Doppler flow velocimetry of the splenic artery in the human fetus: Is it a marker of chronic hypoxia?

Doppler flow velocimetry of the splenic artery in the human fetus: Is it a marker of chronic hypoxia? Alfred

Z. Abuhamad,

Arthur

T. Evans

Norfolk,

Virginia,

MD, III,

Giancarlo

Mari,

MD,

Donna

Bogdan,

RDMS,

and

MD

and New Haven, Connecticut

OBJECTIVE: The aim of this investigation was to describe splenic artery flow velocity waveforms in appropriateand small-for-gestational-age human fetus. STUDY DESIGN: Splenic artery flow velocity waveforms were prospectively obtained from 95 appropriateand 15 small-for-gestational-age fetuses with pulsed Doppler uitrasonography. The resistance index was used to quantify the Doppler waveform. RESULTS: A second-degree polynomial model expressed the changes of the resistance index in appropriate-for-gestational-age fetuses with advancing gestation ( y = 0.057x [Weeks] - 0.001x’, r = 0.53, p c 0.001). In 14 of 15 (93%) small-for-gestational-age fetuses the splenic artery resistance index was below the mean for gestational age. In five of 15 (33%) small-for-gestational-age fetuses resistance index of the splenic artery was c 2 SEMs. A trend toward a higher hematocrit was noted five fetuses with splenic artery resistance index values < 2 SEMs (50.2%) compared with other small-for-gestational-age fetuses (43.0%). CONCLUSION: Our results suggest that some small-for-gestational-age fetuses have decreased resistance at the level of the splenic artery. We postulate that the increased erythropoietin level, stimulated by hypoxia, results in decreased resistance at the level of the splenic artery in small-for-gestational-age fetuses. Finally, management of the small-for-gestational-age fetus may be by the study of the splenic artery waveforms. (AM J OBSTET GYNECOL 1995;172:820-5.) Key

words:

Splenic

artery, small-for-gestational-age,

resistance

Doppler flow velocimetry is a noninvasive method for investigating the maternal and fetal circulations. Although the validity of Doppler flow velocimetry in screening for fetal growth retardation is controversial, the introduction of this technique to perinatal medicine has advanced our understanding of fetal physiologic features and fetal adaptation to hypoxia. Doppler flow velocimetry waveforms of several fetal vessels have been previously described.‘.’ Of those, middle cerebral and umbilical artery velocimetry waveforms are most commonly used, because they reflect blood flow redistribution in fetal hypoxemia.’ The fetal spleen has recently received renewed interest in the literature.6. ’ A significant positive correlation has been found between increased splenic perimeter

index,

820

the in the

aided

erythropoietin

and fetal hemoglobin deficit in red blood cell-alloimmunized pregnancies.” Fetal splenomegaly has also been described in association with congenital transplacental infections.’ This study was undertaken to assess the splenic artery resistance index in 95 normal human fetuses. From this information normal values were defined for the resistance index of the fetal splenic artery. The variability of the resistance index was also evaluated in our population. In addition, splenic artery velocity waveforms of 15 small-for-gestational-age (SGA) fetuses are reported and are compared with those that were obtained in normal fetuses. Material

and methods This study was carried out with data collected in a cross-sectional manner from 95 normal fetuses (appropriate-for-gestational-age, group 1) and 15 SGA fetuses (group 2). Verbal informed consent was obtained from all the patients. Fetal age determination was based on the last menstrual period and confirmed by first- or second-trimester ultrasonography in all patients. Patients were excluded from the study if gestational age determination by ultrasonography differed from the last menstrual period determined age by 2 7 days in the first Subjects.

From the Department of Obstetrics and Gynecology Eastern Virginia Medical School, and the Department of Obstetrics and Gynecology;, Yale University School of Medicine. Received for publication May 13, 1994; revised July 8, 19.94; accepted August I I, 1994. Reprint requests: Alfred 2. Abuhamad, MD, Diviszon of MaternalFetal Med&ne, Department of Obstetrics and Gyneco& Eastern Virginia Medical School, 825 Fairfax Ave.. Suite 301. , No&k.i VA 23507. Copyright 0 1995 by Mosby-Year Book, Inc. 0002.9378/95 $3.00 + 0 6/l/59745

the

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Fig. 1. Transverse view of fetal abdomen at 20 weeks of gestation with color Doppler ultrasonography of the splenic artery. Note posterior course of splenic artery behind stomach (open arrow) and into splenic hilum. Straight solid arrozu, Descending aorta; curved solid arrow, splenic artery.

