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The effect of thigh-length support stockings on the hemodynamic response to ambulation in pregnancy
The effect of thigh-length support stockings on the hemodynamic response to ambulation in pregnancy Calvin J. Hobel, MD, Lony Castro, MD, Doron Rosen, MD, Jeffrey S. Greenspoon, MD, and Sharon Nessim, DrPH Los Angeles, California OBJECTIVE: Our purpose was to determine the effect of thigh-length support stockings on hemodynamic response when pregnant subjects change from the sitting to the lateral recumbent position and then after standing with ambulation. STUDY DESIGN: Eighteen subjects in the late second and early third trimester of pregnancy acted as their own controls. The cardiovascular status of the subjects was assessed by a noninvasive technique--thoracic electrical bioimpedance before and after wearing support stockings for 1 week. Urine catecholamines were measured in 13 patients before and after wearing support stockings to assess the release of catecholamines. Samples were collected after the subjects had been in the lateral recumbent position 40 minutes and again 40 minutes later after standing with ambulation. RESULTS: Heart rate and mean arterial blood pressure decreased significantly when subjects changed from the sitting to the lateral recumbent position and then increased with ambulation. Wearing compression stockings significantly increased mean arterial pressure and afterload in all three positions, Position change from lateral recumbent to standing and ambulation marginally increased urinary dopamine levels (p = 0.097) and significantly increased norepinephrine levels (p = 0.006). CONCLUSIONS: There are significant hemodynamic changes in pregnant subjects when they change from the sitting position to the lateral recumbent position and then change to standing with ambulation. Support stockings have a significant mechanical effect: they significantly increase afterload and systemic vascular resistance by preventing pooling of blood in the lower extremities. There may also be a biochemical effect that results in less catecholamine release. These results suggest that compression stockings could play an important role in supporting the circulation during ambulation. (Am J Obstet Gynecol 1996;174:1734-41 .)
Key words: Support stockings, thoracic electrical bioimpedance, catecholamines, orthostatic stress
The change from the recumbent to the standing position is associated with acute hemodynamic changes that are exaggerated during pregnancy. First, blood may pool in the lower extremities as a result of venous dilatation caused by hormonal changes. Second, as the uterus enlarges, it mechanically obstructs venous return from the lower extremities. The net result is that in the third trimester the standing position causes a decrease in blood pressure and cardiac output, followed by compensatory increases in both maternal heart rate and systemic vascular resistance)
From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Cedars Sinai Hospital Supported by GCRC grant No. MO1-RRO0425, National Centerfor Research Resources, and Kendall Health CareProducts Company. Presented at the Sixty-second Annual Meeting of the Pacific Coast Obstetrical and GynecologicalSociety, Squaw Va{ley, California, September 16-21, 1995. Reprint requests: Calvin J. Hobel, MD, Department of Obstetrics and Gynecology, Division of MaternaLFetal Medicine, 8700 Beverly Blvd., Los Angeles, CA 90048. Copyright © 1996 by Mosby-Year Book, Inc. 0002-9378/96 $5.00+ 0 6/6/72173 1734
Graduated elastic compression stockings increase venous flow velocity, increase venous emptying, and reduce the venous refilling rateJ These mechanical and physiologic effects result in less discomfort and edema and may improve maternal and fetal hemodynamics?' * The current investigation was performed to assess the hemodynamic changes that occur when the maternal position changes from the sitting position to the lateral recumbent position and then to the poststanding and ambulation position with and without stockings. These assessments were performed during the late second and early third trimester of pregnancy with a noninvasive technique to assess blood flow, systemic vascular resistance index, and afterload. The utility of the noninvasive technique of thoracic electrical bioimpedance in assessing comparative cardiac output changes in pregnancy has previously been described by Masaki etal. ~ The cardiovascular response to circulating catecholamines is blunted (decreased) during pregnancy. Therefore we also assessed the changes in urinary catecholamines between the lateral recumbent position and after ambulation in subjects with and without support stock-
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ings to determine whether support stockings would have a systemic biochemical and mechanical effect, s' 7
Material and methods Eighteen normal pregnant volunteers between 23 and 33 weeks of pregnancy we~'e studied between J u n e 1993 and February 1995. This investigation was approved by the Cedars-Sinai Institutional Review Board. The study subjects had a mean _+ 1 SD age of 27.9 _+5.0 years, a gravidity of 3.1 + 2.4, and a parity of 1.0 + 1.1. All subjects had a normal body mass index except for one who was obese. Four patients had employment outside of the home, and none of the patients exercised on a regular basis. The study subjects were evaluated at two time periods. The first evaluation established a baseline. The subjects then wore elastic support stockings for 1 week during the day only and were evaluated again while wearing stockings after 7 to 9 days of stocking use. The compliance for wearing the stockings for >12 hours each day was 73%. The stockings were removed at bedtime. The support stockings (TED hose; Kendall, Mansfield, Mass.) applied compression pressures of 18 m m Hg at the ankle and 10 mm Hg at midthigh. At each evaluation the subjects were studied u n d e r three conditions: sitting, after lying in the lateral recumbent position for 40 minutes, and then in the standing position after ambulation for 40 minutes. Thirteen of the 18 subjects provided a urine sample before sitting, immediately on standing up after 40 minutes in the lateral recumbent position, and after the 40 minutes of ambulation. The sample obtained immediately after the recumbent position is considered to represent urinary excretion of catecholamines over the prior 40 minutes. Urine samples were placed in special containers containing 0.1N hydrochloric acid and frozen at -70 ° C until assayed for dopamine, epinephrine, and norepinephrine by high-performance liquid chromatography by electrochemical detection. ~' 9 Cardiac output by thoracic electrical bioimpedance was estimated with an NCCOM-6 (noninvasive continuous cardiac output monitor, model 6; Biomed Medical Manufacturing, Irvine, Calif.) connected to a laptop corn± puter for data storage. Blood pressures were obtained with a standard arm cuff to identify the phase 1 and phase 5 Korotkoff sound for systolic and diastolic pressures, respectively. The NCCOM-6 unit measures heart and stroke volume, the latter estimated from thoracic electrical bioimpedance. The subject's blood pressure was measured and entered. The device cal
Hobel et al. 1735
assessment of after-load (Sramek BB. Personal communication). Each variable was assessed three times at approx imately 2-minute intervals for each assessment. MAP was calculated from the systolic and diastolic blood pressures obtained by sphygmomanometer. All cardiovascular study parameters are represented as the mean of the three repeated measurements for all analyses. Distributions were checked for skewness and outliers; when needed, a log transformation was used to normalize data before statistical analysis. A two-factor repeated-measures analysis of variance was used to test for differences in clinical measurements resulting from the use of stockings or position change. The model also considered an interaction term. Where data were log transformed, geometric means and 95% confidence intervals derived from the log distributions were calculated. All testing was two sided, with an (zvalue of 0.05. Statistical analysis was carried out by SAS statistical software (SAS Institute, Cary, N.C.) and a procedure for general linear models.
