Schneider & Deckardt, Implication of upright posture on pregnancy
J. Perinat. Med. 19(1991) 121-131
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The implication of upright posture on pregnancy Karl-Theo M. Schneider and Rainer Deckardt
Gynecological Clinic („Frauenklinik rechts der Isar") of the Technical University Munich, Munich, Fed. Rep. of Germany
1
Introduction
The upright posture is one of the outstanding characteristics that distinguishes the human from the animal. Pregnant women usually spend more than half of the day in the upright position. In contrast, the majority of investigations on the physiological changes during pregnancy deal only with women in the recumbent position. This paper presents new and established facts about the upright position and its clinical relevance for the mother and the fetus during early and late pregnancy. 2
Early pregnancy
2.1 Cardiovascular changes during maternal upright posture
A frequent problem during early pregnancy is maternal syncope following a positional change into the upright position. The leading cause for this is believed to be an increased vessel diameter in conjunction with an insufficient adaptation of the vascular autoregulation. Vasodilation during early pregnancy is supported by the trophoblastic invasion, estrogen and progesterone mediated relaxation of the venous smooth muscle tone, a reduced tone of the striated muscles and a marked shift in the production of prostaglandin derivatives from thromboxane to vessel dilating prostacyclin [2, 8, 10, 11, 12, 15, 24, 25].
Curriculum vitae KARL-THEO M. SCHNEIDER, M. D., born in 1950, was graduated from the University of Würzburg, Germany in 1977. He worked in Pathology and Internal Medicine for two years. From 1979 to 1982 he did his residency in Obstetrics and Gynecology at the Hospital Waldfriede, Berlin. From 1982—1985 he had a Swiss National font grant and attended at the University Hospital of Zurich, Switzerland. In 1986 he joined the faculty of Obstetrics and Gynecology rechts der Isar, University of Technology, Munich ('Habilitation' 1987, 'Privatdozent' 1988, 'Professor (Extraordinarius) ' 1990). Main fields of interest include: Feto-maternal cardiovascular physiology, perinatal surveillance techniques, quality control, prenatal diagnosis and therapy.
about 8% of women experience dizziness in early pregnancy after standing for 8 to 10 minutes and are not able to stand any longer. A reduction in systolic blood pressure by more than 20 mmHg and an increased heart rate can be observed in most of these cases [10, 12, 15, 24].
Orthostatic dysregulation can be found ten times more frequently in hypotensive women as compared with normotensive women [13]. About Despite the common knowledge that fainting is one-third of pregnant women have a systolic a typical phenomenon during early pregnancy, blood pressure below 100 mmHg and therefore there is little precise information about the in- fulfil the criteria of "hypotension." Orthostatic cidence of this cardiovascular decompensation. dysregulation seems to be of more importance From published works it can be calculated thatby | New thanYork lowUniversity blood pressure per seTechnical [10, 13,Services 15]. Brought to you Bobst Library 1991 by Walter de Gruyter & Co. Berlin · New York
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Schneider & Deckardt, Implication of upright posture on pregnancy
Because of inadequate monitoring equipment and the shortness of these episodes which rarely exceed 2 minutes, there is no knowledge about the implications of these sudden cardiovascular changes on the embryo. The incidence of spontaneous abortions, low birth-weight infants and still-births is increased in women with early orthostatic dysregulation [13]. 2.2 Pulmonary changes during maternal upright posture
Despite the well established knowledge of markedly changed lung volumes and respiratory parameters even during very early pregnancy [6, 9, 19] and despite the knowledge about the influence of body position on lung function in the non-pregnant woman [5, 18], there are no publications which outline the changes of lung function due to the upright posture in early pregnancy. 3
Late pregnancy*
3.1 Pulmonary changes in the maternal upright posture
reserve in an apneic patient, thus resulting in less hypoxemia than with a decreased FRC. Considering these results, one can declare that upright position during late pregnancy is one safety measure against hypoxemia. Regarding the respiratory changes in the upright position during pregnancy, there is a significant (p < 0.001) increase in minute ventilation. This is primarily the result of an increased tidal volume with little change in respiratory rate. Oxygen consumption was significantly increased (p < 0.001), as was the elimination of carbon dioxide. This increase in breathing work during pregnancy has been even more pronounced in the upright position (figure 2). 3.2 Cardiovascular changes during maternal upright posture
During the assessment of the lung volumes by spirometry, additional parameters such as maternal and fetal electrocardiograms had been recorded. We experienced a new cardiovascular phenomenon in 33 out of 51 standing women, which had not been described before [27].
Change from the left lateral position to unsupported standing led to a transitional increase in The upright position and its implication on pregnancy during the last trimester also has not been maternal heart rate with a mean increase of 27 studied in detail [1, 23, 32]. In order to gather beats per minute (bpm) and a duration of 105 more knowledge about this topic, we investigated seconds in two-thirds of the women. Figure 3 15 healthy pregnant women during their last delineates the observed changes in the women. gestational trimester with a commercial lung With a change from the left lateral to the upright function system (Ergostar, Co., Dr. Fenyves & posture, one can detect a concurrent fall of the Gut, Basel, 30). Statistical analyses were per- cardiac output, a transitional rise of the maternal formed using the Wilcoxon test. Statistical sig- heart rate, fall of the systolic blood pressure and nificance was assessed when the probability was an increase in oxygen consumption. more than 5%. This phenomenon was less pronounced when the woman was asked to activate her muscle pump The upright position causes an increase in all by specific movements. Leaning forward also lung volumes except in the inspiratory reserve normalized maternal heart rate fluctuations; volume (IRV) which decreases by 5% (figure 1). whereas, standing again resulted in an increase A significant increase in the functional residual in maternal heart rate fluctuations. After delivery capacity (FRC) was due mainly to an increase of the expiratory reserve volume (ERV) by the changes in the maternal heart rate pattern around one-third. The FRC serves as a buffer during standing were not reproduced in any of against rapid changes in oxygen supply. As an the women. example, an increased FRC elevates the oxygen Measurement of the flow velocity in the maternal femoral artery displayed a cyclic decrease of systolic and even more pronounced change in dia* Most of the reported investigation were performed stolic flow velocities. Measurement of the flow in the Perinatal Physiology Unit of Profs. ALBERT velocity in the maternal femoral vein displayed and RENATE HUGH, Department of Obstetrics, Uni- a marked decrease of venous flow during periods York Universitymaternal Bobst Library Technical Services4). An versity of Zurich, Switzerland. Brought to you by | Newof increased heart rate (figure Authenticated Download Date | 6/23/15 5:32 PM
J. Perinat. Med. 19 (1991)
Schneider & Deckardt, Implication of upright posture on pregnancy
4.0
123
inspiratory reserve volume Δ -5%
3.0
tidal volume Δ + 8% 2.0
exspiratory reserve volume Δ+31 1.0
residual volume Δ + 12%
Figure 1. Effect of upright posture upon lung volumes and capacities during the last trimester (n = 15). FRC = functional residual capacity
creases in order to maintain cardiac output. Uterine contractions or leaning forward, improves the venous return by positional or configurational changes of the uterus. Activation of the muscle pump is another mechanism which partially overcomes this phenomenon by an imSurprisingly, uterine contractions are the cause. provement of venous return. With every onset of a contraction, maternal heart rate normalizes. Every relaxation is answered To learn about the time of onset and developwith an instant increase in heart rate (figure 5). ment of this occurrence, we longitudinally invesOur conclusion from this preliminary study was tigated 40 healthy pregnant women from the that the relaxed uterus more frequently causes 20th gestational week onwards with a total of compression of the maternal pelvic vessels during 358 investigations [28]. The marker utilized in the upright position than has been reported from our facility to identify this phenomenon is the the recumbent position [1,17]. The venous return occurrence of maternal heart rate accelerations. to the right ventricle becomes impeded, the A positive reaction is defined as the requirement to you University Bobst Technical Services that York there be three or Library more such cycles/10 min stroke volume falls, and maternal Brought heart rate in-by | New
increase of femoral flow velocity resulted in a normalization of maternal heart rate. We attempted to determine which mechanism was responsible for the observed spontaneous restoration of venous flow and heart rate to normal.
