Measurement of cardiac output in pregnancy by thoracic electrical bioimpedance and thermodilution. A preliminary report

Thoracic electrical bioimpedance is a noninvasive, continuous method of obtaining cardiac output that requires no operator skill. However, the most recent thoracic electrical bioimpedance technology has not been validated in pregnancy. We therefore compared two methods of measuring cardiac output in pregnancy, thoracic electrical bioimpedance and thermodilution. We studied 11 patients who required pulmonary artery catheterization for peripartum management and measured cardiac output simultaneously by thoracic electrical bioimpedance and thermodilution. Among eight of nine patients, there was agreement (within +/- 20%) between the two methods. Bivariate linear regression with these nine cases showed excellent correlation (r = 0.91, p less than 0.001) with a slope of 1.04, which indicated a one-to-one relationship between thoracic electrical bioimpedance and thermodilution. The remaining two cases were removed from analysis because of septic shock in one case (which invalidates thoracic electrical bioimpedance) and 4+ tricuspid regurgitation in another case (which invalidates thermodilution). These data support that thoracic electrical bioimpedance measurement of cardiac output may be valid in most peripartum patients.     

Hemodynamic changes during pregnancy and postpartum: a prospective study using thoracic electrical bioimpedance

Objective.?To describe hemodynamic changes in normal pregnancy and postpartum by means of thoracic electrical bioimpedance (TEB).

Methods.?Eighteen healthy pregnant women were included in the study. Eight different hemodynamic variables were measured by thoracic electrical bioimpedance, from 12th week of gestation until 6th month of postpartum period. Data along pregnancy and postpartum were analyzed with SAS statistical software to compare the different values, so normality curves are reported.

Results.?Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and peripheral vascular resistances (PVRs) seem to significantly decrease until 24th week of gestation, and then they seem to increase until delivery, recovering normal values gradually during postpartum period. End-diastolic volume (EDV), systolic volume (SV), cardiac output (CO), and ejection fraction (EF) seem to decrease until 48?h after delivery; statistical significance was found.

Conclusions.?Thoracic electrical bioimpedance may be the most appropriate and accurate technique to measure normal hemodynamic changes during pregnancy and postpartum.     

Immune complexes in preeclampsia and normal pregnancy

We determined in normal nonpregnant (group I) and normal pregnant (group II) women and in patients with preeclampsia (group III): (1) immunoglobulins and complement C3b associated with polymorphonuclear leukocytes and platelet surfaces in an attempt to evaluate the interaction in vivo of immune complexes with the membranes of these cells; (2) the occurrence of circulating immune complexes; (3) the serum levels of immunoglobulins, C3, and C4; and (4) the plasma levels of complement C3d. In patients with preeclampsia (group III), the percentages of polymorphonuclear leukocytes and platelets positive for membrane-bound IgG, IgM, IgA, and C3 were significantly higher than the percentages in groups I and II. In group III, there also was a significant increase in circulating immune complexes, as compared to groups I and II. However, circulating immune complexes were also present in significant amounts in normal pregnancy (group II). The plasma levels of complement C3d were markedly increased in the most severe cases of preeclampsia.     

Haemodynamic changes in the second half of pregnancy: a longitudinal, noninvasive study with thoracic electrical bioimpedance

Objective  Maternal cardiovascular adaptations to pregnancy are necessary for an adequate fetomaternal circulation. However, the time course of physiological haemodynamic changes during the second half of pregnancy remains unclear. Various methods, invasive and noninvasive, are described to measure these changes. The thoracic electrical bioimpedance (TEB) technique is a method which is especially suitable to measure haemodynamic changes over time. The aim of the study was to determine both individual and group trends of haemodynamic changes in healthy pregnant women during the second half of pregnancy by means of TEB. Outcome variables are heart rate (HR), stroke volume (SV), cardiac output (CO) and blood pressure.
Design  Longitudinal study.
Setting  Outpatient antenatal care clinic of university hospital.
Population  A total of 22 healthy nonsmoking women with an uncomplicated singleton pregnancy and without pre-existing vascular disorders were invited.
Methods  TEB and blood pressure measurements were performed at each regular visit from about 24 weeks of gestation through term age.
Main outcome measures  Trends were calculated with the random effects model.
Results  Data obtained from 19 women were analysed, with a median of eight (range 3–11) measurements. HR showed a linear increase ( P < 0.0005) and a quadratic trend ( P < 0.0005). SV decreased linearly ( P = 0.046), without a quadratic course. CO remained stable over time.
Conclusion  During the second half of physiological pregnancy, significant trends could be determined. An increase in HR, a decrease in SV, a stable CO and an increase in systolic and diastolic blood pressures were found.     