Results The mean _+1 SD for gestational age at the first study period was 29.9 -+ 3.2 weeks (range 22.9 to 34.4 weeks), and the second study was performed at a mean + 1 SD of 30.9 + 3.3 weeks. All patients were delivered at term except for one who was delivered at 34.3 weeks. The mean gestational age at delivery was 38.8 + 1.6 weeks and the mean birth weight was 3434+749 gm (range 2311 to 4975 gm). There was a significant change in the maternal heart rate as a result of position change (p = 0.0001). The mean heart rate decreased from 90.5 + 2.2 beats per minute (sitting) to 84.4 _+2.1 beats per minute (supine) and then increased to 99.4_+ 2.7 beats per minute (postambulation). All values are reported as mean _+1 SEM unless specified. After 1 week of support stocking use the significant changes in heart rate from position change remained, but we observed a "no stocking effect" (Fig. 1). Position change had a significant (p = 0.017) effect on MAP. The MAP decreased from 76.2 _+2.9 mm Hg (sitting) to 71.2 + 2.1 mm Hg (lateral recumbent) and then increased to 76.9 _+2.1 m m Hg after ambulation. There was a significant stocking effect (p = 0.049) resulting in an increase in MAP in each of the positions compared with the study period before the stockings were worn (Fig. 2). Stroke index, an assessment of blood flow, increased from 46 m l / b e a t / m 2 (95% confidence interval 41 to 52) (sitting) to 51 m l / b e a t / m 2 (95% confidence interval 45 to 58) (lateral recument) and then decreased to 48 m l / b e a t / m ~ (95%' confidence interval 44 to 52) with ambulation. These changes were not significant; however, there was a significant (p = 0.049) stocking effect. In each position--sitting, lateral recumbent, and postambulat i o n - - t h e r e was a decrease in the stroke index while the stockings were worn (Fig. 3).
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June 1996 Amj Obstet Gynecol
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Fig. 1. Relationship between maternal heart rate (beats per minute) (mean + 1 SEM) in three positions (sitting, lateral recumbent, and postambulation) before and after wearing support stockings for 1 week. Position effect, p = 0.001; stocking effect, not significant; interaction, not significant.
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Fig, 2. Relationship between maternal arterial pressure (millinmters of mercury) (mean _+SEM) in three positions (sitting, lateral recumbent, and postambulation) before and after wearing support stockings for 1 week. Position effect, p = 0.017; stocking effect, p = 0.049; interaction, not significant. Stroke systemic vascular index, a measure of afterload, decreased from 126 (95% confidence interval 111 to 142) (sitting) to 106 (95% confidence interval 93 to 120) (lateral r e c u m b e n t ) a n d t h e n increased to 124 (95% confidence interval 113 to 135) after ambulation. The effect of position on the stroke systemic vascular resistance index was significant ( p = 0.014). There was also a significant stocking effect (p = 0.006) with an increase in afterload in all three positions (Fig. 4). W h e n the position was c h a n g e d from sitting to r e c u m b e n t , the stroke systemic vascular resistance index decreased 15.7% without stockings b u t decreased only 10.4% with stockings. Changes in u r i n a r y catecholamines were assessed only when position was c h a n g e d from lateral r e c u m b e n c y to the e n d of ambulation. Mean e p i n e p h r i n e levels (micrograms per milligram of creatinine) increased slightly w h e n the lateral r e c u m b e n t position was compared with p o s t a m b u l a t i o n d u r i n g both the prestocking a n d poststocking periods; this was n o t statistically significant (Fig.
5). There was a statistically marginal (p = 0.097) interaction on u r i n a r y d o p a m i n e levels between position change with a n d without stockings. Before stockings were worn, m e a n levels of d o p a m i n e increased with ambulation, b u t after 1 week of stocking wear there was a decrease in m e a n d o p a m i n e levels after a m b u l a t i o n (Fig. 6). There was a significant (p=0.006) position effect o n (mean + SE) n o r e p i n e p h r i n e levels in the lateral recumb e n t position, 4.0 _+0.6 lag/nag creatinine, compared with the post-ambulation period, 6.4 + 0.7/lag/rag creatinine. This increase in n o r e p i n e p h r i n e was of lesser m a g n i t u d e after support stockings were worn, although this difference was n o t significant (Fig. 7).
Comment The primary purpose of our study was to assess the mechanical effect of s u p p o r t stockings on h e m o d y n a m i c parameters as d e t e r m i n e d by a noninvasive method. Recently Clark et al. 1° c o m p a r e d thoracic electrical bio-
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Hobel et al.
1737
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Fig. 3. Relationship between maternal stroke index (milliliters per beats per square meter) (mean and 95% confidence interval) in the three positions (sitting, lateral recumbent, and postambulation) before and after support stockings were worn for 1 week. Position effect, Not significant; stocking effect, p = 0.049; interaction, not significant.
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Fig. 4. Relationship between maternal stroke systemic vascular resistance (SSVR) index (mean and 95% confidence interval) in three positions (sitting, lateral recumbent, and postambulation) before and after support stockings were worn for 1 week. Position effect, p = 0.014; stocking effect, p = 0.006; interaction, not significant.
i m p e d a n c e with the invasive oxygen extraction t e c h n i q u e in the late third trimester and f o u n d g o o d correlations between the two techniques for cardiac o u t p u t in the lateral r e c u m b e n t position, but n o t during sitting or standing. In the c u r r e n t study each patient acted as h e r own control; therefore we can make valid comparisons between prestockings and poststockings comparisons with thoracic electrical b i o i m p e d a n c e . H e m o d y n a m i c parameters were m e a s u r e d before support stockings were w o r n and then r e p e a t e d after 1 week of stocking wear. It is known that orthostatic stress is associated with acute hem o d y n a m i c changes. During standing b l o o d pools in the lower extremities, resulting in a decrease in venous r e t u r n and afterload. As a result of the acute change to a m o r e erect position, b l o o d pressure decreases and h e a r t rate increases. To c o m p e n s a t e for these postural changes, catec h o l a m i n e s are released to increase peripheral vascular
resistance and normalize pressure and heart rate. This study evaluated changes after 40 minutes of ambulation, n o t the acute changes f r o m the supine to the standing position. The response of h e a r t rate to a change in position is t h o u g h t to be blunted during pregnancy. ~ ' n Whittaker et al. n evaluated a g r o u p of w o m e n before p r e g n a n c y and at 36 weeks' gestation and observed that during pregn a n c y w o m e n had a m o r e variable response than w h e n n o n p r e g n a n t . As a group, p r e g n a n t w o m e n showed no change in heart rate w h e n they assumed a standing position. We observed a significant effect of position on heart rate, which was n o t m o d i f i e d by support stockings. In regard to changes in MAP, studies by Whittaker et al) ~ have shown that p r e g n a n t w o m e n have significantly smaller changes in MAP with standing than n o n p r e g n a n t w o m e n do. Easterling et al) r e p o r t e d no n e t changes in
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Hobel et al.
June 1996 AmJ Obstet Gynecol
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MAP when they studied patients who c h a n g e d from rec u m b e n c y to standing. O u r patients had significant changes in MAP because of position, the lowest values occurring in the lateral position. Support stockings significantly increased MAPs in all three positions, which we i n t e r p r e t as a mechanical stocking effect. Easterling et al.1 showed that both cardiac o u t p u t a n d stroke volume are significantly higher d u r i n g recumbency a n d decrease significantly with standing. O u r measure of blood flow, the stroke index, showed an increase in blood flow in the lateral position a n d t h e n a decrease in the standing position alter ambulation, although this was n o t significant. O f interest was the significant stocking effect o n stroke index (blood flow) in which we observed a decrease in stroke i n d e x in each of the positions studied. This paradoxic finding is difficult to explain because a n increase in stroke i n d e x would be expected when venous pooling is r e d u c e d with support stockings.