J. Perinat. Med. 19 (1991)
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respiratory rate (times/min)
Schneider & Deckardt, Implication of upright posture on pregnancy tidal volume oxygen consumption carbon dioxideelimination (ml, ml/min)
whose amplitude is 15 bpm or more. Using this definition, we could observe accelerations in two women as early as in the 24th week of gestation. A peak was observed during the 38th week of gestation where 71% of the tested women had positive test results. We were unable to reproduce these findings with the women in the left lateral position or after delivery. When we simultaneously recorded the incidence of spontaneous contractions and heart rate cycles during pregnancy, there was a close correlation between the occurrence of this maternal heart rate phenomenon and the occurrence of uterine contractions (figure 6). The change from the left lateral to the standing posture resulted in a 3.5-fold increase of spontaneous uterine contractions. Fifty-five percent of these contractions during the upright position were related to orthostatic regulation [29, 30]. The stroke volume equivalent, 'stroke distance', measured by transcutaneous aortovelography [20], showed a significant 22% decrease during the peak of the heart rate accelerations. Despite a significant increase in heart rate, the minute volume equivalent, 'minute distance', dropped by around 11%.
Figure 2. Influence of upright posture upon respiratory parameters during the last trimester (n = 15). left lateral
standing
activation of the muscle pump Figure 3. Effects of a change in body position from the recumbent to the upright posture on cardiac output (Q), maternal heart rate (MHR) in beats per minute (bpm), blood pressure (BP) and oxygen consumption (VO2) Brought by | NewofYork University Bobst Library Technical Services in one pregnant woman. On the right side to theyou influence the muscle pump is presented. Authenticated Download Date | 6/23/15 5:32 PM J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
maternal HR
femoral venous flow velocity
Figure 4. Maternal heart rate and venous femoral flow velocity in one pregnant woman during standing. Each decrease in flow velocity is answered by an increase in maternal heart rate.
fetal HR
standing
S.P. (40 4/r)
Figure 5. Typical tracing of maternal heart rate and uterine contractions recorded by external tocography. Maternal heart rate normalizes with every onset of a contraction. After relaxation of the uterus, maternal heart Brought tooccurs. you by | New York University Bobst Library Technical Services rate increases again until the next contraction J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
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Maternal heart rate cycles & contractions (standing) 30-
20-
10-
18 20 22 24 26 28 30 32 34 36 38 40 42 gestational age/weeks
Figure 6. Development of antenatal contractions (Alvarez and Braxton Hicks) and maternal heart rate cycles (> 15 bpm) during one hour with the mother in the standing position.
figure 7) [36]. Table I summarizes the differences in the upright position of pregnant and nonpregnant women: Because of the decreased vascular resistance, pregnancy exerts a greater effect on blood flow. The regulating mechanism of the muscle pump, which normally restores one-third of the volume, and the venous constriction are less effective in the pregnant woman. The size and configuration of the uterus in the upright position further adds to the reduced venous return. This seems to trigger uterine contractions which improve the venous flow from the lower extremities [22, 35]. The major difference between the pregnant and non-pregnant woman in the upright position is the more difficult and less sufficient regulatory mechanism which fails to achieve a steady state in two-thirds of the women [8,14]. Effect of leg compression on maternal hemodynamics (n=21) r 22
3.3 Clinical relevance of cardiovascular changes in the upright posture for the mother In four women there was a history of decompensation. One woman fainted several times a day during standing. Neither routine clinical nor neurological examination disclosed any cause. The heart rate in this women doubled during accelerations in the upright position. Most likely syncope had been caused by a reduced preload of the right ventricle. The maternal cardiovascular disorder was alleviated by leg compression. Maternal heart rate and stroke volume changed significantly with increaseing pressures caused by an adjustable pressure device (Hydroven, Sanol Schwartzkopf,
-21 82-
-20
80-
•19
8
78-18
76-
17
74
0 10 20 30 40 50 60 leg compression (mm mercury)
Figure 7. Effect of different leg compression pressures on maternal heart rate and on the stroke volume equivalent 'stroke distance'.
Table I. Effect of upright posture on hemodynamics and their regulation in non-pregnant and pregnant women Non pregnant
Pregnant (last trimester)
Effect of the upright posture: — 500 ml venous blood pooling in the lower extremities
> 500 ml blood in the lower extremities — impedance of venous return by the relaxed uterus
0
Regulation: l /3 restored by the muscle pump Ys restored by venous constriction — increasing heart rate in order to maintain cardiac output
0
— reaching a steady state
Va by the muscle pump Ys by venous constriction increasing heart rate in order to maintain cardiac output uterine contractions release venous return in 2/3 of the cases reaching no steady state
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Schneider & Deckardt, Implication of upright posture on pregnancy
delivery by a relative risk of 1.6 in the standing group as compared with the sitting or the nonworking women (table III) [3, 4, 16, 21, 26].
3.4 Clinical relevance of cardiovascular changes in the maternal upright posture for the fetus
How does the fetus react during maternal standing? Fetal heart rate baseline is significantly increased during maternal standing compared with women in the left lateral position. The fetal heart rate acceleration frequency is significantly (p < 0.001) reduced in the upright position. The fetal deceleration frequency was not significantly different in the two positions. Fetal oscillation amplitude and fetal movements (detected by tocography) during pregnancy tended to be reduced in the upright position. This change was not statistically significant (p > 0.05) [37] (table II). In individual cases, as shown in figure 8, a reduction of the oscillation amplitude and a decrease of accelerations as an answer to the maternal upright position could be demonstrated. Are these findings in the fetus of clinical relevance? Epidemiological studies which compared pregnant women doing comparable light work in a standing or a sitting position with nonworking pregnant women demonstrate a significant reduction in fetal birth weight, a three-fold increase in stillbirths and an increase of preterm
To the best of our knowledge there are only two studies in the literature which deal with the uteroplacental perfusion in the standing pregnant woman. SUONIO [34] measured the placental Technetium load of 20 pregnant women between the 33rd and 42nd weeks of gestation. He reports a 23% decrease as compared with the recumbent position. One of the women he investigated showed signs of a collapse, so he defined an 'upright syndrome' with adverse effects to the fetal blood supply and a potential explanation for otherwise unexplained stillbirths during late pregnancy. SOHN [33] investigated the resistance index in the umbilical artery in ten pregnant women near term; this is reciprocal to placental perfusion. He found a 34% increase. Maternal standing seems to be a physiological stress situation for both the mother and the fetus. It presents a challenge to the maternal and fetal cardiovascular adaptation. It leads to a significant increase in uterine contractions which seem
Table Π. Fetal reaction on maternal standing (n = 318) Variables
Left lateral
Standing
Significance
Fetal heart rate baseline (bpm) Oscillation amplitude (bpm) Oscillation frequency (n/min) Acceleration frequency (n/10 min) Deceleration frequency (n/10 min) Fetal movements (n/10 min)
139.5 13.1 9.8 1.8 0.7 8.2
141.3 12.7 9.6 1.3 0.6 7.5
p < 0.001 n. s. n.s. p < 0.001 n.s. n.s.
± + + ± ± ±
8.6 5.1 2.8 1.8 1.1 5.2
+ ± + ± ± ±
9.3 5.0 4.1 1.5 0.9 4.3
***^A/^*^^ left lateral
;
-
'"" - : : · ;
100
- - ·
_
'J
:
f standing
........
\f
- · 200
" fetal heart rate " ifflvi^JH^^
"-·'·>
J>U,
t
'
Figure 8. Trace of fetal heart rate pattern with cardiovascular disturbance during standing. Brought to maternal you by | New York University Bobst Library Technical Services J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
Table III. Standing work during pregnancy and fetal outcome (published data) Author
Year
Work & Posture (n)
Birth weight (g)
HIRSCH BALFOUR BALFOUR MAMELLE SAUREL
1927 1930 1938 1983 1987
2751V4143' 134V2364 1974V2363 945V9832 780V14893
2441/2641** 3386/3468* — lower**
Relative risk of standing work:
1.1
Preterm delivery
Stillbirth rate (%)
(%)
4.1/1.1
— — 7.2/4.5* higher**
20.3/6.3 — — 3.5
1.6
= standing, 2 = standing < 3 h/die, 3 = sitting, 4 = no work, * p < 0.05, ** p < 0.01
to play an important role in orthostatic regulation. We demonstrated the value of FHR behavior during maternal standing for the prediction of fetal metabolic acidosis. We compared the value of the resistance index in the umbilical artery of 77 pregnant women in the left lateral and standing positions with conventional stress tests, such as the non-stress test and the oxytocin challenge test. As the mode of delivery affected the proof criteria, the positive predictive value was poor in each test. The positive and negative predictive values ranked highest in the umbilical artery measurements during standing (table IV) [31].