The role of endothelium in normal pregnancy and pregnancy complicated by preeclampsia]

Endothelial cell dysfunction is thought to play a role in preeclampsia and the reduced production by vascular endothelial cells of the antiaggregatory and vasodilatory factors is well documented. The present study was designed to evaluate endothelial cells function in preeclamptic and healthy pregnant subjects. The nitric oxide plasma concentration in women with preeclampsia was significantly lower as compared with normotensive pregnant women. A significant increase in ET concentration was found in preeclamptic women as compared with normal pregnant patients and normal non-pregnant. The plasma concentrations of von Willebrand factor were significantly increased in healthy pregnancy as compared with preeclamptic patients. The results of our study demonstrate a significant endothelial cells damage in preeclamptic patients. Whether these observations contribute to the vascular pathophysiologic features of preeclampsia remains to be proved.     

Atrial natriuretic peptide concentrations and hemodynamic effects of acute plasma volume expansion in normal pregnancy and preeclampsia.

Plasma atrial natriuretic peptide (ANP) and circulatory responses were studied during rapid plasma volume expansion with crystalloid solutions. Sixteen women with preeclampsia and 16 healthy controls in the third trimester were compared. Basal mean (+/- standard error of the mean) ANP levels were not significantly higher in the preeclamptics than in controls (13.6 +/- 3.5 versus 6.4 +/- 1.1 pmol/L; not significant), but the increment following volume expansion was more pronounced (12.9 +/- 2.6 versus 6.1 +/- 2.3 pmol/L; P less than .05). The mean plasma volume expansion was less in the preeclamptic group (6.1 +/- 0.8 versus 9.3 +/- 1.1%; P less than .05), reflecting a higher capillary permeability in this disease. Left ventricular posterior-wall thickness in diastole was increased in the preeclamptics under basal conditions as compared with the controls (9.8 +/- 0.3 versus 8.9 +/- 0.3 mm; P less than .05), as was the thickness of the interventricular septum in systole (14.3 +/- 0.5 versus 12.3 +/- 0.6 mm; P less than .05). Systemic vascular resistance was higher in the preeclamptic group (19.7 +/- 0.8 versus 15.1 +/- 1.1 peripheral resistance units; P less than .01). In the controls, cardiac output increased by 23 +/- 4% and systemic vascular resistance decreased by 17 +/- 3%. The preeclamptic women reacted in a similar way. Our results indicate that preeclampsia is associated with an enhanced ANP response despite a less pronounced increase in plasma volume during acute fluid challenge.     

Skeletal muscle ultrastructure in normal pregnancy and preeclampsia

The aim of this study was to assess by quantitative methods whether the assumed metabolic disturbance underlying preeclampsia would be reflected in muscle cell composition of lipid, mitochondria, or glycogen. We have reported mitochondrial dysfunction in preeclampsia, and since accumulation of lipid in skeletal muscle is a feature in mitochondrial disorders, our hypothesis was that preeclamptic women would have an increased content of triglyceride droplets. Quantitative investigation of the skeletal muscle ultrastructure was performed in 10 women with severe preeclampsia and in 6 normotensive pregnant women. Biopsy specimens from musculus rectus abdominis were taken during cesarean section and prepared for electron microscopy. Random pictures were taken by transmission electron microscopy, and point-counting stereology was performed. Preeclamptic women did not have a higher lipid volume fraction than normotensive pregnant women, and we had to reject our hypothesis. On the contrary, there was a tendency towards a lower triglyceride volume fraction in pre eclampsia. We did not detect differences in relative volumes of mitochondria or glycogen in skeletal muscle between the two groups.     

Angiotensin-converting enzyme gene polymorphism in preeclampsia and normal pregnancy

OBJECTIVE: The purpose of this study was to evaluate the angiotensin-converting enzyme gene polymorphism in pregnant women with and without preeclampsia. STUDY DESIGN: Preeclampsia was defined as hypertension and pathologic proteinuria in pregnant women after gestational week 20. Genomic DNA was isolated from leukocytes. The insertion-deletion polymorphism in intron 16 of the angiotensin-converting enzyme gene was detected in DNA samples with the use of the polymerase chain reaction. Chi-squared and Student t tests were used for statistical analysis. RESULTS: In preeclampsia (n=51 women) angiotensin-converting enzyme genotypes were deletion-D (DD) in 16 women (31%), insertion-I (II) in 12 women (24%), and insertion-deletion in 23 women (45%); in the control group (n=71), the angiotensin-converting enzyme genotypes were DD in 21 women (30%), II in 17 women (24%), and insertion-deletion in 33 women (46%). Angiotensin-converting enzyme genotype distribution and allelic frequencies were not different between groups. CONCLUSION: No difference in the angiotensin-converting enzyme genotype distribution was found between preeclampsia and normal pregnancy. The results showed no association between angiotensin-converting enzyme polymorphism and the development of preeclampsia.     