trimester or 2 10 days in the second trimester. The patients in group 1 were delivered of infants after 37 weeks’ gestation, with no evidence of growth retardation or congenital anomalies. SGAwas defined on the basis of ultrasonographic measurements of fetal weigh? < 10th percentile for gestational age.” SGA was confirmed by birth weight < 10th percentile for gestational age in all but two fetuses in group 2 (87%). Doppler ultrasonographic examinations. Doppler examination of the fetal splenic artery was performed with the mother in the semirecumbent position. The fetal abdomen was imaged in an axial view at the level of the stomach by means of real-time ultrasonography with a 3.5 or 5.0 MHz transducer with color and pulsed Doppler capabilities (Acuson 128 XP 10 ob, Mountain View, Calif.). Color Doppler was used to localize the splenic artery as it arose from the celiac axis and coursed behind the stomach into the splenic hilum (Fig. 1). Pulsed Doppler evaluation was performed with a sample volume of 3 mm, a pass filter between 0 and 50 Hz, and an angle of incidence between 0 and 30 degrees from the ultrasonography beam. The sample volume was positioned along the splenic artery in close proximity to its origin from the celiac axis. Peak systolic velocity and lowest diastolic velocity were calculated with electronic calipers. Three consecutive waveforms

were analyzed and the results averaged. The resistance index (peak systolic velocity - lowest diastolic velocity/peak systolic velocity) was then calculated with the software included in the ultrasonography system. Measurements were obtained during fetal apnea, which was defined as the absence of variable changes in the waveform patterns for Z 10 waveforms. Data analysis. For fetuses in group 1 changes in resistance index with gestational age were quantified by fitting mathematic functions to the experimental data. Only one resistanc,e index measurement was obtained in each fetus (average of three measurements). We looked for the optimal polynomial model on the basis of three criteria: coefficients different from zero, maximal coefficient of correlation, and residual plots. Analysis of variance was used to determine whether the regression accounted for a significant part of the variability in the dependent variable. A value of p < 0.05 was considered to indicate statistical significance. The optimal polynomial model was used to obtain the predicted values for gestational age. The mean and SE were calculated, and twice the latter was used as the measure of resistance index variability at different times in pregnancy. The resistance index values for the SGA fetuses (group 2) were compared with our reference limits for gestation. The Student t test was used to

822

Abuhamad

Table

March 1995 Am J Obstet Gynecol

etal.

I. Splenic Gestational Cwk) 15 16 17

artery resistance age

index

standard Lower limit (-2 SEM)

20 21 22 23 24 25 26 27 28 29 30

0.53 0.56 0.58 0.60 0.62 0.64 0.66 0.67 0.68 0.69 0.70 0.70 0.71 0.72 0.71 0.71

31

0.71

32 33 34 35 36 37 38 39 40 41 42

0.70 0.69 0.68 0.67 0.66 0.64 0.62 0.60 0.58 0.56 0.53

18 19

curve Predicted

value

Upper limit (+2 SEM)

0.63 0.66 0.68 0.70 0.72 0.74 0.76 0.77 0.78 0.79 0.80 0.80

0.73 0.76 0.78 0.80 0.82 0.84 0.86 0.87 0.88 0.89 0.90 0.90

0.81

0.91

0.82 0.81 0.81 0.81 0.80 0.79 0.78 0.77 0.76 0.74 0.72 0.70 0.68 0.66 0.63

0.92

0.91 0.91 0.91 0.90 0.89 0.88 0.87 0.86 0.84 0.82 0.80 0.78 0.76 0.73,

Resistance index = 0.057 GA - 0.001 (GA)‘, where GA is gestational age.

compare continuous variables for parametric the Mann-Whitney U test for nonparametric

data

and

data.

Results The intraobserver variability (coefficient of variation) for the resistance index of the splenic artery was 8.3% and was determined by examining 12 normal fetuses. Gestational age for group 1 ranged from 15 to 40 weeks with a mean of 27.6 + 7.1 weeks. A secondorder polynomial model expressed the changes of the splenic artery resistance index with advancing gestational age (y = 0.057~ [Weeks] - 0.001x’, r = 0.53, Jo < 0.001) (Table I). The splenic artery resistance index manifested a higher value between 24 and 32 weeks of gestation (Fig. 2). Gestational age in fetuses in group 2 ranged from 24 to 38 weeks with a mean of 31 i 4.4 weeks. Birth weights were ~10th percentile for gestational age in all but two newborns in group 2. In 14 of 15 (93%) SGA fetuses the splenic artery resistance index was below the mean for gestational age. In five of 15 (33%) SGA fetuses the resistance index of the splenic artery was below our reference range (Fig. 3). The splenic artery resistance index of the two newborns with normal birth weights in group 2 were within 2 SEMs. Gestational age at delivery in group 2 ranged from 27 to 41 weeks, with an average of 34.1 ir 4.9 weeks.