4.2
4 Summary 4.1
cantly improves the FRC. This is an important mechanism to compensate for irregularities in oxygen supply. On the other hand, standing increases the work of breathing. Standing causes a cardiovascular disturbance in two-thirds of all women due to an impedance of venous return caused by the gravid uterus. Decompensation occurs in only 1 % of all women, because a threefold increase in spontaneous uterine contractions in the upright position restores venous blood supply. Thus, there is an 'uterovascular syndrome'. Leg compression and the left lateral position lessens this phenomenon; after delivery, it no longer occurs.
Upright posture and the mother
Maternal standing during early pregnancy causes episodes of syncope or fainting in 8% of the women because of a decrease in vascular resistance and an insufficient cardiovascular regulatory mechanism. The effects on maternal lung function and the consequences for the fetus during this period are generally unknown. During the second half of pregnancy, standing signifi-
Upright posture and the fetus
The fetal reaction to the upright position during early pregnancy is unknown due to the lack of adequate surveillance methods. During the second half of pregnancy, the fetus experiences some significant changes in its heart rate pattern: An increase of the baseline, and a decrease in oscillation amplitude and acceleration frequency. In agreement with the knowledge from epidemiological studies and measurements dealing with standing women and their fetuses, prolonged
Table IV. Stress tests and resistance index in predicting fetal metabolic acidosis (pH umbilical artery < 7.20 + base excess < —10; n = 77) Predictive value Positive Negative 1
Tests
NST1
OCT2
RI-UA3
Ri-UA-S4
7% 88%
14% 90%
5% 88%
13% 90%
4 Brought to you by |3 New York University Bobst Library Technical = Non-Stress-Test, 2 = Oxytocin-Challenge-Test, = Resistance-Index-Umbilical Artery, = Services -Standing
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J. Perinat. Med. 19 (1991)
Schneider & Deckardt, Implication of upright posture on pregnancy
standing during late pregnancy may imply risks for the fetus such as low birth weight, prematurity and an increase in stillbirths.
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DARWIN stated in his work that 'evolution can never be perfect' [7]. Perhaps there is a price to be paid for upright posture.
Abstract
Pregnant women spend more than half of the day in an upright position. The physiological effects of this posture on the mother and the fetus are evaluated. Changes in vascular autoregulation and anatomy lead to maternal fainting in about 8% of women during early pregnancy. The immediate effects of such episodes on the fetus are unknown. There is a positive correlation of orthostatic dysregulations and abortions. In late pregnancy we found a significant increase in functional residual capacity in the upright posture. Minute volume and oxygen consumption were also significantly increased (p < 0.001). Regarding the cardiovascular changes we detected a rhythmic change of the materaal heart rate with the change to upright position, which had not been published before. Change from the left lateral position to unsupported standing increased maternal heart rate by a mean of 27 beats per minute and a mean duration of 105 seconds in two
thirds of the women. This was accompanied by a decreased cardiac output, systolic blood pressure and an increased oxygen consumption. The gravid uterus is responsible for these changes. During the upright position, the venous flow to the right ventricle is inhibited by the relaxed uterus. Contractions, leaning forward and the muscle pump improve the venous return. The phenomenon reached its maximum during the 38th week, where 71% of pregnant women displayed a cyclic change in heart rate. The fetal heart rate baseline is significantly increased in the upright position with a significantly reduced acceleration frequency (p < 0.001). Combined with the data from epidemiologic studies, prolonged standing during late pregnancy may signal potential risks for the fetus such as low birth weight, prematurity and stillbirths because of an 'uterovascular syndrome'. Maternal standing possibly may be used as a physiological fetal stress test.
Keywords: Cardiovasculary function, fetal heart rate pattern, pregnancy, pulmonary function, upright posture. Zusammenfassung Die Auswirkung der aufrechten Körperhaltung auf die Schwangerschaft
Schwangere Frauen verbringen mehr als die Hälfte des Tages in der aufrechten Körperhaltung. Die physiologischen Effekte dieser Körperhaltung auf die Schwangere und den Feten werden in der vorliegenden Arbeit dargestellt. Veränderungen in der Autoregulation der Blutgefäße sowie endokrine Einflüsse führen bei 8% der Schwangeren zu Ohnmachtsanfallen in der Frühschwangerschaft. Der unmittelbare Effekt derartiger Episoden auf den Fetus ist, abgesehen von einer gewissen AbortHäufung bei rezidivierenden orthostatischen Dysregulationen unbekannt. In der 2. Schwangerschaftshälfte fanden wir in der aufrechten Körperhaltung eine Zunahme der funktioneilen Residualkapazität bei gleichzeitig signifikant zunehmendem Atemminutenvolumen und Sauerstoffverbrauch (p < 0,001). Die mütterliche Herzfrequenz zeigte bei einem Großteil der Schwangeren zyklisch persistierende Akzelerationen mit dem Wechsel zur aufrechten Körperhaltung, die bisher noch nicht beschrieben wurden. Ein Lagewechsel von der linken Seitenlage zum nichtunterstützten Stehen führte bei % der untersuchten Frauen zu einem Anstieg der mütterlichen Herzfrequenz im Mittel von 27 Schlägen/min.
bei einer durchschnittlichen Dauer von 105 sec. Trotz des Herzfrequenzanstiegs konnte durch den Abfall des Schlagvolumens das Herzminutenvolumen nicht konstant gehalten werden, es kam ebenfalls zu einem Abfall des systolischen Blutdrucks und zu einem Anstieg des Sauerstoffverbrauchs. Es zeigte sich, daß die schwangere Gebärmutter in der aufrechten Körperhaltung den venösen Rückfluß aus den unteren Extreminitäten durch Kompression pelviner Gefäße behinderte und so das Preload zum rechten Herz vermindert wurde. Dieses Phänomen erreichte in der 38. Schwangerschaftwoche seine höchste Inzidenz, wo 71% der untersuchten Frauen das zyklische Herzfrequenzverhalten aufwiesen. Die basale fetale Herzfrequenz ist in der aufrechten Körperhaltung der Mutter signifikant erhöht und zeigt eine ebenfalls signifikant reduzierte Inzidenz von Herzfrequenzakzelerationen (p < 0,001). In Übereinstimmung mit epidemiologischen Untersuchungen könnte die beschriebene Veränderung in der 2. Schwangerschaftshälfte für fetale Risiken wie niedriges Geburtsgewicht, Frühgeburtsbestrebung und unklare intrauterine Todesfalle mitverantwortlich sein. Mütterliches Stehen könnte daher als physiologischer fetaler Streßtest genutzt werden.
Schlüsselwörter: Aufrechte Körperhaltung, fetales Herzfrequenzmuster, Herz-Kreislauf-Funktion, Lungenfunktion, Schwangerschaft. Brought to you by | New York University Bobst Library Technical Services J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
Resume Implication de la station debout sur la grossesse Les femmes enceintes passent plus d'une demie journee en position verticale. Les effets physiologiques de cette posture sur la mere et le foetus sont evalues. Les modifications de l'autoregulation vasculaire et de Panatomie entrainent un evanouissement maternel chez 8% des femmes en debut de grossesse. Les effets immediate de tels episodes sur le foetus ne sont pas connus. Mais il existe une correlation positive entre dysregulations orthostatiques et avortements. En fin de grossesse, nous avons trouve une augmentation significative de la capacite residuelle fonctionelle en position debout. Le volume par minute et la consommation d'oxygene sont egalement augmentes de fagon significative (p < 0,001). En etudiant les modifications cardiovasculaires, nous avons detecte des modifications rythmiques du rythme cardiaque maternel avec le passage en position debout, ce qui n'avait pas ete public auparavant. Le passage du decubitus lateral gauche a la position debout mal supportee augmente le rythme cardiaque maternel d'une moyenne de 27 battements par minute, pendant une duree moyenne de 105 secondes chez deux tiers des
femmes. Ce phenomene s'accompagne d'une diminution du debit cardiaque, de la pression sanguine systolique et d'une augmentation de la consommation d'oxygene. L'uterus gravide est responsable de ces modifications. En position debout, le retour veineux vers le ventricule droit est entrave par 1'uterus relache. Les contractions, appuyant en avant, et la pompe musculaire ameliorent le retour veineux. Le phenomene atteint son maximum au cours de la 3Seme semaine, periode pendant laquelle 71% des femmes enceintes presentent une modification cyclique du rythme cardiaque. Le rythme cardiaque foetal de base est significativement augmente en position debout avec une diminution significative de la frequence des accelerations (p < 0,001). En accord avec la connaissance des etudes epidemiologiques, la position debout prolonge en fin de grossesse peut entrainer des risques pour le foetus tels que faible poids de naissance, prematurite et mortinatalite en raison d'un "syndrome utero vasculaire". La station debout maternelle peut etre utilisee comme un stress test foetal physiologique.