Because each patient acted as h e r own control, we would n o t expect these findings to totally question the validity of thoracic electrical b i o i m p e d a n c e as a measure of blood flow. We must await studies using invasive techniques measuring stroke volume with a n d without support stockings in the standing position. Both Nisell et al2 a n d Barron et al.7 reported serum n o r e p i n e p h r i n e levels in n o n p r e g n a n t w o m e n that are approximately twice the levels d u r i n g pregnancy. This r e d u c e d c o n c e n t r a t i o n of n o r e p i n e p h r i n e d u r i n g pregnancy results in a state of lower systemic vascular resistance. 11 In our subjects u r i n a r y n o r e p i n e p h r i n e levels increased significantly while standing, b u t this increase was of lesser m a g n i t u d e when subjects wore support stockings. These results suggest that the mechanical effect of the stockings to increase afterload blunts the release of n o r e p i n e p h r i n e , probably by autoregulation. The a p p a r e n t interaction effect between change in ma-
Volume 174, Number 6 AmJ Obstet Gynecol
Hobel eta[.
1739
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Fig. 7. Relationship between urine norepinephrine levels (micrograms per milligram of creatinine) (mean + 1 SEM) in two positions (lateral recumbent and postambulation) before and after support stockings were worn for 1 week. Position effect, p -- 0.006; stocking effect, not significant.
ternal position and the use of stockings on urinary dopam i n e levels is consistent with the c o n c e p t that support stockings r e d u c e orthostatic stress. A r e d u c t i o n in norepin e p h r i n e levels associated with stocking use may also be clinically i m p o r t a n t because n o r e p i n e p h r i n e can cause uterine contractions. Consistent with this view is the observation o f Weber et al? that there were fewer uterine contractions d u r i n g standing w h e n the subjects wore supp o r t stockings. These data imply that the use of support stockings may be useful clinically to r e d u c e the increase in n u m e r of contractions that o c c u r with standing. Thus the mechanical, physiologic, and h o r m o n a l effects o f the stockings may be clinically important. In the U n i t e d S a t e s scant attention has b e e n paid to the effect of compression stockings on h e m o d y n a m i c s during pregnancy. 12 In Switzerland Weber et al. 3 studied 21 w o m e n d u r i n g late pregnancy. Compression of 40 m m H g at the ankle caused measurable i m p r o v e m e n t s in b o t h m a t e r n a l and fetal hemodynamics. In Sweden Nilsson et al. 2 studied with plethysmography the effect of c o m p r e s sion hosiery on 29 p r e g n a n t w o m e n at >35 weeks' gestation. T h e use of stockings p r o d u c i n g 25 m m H g c o m p r e s sion at the ankle and 12 m m H g at m i d t h i g h are associated with a significant increase in e x p e l l e d v o l u m e f r o m the lower extremities, followed by a r e d u c e d filling rate. O n e question remains. W h a t are the optimal effective pressures at ankle and m i d t h i g h that provide an adequate m e c h a n i c a l effect? Sjoberg et al. is evaluated f o u r differe n t compression stockings that e x e r t e d pressures ranging f r o m 18 to 35 m m H g at the ankle in n o n p r e g n a n t subjects. Venous emptying from the foot and leg was significandy increased with all f o u r stockings; there was no difference between types. Because the support stockings with the g r e a t e s t c o m p r e s s i o n at the ankle are m o r e difficult to p u t on and are considered uncomfortable~ it thus appears that stockings with about 18 to 22 m m H g at the
ankle would be effective in achieving the benefits reported. Support stockings in the p r e g n a n t subjects in this study were associated with favorable cardiovascular changes. Future r a n d o m i z e d trials should be considered to study the benefit of support stockings on p r e g n a n c y o u t c o m e s such as low birth weight and p r e t e r m birth, especially in w o m e n at increased risk because they s a n d or work for p r o l o n g e d periods. We thank the research nurses, Julie Schmidt, RN, Ricki Verne, RN, and Dyan Miano, RN, who facilitated the r e c r u i t m e n t of patients and the p e r f o r m a n c e of this study. We also thank C h a n d e r R A r o r a for p e r f o r m i n g the c a t e c h o l a m i n e assays.
REFERENCES 1. Easterling JR, Schmucker BC, Benedetti TJ. The hemodynamic effects of orthostatic stress during pregnancy. Obstet Gynecol 1988;72:550-2. 2. Nilsson L, Austrell CH, Norgren L. Venous function during late pregnancy, the effect of elastic compression hosiery. Vasa 1992;21:203-5. 3. Weber S, Schneider KTM, Bung P, Fallenstein F, Huch A, Huch R. Effect of compression stockings on circulation in late pregnancy. Geburtshilfe Frauenheilkd 1987;47:395-400. 4. Austrell C, Nilsson L, Norgren L. Maternal and fetal hemodynamics during late pregnancy: effect of compression hosiery treatment. Phlebology 1993;8:155-7. 5. Masaki DI, Greenspo0n JS, Ouzounian BS. Measurement of cardiac output in pregnancy by thoracic electrical bioimpedance and thermodilution. Am j Obstet Gynecol 1989;161: 680-4. 6. Nisell H, Hejemdali P, Linde B, Lunell NO. Sympathoadrehal and cardiovascular reactivity in pregnancy-induced hypertension. Am J Obstet Gynecol 1985;152:554-60. 7. Barron WM, Mujals SK, Zinaman M, Bravo EL, Lindheimer MD. Plasma catecholamine response to physiologic stimuli in the human pregnancy. Am J Obstet Gynecol 1986;154: 80-4. 8. Hashimoto H, Maruyama. High performance liquid chromatography with electrochemical detection. In: Parvez S,
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9.
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11. 12. 13.
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Nagatsu T, Nagatsu I, Parvez H, editors. Methods in biogenic amine research. Amsterdam: Elsevier, 1983:35-74. Parvez S, Parvez H, Roffi J. Hypophyseal-adrenal role in urinary excretion of epinephrine and norepinephrine in hypophysectomized and adrenalectomized rats. Endocrinology 1974;94:1054-9. Clark SL, SouthwickJ, PivarnikJM, Cotton DB, Hanking DV, Phelan JP. A comparison of cardiac index in normal term pregnancy using thoracic electrical bioimpedance and oxygen extraction (Fick) techniques. Obstet Gynecol 1994;83: 669-71. Whittaker PG, GerrardJ, Lind T. Catecholamine responses to changes in posture during pregnancy. BrJ Obstet Gynaecol 1985;92:586-92. Derman RJ, Coulam CB, Suarez RA, Kelly G, Leon A, Lane SM. Efficacyof light support pamyhose.J Reprod Med 1989; 34:946-9. SjobergJ, Einansson E, Norgren L. Functional evaluation of four different compression stockings in venous insufficiency. Phlebology 1987;2:53-8.