Although the average gestational age in group 2 fetuses with a splenic artery resistance index < 2 SEMs (n = 5) is similar to the average gestational age in the other fetuses in group 2 (n’ = 10) (33.6 + 4.7 weeks for n and 34.5 -t 4.7 weeks for n’, fi = 0.49), a trend toward a higher hematocrit at birth was noted in the fetuses with a splenic artery resistance index <2 SEMs (50.2% ? 7.7% for n and 43.0% + 6.8% for n’, p = 0.43).

Comment There is significant controversy whether the human fetal spleen is a hematopoietic organ under normal conditions. Evidence supporting its involvement in hematopoiesis is derived from studies on nonhuman mammals” and from observations based on conventional histologic studies in the human fetus.” In a latter report that used immunohistologic and cytochemical techniques on 48 human fetal spleens at different gestational ages, no hematopoietic cells of the dividing cell pool were identified, suggesting little evidence of heThe authors concluded that immature matopoiesis.‘3 hematopoietic cells found in the human fetal spleen reflect trapping of circulating precursors in the fetal blood rather than local products of hematopoiesis. The celiac trunk arises from the aorta between the

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3

crura of the diaphragm and at the level of the twelfth thoracic vertebra. It has three main branches, the splenic, common hepatic, and left gastric arteries. The celiac trunk bifurcates into the splenic and the common hepatic artery, with the left gastric artery arising from the celiac trunk between the aorta and the bifurcation (86%). Variations are common and include a gastrosplenic trunk in 6%, a hepatosplenic trunk in 6%, and a complete absence of a celiac trunk in 2% of cases.14 The splenic artery runs posterior to the stomach and into the splenic hilum. It supplies the spleen, a great part of the stomach, and the pancreas. Splenic artery Doppler velocimetry is best obtained in a transverse view of the fetal abdomen, with the fetal spine in the lateral position. The artery is seen coursing behind the stomach and into the splenic hilum (Fig. 1). The celiac axis is not clearly imaged in this fetal position, because it courses perpendicular to the ultrasonography beam. Our results show a parabolic change in the resistance index of the splenic artery with advancing gestation. This finding is similar to the change in the middle cerebral artery pulsatility index with advancing gestation.5 The lower cerebral vascular impedance to blood flow in the human brain during early and late pregnancy can be the result of the major cellular multiplication between 15 and 20 weeks and in the third trimester of pregnancy.5 It is currently not clear to us why the splenic artery resistance to blood flow changes with gestational age. Whether the decrease in blood flow resistance of the splenic artery in the third trimester of pregnancy is attributed to the corresponding increase in fetal erythropoietin levels remains to be established.” SGA fetuses in our series showed decreased resistance to blood flow at the level of the splenic artery. Indeed, all but one SGA fetuses had a splenic artery resistance index below the mean, and five of 15 had values < 2 SEMs. This finding is similar to the change in resistance at the level of the cerebral circulation in hypoxic fetuses. The brain-sparing effect, however, is a wellstudied reflex involving the chemoreceptors and the baroreceptors in the fetus. We could not find any animal or human studies in the literature supporting our findings regarding the splenic artery. We postulate that decreased resistance to blood flow at the level of the splenic artery in SGA fetuses is related to the erythropoietin system. Erythropoietin is a glycoprotein hormone acting as the primary physiologic regulator of red blood cell production.‘G8 ” Hypoxemia is the most important stimulus of erythropoietin synthesis both in adults and fetuses.“. I9 During pregnancy this hormone does not cross the placenta in either Elevated erythropoietin values have been direction.“’ observed

in umbilical

cord

plasma

of SGA

infants

and

in

Fig. 2. Flow velocity waveforms of fetal splenic ferent gestational ages. Top, middle, and bottom from 18, 28, and 40 weeks, respectively.

et al.

823

artery at difwaveforwu are

infants of diabetic mothers.“, ” Elevated erythropoietin values are probably responsible for the significantly higher hemoglobin concentration in SGA newborns and newborns of diabetic mothers, compared with normal controls.“. p3 Furthermore, a positive correlation exists between erythropoietin levels and abnormal fetal heart tracings in term fetusesz4 The fetal spleen may be either directly involved in erythropoiesis or indirectly involved with increased trapping of premature erythrocytes and reticulocytes that are released into the circulation after erythropoietin stimulation. Findings from red blood cell-alloimmunized pregnancies suggest that a positive correlation exists between the splenic perimeter and the hemoglobin deficit.6 Moreover, serial fetal spleen measurements showed a rapidly decreased spleen perimeter after correction

perimeter

of

anemia,

before

followed

by

a gradual

the next fetal transfusion.’

association between hemoglobin poietin exists in normal and

and plasma Rh-immunized

increase

in

An inverse erythrofetuses.”