Mots-cles: Fonction cardiovasculaire, fonction pulmonaire, grossesse, station debout, traces de rythmes cardiaques foetaux.
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[10] DAHLSTRÖM H, K IHRMAN: A clinical and physiological study of pregnancy in a material from northern Sweden. Acta Soc Med Upsal 65 (1960) 117 [11] EASTERLING TR, BC SCHMUCLER, T BENEDETTI: The hemodynamic effects of orthostatic stress during pregnancy. Obstet Gynecol 72 (1988) 550 [12] GEMZELL CA, H ROBBE, G STROEM: Total amount of haemoglobin and physical working capacity in normal pregnancy and the puerperium. Acta Obstet Gynecol Scand 36 (1957) 93 [13] GOESCHEN K, E SALING, H WIKTOR: Fetale Gefahrdungszeichen bei mütterlicher Hypotonie im CTG und therapeutische Konsequenzen. Geburtshilfe Frauenheilkd 43 (1983) 417 [14] HAINSWORTH R, YM AL-SHAMMA: Cardiovascular responses to upright tilting in healthy subjects. Clin Sei 74 (1988) 17 [15] HANSEN E: Ohnmacht und Schwangerschaft. Klin Wochenschr 21 (1942) 241 [16] HIRSCH M: Weiterer Beitrag zur gewerblichen Pathologie von Schwangerschaft und Geburt. Zentralbl Gynaecol 3 (1927) 136 [17] HOLMES F: Incidence of the supine hypotensive syndrome in late pregnancy: A clinical study in 500 subjects. Obstet Gynecol 67 (1960) 254
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Schneider & Deckardt, Implication of upright posture on pregnancy [18] HURTADO A, WW FRAY: Studies of total pulmonary capacity and its subdivisions. III. Changes with body posture. 1 Clin Invest 12 (1933) 825 [19] LEHMANN V, H FABEL: Lungenfunktionsuntersuchungen an Schwangeren. Teil II: Ventilation, Atemmechanik und Diffusionskapazität. Z Geburtshilfe Perinatol 177 (1973) 397 [20] LIGHT H: Transcutaneous aortovelography. A new window on the circulation? Br Heart J 38 (1976) 433 [21] MAMELLE N, B LAUMON, P LAZAR: Occupational activity and issue of the pregnancy. J Psych Obstet Gynaecol 2 (1983) 152 [22] MANDACH U VON, KTM SCHNEIDER, A HUGH, R HUCH: Peripherally detectable hormones — its relation to the increased uterine activity during standing in pregnant women. Biol Res preg perinatol 8 (1987) 7 [23] PYOERAELAE T: Cardiovascular response to the upright position during pregnancy. Thesis, Helsinki 1966 [24] RIMBACH E, E HEILIGENSTEIN: Die klinische Bedeutung der Hypotonie in der Schwangerschaft und während der Geburt. Med Welt 34 (1967) 1950 [25] RUNGE H: Über den Venendruck in der Schwangerschaft, Geburt und Wochenbett. Arch Gynecol 122 (1924) 142 [26] SAUREL-CUBIZOLLES MJ, M KAMINSKI: Pregnant women's working conditions and their changes during pregnancy: a national study in France. Br J Ind Med 44 (1987) 236 [27] SCHNEIDER KTM, A BOLLINGER, A HUCH, R HUCH: The oscillating 'vena cava syndrome' during quiet standing: an unexpected observation in late pregnancy. Br J Obstet Gynaecol 91 (1984) 776 [28] SCHNEIDER KTM, H GRAEFF, S WEBER, P BUNG, A HUCH, R HUCH: Einfluß der Körperhaltung auf die mütterliche Hämodynamik. 3. RheingauWorkshop, 21. März 1986. In: MARTIN E, K PETER, K TAEGER (eds): Anästhesie und Geburtshilfe. Wissenschaftliche Verlagsabteilung Deutsche Abbott GmbH, Wiesbaden 1987
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[29] SCHNEIDER KTM, R HUCH, A HUCH: Premature contractions: are they caused by maternal standing? Acta Genet Med Gemellol 34 (1985) 175 [30] SCHNEIDER KTM, KH STAISCH, L SPÄTLING, R HUCH, A HUCH: Körperhaltung und kardiopulmonale Funktion in Schwangerschaft und Wochenbett: 1. Lungenfunktion. Gynäkol Praxis 9 81985) 641 [31] SCHNEIDER KTM, W Loos, A HASSLER, D PROCHASKA, M RÖBL, H GRAEFF: The use of waveform analysis of fetal vessels as a new fetal stress test. In: Abstract book: XI. European Congress of Perinatal Medicine 1988, Rome, 10. -13. April. CIC Edizioni International! 1988 [32] SCHNEIDER-AFFELD F, E KAUKEL, K NIENSTEDT: Lageabhängige Veränderungen von Lungenfunktions- und Kreislaufparametern bei graviden Frauen am Geburtstermin. Z Geburtshilfe Perinatol 187 (1983) 65 [33] SOHN C, H PENDEL, R WERDIN, P KERSTERNICH, H SCHONLAU: Änderung der uterinen Durchblutung in Abhängigkeit von der Körperposition während der Schwangerschaft. Z Geburtshilfe Perinatol 191 (1987) 169 [34] SUONIO S, AL SIMPANEN, H OLKKONEN, P H ARING: Effect of the left lateral recumbent position compared with the supine and upright positions on placental blood flow in normal late pregnancy. Ann Clin Res 8 (1976) 22 [35] UELAND K, JM HANSEN: Maternal cardiovascular dynamics: II. Posture and uterine contractions. Am J Obstet Gynecol 103 (1969) 1 [36] WEBER S, KTM SCHNEIDER, P BUNG, F FALLENSTEIN, A HUCH, R HUCH: Kreislaufwirkung von Kompressionsstrümpfen in der Spätschwangerschaft. Geburtshilfe Frauenheilkd 47 (1987) 395 [37] WEBER S, KTM SCHNEIDER, P BUNG, A HUCH, R HUCH: Antenatale fetale Herzfrequenz unter besonderer Berücksichtigung der mütterlichen Körperhaltung. Geburtshilfe Frauenheilkd 48 (1988) 35 Prof. Dr. Karl-Theo Schneider Frauenklinik rechts der Isar der Technischen Universität München Ismaningerstr. 22 W-8000 München 80 Fed. Rep. of Germany
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Dictionary of Obstetrics and Gynecology
Compiled by the editorial staff of Pschyrembel's Klinisches Wörterbuch. Managing editor Christoph Zink. Translated by Kathleen R. Dyer, Dietrich W. Roloff and Bernd K. Wittmann 1988.14 21,5 cm. XII, 284 pages. With 442 illustrations and 60 tables. Bound DM 68,- ISBN 311011875 0 This Dictionary of Obstetrics and Gynecology, with over 2600 entries, gives a comprehensive overview of the clinical and theoretical aspects of these specialist areas. At the same time, it reflects the increasingly important roles played by endocrinology, reproductive medicine, psychosomatic, and sexual medicine, perinatology and neonatology in the practice of obstetrics and gynecology. The dictionary was compiled by the editorial staff of Pschyrembel's Klinisches Wörterbuch, a widely-used reference work in German-speaking countries. It comprises contributions by many well-known scientists, over 400 illustrations in color or black and white, and a large number of tables and charts.
