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Uterine blood flow and 02 consumption following fetal death in sheep
FETUS, PLACENTA, AND NEWBORN Uterine blood flow and 02 consumption following fetal death in sheep JOHN
R.
RAYE
A.
P.
KILLAM
F.
C.
BATTAGLIA
E.
L.
MAKOWSKI
G.
MESCHIA
Denver,
Colorado
Uterine blood POWS and 01 consumptions were compared before and after fetal death in 9 unanesthetized pregnant ewes in the last month of gestation. Fetal death was produced by the injection of a bolus of air in a fetal pedal vein. Uterine blood flow did not change significantly in the first hour following fetal death. Afterward, there was a slow decline of the uterine blood flow to approximately 70 per cent of the control value at 24 hr. The abrupt removal of fetal metabolism produced a large drop in uterine 08 consumption. This drop was more pronounced late in pregnancy in agreement with previous data showing that the fraction of the total uterine 0, consumption which is fetal is related to fetal size.
T H E B L 0 0 n F L 0 W t0 an organ iS controlled by many stimuli which may originate within the organ itself (local regulation) or elsewhere in the body (extrinsic regulation). For example, the blood flow to skeletal muscle is controlled by local metabolic demands as well as by neurogenic and humoral fact0rs.l Previous studies of uterine blood flow in pregnancy have clarified some of the characteristics of extrinsic regulation of uterine flo~.~-~ However, there is no information concerning the degree of local regulation
of uterine blood flow. More specifically, there is no information concerning the acute effects upon uterine blood flow of sudden fetal death. The suggestion made by Dawes6 that, “qualitatively the reactions of uterine vasculature are similar to those of the vascular beds of skeletal muscle and the abdominal viscera,” is based on pharmacologic evidence about the effect of extrinsic stimuli on uterine blood flow. The experiments reported in this paper were designed to compare uterine 0, consumption and blood flow before and after fetal death in unanesthetized, pregnant ewes in the last 35 days of pregnancy.
From the Division of Perinatal Medicine and the Department of Physiology, University of Colorado Medical Center. Supported by United Health Service Grants HD 01866.
States Public HD 00781
Materials
and methods
The animal preparation. Fig. 1 presents a diagram of the preparation used in this
and 917
918
Raye
et
Fig. 1. Diagram study.
al.
of the preparation
used in this
study. This consisted of: ( 1) external square wave electromagnetic flow probes implanted over both uterine arteries, and (2) polyvinyl catheters inserted in a fetal pedal artery, a fetal pedal vein, the amniotic sac, a maternal femoral artery, and one of the two uterine veins. The catheterized uterine vein was the one draining the pregnant horn. Preparation for operation and anesthesia were as previously described.? The flow probes (4.0 or 5.0 mm. in diameter) were implanted via a bilateral, extraperitoneal approach. With the ewe in the supine position, the infraperitoneal space on each side was entered through a 10 cm. incision in the lower abdomen, parallel to the inguinal ligament. The incision was carried down through the fascia of the external oblique by sharp dissection; then the uterine artery was reached by blunt dissection in the retroperitoneal area, recognized by palpation. and delivered into the operative field. A 0.5 cm. portion of the artery was freed of surrounding tissue, and the head of the probe was placed around the artery. After replacement of the artery in its natural the fascial plane was repaired position, around the leads of the probes. The leads were brought out through the flank of the animal by a subcutaneous tunnel and stored in a canvas pouch anchored to the skin.
Eittier 4n~llltancously with inrphtatioli of the flow I)robcs or several days later: polyvinyl catheters (inside diameter 0.58 mm., outside diameter 1 .2 mm. ,! were placed in the maternal and fetal blood vessels and the amniotic sac by techniques previously described.‘, S In twin pregnancy the pedal arteries and veins of both twins were cathr:terized. After operation, the ewes were returned to the animal quarters where they received food and water ad libitum. Antibiotics (procaine penicillin, 600,000 U.? and streptomycin, 0.5 Gm.) were given intramuscularly on the first 3 postoperative days. Experimental protocol. All experiments were performed on awake, nonanesthetized ewes brought to the laboratory from 2 to 7 days after the last surgical procedure. During the experiment, the ewes were standing in a rectangular crate and had free access to food and water. For one hour preceding and one hour following fetal death (control and experimental periods, respectively), the following variables were measured continuously : ( 1) blood flow in one uterine artery, (2) maternal arterial blood pressure, and (3) amniotic pressure. Fetal blood pressure was measured continuously in the control period and in the initial phase of the experimental period. The selection of the uterine artery to be monitored continuously was on the basis of greater flow and/or good quality of the electrical signal. The flow through the other uterine artery was measured at the beginning of the control period, at the end of the experimental period, and at intervals thereafter. During both the control and the experimental periods, blood samples were drawn simultaneously from the maternal femoral artery and the uterine vein at 12-min. intervals for a total of 5 sets of determinations in each period. Each sample consisted of 2 ml. of blood drawn in a glass syringe whose dead space had been filled with heparinized saline and 0.3 ml. of blood drawn in a dry heparinized glass capillary tube containing 0.3 mg. of NaF. The blood in the syringe
Volume Number
Uterine
111 7
Fig. 2. Fetal of
injection
arterial pressure, of air in-Fetus
maternal arterial No. 71-001-l.