Venous pulse transit time in normal pregnancy and preeclampsia

Uncomplicated pregnancies (n = 16) were evaluated longitudinally and compared to early- (n = 12) and late-onset (n = 14) preeclampsia patients, assessed once at diagnosis. Pulse transit time (PTT), equivalent to pulse wave velocity, was measured as the time interval between corresponding characteristics of electrocardiography and Doppler waves, corrected for heart rate, at the level of renal interlobar veins, hepatic veins, and arcuate branches of uterine arteries. Impedance cardiography was used to measure PTT at the level of the thoracic aorta. In normal pregnancy, all PTT increased gradually (P ≤ .01). Pulse transit time was shorter in late-onset preeclampsia (P < .05) and also in early-onset preeclampsia, with exception for hepatic veins and thoracic aorta (P > .05). Our results indicate that PTT is an easy and highly accessible measure for vascular reactivity at both arterial and venous sites of the circulation. Our observations correlate well with known gestational cardiovascular adaptation mechanisms. This suggests that PTT could be used as a new parameter in the evaluation and prediction of preeclampsia.     

Calculated capillary hydrostatic pressure in normal pregnancy and preeclampsia

Capillary hydrostatic pressure has been calculated in normal pregnancy and preeclampsia. In humans, capillary hydrostatic pressure cannot be measured directly but may be calculated when the colloid osmotic pressure in plasma and interstitial fluid and interstitial fluid hydrostatic pressure are known (Starling equation). New methods have made it possible to measure the interstitial fluid colloid osmotic pressure and interstitial fluid hydrostatic pressure. In the present study interstitial fluid was collected from the subcutaneous tissue by implanted wicks (wick method), and interstitial fluid colloid osmotic pressure was determined. Interstitial fluid hydrostatic pressure was recorded by the wick-in-needle technique. Capillary hydrostatic pressure was calculated in 10 women in the first trimester and 10 in the third trimester of normal pregnancy, in 15 patients with mild preeclampsia, and in 13 women with severe preeclampsia. In normal pregnancy, capillary hydrostatic pressure increased by about 30% between the first and third trimesters. In mild preeclampsia, capillary hydrostatic pressure values did not differ significantly from those in the third trimester of normal pregnancy. However, in severe preeclampsia capillary hydrostatic pressure was significantly lower (40%) than in mild preeclampsia. Whether the low capillary hydrostatic pressure is caused by the severe general vasospasm seen in this condition or is a secondary event is unknown.     

Serum insulin-like growth factors in normal pregnancy and in pregnancies complicated by preeclampsia

BACKGROUND: Lower levels of insulin-like growth factor I (IGF-I) have been shown to be associated with preeclampsia and also with a reduced risk of breast cancer later in life. Lower levels of IGF before clinical signs of preeclampsia could be one possible mechanism in the etiology of preeclampsia as well as for the reduced risk of breast cancer associated with preeclampsia. We have prospectively investigated maternal serum levels of IGF-I, IGF-II, and the main binding protein insulin-like growth factor binding protein 3 (IGFBP-3) in women with and without preeclampsia. METHODS: We used maternal serum samples from a Swedish-Norwegian cohort study obtained in the 17th and 33rd gestational week from 30 women who subsequently developed preeclampsia and 128 women who did not develop preeclampsia. RESULTS: There were no significant differences in serum concentrations IGF-I and IGFBP-3 in the 17th or the 33rd week of gestation between women who developed preeclampsia or not. Compared with nonpreeclamptic women, preeclamptic women had significantly higher serum levels of IGF-II in week 33, but there was no difference in week 17. CONCLUSION: In women who developed preeclampsia, we found no support for the hypothesis that the disease was preceded by lower serum levels of IGF-I and IGF-II, or higher serum levels of IGFBP-3. However, among women who later developed preeclampsia, serum levels of IGF-II were significantly higher in the 33rd gestational week.     

正常妊娠和子痫前期孕妇血液动力学的季节性变化

目的:探讨不同季节正常孕妇和子痫前期孕妇血液动力学的变化。方法:采用无创妊娠期高血压疾病血液动力学监测系统(MP-PIH)检测150例正常妊娠和110例子痫前期孕妇血液动力学参数,根据其发病季节分为夏季组、过渡季组和冬季组,分析不同季节正常孕妇和子痫前期孕妇血液动力学的变化。结果:(1)冬季正常妊娠组与过渡季正常妊娠组相比,每搏输出量(SV)、心输出量(CO)、血管顺应性(AC)显著升高(P<0.01),外周阻力(TPR)显著下降(P<0.05),心率(HR)及血液黏度(V)无统计学差异(P>0.05);冬季组正常妊娠和夏季组正常妊娠相比,SV、CO、AC显著升高(P<0.05);夏季正常妊娠组与过渡季正常妊娠组相比,各血液动力学指标无统计学差异(P>0.05)。(2)不同季节子痫前期的各项血液动力学指标无明显统计学差异(P>0.05);冬季子痫前期组SV、CO、AC与同季度正常妊娠组相比显著下降(P<0.01);各季度子痫前期组TPR、V与同季度正常妊娠组相比显著升高(P<0.05)。结论:正常妊娠血液动力学随气候变化呈动态平衡;子痫前期孕妇生理性的血液动力自我平衡失调,可能是导致冬季型气候条件下子痫前期发病率增高的原因之一。