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Abuhamad

March 1995 Am 1 Obstet Gynecol

et al.

12

17

37

Fig. 3. Normal

range of splenic artery resistance from study of 95 normal fetuses. Splenic artery reference range.

The

splenic

artery

resistance

in SGA

fetuses

may

index as function resistance index

reflect

splenic response to erythropoietin stimulation. Although we did not measure erythropoietin levels in our fetuses, a trend toward a negative correlation exists between the splenic artery resistance index and hematocrit levels within the SGA group, suggesting a lower splenic resistance with increasing hematocrit. The ability of fetal splenic artery resistance index changes to identify fetuses with hypoxic risks warrants further investigation. As a potential marker for fetal hypoxemia, splenic artery Doppler velocimetry may represent a significant tool in the management of highrisk pregnancies. REFERENCES 1. Mari G. Arterial blood flow velocity waveforms of the pelvis and lower extremities in normal and growth-retarded fetuses. AM J OBSTET GYNECOL 1991;165:143-51. 2. Rizzo G, Arduini D, Romanini C. Inferior vena cava flow velocity waveform in appropriateand small-for-gestational-age fetuses. AM J OBSTET GYNECOL 1992;166:127180. 3. Mari G, Kirshon B, Abuhamad A. Fetal renal artery flow velocity waveforms in normal pregnancies and pregnancies complicated by polyhydramnios and oligohydramnios. Obstet Gynecol 1993;81:560-4. 4. Maulik D, Yarlagadda P, Youngblood JP, Ciston P. Comparative efficacy of umbilical arterial Doppler indices for predicting adverse perinatal outcome. AM J OBSTET GYNECOL 1991;164:1434-40. 5 Mari G, Deter RL. Middle cerebral artery flow velocity waveforms in normal and small-for-gestational age fetuses. AM J OBSTET G~NECOL 1992;166:1262-70. 6 Oepkes D, Meerman RH, Vandenbussche FP, Van Kamp IL, Kok, FG, Kauhai HH. Ultrasonographic fetal spleen measurements in red blood cell-alloimmunized pregnancies. AM Jk OBSTET GYNECOL 1993;169:121-8. 7, . Hata T, Deter RL, Aoki S, Makihara K, Hata K, Kitao M.

8.

9.

10.

11.

12. 13.

14. 15.

16. 17. 18. 19. 20.

21

22.

42

of gestational age constructed of 15 SGA fetuses plotted on

Mathematical modeling of fetal splenic growth: use of the Rossavik growth model. J Clin Ultrasound 1992;20:321-7. Shalev E, Feldman E, Weiner E, Zuckerman H. Fetal splenomegaly, ultrasound diagnosis of cytomegalovirus infection: A case report. J Clin Ultrasound 1984;12:520521. Hadlock FP, Harrist RB, Sharman RS, Deter RL, Park SK. Estimation of fetal weight with the use of head, body, and femur measurements-a prospective study. kzl J OBSTET GYNECOL 1985;151:333-42. Brenner WF, Edelman DA, Hendricks CH. A standard of fetal growth for the United States of America. AM J OBSTET GYNECOL 1976;126:555-64. Djaldetti M, Bessler H, Rifkind RA. Hematopoiesis in the embryonic mouse spleen: an electron microscopic study. Blood 1972;39:826-41. Gilmour JR. Normal haemopoiesis in intra-uterine and neonatal life. J Path01 Bacterial 1941;52:25-55. Wolf BC, Luevano E, Neiman RS. Evidence to suggest that the human fetal spleen is not a hematopoietic organ. Am J Clin Path01 1983;80:140-4. VanDamme JP, Boute J. Vascular anatomy in abdominal surgery. New York: Georg Thieme Verlag, 1990:4-6. Thomas RM, Canning CE, Cotes PM. Erythropoietin and cord blood haemoglobin in the regulation of human fetal erythropoiesis. Br J Obstet Gynaecol 1983;90:795-800. Spivak JL. The mechanism of action of erythropoietin. Int J Cell Cloning 1986;4:139-43. Zanjani ED, Ascensao JL. Erythropoietin. Transfusion 1989;29:46-57. Fischer JW. Control of erythropoietin production. Proc Sot Exp Biol Med 1984;173:289-305. Finne PH, Halvorsen S. Regulation of erythropoiesis in the fetus and newborn. Arch Dis Child 1972;47:683-7. Widness JA, Swayer ST, Schmidt RL, Chestnut DH. Lack of maternal to fetal transfer of 125 I-labeled erythropoietin in sheep. J Dev Physiol 1991;15:139-43. Salveson DR, Brudenell JM, Snijders RJM, Ireland RM, Nicolaides KH. Fetal plasma erythropoietin in pregnancies complicated by maternal diabetes mellitus. AM J OBSTET GYP\‘ECOL 1993;168:88-94. Meberg A, Jakobsen E, Halvorsen K. Humural regulation of erythropoiesis and thrombopoiesis in appropriate and