was analyzed for PO*, PcoZ, and pH. The blood in the capillary was analyzed for total 0, content. The lamb (or lambs in case of twins) was killed by injection of 20 to 50 ml. of air into the pedal vein catheter. The death of the fetus was confirmed by observing the fall in fetal arterial pressure and the cessation of fetal pulse. In 4 animals, following the one-hour experimental period, amniotic and maternal arterial pressures and the blood flows through both uterine arteries were measured for intervals of 30 minutes at various times up to 26 hr. The ewes were then killed. The uterus and fetus were removed and weighed. Analytical methods. The maternal arterial blood pressure was measured with a pressure transducer positioned at the level of the maternal heart. The pressure transducer measuring fetal blood pressure was positioned to read zero pressure when connected with the amniotic catheter. The fluctuations of the maternal pressure and flow signals during the cardiac cycle were electronically integrated before display on the recorder (halftime of the response to step change in flow was 3.3 sec.). The PO*, PcoZ, and pH were measured at 39.5O C. as described previously.7 Total 0, contents were measured on a Beckman GC-2A chromatograph equipped with blood gas extraction accessory, a 5 A molecular sieve, and silica gel parallel column. In each experiment, the following mean
pressure,
blood
and
flow and 02 consumption
uterine
arterial
flow
at the
919
time
values were calculated : ( 1) mean uterine blood flows in the control and the experimental periods (F,,, and Fexp), calculated by averaging the flow recorded each 100 sec.; (2) mean arterial and uterine venous Po2, PcoZ, and pH in the control and experimental period; (3) mean uterine arterialvenous differences of 0, content in the control and the experimental period (aO,~0, ) con and (aO,-v0,) exp. The mean flows and the arterial-venous differences were then used to estimate: (1) the variation of uterine blood flow in the experimental period as a fraction of the control period : variation
F of flow = --% F
;
VI
eon
and (2) the variation of uterine 0, sumption in the experimental period fraction of the control 0, consumption: +oz
..,fio,
con =
F f
con
x
( a02-v02)
exp.
(aOrv0,)
e0n
conas a
PI
Differences between the control and the experimental periods were tested for statistical significance by the t test for paired samples. Results
Variations of uterine blood flow with fetal death. Fig. 2 presents the data for fetal arterial pressure, maternal arterial pressure, and uterine blood flow at the time of the
920
et al.
Raye
I
02
I
I,
4
I
I
TIME
Fig. 3. Uterine blood ing fetal death. The measured in the first of individual 30 min. the 4 animals.
I
I
I
I,,
,
,
88lOl2l416i820222426 (hours)
flows expressed as percentages of the control value in the hours foilowsymbol at time 30 minutes represents the mean + 1 S.D. of the flows hour. The remaining symbols represent means and range of variation measurements in 4 animals. Different symbols were used for each of
Table I. Comparison of mean blood flow through one uterine artery in the control period (the hour preceding fetal death) and in the experimental following fetal death)
period (the hour -.
Fetal age (days)
Sheep No.
70-012-l 70-003-2” 70-020-l 71-001-l 71-007-l 71-010-l 71-009-l 71-037-l 71-041-l *One
Fetal weight (Kg.)
141 134 129 143 134 112 112 119 138
3.30 2.50 3.10 2.50 4.10 1.45 1.71 2.37 4.34
pow
F con (mUmin.)
F ew (mUmin.)
816 787 426 408 648 143 154 304 608
825 752 372 426 690 162 164 328 560
F.w/F,cm
1.01 0.96 0.87 1.04 1.06 1.13 1.06 1.08 0.92 ix-
of twins.
injection of air in Fetus No. 71-001-l which is representaive of the group as a whole. It is clear from this example that fetal death had no immediate effect on uterine blood flow. The comparison of mean uterine blood flows in the control and experimental onehour periods also showed no significant effect of fetal death on uterine blood flow. This comparison for all 9 animals studied is shown in Table I. In order to determine whether
Blood
there
was any trend
within
the one-
hour period following fetal death, this hour was divided into 3 twenty-minute subperiods, and the flows in each period were compared. According to this comparison, the uterine flow in the first 20 min. rose 4 per cent above the control value and then fell 2 per cent below the control value at the 40 to 60 min.
period.
The
6 per cent
difference
between these two periods was statistically significant (P
3 illustrates
the
fact
that
uterine
Volume Number
111 7
Uterine
blood
flow and 02 consumption
921
Table II. Comparison of PO,, PcoZ, and pH in the uterine arterial and venous blood of 9 ewes during the control period (the hour preceding fetal death) and the experimental period (the hour following fetal death). Each set of numbers is the mean and standard error of 9 observations Arterial Period
Control Experimental *Significantly
(mm.
Hg)
75.8 I! 2.1 75.0 f. 1.9 different
from
blood
Venous
PCOl (mm. H.d
Pot
Pot M-f
31.4+ 0.7 32.6 + 0.7 the
control
(paired
(mm.
7.53 + 0.01 7.52 2 0.01 samples
analysis,
H.4
45.5 2 1.3 58.8* t 2.0
blood
PCOl (mm. Hg.)
