,‘s were virtually identical (32.1 versus 29.3) and yet the oxygen saturations were strikingly different (58.0 per cent versus 25.8 per cent) due to the marked pH difference (7.357 versus 7.067). This same relationship of widely different oxygen saturations occurring at approximately the same PO, was seen most dramatically in the fetal circulation. The umbilical arterial oxygen tension, like that in the uterine vein, was fairly constant in all preparations,
across the monkey
3
Cal.
pH
Umbilical artery plasma CO, (mM./L.)
4
placenta
Cal.
5
Col.
6
Cal.
pH
Uterine vein PCO, (mm. Hg)
Umbilical artery PCO, (mm. Hg)
A 195 692 590 200
17.38 16.88 20.43 20.16
21.54 21.45 22.91 25.69
7.331 7.319 7.357 7.364
23.72 22.45 23.85 26.83
7.303 7.325 7.318 7.342
39.70 44.36 39.91 44.06
46.51 44.90 45.26 48.26
6.81 0.54 5.35 4.20
Group v Q H X Q
B 798 192 220 706 178
20.49 11.93 16.44 13.34 18.34
23.93 16.05
7.349 7.227 7.329 7.236 7.211
25.06 19.86 20.51 21.75 22.62
7.258 7.224 7.050 7.246 7.139
40.64 37.07 37.15 43.96 59.62
54.12 46.19 70.03 48.12 63.01
13.48 9.12 32.88 4.16 3.5
Table VI. Maternal carbon
uterine contents
dioxide
arteriovenous
differences
of oxygen
*
and
Carbon Column
Oxveen
7
Umbilical artery uterine vein PCO, (mm. Hg)
Group v X x Q
19.43 24.98
27
4
dioxide Column
5
Column
.I
Column
1
Column
2
Column
3
Uterine
Maternal artery
20.04 20.42 20.29 16.86
15.42 16.33 17.80 13.66
22.92 17.48
16.16 12.72
Animal identification No. v 195 X 692 x 590 H 220 Mean
6.03 7.01 6.48 8.96
v Q x
8.46 6.59 6.93
191 178 292
7:4:9 7.424 7.415 7.388
7.480 7.390 7.360
2.49 3.42 3.67 5.92
7.65 0.68 2.17
PH 7.331 7.319 7.357 7.329
7.424 7.211 7.104
3.45 3.59 2.81 3.04 3.25 0.81 5.91 4.76
t 0.38
4.62 4.09 2.49 3.20 3.60 Macerated 6.76 4.76
t 0.95 fetus
6
28
Hellegers
Jmua,\ I. 1964 .\m. .I. Obat. & Gynec
et al.
approximately 14 mm. Hg. Yet despite the constancy of the PO,, the animals in Group B had significantly lower oxygen saturations (p< 0.05) than the animals in Group A due to the lower pH’s of the Group B animals. The major differences between animals in Groups A and B, therefore, lie in the oxygen saturations and pH’s. The lower oxygen saturations, representing a decrease in the oxygen reserves of the fetuses involved, illustrate the fact that the oxygen pressure gradient alone did not yield a satisfactory indication of the oxygenation of the fetus. The oxygen pressure gradients in the Group B animals are if anything steeper than those in Group A animals. .Yet the fetal acidosis in some animals (e.g., L 242)) was severe enough to lower the oxygen affinity of the hemoglobin to near zero at a normal fetal PO,, i.e., 14 mm. Hg. The values of the umbilical arterial oxygen tension, said to be most representative of the oxygen tension in which the fetus develops, are considerably lower than those to which adult tissues are exposed but they are in striking agreement with those reported for all other fetal species.
The carbon dioxide concentration gradient acrossthe placenta. Table V presents the carbon dioxide concentration gradient between the umbilical artery and the uterine vein. In Group A animals the plasma carbon dioxide concentration in the umbilical artery (Column 4)) closely approximates that in the uterine vein. In all cases but one the fetal carbon dioxide contents and carbon dioxide tensions were slightly higher than in the maternal values. Only in Animal Q 178 was the plasma carbon dioxide content in the umbilical artery lower than in the maternal vein. There is close agreement between the carbon dioxide concentration gradient in this species and that reported in the human by Prystowsky, Hellegers, and Bruns.6 The very high fetal PCO,‘s in Animals H 220 and Q 178 occurred as a result of difficulty encountered in the delivery of the fetus necessitating transection of the placenta. The CO, pressure gradient across
the placenta arations.