Editors' note: This manuscript was revised after these dis-
cussions were presented. Discussion
De, EZRAC. DAVIDSON,Jl~, Los Angeles, California. In general, both invasive and noninvasive investigations show an increase in maternal heart rate, a decrease in cardiac output, a decrease in stroke volume, an increase in systemic vascular resistance, and little or no change in MAP with sitting and standing compared with recumbent positions. The authors studied the effect of support stockings on these hemodynamic changes, with the addition of ambulation. For clarity in comparison to other studies, it would be helpful if the authors (1) explained why cardiac output was not reported as such, (2) how stroke index relates to cardiac output or cardiac index, and (3) how stroke systemic vascular resistance relates to systemic vascular resistance. Although the authors refer to midpregnancy evaluations, these are essentially early-third-trimester evaluations, with the baseline and post-support hose subjects having a mean of 29.9 and 30.9 weeks' gestation, respectively. The patients were studied in the sitting position, after lying in the lateral recumbent position for 40 minutes, immediately on standing, and after ambulation for 40 minutes. Studies were repeated after support hose use for 1 week with ankle compression of 22 mm Hg and midthigh compression of 10 m m Hg. A subgroup of patients provided urine samples during two test periods; immediately on standing and from the lateral recumbent position for 40 minutes and 40 minutes after ambulation to test catecholamine response to these positional changes. Of the four index values testing mechanical effect of position changes, heart rate, MAP, stroke index, and stroke systemic vascular resistance index, the latter three were interpreted to show significant stocking effect: a decrease in MAP in all positions after the wearing of stockings, an increase in the stroke index while stockings were worn, and improvement in afterload in all three positions. When compared with the results of other studies, the trends are similar except for the increase in MAP with sitting and standing.
June 1996 Amj Obstet Gynecol
Urinary epinephrine levels increased slightly after ambulation with and without stockings. Urinary norepinephrine levels increased less after stocking wear than before stocking wear with ambulation, and dopamine levels increased with ambulation before stockings and decreased on poststocking analysis. These changes are consistent with the physiologic response to maintain MAP. The trend toward reduction of dopamine may be one of the more important poststocking changes, indicating that less compensatory vasoconstriction is necessary. The authors adequately discuss their rationale for using compression support stockings to minimize hemodynamic changes with position by increasing venous flow and prevention of venous pooling in the lower extremities with sitting and ambulation. Most other studies of acute hemodynamic changes compared various recumbent positions to sitting and standing. Did ambulation, as opposed to standing only, result in more activity and stimulation, which would explain the increase in MAP changes seen in this study compared with others in the literature? Or, how do you reconcile the differences? If the difference in MAP is due to earlier gestation, this should be clarified by testing near term. Is it necessary to have chronic compression stockings used as this study observed, or could these changes be observed on short periodic use of the stockings (i.e., even after an hour or two)? The size of these women is not described. Is it easy m get fittings that comply with these compressmns on different-sized women? Can you comment on the compliance of women wearing these compression support stockings? H o n e t al. 1 have shown that in 550 normal pregnant women the changes in heart rate throughout pregnancy compared with sitting and standing positions varied only 8 to 10 beats/min. This appears to be relatively minor in normal women. Although these authors achieved statistical significance of stocking effect in MAP. an overall decrease in stroke index, and an improvement in the afterload, do you feel these statistical changes are of clinical significance? I am challenged by the author's recommendation that all pregnant women should wear support stockings during pregnancy with unsubstantiated pregnancy outcome benefit. It would be a major added cost to the 4 million births that occur annually in the United States. O n the basis of the data, it is justifiable to suggest studies to determine the appropriate compressions at the ankle and clinical studies to test whether adverse pregnancy outcomes such as low birth weight and preterm birth are affected by compression support hose or that uterine blood flow is affected. The core uterine circulation maybe unaffected by these changes. ~ Given the findings that standing, and perhaps ambulation, increase uterine contractions,2 thereby decreasing uteroplacental perfusion, and also decrease stroke volume and cardiac output, suggests that more frequent rest periods for pregn a n t women in recumbency would be beneficial. REFERENCES
1. Hon EH, Fukushima T, ParkJM,JelekJ. Apparatus for assessing the maternal cardiovascular system during pregnancy. J Matern Fetal Med 1993;2:97-102.
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2. Schneider KTM, Bung P, Weber S, Huch A, Huch R. An orthostatic uterovascular syndrome--a prospective, longitudinal study. AmJ Obstet Gynecol 1993;169:183-8. D~. ROBrJ~TC. GooDu~, Placerville, California. Guyton I says that these effects after leg hose are only temporary. The blood volume changes! Did the authors measure some indicators of change in plasma volume such as hematocrit? It has also been stated that pregnancy-induced hypertension does not develop in pregnant women with large varicose veins. Do the authors have any concerns that wearing these hose might cause future hypertension? It appeared that a n u m b e r of these patients had a positive orthostatic stress test, which is often associated with relative hypovolemia. Where there any complications in these groups such as premature labor, intrauterine growth restriction, or hypertension? REFERENCE
1. Guyton AC. Arterial pressure and hypertension. Philadelphia: WB Saunders, 1980. DR. I~YNETn BURRY, Portland, Oregon. Because your power analysis showed that the addition of 10 more patients may show significance in catecholamine production, do you plan to complete those 10 patients to get that statistical significance? It would seem to b e a simple, inexpensive study. DR. Cn~,~i~s BROB~, Pasadena, California. You mentioned increased uterine Contractility early in the report but did not provide any results. Were these contractions diminished and have we hit on a way, by giving women support stockings, of treating the troublesome increased uterine contractions that we seen so often in later pregnancy, or should these women still be treated with tocolysis? DI~ HoB~ (Closing). First, the differences in MAP that we observed were probably due to gestational age. Almost all the other studies were done late in pregnancy. Second, cardiac output is usually measured invasively as liters per minute, but when indexed to body surface and heart rate cardiac index or stroke index can be calculated. Cardiac output is indexed to surface area because subject size influences cardiac output, so it must be indexed to body size. Using stroke index, as in our study (indexed to heart rate), we were looking at the output per heart beat. In this way, the thoracic electrical bioimpedance system was developed. Essentially, there is close similarity between these three parameters. Regarding wearing support stockings for shorter periods of time, there was a Swedish study in 1973 that studied n o n p r e g n a n t subjects whose venous velocity persisted for at least 30 minutes after taking Off the stockings.1 These are the only data that I am
Hobel et al.
1741
aware of as to how long this effect could last. Regarding compliance, our patients were very compliant. Seventythree percent wore the stockings throughout the day. We gave them several pairs so that they could wash them and wear them continuously during the day; however, they did take them off at night. Eighty-five percent of the patients said they enjoyed wearing them a n d wanted to continue to do so after the study. Regarding clinical effectiveness, that will have to await randomized trials. I feel that support stockings benefit some patients. We need to look at the confounders to assess their direct effect. With regard to uterine blood flow and whether stockings could improve it, investigators in Europe have looked at uterine artery Doppler flow.2 With the use of support stockings, they showed an increase in the uterine artery pulsatility index. However, their sample size was too small to show significant effects. Someone should repeat those studies. Regarding Dr. Goodlin's questions, we have hematocrits, but have not gone back to look at this as yet, but we should assess whether some of the patients who had augmented stress response might have altered hematocrits. I am concerned about support stockings and potentially adverse effects, especially in individuals with varicose veins and the increased risk that some patients might have for preeclampsia. To answer Dr. Burry's question on the urinary catecholamines, with the help of our clinical study center, we are going to continue to look at the effect of support stockings on urinary norepinephrine and dopamine levels. The trends are very interesting. To answer Dr. Broberg's question on the value of support stockings to prevent uterine contractions, in terms of increased uterine activity, there is an excellent study published in the German literature in 1987 by a group from Zurich? They looked at the effect of support stockings on uterine contractility. Compared with the prestocking period, wearing support stockings resulted in the complete absence of uterine contractility. Support stockings might decrease uterine activity in some patients, thus reducing the need for oral tocolytics.