#H
35.9 2 0.9 34.1” k 0.8
7.49 r 0.02 7.52* + 0.01
P < 0.01).
Table III. Mean arterial 0, contents and arterial-venous differences of 0, per liter of blood across the pregnant uterus in the control period (the hour preceding fetal death) and in the experimental period (the hour following fetal death). The last column shows the uterine 0, consumption after fetal death as a fraction of the control value Sheep No.
70-012-l 70-003-2 70-020-l 71-001-l 71-007-I 71-010-l 71-009-l 71-037-l 71-041-l
(aOz
5.88 4.75 4.65 5.64 7.00 6.01 5.17 6.25 4.83
- ~OS),,, (mM)
(aOz
1.22 1.25 1.56 1.15 1.70 1.42 1.56 1.21 1.26
flow did fall gradually in the following 26 hr. to approximately 70 per cent of the control value at 24 hr. Throughout this period, there were no significant changes in intraamniotic pressure or in maternal arterial pressure. Variations of uterine venous Paz, Pcoz, and pH with fetal death. In the experimental period following fetal death, the uterine vein PO, rose 13 mm. Hg, the Pcoz fell 1.8 mm. Hg, and the pH rose 0.03 U. These changes are summarized for the 9 animals in Table II. Variations of uterine 0, consumption with fetal death. In each experiment, fetal death caused a substantial rise of the 0, content in the uterine vein and narrowed the arterial-venous difference of 0, content across the uterine circulation to approximately one third of the normal value (Table III). These changes in arterial-venous differences were used to compute the fall in
- ~OZ),,, (mM)
0.35 0.31 0.59 0.36 0.57 0.67 0.57 0.56 0.28
co*,.
ire*,,,
0.29 0.24 0.33 0.33 0.36 0.53 0.39 0.50 0.20
uterine 0, consumption that followed the abolition of fetal metabolic demands. The calculations were made by means of Equation No. 2 and are presented in Table III. Comment
The results presented in this paper show that the abrupt removal of fetal metabolism produces a large drop in total uterine 0, consumption. The relative magnitude of this drop will depend upon the relative magnitudes of fetal and nonfetal” uterine 0, uptakes prior to fetal death and also on the possible effect that the interruption of the umbilical circulation might have on placental metabolism. These considerations raise two interesting questions, namely: (1) What fraction of the total uterine consumption is nonfetal? (2) Is the relative drop of uterine 0, uptake after fetal death comparable to *In this paper we designate BS nonfetal 0s uptake the 02 coasurnption of placenta, endometrium, and myometrium.
922
Raye
et al
* MESCHIAetal. CASTPSELL et al. . PRESENT STUDY
.25 t
L
1
2
3
4
5
FETAL WEIGHT (Kg. )
Fig. 4. The weight. The 10, and 11. second-order
fraction of total uterine 0, consumption which is nonfetal is plotted against fetal data labeled Meschia et al. were calculated from data published in References 0, The data of Campbell et al. were from Reference 12. The line was computed by regression analysis.
this fraction? In order to provide an answer to these questions we have collected and analyzed the pertinent data in the literature. The results of this analysis are presented in Fig. 4. In this figure the fraction of total uterine 0, consumption which is nonfetal is plotted against fetal weight. The black dots represent data obtained by measuring simultaneously uterine and umbilical blood flows and uptakes by the method of Meschia and coland associates91 I1 and Battaglia leagues.lO The open circles represent data obtained by ventilating the fetal lungs in utero after severing the maternal aorta and measuring fetal 0, uptake before and after cord occlusion.12 Finally, the crosses represent the data collected in the present series of experiments. It is apparent from the graph that there is substantial agreement in the results obtained by these three very different techniques. This agreement suggests the following two inferences : (1) Myometrial 0, consumption (in the absence of uterine contractions) is probably a small fraction of the total because the nonfetal 0, uptakes measured by Campbell and coworker9 did not include the myometrial fraction and yet are not systematically lower than the uptakes measured by the other two methods. This interpretation is further
strengthened by the fact that late in pregnancy the myometrium receives only 3 per cent of the total uterine blood flow.13 (2) In the first hour following fetal death, placental and endometrial 0, consumptions continue at approximately the control levels. This inference is based on the fact that the nonfetal fractions of 0, uptake measured over the first hour following fetal death in this study are similar to those measured in the intact preparation. Fig. 4 demonstrates that the nonfetal fraction of uterine 0, consumption is inversely related to fetal weight. Early in pregnancy, the largest fraction of the uterine 0, consumption is nonfetal. By the time the fetus weighs 1.7 kilograms, the fetal and nonfetal tissues consume approximately equal amounts of 0,. Then, as the fetus grows larger, fetal 0, uptake becomes the larger fraction of the total uterine uptake. The older fetus represents a larger fraction of the total uterine weight than the younger fetus (as can be seen in Fig. 5). Thus, it may seem reasonable that the older fetus should consume a larger fraction of the total uterine 0, uptake. However, the fetus depends upon the placenta for its nutrition, and there is reason to believe that the placental transport of some nutrients (e.g., amino acids) may
Volume Number
111 7
involve active transport mechanisms. Consequently, it is not obvious why the 0, consumptions of fetal and nonfetal tissues do not grow proportionally. The shift in the distribution of 0, consumptions within the pregnant uterus that takes place during gestation implies that the growth curves of total uterine 0, consumption and fetal 0, consumption are quite different. For example, if one assumes that fetal 0, consumption increases approximately fourfold when the fetus grows from 1 to 4 kilograms, one can calculate from the data in Fig. 4 that total uterine 0, consumption in the same period of growth would only increase twofold. The remainder of the total 0, consumption would be accounted for by the redistribution of O? uptakes within the pregnant uterus. The experiments described in this paper clearly demonstrate the absence of acute changes of uterine blood flow following the removal of fetal metabolic demands. The absence of an acute response is particularly significant in late pregnancy when fetal death reduces uterine 0, consumption to approximately one fourth of the normal value. This observation corroborates the hypothesis that acute changes of partial pressure of 0, have no appreciable effect on placental perfusion. The other experimental observations in favor of this hypothesis are as follows: ( 1) The blood flow to the pregnant uterus does not rise above control values after the temporary occlusion of the maternal aorta (absence of reactive hyperemia). We have verified this phenomenon, originally described by Greiss,4 in nonanesthetized pregnant animals, subjected to aortic occlusion for as long as two minutes.14 (2) Maternal inhalation of 100 per cent 0, does not change uterine blood flow significantly.lOT I5 This observation was also confirmed in nonanesthetized animals.14 (3) Moderate maternal hypoxia in nonanesthetized sheep does not change uterine blood flow significantly.14
REFERENCES
1.