was increased
in the bad prep-
Arteriovenous differences of oxygen and carbon dioxide contents along the maternal surface of the placenta. The arteriovenous differences of oxygen and CO, are presented in Table VI. The animals in Group A had a mean artery-vein (A-V) difference in oxygen contents of 3.25 mM. and vein-artery (V-A) difference in carbon dioxide contents of 3.60 mM. per liter. In animals in Group B (Q 178 and X 292) the A-V differences were considerably larger. In both these cases the oxygen contents in the uterine vein were the lowest of the entire series, as were the pH’s. Both cases showed distention of the uterine vein, giving it the appearance of a varicosity. Hence, the values in both preparations probably represent examples of A-V differences with decreased blood flow along the maternal surface of the placenta. This is also reflected in the fact that these animals had the highest A-V glucose concentration diff erencesG In one animal an identical experiment was carried out in the presence of a fetus which had been dead for more than thirty days. The A-V oxygen difference in that preparation was 0.8 mM. per liter and represents predominantly the oxygen consumption by the uterus. If the oxygen consumption by the uteri themselves in the other preparations were of the same order of magnitude, the A-V oxygen difference due to uterine contents, alone, would be of the order of 2.4 mM. per liter. Comment
The applicability of the Van SlykeSendroy nomogram to adult and fetal monkey blood is evidence that the distribution of bicarbonate between the red cell and the plasma in human and monkey blood is similar. The minor differences found may be in part explained by the fact that the BohrHaldane effect in adult and fetal monkey blood differs from that in adult human blood.3 The magnitude of this effect in the fetal and maternal blood of the monkey is similar to that in fetal human blood.
Volume Number
88 1
Transplacental
transfer
of 0,
and
CO,
Unfortunately no data on this aspect are available. In the present report the oxygen saturations in the umbilical artery vary widely between the Group A and Group B animals, despite a relatively constant oxygen tension. Fig. 2 illustrates this variation. Three isobars are drawn at PO,‘s of 17, 14j and 12 mm. Hg, respectively, using the data of Behrman and associates3 for fetal monkey blood. Along each isobar one can determine the change in oxygen saturation for a given change in PH. PO,‘s of 12 to 17 mm. Hg represent the range found in fetal umbilical artery samples. A POz of 14 mm. Hg represents the mean oxygen tension of the cases. At this tension a fall in fetal pH from 7.40 to 6.80 would so decrease the oxygen affinity of fetal monkey red cells as to cause the saturation to fall from 42 per cent to 7.9 per cent. The reasons for the difference between oxygen saturations reported here for umbilical artery blood and those reported by Dawes and co-workers18 for fetal femoral artery blood cannot be determined in the absence of either simultaneous pH or PO, measurements accompanying those oxygen saturations. It will be noted from Table V that with respect to the bicarbonate and physically
The Van Slyke-Sendroy nomogram is ap plicable to monkey blood unless the buffering capacity of the red cells in this species is markedly different than in the human. The present report offers evidence that if Hufnefs coefficient is applicable to monkey blood the mean corpuscu1a.r hemoglobin concentrations in the red cells of human and monkey blood would be identical. This is, of course, consistent with the applicability of the Van Slyke-Sendroy nomogram. A comparison of the oxygen capacities of maternal and fetal monkey blood reveals significant differences from the human. The monkey’s fetal oxygen capacity is not invariably higher than the maternal, as it is in the human. In this respect the monkey more closely resembles the sheep7 and the goats than the human9 Thus, while the fetuses of many species develop in the same environment of low oxygen tension,T* 8* lo-l1 they do not all respond to this diminished oxygen tension with an elevated oxygen capacity. This elevation then, is not a universally required adaptation to the low oxygen tension. In comparing fetal blood of the monkey and the human, the similarity in the mean corpuscular hemoglobin concentration and the difference in oxygen capacities suggest that the red blood cell count in the monkey fetus would be lower than in the human.
PO, 17
. ,/
O6!8
29
I 6.9
I
10
/
PO,14
I
I
I
I
1.2
7.3
7.4
pH to percentage PO*‘s.
-
42.0%
-
1.9%
PO* 12
1.1
PH Fig. 2. Plot relating saturation at various
.