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J. Perinat. Med. 19(1991) 121-131
121
The implication of upright posture on pregnancy Karl-Theo M. Schneider and Rainer Deckardt
Gynecological Clinic („Frauenklinik rechts der Isar") of the Technical University Munich, Munich, Fed. Rep. of Germany
1
Introduction
The upright posture is one of the outstanding characteristics that distinguishes the human from the animal. Pregnant women usually spend more than half of the day in the upright position. In contrast, the majority of investigations on the physiological changes during pregnancy deal only with women in the recumbent position. This paper presents new and established facts about the upright position and its clinical relevance for the mother and the fetus during early and late pregnancy. 2
Early pregnancy
2.1 Cardiovascular changes during maternal upright posture
A frequent problem during early pregnancy is maternal syncope following a positional change into the upright position. The leading cause for this is believed to be an increased vessel diameter in conjunction with an insufficient adaptation of the vascular autoregulation. Vasodilation during early pregnancy is supported by the trophoblastic invasion, estrogen and progesterone mediated relaxation of the venous smooth muscle tone, a reduced tone of the striated muscles and a marked shift in the production of prostaglandin derivatives from thromboxane to vessel dilating prostacyclin [2, 8, 10, 11, 12, 15, 24, 25].
Curriculum vitae KARL-THEO M. SCHNEIDER, M. D., born in 1950, was graduated from the University of Würzburg, Germany in 1977. He worked in Pathology and Internal Medicine for two years. From 1979 to 1982 he did his residency in Obstetrics and Gynecology at the Hospital Waldfriede, Berlin. From 1982—1985 he had a Swiss National font grant and attended at the University Hospital of Zurich, Switzerland. In 1986 he joined the faculty of Obstetrics and Gynecology rechts der Isar, University of Technology, Munich ('Habilitation' 1987, 'Privatdozent' 1988, 'Professor (Extraordinarius) ' 1990). Main fields of interest include: Feto-maternal cardiovascular physiology, perinatal surveillance techniques, quality control, prenatal diagnosis and therapy.
about 8% of women experience dizziness in early pregnancy after standing for 8 to 10 minutes and are not able to stand any longer. A reduction in systolic blood pressure by more than 20 mmHg and an increased heart rate can be observed in most of these cases [10, 12, 15, 24].
Orthostatic dysregulation can be found ten times more frequently in hypotensive women as compared with normotensive women [13]. About Despite the common knowledge that fainting is one-third of pregnant women have a systolic a typical phenomenon during early pregnancy, blood pressure below 100 mmHg and therefore there is little precise information about the in- fulfil the criteria of "hypotension." Orthostatic cidence of this cardiovascular decompensation. dysregulation seems to be of more importance From published works it can be calculated thatby | New thanYork lowUniversity blood pressure per seTechnical [10, 13,Services 15]. Brought to you Bobst Library 1991 by Walter de Gruyter & Co. Berlin · New York
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Schneider & Deckardt, Implication of upright posture on pregnancy
Because of inadequate monitoring equipment and the shortness of these episodes which rarely exceed 2 minutes, there is no knowledge about the implications of these sudden cardiovascular changes on the embryo. The incidence of spontaneous abortions, low birth-weight infants and still-births is increased in women with early orthostatic dysregulation [13]. 2.2 Pulmonary changes during maternal upright posture
Despite the well established knowledge of markedly changed lung volumes and respiratory parameters even during very early pregnancy [6, 9, 19] and despite the knowledge about the influence of body position on lung function in the non-pregnant woman [5, 18], there are no publications which outline the changes of lung function due to the upright posture in early pregnancy. 3
Late pregnancy*
3.1 Pulmonary changes in the maternal upright posture
reserve in an apneic patient, thus resulting in less hypoxemia than with a decreased FRC. Considering these results, one can declare that upright position during late pregnancy is one safety measure against hypoxemia. Regarding the respiratory changes in the upright position during pregnancy, there is a significant (p < 0.001) increase in minute ventilation. This is primarily the result of an increased tidal volume with little change in respiratory rate. Oxygen consumption was significantly increased (p < 0.001), as was the elimination of carbon dioxide. This increase in breathing work during pregnancy has been even more pronounced in the upright position (figure 2). 3.2 Cardiovascular changes during maternal upright posture
During the assessment of the lung volumes by spirometry, additional parameters such as maternal and fetal electrocardiograms had been recorded. We experienced a new cardiovascular phenomenon in 33 out of 51 standing women, which had not been described before [27].
Change from the left lateral position to unsupported standing led to a transitional increase in The upright position and its implication on pregnancy during the last trimester also has not been maternal heart rate with a mean increase of 27 studied in detail [1, 23, 32]. In order to gather beats per minute (bpm) and a duration of 105 more knowledge about this topic, we investigated seconds in two-thirds of the women. Figure 3 15 healthy pregnant women during their last delineates the observed changes in the women. gestational trimester with a commercial lung With a change from the left lateral to the upright function system (Ergostar, Co., Dr. Fenyves & posture, one can detect a concurrent fall of the Gut, Basel, 30). Statistical analyses were per- cardiac output, a transitional rise of the maternal formed using the Wilcoxon test. Statistical sig- heart rate, fall of the systolic blood pressure and nificance was assessed when the probability was an increase in oxygen consumption. more than 5%. This phenomenon was less pronounced when the woman was asked to activate her muscle pump The upright position causes an increase in all by specific movements. Leaning forward also lung volumes except in the inspiratory reserve normalized maternal heart rate fluctuations; volume (IRV) which decreases by 5% (figure 1). whereas, standing again resulted in an increase A significant increase in the functional residual in maternal heart rate fluctuations. After delivery capacity (FRC) was due mainly to an increase of the expiratory reserve volume (ERV) by the changes in the maternal heart rate pattern around one-third. The FRC serves as a buffer during standing were not reproduced in any of against rapid changes in oxygen supply. As an the women. example, an increased FRC elevates the oxygen Measurement of the flow velocity in the maternal femoral artery displayed a cyclic decrease of systolic and even more pronounced change in dia* Most of the reported investigation were performed stolic flow velocities. Measurement of the flow in the Perinatal Physiology Unit of Profs. ALBERT velocity in the maternal femoral vein displayed and RENATE HUGH, Department of Obstetrics, Uni- a marked decrease of venous flow during periods York Universitymaternal Bobst Library Technical Services4). An versity of Zurich, Switzerland. Brought to you by | Newof increased heart rate (figure Authenticated Download Date | 6/23/15 5:32 PM
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Schneider & Deckardt, Implication of upright posture on pregnancy
4.0
123
inspiratory reserve volume Δ -5%
3.0
tidal volume Δ + 8% 2.0
exspiratory reserve volume Δ+31 1.0
residual volume Δ + 12%
Figure 1. Effect of upright posture upon lung volumes and capacities during the last trimester (n = 15). FRC = functional residual capacity
creases in order to maintain cardiac output. Uterine contractions or leaning forward, improves the venous return by positional or configurational changes of the uterus. Activation of the muscle pump is another mechanism which partially overcomes this phenomenon by an imSurprisingly, uterine contractions are the cause. provement of venous return. With every onset of a contraction, maternal heart rate normalizes. Every relaxation is answered To learn about the time of onset and developwith an instant increase in heart rate (figure 5). ment of this occurrence, we longitudinally invesOur conclusion from this preliminary study was tigated 40 healthy pregnant women from the that the relaxed uterus more frequently causes 20th gestational week onwards with a total of compression of the maternal pelvic vessels during 358 investigations [28]. The marker utilized in the upright position than has been reported from our facility to identify this phenomenon is the the recumbent position [1,17]. The venous return occurrence of maternal heart rate accelerations. to the right ventricle becomes impeded, the A positive reaction is defined as the requirement to you University Bobst Technical Services that York there be three or Library more such cycles/10 min stroke volume falls, and maternal Brought heart rate in-by | New
increase of femoral flow velocity resulted in a normalization of maternal heart rate. We attempted to determine which mechanism was responsible for the observed spontaneous restoration of venous flow and heart rate to normal.
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respiratory rate (times/min)
Schneider & Deckardt, Implication of upright posture on pregnancy tidal volume oxygen consumption carbon dioxideelimination (ml, ml/min)
whose amplitude is 15 bpm or more. Using this definition, we could observe accelerations in two women as early as in the 24th week of gestation. A peak was observed during the 38th week of gestation where 71% of the tested women had positive test results. We were unable to reproduce these findings with the women in the left lateral position or after delivery. When we simultaneously recorded the incidence of spontaneous contractions and heart rate cycles during pregnancy, there was a close correlation between the occurrence of this maternal heart rate phenomenon and the occurrence of uterine contractions (figure 6). The change from the left lateral to the standing posture resulted in a 3.5-fold increase of spontaneous uterine contractions. Fifty-five percent of these contractions during the upright position were related to orthostatic regulation [29, 30]. The stroke volume equivalent, 'stroke distance', measured by transcutaneous aortovelography [20], showed a significant 22% decrease during the peak of the heart rate accelerations. Despite a significant increase in heart rate, the minute volume equivalent, 'minute distance', dropped by around 11%.