Barcroft! H.: In Handbook of Physiology, Circulation, Washington, D. C., 1963, sec. 2, vol. 2, chap. 40, American Physiological Society, pp. 1353-1385.
Uterine
blood flow and 02 consumption
923
* MESCHIA et (11. 1 PRESENT STUDY
GESTATIONAL
AGE
(days)
Fig. 5. The fraction of total uterine weight which is nonfetal is plotted against fetal age. The data labeled Meschia et al. were obtained in the course of other studies (References 9, 10, and 11).
According to Dilts and associates,le severe hypoxia does induce a significant fall of uterine blood flow. However, it is likely that this fall is secondary to the release of catecholamines in the maternal circulation rather than the direct effect of hypoxia on the uterine vasculature. Although fetal death has no immediate effect on uterine blood flow, there is a gradual constriction of the uterine vascular bed following fetal death. This phenomenon is difficult to interpret at this time. It could represent the release of vasomotor substances from degenerating tissues within the uterus. On the other hand, it could represent the effect of a gradual decline in the concentration of substances, such as estrogens, which are known to have a vasodilating effect on the uterine vasculature and whose synthesis is partially under fetal contro1.l’ The existence of chronic regulatory mechanisms of uterine blood flow in pregnancy mediated by extrinsic and local factors is indeed probable but is yet to be tested by appropriate experimental techniques.
2. 3.
Ahlquist, R. P.: J. Am. Pharm. Assoc. 39: 370, 1950. Ladner, C., Brinkman, C. R., III, Weston, P., and Assali, N. S.: Am. J. Physiol. 218: 257, 1970.
924
4. 5. 6.
7. 8.
9.
10.
11.
Raye
et al.
Greiss, F. C.: AM. .I. OBSTET. GYNECOI.. 96: 41, 1966. Greiss, F. C., Jr., and Gobble, F. L., Jr.: AM. T. OBSTET.GYNECOL.~~:~~~. 1967. Daw&, G. S.: In Foetal and Neoiatal Physiology, Chicago, 1968, Year Book Medical Publishers, Inc., p. 63. Meschia, G., Makowski, E. L., and Battaglia, F. C.: Yale J. Biol. Med. 42: 154, 1970. Rankin, J., Meschia, G., Makowski, E. L., and Battaglia, F. C.: Am. J. Physiol. 219: 9, 1970. Meschia, G., Cotter, J. R., Makowski, E. L., and Barron, D. H.: Quart. J. Exp. Physiol. 52: 1, 1967. Battaglia, F. C., Meschia, G., Makowski, E. L., and Bowes, W. A., Jr.: J. Clin. Invest. 47: 548, 1968. Meschia, G., Battaglia, F. C., Makowski,
E. L., and Droegemueller. W.: ,J, Appt. Physiol. 26: 410, 1969. 12. Campbell, .\, G. M., Dawes? G. S., Fishmarr, A. I’., IIymen, A. I., and James; G. B.: .i. Physiol. 182: 439, 1966. 13. Makowski, E. L., Meschia, G., Droegemueller, W., and Battaglia, F. C.: A&l. J. OBSTET. GYNECOJ.. 101: 409, 1968. 14. Hertz, R., Battaglia, F. C., Makowski, E. I,.? and Meschia, G.: In preparation. 1.5. Kirschbaum, T. H.: Lucas, W. E., DeHaven, J. C., and Assali, N. S.: AM. J. OBSTET. GYNECOL.~~:~~~, 1967. 16. Dilts, P. V., Jr., Brinkman, C. R., III, Kirschbaum, T. H., and Assali, N. S.: AM. J. OBSTET. GYNECOI.. 103: 138, 1969. 17. Diczfalusy, E.: In Excerpta Medica FoundaFoeto-placental Unit, tion, editors: The Milan. 1968. Proc. Int. Symp. pp. 65-109.