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small for gestational age infants. Acta Paediatr Sand 1982;71:769-73. 23. Humbert JR, Abelson H, Hathaway WE, Battaglia FC. Polycythemia in small for gestational age infants. J Pediatr 1969;75:812-9. 24. Widness JA, Teramo KA, Clemons GK, et al. Correlation of the interpretation of fetal heart rate records with cord

et al.

plasma erythropoietin levels. Br J Obstet Gynaecol 1985; 92:326-32. 25. Moya FR, Grannum PA, Widness JA, Clemons GK, Cope1 JA, Hobbins JC. Erythropoietin in human fetuses with immune hemolytic anemia and hydrops fetalis. Obstet Gynecol 1993;82:353-8.

The ‘effect of lipid peroxides on isolated human umbilical artery contraction George R. Saade, MD,” Michael A. Belfort, MD,” David Johnson, PhD,” Yuri P. Vedernikov, MD, PhD,“‘b Helen Hughes, PhD,’ Maya Suresh, MD,b and Kenneth J. Moise, Jr., MD” Houston,

Texas

OBJECTIVE: Our purpose was to determine the effect of oxidized lipids on the contractile activity of isolated human umbilical arteries. STUDY DESIGN: Umbilical artery rings were prepared for isometric tension recording and exposed to cumulative concentrations of oxidized and nonoxidized lipid and control solutions. Rings were also incubated with the lipid or control solutions and then contracted with cumulative concentrations of U46619. A final set of rings in Ca’+ -free depolarized solution was incubated with the agents above, and then the Ca++ concentration was increased cumulatively. RESULTS: The lipids had no direct contractile effect. Both lipids inhibited the response to U46619 and Ca+ +, with the oxidized lipids having the most significant effect. CONCLUSION: Oxidized lipids lack a direct contractile effect on isolated human umbilical arteries and inhibit the contractile response to thromboxane and calcium. (AM J OBSTET GYNECOL 1995;172:825-30.)

Key words:

Human,

umbilical

artery, in vitro, lipid

peroxide,

Although the clinical signs and symptoms of pregnancy-induced hypertension have been extensively studied, the cause of the disorder remains an enigma. There is growing evidence that endothelial dysfunction plays a role in the pathogenesis of the disease.’ This impairment in function is also evident in endothelial cells of umbilical vessels from patients with pregnancyinduced hypertension.” One of the proposed mechanisms for the endothelial damage seen in preeclampsia relates to increased oxidative stress and free radicals,

From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology,” the Department of Anesthesiology’ and the Debartment of Medicine,” Baylor Colle.ce of Medicine. Supported inpart by a &ant from the-WdmenS Fund for HER. Received for publication April 13, 1994; revised August 8, 1994; accepted August 25, 1994. Reprint requests: George R. Saade, MD, Baylor College of Medicine, DeDartmen,t of Obstetrics and Gwecolopu One Baylor Plaza, Hwuston, TX 77030. Copyright 0 1995 by Mosby-Year Book, Inc. 0002-9378/95 $3.00 + 0 6/l/60275 Y_

contraction

including lipid peroxides.3 Blood levels of lipid peroxides are elevated in pregnancies complicated by hypertension compared with those of normal gestations4 Free radicals have been demonstrated to alter vascular tone through an effect on several modulators, including nitric oxide and prostaglandins5, 6 Lipid peroxides can induce vasoconstriction in a variety of organs.‘. a The effect of lipid peroxides on isolated human umbilical artery smooth muscle has not been investigated. We designed this experiment to study the effect of oxidized lipids produced in vitro on the contractile response of isolated human umbilical artery. Material

and

methods

Umbilical cords collected after vaginal or cesarean deliveries were immediately placed in cold Krebs-bicarbonate solution (composition in millimoles: sodium chloride 119, potassium chloride 4.7, magnesium sulfate 1.2, potassium phosphate 1.2, calcium chloride 2.5, sodium bicarbonate 25.0, dextrose 11.1, and sodium

825