30
Hellegers
et al
dissolved carbon dioxide concentrations, the monk(,)- data closely resemble those reported for the human. The data of the table support the concept previously documented that in good preparations the pH, bicarbonate, and dissolved carbon dioxide gradients across the placenta are small.“, I73 ‘K 2ogz The data on arteriovenous oxygen differences reported here are difficult to compare with those reported in the human due to the fact that we have sampled the uterine vein, while, in the human, samples were obtained from the intervillous space. In Animal V 191, in which the fetus had been dead for several weeks, the arteriovenous oxygen difference was 0.8 mM. per liter. Assuming that this difference represents predominantly consumption of oxygen by the uterus, itself, an arteriovenous oxygen difference of 2.4 mM. per liter would be accounted for by the consumption of the fetus and placenta, alone (3.2 minus 0.8). This figure is in good agreement with those reported by Bruns and co-workers,17 who, excepting the first of their cases, found the mean arteriovenous difference between arterial blood and intervillous space blood to be 1.9 mM. per liter in their normal cases. The problem of representative intervillous space samples referred to in methods stems from the difficulty of determining the proximity of the sampling needle to spurts of arterial blood delivered into the intervillous space by arterioles. The possibility of obtain-
ing such samples is inherent in the data 01 Prystowskyt Hellegers, and Hruns,’ showing that samples taken from the intervillous space occasionally showed pH’s of 7.40 or greater, compatible with those of arterial blood. The first of the above-described cases of Bruns, Cooper, and Drosel’ demonstrates the same phenomenon. This would suggest that where intervillous space samples are obtained an arterial sample should be obtained simultaneously since this would provide a check on the intervillous space sample. In the presence of reasonable uterine blood flows, the absence of a pH difference at term seems improbable. Summary
Data are reported showing that the Van Slyke-Sendroy nomogram is applicable to adult and fetal monkey blood. The fetal oxygen capacity, while slightly higher than the maternal, was not invariably so. The data quantitating the oxygen and carbon dioxide pressure gradients across the placenta are reported. The mean arteriovenous oxygen difference along the maternal surface of the placenta was found to be 3.25 mM. per liter of which approximately 2.4 mM. per liter was ascribed to the fetus and placenta. A comparison of these data and those relating to other species is given. The importance of blood pH determinations in the evaluation of fetal oxygenation has been discussed and emphasized.
REFERENCES 1.
2. 3.
4. 5. 6.
7.
Van Slyke, D. D., and Sendroy, J., Jr.: J. Biol. Chem. 179: 781. 1928. Van Slyke, D. D., and Neill, J. M.: J. Biol. Chem. 61: 523, 1924. Behrman, R. E., Heller, C. J., Battaglia, F. C., and Hellegers, A. E.: Quart. J. Exper. Physiol.. 1963. (In press.) Turnbull, E. P. N.,. and Walker, J.: Arch. Dis. Childhood 30: 102. 1955. Prystowsky, H., Hellegeis, A. E., and Bruns, P. D.: AM. J. OBST. GYNEC. 81: 372, 1961. Battaglia, F. C., Hellegers, A. E.,. Heller, R. E.: AM. T. OBST. & c. J., and Behrman. GY&c., 1963. (In press.) ” Metcalfe, J., Meschia. G., Hellegers, A. E.,
Prystowsky, H.. Huckabee, W.> and Barron, D. H.: Quart. J. Exper. Physiol. 47: 74. 1962. 8. Prystowski, H., Meschia, G., and Barron. D. H.: Yale J. Biol. & Med. 32: 441, 1960. 9. Anselmino. L., and Hoffman, F.:. Arch. Gvnlk. 143: 477. 1930. 10. Barron, D. H., and Battaglia, F. C.: Yale J. Biol. & Med. 28: 197, 1955. 11. Beer, R., Bartels, J., and Raczkowski, H. A.: Pflug. Arch. ges. Physiol. 260: 306, 1955. 12. Prystowsky, H., Hellegen, A. E., and Bruns, P. D.: Surg. Gynec. & Obst. 110: 495, 1960. 13. Vasicka, A., Quilligan, E. J., Aznar, R.,
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Lipsitz, P. F., and Bloor, B. M.: AM. J. OBST. & GYNEC. 79: 1041, 1960. Quilkigan, E. J., Vasicka, A., Aznar, R., Lipsitz. P. F.. Moore. T.. and Bloor, B. M.: AM. J. ~BST. ‘& GYN&. $9: 1048, 1560. Meschia, G., Prystowsky, H, Hellegers, A. E., Huckabee, W., Metcalfe, J., and Barron, D. H.: Quart. J. Exper. Physiol. 45: 284, 1960. Sjostedt, S., Rooth, G., and Caligara, F.: Arch. Dis. Childhood 35: 529, 1960. Bruns, P. D., Cooper, W. E., and Drose,
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0,
and
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V. E.: AM. J. OBST. & GYNEC. 82: 1079, 1961. Dawes, G. S., Jacobson, H. N., Mott, J. C., and Shelley, H. J.: J. Physiol. 152: 271, 1960. Sutton, J., Schruefer, J. J. P., and Hellegers, A. E.: AM. .I. OBST. & GYNEC. 82: 793, 1961. Barron, D. H.: Yale J. Biol. & Med. 26: 119, 1953. Young, M. T.: Am. J. Physiol. 170: 434, 1952.