R.
RAYE
A.
P.
KILLAM
F.
C.
BATTAGLIA
E.
L.
MAKOWSKI
G.
MESCHIA
Denver,
Colorado
Uterine blood POWS and 01 consumptions were compared before and after fetal death in 9 unanesthetized pregnant ewes in the last month of gestation. Fetal death was produced by the injection of a bolus of air in a fetal pedal vein. Uterine blood flow did not change significantly in the first hour following fetal death. Afterward, there was a slow decline of the uterine blood flow to approximately 70 per cent of the control value at 24 hr. The abrupt removal of fetal metabolism produced a large drop in uterine 08 consumption. This drop was more pronounced late in pregnancy in agreement with previous data showing that the fraction of the total uterine 0, consumption which is fetal is related to fetal size.
T H E B L 0 0 n F L 0 W t0 an organ iS controlled by many stimuli which may originate within the organ itself (local regulation) or elsewhere in the body (extrinsic regulation). For example, the blood flow to skeletal muscle is controlled by local metabolic demands as well as by neurogenic and humoral fact0rs.l Previous studies of uterine blood flow in pregnancy have clarified some of the characteristics of extrinsic regulation of uterine flo~.~-~ However, there is no information concerning the degree of local regulation
of uterine blood flow. More specifically, there is no information concerning the acute effects upon uterine blood flow of sudden fetal death. The suggestion made by Dawes6 that, “qualitatively the reactions of uterine vasculature are similar to those of the vascular beds of skeletal muscle and the abdominal viscera,” is based on pharmacologic evidence about the effect of extrinsic stimuli on uterine blood flow. The experiments reported in this paper were designed to compare uterine 0, consumption and blood flow before and after fetal death in unanesthetized, pregnant ewes in the last 35 days of pregnancy.
From the Division of Perinatal Medicine and the Department of Physiology, University of Colorado Medical Center. Supported by United Health Service Grants HD 01866.
States Public HD 00781
Materials
and methods
The animal preparation. Fig. 1 presents a diagram of the preparation used in this
and 917
918
Raye
et
Fig. 1. Diagram study.
al.
of the preparation
used in this
study. This consisted of: ( 1) external square wave electromagnetic flow probes implanted over both uterine arteries, and (2) polyvinyl catheters inserted in a fetal pedal artery, a fetal pedal vein, the amniotic sac, a maternal femoral artery, and one of the two uterine veins. The catheterized uterine vein was the one draining the pregnant horn. Preparation for operation and anesthesia were as previously described.? The flow probes (4.0 or 5.0 mm. in diameter) were implanted via a bilateral, extraperitoneal approach. With the ewe in the supine position, the infraperitoneal space on each side was entered through a 10 cm. incision in the lower abdomen, parallel to the inguinal ligament. The incision was carried down through the fascia of the external oblique by sharp dissection; then the uterine artery was reached by blunt dissection in the retroperitoneal area, recognized by palpation. and delivered into the operative field. A 0.5 cm. portion of the artery was freed of surrounding tissue, and the head of the probe was placed around the artery. After replacement of the artery in its natural the fascial plane was repaired position, around the leads of the probes. The leads were brought out through the flank of the animal by a subcutaneous tunnel and stored in a canvas pouch anchored to the skin.
Eittier 4n~llltancously with inrphtatioli of the flow I)robcs or several days later: polyvinyl catheters (inside diameter 0.58 mm., outside diameter 1 .2 mm. ,! were placed in the maternal and fetal blood vessels and the amniotic sac by techniques previously described.‘, S In twin pregnancy the pedal arteries and veins of both twins were cathr:terized. After operation, the ewes were returned to the animal quarters where they received food and water ad libitum. Antibiotics (procaine penicillin, 600,000 U.? and streptomycin, 0.5 Gm.) were given intramuscularly on the first 3 postoperative days. Experimental protocol. All experiments were performed on awake, nonanesthetized ewes brought to the laboratory from 2 to 7 days after the last surgical procedure. During the experiment, the ewes were standing in a rectangular crate and had free access to food and water. For one hour preceding and one hour following fetal death (control and experimental periods, respectively), the following variables were measured continuously : ( 1) blood flow in one uterine artery, (2) maternal arterial blood pressure, and (3) amniotic pressure. Fetal blood pressure was measured continuously in the control period and in the initial phase of the experimental period. The selection of the uterine artery to be monitored continuously was on the basis of greater flow and/or good quality of the electrical signal. The flow through the other uterine artery was measured at the beginning of the control period, at the end of the experimental period, and at intervals thereafter. During both the control and the experimental periods, blood samples were drawn simultaneously from the maternal femoral artery and the uterine vein at 12-min. intervals for a total of 5 sets of determinations in each period. Each sample consisted of 2 ml. of blood drawn in a glass syringe whose dead space had been filled with heparinized saline and 0.3 ml. of blood drawn in a dry heparinized glass capillary tube containing 0.3 mg. of NaF. The blood in the syringe
Volume Number
Uterine
111 7
Fig. 2. Fetal of
injection
arterial pressure, of air in-Fetus
maternal arterial No. 71-001-l.