Figure 2. Influence of upright posture upon respiratory parameters during the last trimester (n = 15). left lateral
standing
activation of the muscle pump Figure 3. Effects of a change in body position from the recumbent to the upright posture on cardiac output (Q), maternal heart rate (MHR) in beats per minute (bpm), blood pressure (BP) and oxygen consumption (VO2) Brought by | NewofYork University Bobst Library Technical Services in one pregnant woman. On the right side to theyou influence the muscle pump is presented. Authenticated Download Date | 6/23/15 5:32 PM J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
maternal HR
femoral venous flow velocity
Figure 4. Maternal heart rate and venous femoral flow velocity in one pregnant woman during standing. Each decrease in flow velocity is answered by an increase in maternal heart rate.
fetal HR
standing
S.P. (40 4/r)
Figure 5. Typical tracing of maternal heart rate and uterine contractions recorded by external tocography. Maternal heart rate normalizes with every onset of a contraction. After relaxation of the uterus, maternal heart Brought tooccurs. you by | New York University Bobst Library Technical Services rate increases again until the next contraction J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
126
Maternal heart rate cycles & contractions (standing) 30-
20-
10-
18 20 22 24 26 28 30 32 34 36 38 40 42 gestational age/weeks
Figure 6. Development of antenatal contractions (Alvarez and Braxton Hicks) and maternal heart rate cycles (> 15 bpm) during one hour with the mother in the standing position.
figure 7) [36]. Table I summarizes the differences in the upright position of pregnant and nonpregnant women: Because of the decreased vascular resistance, pregnancy exerts a greater effect on blood flow. The regulating mechanism of the muscle pump, which normally restores one-third of the volume, and the venous constriction are less effective in the pregnant woman. The size and configuration of the uterus in the upright position further adds to the reduced venous return. This seems to trigger uterine contractions which improve the venous flow from the lower extremities [22, 35]. The major difference between the pregnant and non-pregnant woman in the upright position is the more difficult and less sufficient regulatory mechanism which fails to achieve a steady state in two-thirds of the women [8,14]. Effect of leg compression on maternal hemodynamics (n=21) r 22
3.3 Clinical relevance of cardiovascular changes in the upright posture for the mother In four women there was a history of decompensation. One woman fainted several times a day during standing. Neither routine clinical nor neurological examination disclosed any cause. The heart rate in this women doubled during accelerations in the upright position. Most likely syncope had been caused by a reduced preload of the right ventricle. The maternal cardiovascular disorder was alleviated by leg compression. Maternal heart rate and stroke volume changed significantly with increaseing pressures caused by an adjustable pressure device (Hydroven, Sanol Schwartzkopf,
-21 82-
-20
80-
•19
8
78-18
76-
17
74
0 10 20 30 40 50 60 leg compression (mm mercury)
Figure 7. Effect of different leg compression pressures on maternal heart rate and on the stroke volume equivalent 'stroke distance'.
Table I. Effect of upright posture on hemodynamics and their regulation in non-pregnant and pregnant women Non pregnant
Pregnant (last trimester)
Effect of the upright posture: — 500 ml venous blood pooling in the lower extremities
> 500 ml blood in the lower extremities — impedance of venous return by the relaxed uterus
0
Regulation: l /3 restored by the muscle pump Ys restored by venous constriction — increasing heart rate in order to maintain cardiac output
0
— reaching a steady state
Va by the muscle pump Ys by venous constriction increasing heart rate in order to maintain cardiac output uterine contractions release venous return in 2/3 of the cases reaching no steady state
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Schneider & Deckardt, Implication of upright posture on pregnancy
delivery by a relative risk of 1.6 in the standing group as compared with the sitting or the nonworking women (table III) [3, 4, 16, 21, 26].
3.4 Clinical relevance of cardiovascular changes in the maternal upright posture for the fetus
How does the fetus react during maternal standing? Fetal heart rate baseline is significantly increased during maternal standing compared with women in the left lateral position. The fetal heart rate acceleration frequency is significantly (p < 0.001) reduced in the upright position. The fetal deceleration frequency was not significantly different in the two positions. Fetal oscillation amplitude and fetal movements (detected by tocography) during pregnancy tended to be reduced in the upright position. This change was not statistically significant (p > 0.05) [37] (table II). In individual cases, as shown in figure 8, a reduction of the oscillation amplitude and a decrease of accelerations as an answer to the maternal upright position could be demonstrated. Are these findings in the fetus of clinical relevance? Epidemiological studies which compared pregnant women doing comparable light work in a standing or a sitting position with nonworking pregnant women demonstrate a significant reduction in fetal birth weight, a three-fold increase in stillbirths and an increase of preterm
To the best of our knowledge there are only two studies in the literature which deal with the uteroplacental perfusion in the standing pregnant woman. SUONIO [34] measured the placental Technetium load of 20 pregnant women between the 33rd and 42nd weeks of gestation. He reports a 23% decrease as compared with the recumbent position. One of the women he investigated showed signs of a collapse, so he defined an 'upright syndrome' with adverse effects to the fetal blood supply and a potential explanation for otherwise unexplained stillbirths during late pregnancy. SOHN [33] investigated the resistance index in the umbilical artery in ten pregnant women near term; this is reciprocal to placental perfusion. He found a 34% increase. Maternal standing seems to be a physiological stress situation for both the mother and the fetus. It presents a challenge to the maternal and fetal cardiovascular adaptation. It leads to a significant increase in uterine contractions which seem
Table Π. Fetal reaction on maternal standing (n = 318) Variables
Left lateral
Standing
Significance
Fetal heart rate baseline (bpm) Oscillation amplitude (bpm) Oscillation frequency (n/min) Acceleration frequency (n/10 min) Deceleration frequency (n/10 min) Fetal movements (n/10 min)
139.5 13.1 9.8 1.8 0.7 8.2
141.3 12.7 9.6 1.3 0.6 7.5
p < 0.001 n. s. n.s. p < 0.001 n.s. n.s.
± + + ± ± ±
8.6 5.1 2.8 1.8 1.1 5.2
+ ± + ± ± ±
9.3 5.0 4.1 1.5 0.9 4.3
***^A/^*^^ left lateral
;
-
'"" - : : · ;
100
- - ·
_
'J
:
f standing
........
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- · 200
" fetal heart rate " ifflvi^JH^^
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Figure 8. Trace of fetal heart rate pattern with cardiovascular disturbance during standing. Brought to maternal you by | New York University Bobst Library Technical Services J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
Table III. Standing work during pregnancy and fetal outcome (published data) Author
Year
Work & Posture (n)
Birth weight (g)
HIRSCH BALFOUR BALFOUR MAMELLE SAUREL
1927 1930 1938 1983 1987
2751V4143' 134V2364 1974V2363 945V9832 780V14893
2441/2641** 3386/3468* — lower**
Relative risk of standing work:
1.1
Preterm delivery
Stillbirth rate (%)
(%)
4.1/1.1
— — 7.2/4.5* higher**
20.3/6.3 — — 3.5
1.6
= standing, 2 = standing < 3 h/die, 3 = sitting, 4 = no work, * p < 0.05, ** p < 0.01
to play an important role in orthostatic regulation. We demonstrated the value of FHR behavior during maternal standing for the prediction of fetal metabolic acidosis. We compared the value of the resistance index in the umbilical artery of 77 pregnant women in the left lateral and standing positions with conventional stress tests, such as the non-stress test and the oxytocin challenge test. As the mode of delivery affected the proof criteria, the positive predictive value was poor in each test. The positive and negative predictive values ranked highest in the umbilical artery measurements during standing (table IV) [31].
4.2
4 Summary 4.1
cantly improves the FRC. This is an important mechanism to compensate for irregularities in oxygen supply. On the other hand, standing increases the work of breathing. Standing causes a cardiovascular disturbance in two-thirds of all women due to an impedance of venous return caused by the gravid uterus. Decompensation occurs in only 1 % of all women, because a threefold increase in spontaneous uterine contractions in the upright position restores venous blood supply. Thus, there is an 'uterovascular syndrome'. Leg compression and the left lateral position lessens this phenomenon; after delivery, it no longer occurs.