REFERENCES
1. Sigel B, Edelstein A, Felix R, Memhardt CR. Compression of the deep venous system of the lower leg during inactive recumbency. Arch Surg 1973;106:38-43. 2. Austrell C, Nilson L, Norgen L. Maternal and fetal hemodynamics during late pregnancy: effect of compression hosiery treatment. Phlebology 1993;8:155-7. 3. Weber S, Schneider KTM, Bung P, Fallenstein F, Huch A, Huch R. Effect of compression stockings on circulation in late pregnancy. Geburtshilfe Frauenheilkd 1987;47:395-400.
Key words: Support stockings, thoracic electrical bioimpedance, catecholamines, orthostatic stress
The change from the recumbent to the standing position is associated with acute hemodynamic changes that are exaggerated during pregnancy. First, blood may pool in the lower extremities as a result of venous dilatation caused by hormonal changes. Second, as the uterus enlarges, it mechanically obstructs venous return from the lower extremities. The net result is that in the third trimester the standing position causes a decrease in blood pressure and cardiac output, followed by compensatory increases in both maternal heart rate and systemic vascular resistance)
From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Cedars Sinai Hospital Supported by GCRC grant No. MO1-RRO0425, National Centerfor Research Resources, and Kendall Health CareProducts Company. Presented at the Sixty-second Annual Meeting of the Pacific Coast Obstetrical and GynecologicalSociety, Squaw Va{ley, California, September 16-21, 1995. Reprint requests: Calvin J. Hobel, MD, Department of Obstetrics and Gynecology, Division of MaternaLFetal Medicine, 8700 Beverly Blvd., Los Angeles, CA 90048. Copyright © 1996 by Mosby-Year Book, Inc. 0002-9378/96 $5.00+ 0 6/6/72173 1734
Graduated elastic compression stockings increase venous flow velocity, increase venous emptying, and reduce the venous refilling rateJ These mechanical and physiologic effects result in less discomfort and edema and may improve maternal and fetal hemodynamics?' * The current investigation was performed to assess the hemodynamic changes that occur when the maternal position changes from the sitting position to the lateral recumbent position and then to the poststanding and ambulation position with and without stockings. These assessments were performed during the late second and early third trimester of pregnancy with a noninvasive technique to assess blood flow, systemic vascular resistance index, and afterload. The utility of the noninvasive technique of thoracic electrical bioimpedance in assessing comparative cardiac output changes in pregnancy has previously been described by Masaki etal. ~ The cardiovascular response to circulating catecholamines is blunted (decreased) during pregnancy. Therefore we also assessed the changes in urinary catecholamines between the lateral recumbent position and after ambulation in subjects with and without support stock-
Volume 174, Number 6 AmJ Obstet Gynecol
ings to determine whether support stockings would have a systemic biochemical and mechanical effect, s' 7
Material and methods Eighteen normal pregnant volunteers between 23 and 33 weeks of pregnancy we~'e studied between J u n e 1993 and February 1995. This investigation was approved by the Cedars-Sinai Institutional Review Board. The study subjects had a mean _+ 1 SD age of 27.9 _+5.0 years, a gravidity of 3.1 + 2.4, and a parity of 1.0 + 1.1. All subjects had a normal body mass index except for one who was obese. Four patients had employment outside of the home, and none of the patients exercised on a regular basis. The study subjects were evaluated at two time periods. The first evaluation established a baseline. The subjects then wore elastic support stockings for 1 week during the day only and were evaluated again while wearing stockings after 7 to 9 days of stocking use. The compliance for wearing the stockings for >12 hours each day was 73%. The stockings were removed at bedtime. The support stockings (TED hose; Kendall, Mansfield, Mass.) applied compression pressures of 18 m m Hg at the ankle and 10 mm Hg at midthigh. At each evaluation the subjects were studied u n d e r three conditions: sitting, after lying in the lateral recumbent position for 40 minutes, and then in the standing position after ambulation for 40 minutes. Thirteen of the 18 subjects provided a urine sample before sitting, immediately on standing up after 40 minutes in the lateral recumbent position, and after the 40 minutes of ambulation. The sample obtained immediately after the recumbent position is considered to represent urinary excretion of catecholamines over the prior 40 minutes. Urine samples were placed in special containers containing 0.1N hydrochloric acid and frozen at -70 ° C until assayed for dopamine, epinephrine, and norepinephrine by high-performance liquid chromatography by electrochemical detection. ~' 9 Cardiac output by thoracic electrical bioimpedance was estimated with an NCCOM-6 (noninvasive continuous cardiac output monitor, model 6; Biomed Medical Manufacturing, Irvine, Calif.) connected to a laptop corn± puter for data storage. Blood pressures were obtained with a standard arm cuff to identify the phase 1 and phase 5 Korotkoff sound for systolic and diastolic pressures, respectively. The NCCOM-6 unit measures heart and stroke volume, the latter estimated from thoracic electrical bioimpedance. The subject's blood pressure was measured and entered. The device cal
Hobel et al. 1735
assessment of after-load (Sramek BB. Personal communication). Each variable was assessed three times at approx imately 2-minute intervals for each assessment. MAP was calculated from the systolic and diastolic blood pressures obtained by sphygmomanometer. All cardiovascular study parameters are represented as the mean of the three repeated measurements for all analyses. Distributions were checked for skewness and outliers; when needed, a log transformation was used to normalize data before statistical analysis. A two-factor repeated-measures analysis of variance was used to test for differences in clinical measurements resulting from the use of stockings or position change. The model also considered an interaction term. Where data were log transformed, geometric means and 95% confidence intervals derived from the log distributions were calculated. All testing was two sided, with an (zvalue of 0.05. Statistical analysis was carried out by SAS statistical software (SAS Institute, Cary, N.C.) and a procedure for general linear models.
Results The mean _+1 SD for gestational age at the first study period was 29.9 -+ 3.2 weeks (range 22.9 to 34.4 weeks), and the second study was performed at a mean + 1 SD of 30.9 + 3.3 weeks. All patients were delivered at term except for one who was delivered at 34.3 weeks. The mean gestational age at delivery was 38.8 + 1.6 weeks and the mean birth weight was 3434+749 gm (range 2311 to 4975 gm). There was a significant change in the maternal heart rate as a result of position change (p = 0.0001). The mean heart rate decreased from 90.5 + 2.2 beats per minute (sitting) to 84.4 _+2.1 beats per minute (supine) and then increased to 99.4_+ 2.7 beats per minute (postambulation). All values are reported as mean _+1 SEM unless specified. After 1 week of support stocking use the significant changes in heart rate from position change remained, but we observed a "no stocking effect" (Fig. 1). Position change had a significant (p = 0.017) effect on MAP. The MAP decreased from 76.2 _+2.9 mm Hg (sitting) to 71.2 + 2.1 mm Hg (lateral recumbent) and then increased to 76.9 _+2.1 m m Hg after ambulation. There was a significant stocking effect (p = 0.049) resulting in an increase in MAP in each of the positions compared with the study period before the stockings were worn (Fig. 2). Stroke index, an assessment of blood flow, increased from 46 m l / b e a t / m 2 (95% confidence interval 41 to 52) (sitting) to 51 m l / b e a t / m 2 (95% confidence interval 45 to 58) (lateral recument) and then decreased to 48 m l / b e a t / m ~ (95%' confidence interval 44 to 52) with ambulation. These changes were not significant; however, there was a significant (p = 0.049) stocking effect. In each position--sitting, lateral recumbent, and postambulat i o n - - t h e r e was a decrease in the stroke index while the stockings were worn (Fig. 3).