was analyzed for PO*, PcoZ, and pH. The blood in the capillary was analyzed for total 0, content. The lamb (or lambs in case of twins) was killed by injection of 20 to 50 ml. of air into the pedal vein catheter. The death of the fetus was confirmed by observing the fall in fetal arterial pressure and the cessation of fetal pulse. In 4 animals, following the one-hour experimental period, amniotic and maternal arterial pressures and the blood flows through both uterine arteries were measured for intervals of 30 minutes at various times up to 26 hr. The ewes were then killed. The uterus and fetus were removed and weighed. Analytical methods. The maternal arterial blood pressure was measured with a pressure transducer positioned at the level of the maternal heart. The pressure transducer measuring fetal blood pressure was positioned to read zero pressure when connected with the amniotic catheter. The fluctuations of the maternal pressure and flow signals during the cardiac cycle were electronically integrated before display on the recorder (halftime of the response to step change in flow was 3.3 sec.). The PO*, PcoZ, and pH were measured at 39.5O C. as described previously.7 Total 0, contents were measured on a Beckman GC-2A chromatograph equipped with blood gas extraction accessory, a 5 A molecular sieve, and silica gel parallel column. In each experiment, the following mean
pressure,
blood
and
flow and 02 consumption
uterine
arterial
flow
at the
919
time
values were calculated : ( 1) mean uterine blood flows in the control and the experimental periods (F,,, and Fexp), calculated by averaging the flow recorded each 100 sec.; (2) mean arterial and uterine venous Po2, PcoZ, and pH in the control and experimental period; (3) mean uterine arterialvenous differences of 0, content in the control and the experimental period (aO,~0, ) con and (aO,-v0,) exp. The mean flows and the arterial-venous differences were then used to estimate: (1) the variation of uterine blood flow in the experimental period as a fraction of the control period : variation
F of flow = --% F
;
VI
eon
and (2) the variation of uterine 0, sumption in the experimental period fraction of the control 0, consumption: +oz
..,fio,
con =
F f
con
x
( a02-v02)
exp.
(aOrv0,)
e0n
conas a
PI
Differences between the control and the experimental periods were tested for statistical significance by the t test for paired samples. Results
Variations of uterine blood flow with fetal death. Fig. 2 presents the data for fetal arterial pressure, maternal arterial pressure, and uterine blood flow at the time of the
920
et al.
Raye
I
02
I
I,
4
I
I
TIME
Fig. 3. Uterine blood ing fetal death. The measured in the first of individual 30 min. the 4 animals.
I
I
I
I,,
,
,
88lOl2l416i820222426 (hours)
flows expressed as percentages of the control value in the hours foilowsymbol at time 30 minutes represents the mean + 1 S.D. of the flows hour. The remaining symbols represent means and range of variation measurements in 4 animals. Different symbols were used for each of
Table I. Comparison of mean blood flow through one uterine artery in the control period (the hour preceding fetal death) and in the experimental following fetal death)
period (the hour -.
Fetal age (days)
Sheep No.
70-012-l 70-003-2” 70-020-l 71-001-l 71-007-l 71-010-l 71-009-l 71-037-l 71-041-l *One
Fetal weight (Kg.)
141 134 129 143 134 112 112 119 138
3.30 2.50 3.10 2.50 4.10 1.45 1.71 2.37 4.34
pow
F con (mUmin.)
F ew (mUmin.)
816 787 426 408 648 143 154 304 608
825 752 372 426 690 162 164 328 560
F.w/F,cm
1.01 0.96 0.87 1.04 1.06 1.13 1.06 1.08 0.92 ix-
of twins.
injection of air in Fetus No. 71-001-l which is representaive of the group as a whole. It is clear from this example that fetal death had no immediate effect on uterine blood flow. The comparison of mean uterine blood flows in the control and experimental onehour periods also showed no significant effect of fetal death on uterine blood flow. This comparison for all 9 animals studied is shown in Table I. In order to determine whether
Blood
there
was any trend
within
the one-
hour period following fetal death, this hour was divided into 3 twenty-minute subperiods, and the flows in each period were compared. According to this comparison, the uterine flow in the first 20 min. rose 4 per cent above the control value and then fell 2 per cent below the control value at the 40 to 60 min.
period.
The
6 per cent
difference
between these two periods was statistically significant (P
3 illustrates
the
fact
that
uterine
Volume Number
111 7
Uterine
blood
flow and 02 consumption
921
Table II. Comparison of PO,, PcoZ, and pH in the uterine arterial and venous blood of 9 ewes during the control period (the hour preceding fetal death) and the experimental period (the hour following fetal death). Each set of numbers is the mean and standard error of 9 observations Arterial Period
Control Experimental *Significantly
(mm.
Hg)
75.8 I! 2.1 75.0 f. 1.9 different
from
blood
Venous
PCOl (mm. H.d
Pot
Pot M-f
31.4+ 0.7 32.6 + 0.7 the
control
(paired
(mm.
7.53 + 0.01 7.52 2 0.01 samples
analysis,
H.4
45.5 2 1.3 58.8* t 2.0
blood
PCOl (mm. Hg.)
#H
35.9 2 0.9 34.1” k 0.8
7.49 r 0.02 7.52* + 0.01
P < 0.01).