Upright posture and the mother
Maternal standing during early pregnancy causes episodes of syncope or fainting in 8% of the women because of a decrease in vascular resistance and an insufficient cardiovascular regulatory mechanism. The effects on maternal lung function and the consequences for the fetus during this period are generally unknown. During the second half of pregnancy, standing signifi-
Upright posture and the fetus
The fetal reaction to the upright position during early pregnancy is unknown due to the lack of adequate surveillance methods. During the second half of pregnancy, the fetus experiences some significant changes in its heart rate pattern: An increase of the baseline, and a decrease in oscillation amplitude and acceleration frequency. In agreement with the knowledge from epidemiological studies and measurements dealing with standing women and their fetuses, prolonged
Table IV. Stress tests and resistance index in predicting fetal metabolic acidosis (pH umbilical artery < 7.20 + base excess < —10; n = 77) Predictive value Positive Negative 1
Tests
NST1
OCT2
RI-UA3
Ri-UA-S4
7% 88%
14% 90%
5% 88%
13% 90%
4 Brought to you by |3 New York University Bobst Library Technical = Non-Stress-Test, 2 = Oxytocin-Challenge-Test, = Resistance-Index-Umbilical Artery, = Services -Standing
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Schneider & Deckardt, Implication of upright posture on pregnancy
standing during late pregnancy may imply risks for the fetus such as low birth weight, prematurity and an increase in stillbirths.
129
DARWIN stated in his work that 'evolution can never be perfect' [7]. Perhaps there is a price to be paid for upright posture.
Abstract
Pregnant women spend more than half of the day in an upright position. The physiological effects of this posture on the mother and the fetus are evaluated. Changes in vascular autoregulation and anatomy lead to maternal fainting in about 8% of women during early pregnancy. The immediate effects of such episodes on the fetus are unknown. There is a positive correlation of orthostatic dysregulations and abortions. In late pregnancy we found a significant increase in functional residual capacity in the upright posture. Minute volume and oxygen consumption were also significantly increased (p < 0.001). Regarding the cardiovascular changes we detected a rhythmic change of the materaal heart rate with the change to upright position, which had not been published before. Change from the left lateral position to unsupported standing increased maternal heart rate by a mean of 27 beats per minute and a mean duration of 105 seconds in two
thirds of the women. This was accompanied by a decreased cardiac output, systolic blood pressure and an increased oxygen consumption. The gravid uterus is responsible for these changes. During the upright position, the venous flow to the right ventricle is inhibited by the relaxed uterus. Contractions, leaning forward and the muscle pump improve the venous return. The phenomenon reached its maximum during the 38th week, where 71% of pregnant women displayed a cyclic change in heart rate. The fetal heart rate baseline is significantly increased in the upright position with a significantly reduced acceleration frequency (p < 0.001). Combined with the data from epidemiologic studies, prolonged standing during late pregnancy may signal potential risks for the fetus such as low birth weight, prematurity and stillbirths because of an 'uterovascular syndrome'. Maternal standing possibly may be used as a physiological fetal stress test.
Keywords: Cardiovasculary function, fetal heart rate pattern, pregnancy, pulmonary function, upright posture. Zusammenfassung Die Auswirkung der aufrechten Körperhaltung auf die Schwangerschaft
Schwangere Frauen verbringen mehr als die Hälfte des Tages in der aufrechten Körperhaltung. Die physiologischen Effekte dieser Körperhaltung auf die Schwangere und den Feten werden in der vorliegenden Arbeit dargestellt. Veränderungen in der Autoregulation der Blutgefäße sowie endokrine Einflüsse führen bei 8% der Schwangeren zu Ohnmachtsanfallen in der Frühschwangerschaft. Der unmittelbare Effekt derartiger Episoden auf den Fetus ist, abgesehen von einer gewissen AbortHäufung bei rezidivierenden orthostatischen Dysregulationen unbekannt. In der 2. Schwangerschaftshälfte fanden wir in der aufrechten Körperhaltung eine Zunahme der funktioneilen Residualkapazität bei gleichzeitig signifikant zunehmendem Atemminutenvolumen und Sauerstoffverbrauch (p < 0,001). Die mütterliche Herzfrequenz zeigte bei einem Großteil der Schwangeren zyklisch persistierende Akzelerationen mit dem Wechsel zur aufrechten Körperhaltung, die bisher noch nicht beschrieben wurden. Ein Lagewechsel von der linken Seitenlage zum nichtunterstützten Stehen führte bei % der untersuchten Frauen zu einem Anstieg der mütterlichen Herzfrequenz im Mittel von 27 Schlägen/min.
bei einer durchschnittlichen Dauer von 105 sec. Trotz des Herzfrequenzanstiegs konnte durch den Abfall des Schlagvolumens das Herzminutenvolumen nicht konstant gehalten werden, es kam ebenfalls zu einem Abfall des systolischen Blutdrucks und zu einem Anstieg des Sauerstoffverbrauchs. Es zeigte sich, daß die schwangere Gebärmutter in der aufrechten Körperhaltung den venösen Rückfluß aus den unteren Extreminitäten durch Kompression pelviner Gefäße behinderte und so das Preload zum rechten Herz vermindert wurde. Dieses Phänomen erreichte in der 38. Schwangerschaftwoche seine höchste Inzidenz, wo 71% der untersuchten Frauen das zyklische Herzfrequenzverhalten aufwiesen. Die basale fetale Herzfrequenz ist in der aufrechten Körperhaltung der Mutter signifikant erhöht und zeigt eine ebenfalls signifikant reduzierte Inzidenz von Herzfrequenzakzelerationen (p < 0,001). In Übereinstimmung mit epidemiologischen Untersuchungen könnte die beschriebene Veränderung in der 2. Schwangerschaftshälfte für fetale Risiken wie niedriges Geburtsgewicht, Frühgeburtsbestrebung und unklare intrauterine Todesfalle mitverantwortlich sein. Mütterliches Stehen könnte daher als physiologischer fetaler Streßtest genutzt werden.
Schlüsselwörter: Aufrechte Körperhaltung, fetales Herzfrequenzmuster, Herz-Kreislauf-Funktion, Lungenfunktion, Schwangerschaft. Brought to you by | New York University Bobst Library Technical Services J. Perinat. Med. 19 (1991)
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Schneider & Deckardt, Implication of upright posture on pregnancy
Resume Implication de la station debout sur la grossesse Les femmes enceintes passent plus d'une demie journee en position verticale. Les effets physiologiques de cette posture sur la mere et le foetus sont evalues. Les modifications de l'autoregulation vasculaire et de Panatomie entrainent un evanouissement maternel chez 8% des femmes en debut de grossesse. Les effets immediate de tels episodes sur le foetus ne sont pas connus. Mais il existe une correlation positive entre dysregulations orthostatiques et avortements. En fin de grossesse, nous avons trouve une augmentation significative de la capacite residuelle fonctionelle en position debout. Le volume par minute et la consommation d'oxygene sont egalement augmentes de fagon significative (p < 0,001). En etudiant les modifications cardiovasculaires, nous avons detecte des modifications rythmiques du rythme cardiaque maternel avec le passage en position debout, ce qui n'avait pas ete public auparavant. Le passage du decubitus lateral gauche a la position debout mal supportee augmente le rythme cardiaque maternel d'une moyenne de 27 battements par minute, pendant une duree moyenne de 105 secondes chez deux tiers des
femmes. Ce phenomene s'accompagne d'une diminution du debit cardiaque, de la pression sanguine systolique et d'une augmentation de la consommation d'oxygene. L'uterus gravide est responsable de ces modifications. En position debout, le retour veineux vers le ventricule droit est entrave par 1'uterus relache. Les contractions, appuyant en avant, et la pompe musculaire ameliorent le retour veineux. Le phenomene atteint son maximum au cours de la 3Seme semaine, periode pendant laquelle 71% des femmes enceintes presentent une modification cyclique du rythme cardiaque. Le rythme cardiaque foetal de base est significativement augmente en position debout avec une diminution significative de la frequence des accelerations (p < 0,001). En accord avec la connaissance des etudes epidemiologiques, la position debout prolonge en fin de grossesse peut entrainer des risques pour le foetus tels que faible poids de naissance, prematurite et mortinatalite en raison d'un "syndrome utero vasculaire". La station debout maternelle peut etre utilisee comme un stress test foetal physiologique.
Mots-cles: Fonction cardiovasculaire, fonction pulmonaire, grossesse, station debout, traces de rythmes cardiaques foetaux.