1736
Hobel et al.
June 1996 Amj Obstet Gynecol
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Fig. 1. Relationship between maternal heart rate (beats per minute) (mean + 1 SEM) in three positions (sitting, lateral recumbent, and postambulation) before and after wearing support stockings for 1 week. Position effect, p = 0.001; stocking effect, not significant; interaction, not significant.
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Fig, 2. Relationship between maternal arterial pressure (millinmters of mercury) (mean _+SEM) in three positions (sitting, lateral recumbent, and postambulation) before and after wearing support stockings for 1 week. Position effect, p = 0.017; stocking effect, p = 0.049; interaction, not significant. Stroke systemic vascular index, a measure of afterload, decreased from 126 (95% confidence interval 111 to 142) (sitting) to 106 (95% confidence interval 93 to 120) (lateral r e c u m b e n t ) a n d t h e n increased to 124 (95% confidence interval 113 to 135) after ambulation. The effect of position on the stroke systemic vascular resistance index was significant ( p = 0.014). There was also a significant stocking effect (p = 0.006) with an increase in afterload in all three positions (Fig. 4). W h e n the position was c h a n g e d from sitting to r e c u m b e n t , the stroke systemic vascular resistance index decreased 15.7% without stockings b u t decreased only 10.4% with stockings. Changes in u r i n a r y catecholamines were assessed only when position was c h a n g e d from lateral r e c u m b e n c y to the e n d of ambulation. Mean e p i n e p h r i n e levels (micrograms per milligram of creatinine) increased slightly w h e n the lateral r e c u m b e n t position was compared with p o s t a m b u l a t i o n d u r i n g both the prestocking a n d poststocking periods; this was n o t statistically significant (Fig.
5). There was a statistically marginal (p = 0.097) interaction on u r i n a r y d o p a m i n e levels between position change with a n d without stockings. Before stockings were worn, m e a n levels of d o p a m i n e increased with ambulation, b u t after 1 week of stocking wear there was a decrease in m e a n d o p a m i n e levels after a m b u l a t i o n (Fig. 6). There was a significant (p=0.006) position effect o n (mean + SE) n o r e p i n e p h r i n e levels in the lateral recumb e n t position, 4.0 _+0.6 lag/nag creatinine, compared with the post-ambulation period, 6.4 + 0.7/lag/rag creatinine. This increase in n o r e p i n e p h r i n e was of lesser m a g n i t u d e after support stockings were worn, although this difference was n o t significant (Fig. 7).
Comment The primary purpose of our study was to assess the mechanical effect of s u p p o r t stockings on h e m o d y n a m i c parameters as d e t e r m i n e d by a noninvasive method. Recently Clark et al. 1° c o m p a r e d thoracic electrical bio-
Volume 174, Number 6 AmJ Obstet Gynecol
Hobel et al.
1737
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Fig. 3. Relationship between maternal stroke index (milliliters per beats per square meter) (mean and 95% confidence interval) in the three positions (sitting, lateral recumbent, and postambulation) before and after support stockings were worn for 1 week. Position effect, Not significant; stocking effect, p = 0.049; interaction, not significant.
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i m p e d a n c e with the invasive oxygen extraction t e c h n i q u e in the late third trimester and f o u n d g o o d correlations between the two techniques for cardiac o u t p u t in the lateral r e c u m b e n t position, but n o t during sitting or standing. In the c u r r e n t study each patient acted as h e r own control; therefore we can make valid comparisons between prestockings and poststockings comparisons with thoracic electrical b i o i m p e d a n c e . H e m o d y n a m i c parameters were m e a s u r e d before support stockings were w o r n and then r e p e a t e d after 1 week of stocking wear. It is known that orthostatic stress is associated with acute hem o d y n a m i c changes. During standing b l o o d pools in the lower extremities, resulting in a decrease in venous r e t u r n and afterload. As a result of the acute change to a m o r e erect position, b l o o d pressure decreases and h e a r t rate increases. To c o m p e n s a t e for these postural changes, catec h o l a m i n e s are released to increase peripheral vascular
resistance and normalize pressure and heart rate. This study evaluated changes after 40 minutes of ambulation, n o t the acute changes f r o m the supine to the standing position. The response of h e a r t rate to a change in position is t h o u g h t to be blunted during pregnancy. ~ ' n Whittaker et al. n evaluated a g r o u p of w o m e n before p r e g n a n c y and at 36 weeks' gestation and observed that during pregn a n c y w o m e n had a m o r e variable response than w h e n n o n p r e g n a n t . As a group, p r e g n a n t w o m e n showed no change in heart rate w h e n they assumed a standing position. We observed a significant effect of position on heart rate, which was n o t m o d i f i e d by support stockings. In regard to changes in MAP, studies by Whittaker et al) ~ have shown that p r e g n a n t w o m e n have significantly smaller changes in MAP with standing than n o n p r e g n a n t w o m e n do. Easterling et al) r e p o r t e d no n e t changes in
1738
Hobel et al.
June 1996 AmJ Obstet Gynecol
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MAP when they studied patients who c h a n g e d from rec u m b e n c y to standing. O u r patients had significant changes in MAP because of position, the lowest values occurring in the lateral position. Support stockings significantly increased MAPs in all three positions, which we i n t e r p r e t as a mechanical stocking effect. Easterling et al.1 showed that both cardiac o u t p u t a n d stroke volume are significantly higher d u r i n g recumbency a n d decrease significantly with standing. O u r measure of blood flow, the stroke index, showed an increase in blood flow in the lateral position a n d t h e n a decrease in the standing position alter ambulation, although this was n o t significant. O f interest was the significant stocking effect o n stroke index (blood flow) in which we observed a decrease in stroke i n d e x in each of the positions studied. This paradoxic finding is difficult to explain because a n increase in stroke i n d e x would be expected when venous pooling is r e d u c e d with support stockings.
Because each patient acted as h e r own control, we would n o t expect these findings to totally question the validity of thoracic electrical b i o i m p e d a n c e as a measure of blood flow. We must await studies using invasive techniques measuring stroke volume with a n d without support stockings in the standing position. Both Nisell et al2 a n d Barron et al.7 reported serum n o r e p i n e p h r i n e levels in n o n p r e g n a n t w o m e n that are approximately twice the levels d u r i n g pregnancy. This r e d u c e d c o n c e n t r a t i o n of n o r e p i n e p h r i n e d u r i n g pregnancy results in a state of lower systemic vascular resistance. 11 In our subjects u r i n a r y n o r e p i n e p h r i n e levels increased significantly while standing, b u t this increase was of lesser m a g n i t u d e when subjects wore support stockings. These results suggest that the mechanical effect of the stockings to increase afterload blunts the release of n o r e p i n e p h r i n e , probably by autoregulation. The a p p a r e n t interaction effect between change in ma-
Volume 174, Number 6 AmJ Obstet Gynecol
Hobel eta[.