Table III. Mean arterial 0, contents and arterial-venous differences of 0, per liter of blood across the pregnant uterus in the control period (the hour preceding fetal death) and in the experimental period (the hour following fetal death). The last column shows the uterine 0, consumption after fetal death as a fraction of the control value Sheep No.
70-012-l 70-003-2 70-020-l 71-001-l 71-007-I 71-010-l 71-009-l 71-037-l 71-041-l
(aOz
5.88 4.75 4.65 5.64 7.00 6.01 5.17 6.25 4.83
- ~OS),,, (mM)
(aOz
1.22 1.25 1.56 1.15 1.70 1.42 1.56 1.21 1.26
flow did fall gradually in the following 26 hr. to approximately 70 per cent of the control value at 24 hr. Throughout this period, there were no significant changes in intraamniotic pressure or in maternal arterial pressure. Variations of uterine venous Paz, Pcoz, and pH with fetal death. In the experimental period following fetal death, the uterine vein PO, rose 13 mm. Hg, the Pcoz fell 1.8 mm. Hg, and the pH rose 0.03 U. These changes are summarized for the 9 animals in Table II. Variations of uterine 0, consumption with fetal death. In each experiment, fetal death caused a substantial rise of the 0, content in the uterine vein and narrowed the arterial-venous difference of 0, content across the uterine circulation to approximately one third of the normal value (Table III). These changes in arterial-venous differences were used to compute the fall in
- ~OZ),,, (mM)
0.35 0.31 0.59 0.36 0.57 0.67 0.57 0.56 0.28
co*,.
ire*,,,
0.29 0.24 0.33 0.33 0.36 0.53 0.39 0.50 0.20
uterine 0, consumption that followed the abolition of fetal metabolic demands. The calculations were made by means of Equation No. 2 and are presented in Table III. Comment
The results presented in this paper show that the abrupt removal of fetal metabolism produces a large drop in total uterine 0, consumption. The relative magnitude of this drop will depend upon the relative magnitudes of fetal and nonfetal” uterine 0, uptakes prior to fetal death and also on the possible effect that the interruption of the umbilical circulation might have on placental metabolism. These considerations raise two interesting questions, namely: (1) What fraction of the total uterine consumption is nonfetal? (2) Is the relative drop of uterine 0, uptake after fetal death comparable to *In this paper we designate BS nonfetal 0s uptake the 02 coasurnption of placenta, endometrium, and myometrium.
922
Raye
et al
* MESCHIAetal. CASTPSELL et al. . PRESENT STUDY
.25 t
L
1
2
3
4
5
FETAL WEIGHT (Kg. )
Fig. 4. The weight. The 10, and 11. second-order
fraction of total uterine 0, consumption which is nonfetal is plotted against fetal data labeled Meschia et al. were calculated from data published in References 0, The data of Campbell et al. were from Reference 12. The line was computed by regression analysis.
this fraction? In order to provide an answer to these questions we have collected and analyzed the pertinent data in the literature. The results of this analysis are presented in Fig. 4. In this figure the fraction of total uterine 0, consumption which is nonfetal is plotted against fetal weight. The black dots represent data obtained by measuring simultaneously uterine and umbilical blood flows and uptakes by the method of Meschia and coland associates91 I1 and Battaglia leagues.lO The open circles represent data obtained by ventilating the fetal lungs in utero after severing the maternal aorta and measuring fetal 0, uptake before and after cord occlusion.12 Finally, the crosses represent the data collected in the present series of experiments. It is apparent from the graph that there is substantial agreement in the results obtained by these three very different techniques. This agreement suggests the following two inferences : (1) Myometrial 0, consumption (in the absence of uterine contractions) is probably a small fraction of the total because the nonfetal 0, uptakes measured by Campbell and coworker9 did not include the myometrial fraction and yet are not systematically lower than the uptakes measured by the other two methods. This interpretation is further
strengthened by the fact that late in pregnancy the myometrium receives only 3 per cent of the total uterine blood flow.13 (2) In the first hour following fetal death, placental and endometrial 0, consumptions continue at approximately the control levels. This inference is based on the fact that the nonfetal fractions of 0, uptake measured over the first hour following fetal death in this study are similar to those measured in the intact preparation. Fig. 4 demonstrates that the nonfetal fraction of uterine 0, consumption is inversely related to fetal weight. Early in pregnancy, the largest fraction of the uterine 0, consumption is nonfetal. By the time the fetus weighs 1.7 kilograms, the fetal and nonfetal tissues consume approximately equal amounts of 0,. Then, as the fetus grows larger, fetal 0, uptake becomes the larger fraction of the total uterine uptake. The older fetus represents a larger fraction of the total uterine weight than the younger fetus (as can be seen in Fig. 5). Thus, it may seem reasonable that the older fetus should consume a larger fraction of the total uterine 0, uptake. However, the fetus depends upon the placenta for its nutrition, and there is reason to believe that the placental transport of some nutrients (e.g., amino acids) may
Volume Number
111 7
involve active transport mechanisms. Consequently, it is not obvious why the 0, consumptions of fetal and nonfetal tissues do not grow proportionally. The shift in the distribution of 0, consumptions within the pregnant uterus that takes place during gestation implies that the growth curves of total uterine 0, consumption and fetal 0, consumption are quite different. For example, if one assumes that fetal 0, consumption increases approximately fourfold when the fetus grows from 1 to 4 kilograms, one can calculate from the data in Fig. 4 that total uterine 0, consumption in the same period of growth would only increase twofold. The remainder of the total 0, consumption would be accounted for by the redistribution of O? uptakes within the pregnant uterus. The experiments described in this paper clearly demonstrate the absence of acute changes of uterine blood flow following the removal of fetal metabolic demands. The absence of an acute response is particularly significant in late pregnancy when fetal death reduces uterine 0, consumption to approximately one fourth of the normal value. This observation corroborates the hypothesis that acute changes of partial pressure of 0, have no appreciable effect on placental perfusion. The other experimental observations in favor of this hypothesis are as follows: ( 1) The blood flow to the pregnant uterus does not rise above control values after the temporary occlusion of the maternal aorta (absence of reactive hyperemia). We have verified this phenomenon, originally described by Greiss,4 in nonanesthetized pregnant animals, subjected to aortic occlusion for as long as two minutes.14 (2) Maternal inhalation of 100 per cent 0, does not change uterine blood flow significantly.lOT I5 This observation was also confirmed in nonanesthetized animals.14 (3) Moderate maternal hypoxia in nonanesthetized sheep does not change uterine blood flow significantly.14
REFERENCES
1.