References [1] AHLTORP G: Über Rückenlagebeschwerden bei Graviden. Acta Obstet Gynecol 15 (1933) 295 [2] ATKINS AJF, JM WATT, P MILAN, P DAVIES, JS CRAWFORD: The influence of posture upon cardiovascular dynamics throughout pregnancy. Eur J Obstet Gynecol Reprod Biol 12 (1981) 357 [3] BALFOUR MI, SK TALPADE: The maternity conditions of women millworkers in India. Indian Med Gazette 65 (1930) 241 [4] BALFOUR MI: The effect of occupation on pregnancy and neonatal mortality. Public Health J Soc Med Officers Health 51 (1938) 106 [5] BLAIR E, JB HICKMAN: The effect of change in body position on lung volume and intrapulmonary gas mixing in normal subjects. J Clin Invest 34 (1955) 383 [6] BONICA JJ: Maternal respiratory changes during pregnancy and parturition. In: MAD GF (ed.): Parturition and Perinatology. Davis Comp, Philadelphia 1973 [7] BRIEND A: Fetal malnutrition — the prize of upright posture. Br Med J 4 (1979) 317 [8] BUSSE R: Kreislaufphysiologie. Georg Thieme Verlag 1982 [9] CUGELL DW et al: Pulmonary function in pregnancy. Am Rev Tuberc 67 (1953) 568
[10] DAHLSTRÖM H, K IHRMAN: A clinical and physiological study of pregnancy in a material from northern Sweden. Acta Soc Med Upsal 65 (1960) 117 [11] EASTERLING TR, BC SCHMUCLER, T BENEDETTI: The hemodynamic effects of orthostatic stress during pregnancy. Obstet Gynecol 72 (1988) 550 [12] GEMZELL CA, H ROBBE, G STROEM: Total amount of haemoglobin and physical working capacity in normal pregnancy and the puerperium. Acta Obstet Gynecol Scand 36 (1957) 93 [13] GOESCHEN K, E SALING, H WIKTOR: Fetale Gefahrdungszeichen bei mütterlicher Hypotonie im CTG und therapeutische Konsequenzen. Geburtshilfe Frauenheilkd 43 (1983) 417 [14] HAINSWORTH R, YM AL-SHAMMA: Cardiovascular responses to upright tilting in healthy subjects. Clin Sei 74 (1988) 17 [15] HANSEN E: Ohnmacht und Schwangerschaft. Klin Wochenschr 21 (1942) 241 [16] HIRSCH M: Weiterer Beitrag zur gewerblichen Pathologie von Schwangerschaft und Geburt. Zentralbl Gynaecol 3 (1927) 136 [17] HOLMES F: Incidence of the supine hypotensive syndrome in late pregnancy: A clinical study in 500 subjects. Obstet Gynecol 67 (1960) 254
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Schneider & Deckardt, Implication of upright posture on pregnancy [18] HURTADO A, WW FRAY: Studies of total pulmonary capacity and its subdivisions. III. Changes with body posture. 1 Clin Invest 12 (1933) 825 [19] LEHMANN V, H FABEL: Lungenfunktionsuntersuchungen an Schwangeren. Teil II: Ventilation, Atemmechanik und Diffusionskapazität. Z Geburtshilfe Perinatol 177 (1973) 397 [20] LIGHT H: Transcutaneous aortovelography. A new window on the circulation? Br Heart J 38 (1976) 433 [21] MAMELLE N, B LAUMON, P LAZAR: Occupational activity and issue of the pregnancy. J Psych Obstet Gynaecol 2 (1983) 152 [22] MANDACH U VON, KTM SCHNEIDER, A HUGH, R HUCH: Peripherally detectable hormones — its relation to the increased uterine activity during standing in pregnant women. Biol Res preg perinatol 8 (1987) 7 [23] PYOERAELAE T: Cardiovascular response to the upright position during pregnancy. Thesis, Helsinki 1966 [24] RIMBACH E, E HEILIGENSTEIN: Die klinische Bedeutung der Hypotonie in der Schwangerschaft und während der Geburt. Med Welt 34 (1967) 1950 [25] RUNGE H: Über den Venendruck in der Schwangerschaft, Geburt und Wochenbett. Arch Gynecol 122 (1924) 142 [26] SAUREL-CUBIZOLLES MJ, M KAMINSKI: Pregnant women's working conditions and their changes during pregnancy: a national study in France. Br J Ind Med 44 (1987) 236 [27] SCHNEIDER KTM, A BOLLINGER, A HUCH, R HUCH: The oscillating 'vena cava syndrome' during quiet standing: an unexpected observation in late pregnancy. Br J Obstet Gynaecol 91 (1984) 776 [28] SCHNEIDER KTM, H GRAEFF, S WEBER, P BUNG, A HUCH, R HUCH: Einfluß der Körperhaltung auf die mütterliche Hämodynamik. 3. RheingauWorkshop, 21. März 1986. In: MARTIN E, K PETER, K TAEGER (eds): Anästhesie und Geburtshilfe. Wissenschaftliche Verlagsabteilung Deutsche Abbott GmbH, Wiesbaden 1987
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[29] SCHNEIDER KTM, R HUCH, A HUCH: Premature contractions: are they caused by maternal standing? Acta Genet Med Gemellol 34 (1985) 175 [30] SCHNEIDER KTM, KH STAISCH, L SPÄTLING, R HUCH, A HUCH: Körperhaltung und kardiopulmonale Funktion in Schwangerschaft und Wochenbett: 1. Lungenfunktion. Gynäkol Praxis 9 81985) 641 [31] SCHNEIDER KTM, W Loos, A HASSLER, D PROCHASKA, M RÖBL, H GRAEFF: The use of waveform analysis of fetal vessels as a new fetal stress test. In: Abstract book: XI. European Congress of Perinatal Medicine 1988, Rome, 10. -13. April. CIC Edizioni International! 1988 [32] SCHNEIDER-AFFELD F, E KAUKEL, K NIENSTEDT: Lageabhängige Veränderungen von Lungenfunktions- und Kreislaufparametern bei graviden Frauen am Geburtstermin. Z Geburtshilfe Perinatol 187 (1983) 65 [33] SOHN C, H PENDEL, R WERDIN, P KERSTERNICH, H SCHONLAU: Änderung der uterinen Durchblutung in Abhängigkeit von der Körperposition während der Schwangerschaft. Z Geburtshilfe Perinatol 191 (1987) 169 [34] SUONIO S, AL SIMPANEN, H OLKKONEN, P H ARING: Effect of the left lateral recumbent position compared with the supine and upright positions on placental blood flow in normal late pregnancy. Ann Clin Res 8 (1976) 22 [35] UELAND K, JM HANSEN: Maternal cardiovascular dynamics: II. Posture and uterine contractions. Am J Obstet Gynecol 103 (1969) 1 [36] WEBER S, KTM SCHNEIDER, P BUNG, F FALLENSTEIN, A HUCH, R HUCH: Kreislaufwirkung von Kompressionsstrümpfen in der Spätschwangerschaft. Geburtshilfe Frauenheilkd 47 (1987) 395 [37] WEBER S, KTM SCHNEIDER, P BUNG, A HUCH, R HUCH: Antenatale fetale Herzfrequenz unter besonderer Berücksichtigung der mütterlichen Körperhaltung. Geburtshilfe Frauenheilkd 48 (1988) 35 Prof. Dr. Karl-Theo Schneider Frauenklinik rechts der Isar der Technischen Universität München Ismaningerstr. 22 W-8000 München 80 Fed. Rep. of Germany
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Dictionary of Obstetrics and Gynecology
Compiled by the editorial staff of Pschyrembel's Klinisches Wörterbuch. Managing editor Christoph Zink. Translated by Kathleen R. Dyer, Dietrich W. Roloff and Bernd K. Wittmann 1988.14 21,5 cm. XII, 284 pages. With 442 illustrations and 60 tables. Bound DM 68,- ISBN 311011875 0 This Dictionary of Obstetrics and Gynecology, with over 2600 entries, gives a comprehensive overview of the clinical and theoretical aspects of these specialist areas. At the same time, it reflects the increasingly important roles played by endocrinology, reproductive medicine, psychosomatic, and sexual medicine, perinatology and neonatology in the practice of obstetrics and gynecology. The dictionary was compiled by the editorial staff of Pschyrembel's Klinisches Wörterbuch, a widely-used reference work in German-speaking countries. It comprises contributions by many well-known scientists, over 400 illustrations in color or black and white, and a large number of tables and charts.
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