1739
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Post-stocking
Fig. 7. Relationship between urine norepinephrine levels (micrograms per milligram of creatinine) (mean + 1 SEM) in two positions (lateral recumbent and postambulation) before and after support stockings were worn for 1 week. Position effect, p -- 0.006; stocking effect, not significant.
ternal position and the use of stockings on urinary dopam i n e levels is consistent with the c o n c e p t that support stockings r e d u c e orthostatic stress. A r e d u c t i o n in norepin e p h r i n e levels associated with stocking use may also be clinically i m p o r t a n t because n o r e p i n e p h r i n e can cause uterine contractions. Consistent with this view is the observation o f Weber et al? that there were fewer uterine contractions d u r i n g standing w h e n the subjects wore supp o r t stockings. These data imply that the use of support stockings may be useful clinically to r e d u c e the increase in n u m e r of contractions that o c c u r with standing. Thus the mechanical, physiologic, and h o r m o n a l effects o f the stockings may be clinically important. In the U n i t e d S a t e s scant attention has b e e n paid to the effect of compression stockings on h e m o d y n a m i c s during pregnancy. 12 In Switzerland Weber et al. 3 studied 21 w o m e n d u r i n g late pregnancy. Compression of 40 m m H g at the ankle caused measurable i m p r o v e m e n t s in b o t h m a t e r n a l and fetal hemodynamics. In Sweden Nilsson et al. 2 studied with plethysmography the effect of c o m p r e s sion hosiery on 29 p r e g n a n t w o m e n at >35 weeks' gestation. T h e use of stockings p r o d u c i n g 25 m m H g c o m p r e s sion at the ankle and 12 m m H g at m i d t h i g h are associated with a significant increase in e x p e l l e d v o l u m e f r o m the lower extremities, followed by a r e d u c e d filling rate. O n e question remains. W h a t are the optimal effective pressures at ankle and m i d t h i g h that provide an adequate m e c h a n i c a l effect? Sjoberg et al. is evaluated f o u r differe n t compression stockings that e x e r t e d pressures ranging f r o m 18 to 35 m m H g at the ankle in n o n p r e g n a n t subjects. Venous emptying from the foot and leg was significandy increased with all f o u r stockings; there was no difference between types. Because the support stockings with the g r e a t e s t c o m p r e s s i o n at the ankle are m o r e difficult to p u t on and are considered uncomfortable~ it thus appears that stockings with about 18 to 22 m m H g at the
ankle would be effective in achieving the benefits reported. Support stockings in the p r e g n a n t subjects in this study were associated with favorable cardiovascular changes. Future r a n d o m i z e d trials should be considered to study the benefit of support stockings on p r e g n a n c y o u t c o m e s such as low birth weight and p r e t e r m birth, especially in w o m e n at increased risk because they s a n d or work for p r o l o n g e d periods. We thank the research nurses, Julie Schmidt, RN, Ricki Verne, RN, and Dyan Miano, RN, who facilitated the r e c r u i t m e n t of patients and the p e r f o r m a n c e of this study. We also thank C h a n d e r R A r o r a for p e r f o r m i n g the c a t e c h o l a m i n e assays.
REFERENCES 1. Easterling JR, Schmucker BC, Benedetti TJ. The hemodynamic effects of orthostatic stress during pregnancy. Obstet Gynecol 1988;72:550-2. 2. Nilsson L, Austrell CH, Norgren L. Venous function during late pregnancy, the effect of elastic compression hosiery. Vasa 1992;21:203-5. 3. Weber S, Schneider KTM, Bung P, Fallenstein F, Huch A, Huch R. Effect of compression stockings on circulation in late pregnancy. Geburtshilfe Frauenheilkd 1987;47:395-400. 4. Austrell C, Nilsson L, Norgren L. Maternal and fetal hemodynamics during late pregnancy: effect of compression hosiery treatment. Phlebology 1993;8:155-7. 5. Masaki DI, Greenspo0n JS, Ouzounian BS. Measurement of cardiac output in pregnancy by thoracic electrical bioimpedance and thermodilution. Am j Obstet Gynecol 1989;161: 680-4. 6. Nisell H, Hejemdali P, Linde B, Lunell NO. Sympathoadrehal and cardiovascular reactivity in pregnancy-induced hypertension. Am J Obstet Gynecol 1985;152:554-60. 7. Barron WM, Mujals SK, Zinaman M, Bravo EL, Lindheimer MD. Plasma catecholamine response to physiologic stimuli in the human pregnancy. Am J Obstet Gynecol 1986;154: 80-4. 8. Hashimoto H, Maruyama. High performance liquid chromatography with electrochemical detection. In: Parvez S,
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9.
10.
11. 12. 13.
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Nagatsu T, Nagatsu I, Parvez H, editors. Methods in biogenic amine research. Amsterdam: Elsevier, 1983:35-74. Parvez S, Parvez H, Roffi J. Hypophyseal-adrenal role in urinary excretion of epinephrine and norepinephrine in hypophysectomized and adrenalectomized rats. Endocrinology 1974;94:1054-9. Clark SL, SouthwickJ, PivarnikJM, Cotton DB, Hanking DV, Phelan JP. A comparison of cardiac index in normal term pregnancy using thoracic electrical bioimpedance and oxygen extraction (Fick) techniques. Obstet Gynecol 1994;83: 669-71. Whittaker PG, GerrardJ, Lind T. Catecholamine responses to changes in posture during pregnancy. BrJ Obstet Gynaecol 1985;92:586-92. Derman RJ, Coulam CB, Suarez RA, Kelly G, Leon A, Lane SM. Efficacyof light support pamyhose.J Reprod Med 1989; 34:946-9. SjobergJ, Einansson E, Norgren L. Functional evaluation of four different compression stockings in venous insufficiency. Phlebology 1987;2:53-8.
Editors' note: This manuscript was revised after these dis-
cussions were presented. Discussion
De, EZRAC. DAVIDSON,Jl~, Los Angeles, California. In general, both invasive and noninvasive investigations show an increase in maternal heart rate, a decrease in cardiac output, a decrease in stroke volume, an increase in systemic vascular resistance, and little or no change in MAP with sitting and standing compared with recumbent positions. The authors studied the effect of support stockings on these hemodynamic changes, with the addition of ambulation. For clarity in comparison to other studies, it would be helpful if the authors (1) explained why cardiac output was not reported as such, (2) how stroke index relates to cardiac output or cardiac index, and (3) how stroke systemic vascular resistance relates to systemic vascular resistance. Although the authors refer to midpregnancy evaluations, these are essentially early-third-trimester evaluations, with the baseline and post-support hose subjects having a mean of 29.9 and 30.9 weeks' gestation, respectively. The patients were studied in the sitting position, after lying in the lateral recumbent position for 40 minutes, immediately on standing, and after ambulation for 40 minutes. Studies were repeated after support hose use for 1 week with ankle compression of 22 mm Hg and midthigh compression of 10 m m Hg. A subgroup of patients provided urine samples during two test periods; immediately on standing and from the lateral recumbent position for 40 minutes and 40 minutes after ambulation to test catecholamine response to these positional changes. Of the four index values testing mechanical effect of position changes, heart rate, MAP, stroke index, and stroke systemic vascular resistance index, the latter three were interpreted to show significant stocking effect: a decrease in MAP in all positions after the wearing of stockings, an increase in the stroke index while stockings were worn, and improvement in afterload in all three positions. When compared with the results of other studies, the trends are similar except for the increase in MAP with sitting and standing.