Barcroft! H.: In Handbook of Physiology, Circulation, Washington, D. C., 1963, sec. 2, vol. 2, chap. 40, American Physiological Society, pp. 1353-1385.
Uterine
blood flow and 02 consumption
923
* MESCHIA et (11. 1 PRESENT STUDY
GESTATIONAL
AGE
(days)
Fig. 5. The fraction of total uterine weight which is nonfetal is plotted against fetal age. The data labeled Meschia et al. were obtained in the course of other studies (References 9, 10, and 11).
According to Dilts and associates,le severe hypoxia does induce a significant fall of uterine blood flow. However, it is likely that this fall is secondary to the release of catecholamines in the maternal circulation rather than the direct effect of hypoxia on the uterine vasculature. Although fetal death has no immediate effect on uterine blood flow, there is a gradual constriction of the uterine vascular bed following fetal death. This phenomenon is difficult to interpret at this time. It could represent the release of vasomotor substances from degenerating tissues within the uterus. On the other hand, it could represent the effect of a gradual decline in the concentration of substances, such as estrogens, which are known to have a vasodilating effect on the uterine vasculature and whose synthesis is partially under fetal contro1.l’ The existence of chronic regulatory mechanisms of uterine blood flow in pregnancy mediated by extrinsic and local factors is indeed probable but is yet to be tested by appropriate experimental techniques.
2. 3.
Ahlquist, R. P.: J. Am. Pharm. Assoc. 39: 370, 1950. Ladner, C., Brinkman, C. R., III, Weston, P., and Assali, N. S.: Am. J. Physiol. 218: 257, 1970.
924
4. 5. 6.
7. 8.
9.
10.
11.
Raye
et al.
Greiss, F. C.: AM. .I. OBSTET. GYNECOI.. 96: 41, 1966. Greiss, F. C., Jr., and Gobble, F. L., Jr.: AM. T. OBSTET.GYNECOL.~~:~~~. 1967. Daw&, G. S.: In Foetal and Neoiatal Physiology, Chicago, 1968, Year Book Medical Publishers, Inc., p. 63. Meschia, G., Makowski, E. L., and Battaglia, F. C.: Yale J. Biol. Med. 42: 154, 1970. Rankin, J., Meschia, G., Makowski, E. L., and Battaglia, F. C.: Am. J. Physiol. 219: 9, 1970. Meschia, G., Cotter, J. R., Makowski, E. L., and Barron, D. H.: Quart. J. Exp. Physiol. 52: 1, 1967. Battaglia, F. C., Meschia, G., Makowski, E. L., and Bowes, W. A., Jr.: J. Clin. Invest. 47: 548, 1968. Meschia, G., Battaglia, F. C., Makowski,
E. L., and Droegemueller. W.: ,J, Appt. Physiol. 26: 410, 1969. 12. Campbell, .\, G. M., Dawes? G. S., Fishmarr, A. I’., IIymen, A. I., and James; G. B.: .i. Physiol. 182: 439, 1966. 13. Makowski, E. L., Meschia, G., Droegemueller, W., and Battaglia, F. C.: A&l. J. OBSTET. GYNECOJ.. 101: 409, 1968. 14. Hertz, R., Battaglia, F. C., Makowski, E. I,.? and Meschia, G.: In preparation. 1.5. Kirschbaum, T. H.: Lucas, W. E., DeHaven, J. C., and Assali, N. S.: AM. J. OBSTET. GYNECOL.~~:~~~, 1967. 16. Dilts, P. V., Jr., Brinkman, C. R., III, Kirschbaum, T. H., and Assali, N. S.: AM. J. OBSTET. GYNECOI.. 103: 138, 1969. 17. Diczfalusy, E.: In Excerpta Medica FoundaFoeto-placental Unit, tion, editors: The Milan. 1968. Proc. Int. Symp. pp. 65-109.