A Longitudinal Study of the Relationship Between Maternal Cardiac Output Measured by Impedance Cardiography and Uterine Artery Blood Flow in the Second Half of Pregnancy

Abstract

Please cite this paper as: Flo K, Wilsgaard T, Vårtun Å, Acharya G. A longitudinal study of the relationship between maternal cardiac output measured by impedance cardiography and uterine artery blood flow in the second half of pregnancy. BJOG 2010;117:837–844. Objective To study serial changes in maternal systemic and uterine artery haemodynamics and establish reference ranges for the second half of pregnancy. Design Prospective longitudinal observational study. Setting University hospital in Norway. Population Low‐risk pregnant women. Methods Fifty‐three low‐risk pregnancies were evaluated at approximately 4‐weekly intervals. Maternal systemic haemodynamics was assessed with impedance cardiography. Uterine artery blood velocity and diameter were measured using Doppler ultrasonography and uterine artery volume blood flow (Quta) was calculated as the product of mean velocity and cross‐sectional area of the uterine artery. The fraction of cardiac output (CO) distributed to the uterine circulation was calculated as: Quta/CO × 100. Main outcome measures CO, Quta, uterine vascular resistance (Ruta) and the fraction of CO distributed to the uterine circulation. Results The CO increased (P = 0.0063) until 34 weeks and remained stable until term. Total Quta increased from 299 to 673 ml/minute and Ruta halved from 0.26 to 0.13 mmHg/ml/minute (P < 0.0001). The fraction of CO distributed to the uterine circulation increased from 5.6% to 11.7% (P < 0.0001). Conclusion During the second half of pregnancy, Quta and the fraction of maternal CO distributed to the uterine circulation increase approximately two‐fold, mainly as a result of decrease in Ruta.

Non-invasive assessment of gestational hemodynamics: benefits and limitations of impedance cardiography versus other techniques

“…Where most authors describe an increase of CO in early pregnancy with a maximum around 32-34 weeks of gestation [63,64] and maintenance of the CO in late pregnancy [65], some others describe different findings. van Oppen et al published a longitudinal study in which they observed that mean CO and mean SV decreased in late pregnancy, although this course of CO was not uniform in all 50 subjects [66].…”

SPIO‐enhanced magnetic resonance imaging study of placental perfusion in a rat model of intrauterine growth restriction

“…1,2 Moreover, Doppler ultrasound cannot be routinely used to quantify placental perfusion, a parameter that could in theory be measured in millilitres of blood per gram of placenta per minute, even though several studies have measured uterine artery blood flow volume during pregnancy. [4][5][6][7] Several experimental approaches have been developed to assess placental function, including the use of radioactive microspheres and angiography, but their routine clinical use is severely restricted by concerns for both fetal and maternal safety. 8 Magnetic resonance imaging (MRI) is being increasingly used as a diagnostic tool in human pregnancy, and recent reports suggest that it may provide important information on placental function.…”

Cardiovascular alterations in the parturient undergoing cesarean delivery with neuraxial anesthesia

“…One study indicates that a fixed rate of 75 or 100 mcg/min phenylephrine is associated with more episodes of hypertension (than placebo or rates of 25 or 50 mcg/min) and a 100 mcg/min infusion was associated with episodes of sinus bradycardia requiring treatment with glycopyrrolate [164]. Citing a study that shows that bolus phenylephrine reduces maternal CO in close correlation to maternal HR [41], other experts feel that phenylephrine can be administered in bolus doses titrated to maintain a stable HR.…”