June 1996 Amj Obstet Gynecol
Urinary epinephrine levels increased slightly after ambulation with and without stockings. Urinary norepinephrine levels increased less after stocking wear than before stocking wear with ambulation, and dopamine levels increased with ambulation before stockings and decreased on poststocking analysis. These changes are consistent with the physiologic response to maintain MAP. The trend toward reduction of dopamine may be one of the more important poststocking changes, indicating that less compensatory vasoconstriction is necessary. The authors adequately discuss their rationale for using compression support stockings to minimize hemodynamic changes with position by increasing venous flow and prevention of venous pooling in the lower extremities with sitting and ambulation. Most other studies of acute hemodynamic changes compared various recumbent positions to sitting and standing. Did ambulation, as opposed to standing only, result in more activity and stimulation, which would explain the increase in MAP changes seen in this study compared with others in the literature? Or, how do you reconcile the differences? If the difference in MAP is due to earlier gestation, this should be clarified by testing near term. Is it necessary to have chronic compression stockings used as this study observed, or could these changes be observed on short periodic use of the stockings (i.e., even after an hour or two)? The size of these women is not described. Is it easy m get fittings that comply with these compressmns on different-sized women? Can you comment on the compliance of women wearing these compression support stockings? H o n e t al. 1 have shown that in 550 normal pregnant women the changes in heart rate throughout pregnancy compared with sitting and standing positions varied only 8 to 10 beats/min. This appears to be relatively minor in normal women. Although these authors achieved statistical significance of stocking effect in MAP. an overall decrease in stroke index, and an improvement in the afterload, do you feel these statistical changes are of clinical significance? I am challenged by the author's recommendation that all pregnant women should wear support stockings during pregnancy with unsubstantiated pregnancy outcome benefit. It would be a major added cost to the 4 million births that occur annually in the United States. O n the basis of the data, it is justifiable to suggest studies to determine the appropriate compressions at the ankle and clinical studies to test whether adverse pregnancy outcomes such as low birth weight and preterm birth are affected by compression support hose or that uterine blood flow is affected. The core uterine circulation maybe unaffected by these changes. ~ Given the findings that standing, and perhaps ambulation, increase uterine contractions,2 thereby decreasing uteroplacental perfusion, and also decrease stroke volume and cardiac output, suggests that more frequent rest periods for pregn a n t women in recumbency would be beneficial. REFERENCES
1. Hon EH, Fukushima T, ParkJM,JelekJ. Apparatus for assessing the maternal cardiovascular system during pregnancy. J Matern Fetal Med 1993;2:97-102.
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2. Schneider KTM, Bung P, Weber S, Huch A, Huch R. An orthostatic uterovascular syndrome--a prospective, longitudinal study. AmJ Obstet Gynecol 1993;169:183-8. D~. ROBrJ~TC. GooDu~, Placerville, California. Guyton I says that these effects after leg hose are only temporary. The blood volume changes! Did the authors measure some indicators of change in plasma volume such as hematocrit? It has also been stated that pregnancy-induced hypertension does not develop in pregnant women with large varicose veins. Do the authors have any concerns that wearing these hose might cause future hypertension? It appeared that a n u m b e r of these patients had a positive orthostatic stress test, which is often associated with relative hypovolemia. Where there any complications in these groups such as premature labor, intrauterine growth restriction, or hypertension? REFERENCE
1. Guyton AC. Arterial pressure and hypertension. Philadelphia: WB Saunders, 1980. DR. I~YNETn BURRY, Portland, Oregon. Because your power analysis showed that the addition of 10 more patients may show significance in catecholamine production, do you plan to complete those 10 patients to get that statistical significance? It would seem to b e a simple, inexpensive study. DR. Cn~,~i~s BROB~, Pasadena, California. You mentioned increased uterine Contractility early in the report but did not provide any results. Were these contractions diminished and have we hit on a way, by giving women support stockings, of treating the troublesome increased uterine contractions that we seen so often in later pregnancy, or should these women still be treated with tocolysis? DI~ HoB~ (Closing). First, the differences in MAP that we observed were probably due to gestational age. Almost all the other studies were done late in pregnancy. Second, cardiac output is usually measured invasively as liters per minute, but when indexed to body surface and heart rate cardiac index or stroke index can be calculated. Cardiac output is indexed to surface area because subject size influences cardiac output, so it must be indexed to body size. Using stroke index, as in our study (indexed to heart rate), we were looking at the output per heart beat. In this way, the thoracic electrical bioimpedance system was developed. Essentially, there is close similarity between these three parameters. Regarding wearing support stockings for shorter periods of time, there was a Swedish study in 1973 that studied n o n p r e g n a n t subjects whose venous velocity persisted for at least 30 minutes after taking Off the stockings.1 These are the only data that I am
Hobel et al.
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aware of as to how long this effect could last. Regarding compliance, our patients were very compliant. Seventythree percent wore the stockings throughout the day. We gave them several pairs so that they could wash them and wear them continuously during the day; however, they did take them off at night. Eighty-five percent of the patients said they enjoyed wearing them a n d wanted to continue to do so after the study. Regarding clinical effectiveness, that will have to await randomized trials. I feel that support stockings benefit some patients. We need to look at the confounders to assess their direct effect. With regard to uterine blood flow and whether stockings could improve it, investigators in Europe have looked at uterine artery Doppler flow.2 With the use of support stockings, they showed an increase in the uterine artery pulsatility index. However, their sample size was too small to show significant effects. Someone should repeat those studies. Regarding Dr. Goodlin's questions, we have hematocrits, but have not gone back to look at this as yet, but we should assess whether some of the patients who had augmented stress response might have altered hematocrits. I am concerned about support stockings and potentially adverse effects, especially in individuals with varicose veins and the increased risk that some patients might have for preeclampsia. To answer Dr. Burry's question on the urinary catecholamines, with the help of our clinical study center, we are going to continue to look at the effect of support stockings on urinary norepinephrine and dopamine levels. The trends are very interesting. To answer Dr. Broberg's question on the value of support stockings to prevent uterine contractions, in terms of increased uterine activity, there is an excellent study published in the German literature in 1987 by a group from Zurich? They looked at the effect of support stockings on uterine contractility. Compared with the prestocking period, wearing support stockings resulted in the complete absence of uterine contractility. Support stockings might decrease uterine activity in some patients, thus reducing the need for oral tocolytics.
REFERENCES
1. Sigel B, Edelstein A, Felix R, Memhardt CR. Compression of the deep venous system of the lower leg during inactive recumbency. Arch Surg 1973;106:38-43. 2. Austrell C, Nilson L, Norgen L. Maternal and fetal hemodynamics during late pregnancy: effect of compression hosiery treatment. Phlebology 1993;8:155-7. 3. Weber S, Schneider KTM, Bung P, Fallenstein F, Huch A, Huch R. Effect of compression stockings on circulation in late pregnancy. Geburtshilfe Frauenheilkd 1987;47:395-400.