Kari Flo

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

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.

A longitudinal study of maternal endothelial function, inflammatory response and uterine artery blood flow during the second half of pregnancy

The objective of this study was to investigate serial changes in maternal endothelial function, inflammatory response and uterine artery blood flow in normal pregnancy, and to explore their inter‐relation.

Effect of Passive Leg Raising on Systemic Hemodynamics of Pregnant Women: A Dynamic Assessment of Maternal Cardiovascular Function at 22–24 Weeks of Gestation

Objective To investigate functional hemodynamic response to passive leg raising in healthy pregnant women and compare it with non-pregnant controls. Materials and Methods This was a prospective cross-sectional study with a case-control design. A total of 108 healthy pregnant women at 22–24 weeks of gestation and 54 non-pregnant women were included. Cardiac function and systemic hemodynamics were studied at baseline and 90 seconds after passive leg raising using non-invasive impedance cardiography. Main outcome measures Trends and magnitudes of changes in impedance cardiography derived parameters of cardiac function and systemic hemodynamics caused by passive leg raising, and preload responsiveness defined as >10% increase in stroke volume or cardiac output after passive leg raising compared to baseline. Results The hemodynamic parameters in both pregnant and non-pregnant women changed significantly during passive leg raising compared to baseline, but the magnitude and trend of change was similar in both groups. The stroke volume increased both in pregnant (p = 0.042) and non-pregnant (p = 0.018) women, whereas the blood pressure and systemic vascular resistance decreased (p<0.001) following passive leg raising in both groups. Only 14.8% of pregnant women and 18.5% of non-pregnant women were preload responsive and the difference between groups was not significant (p = 0.705). Conclusion Static measures of cardiovascular status are different between healthy pregnant and non-pregnant women, but the physiological response to passive leg raising is similar and not modified by pregnancy at 22–24 weeks of gestation. Whether physiological response to passive leg raising is different in earlier and later stages of pregnancy merit further investigation.

Longitudinal reference ranges for umbilical vein blood flow at a free loop of the umbilical cord

To establish longitudinal reference ranges for the umbilical vein (UV) diameter, velocities and volume blood flow (Quv) at a free loop of the umbilical cord and estimate the UV spatial velocity profile at this site.

Relation between utero-placental and feto-placental circulations: a longitudinal study

Objective. To explore the relation between total utero‐placental (TQuta) and feto‐placental (Quv) blood flows and establish longitudinal reference ranges for the TQuta/Quv ratio and the mean uterine artery and umbilical artery pulsatility (UtaPI/UAPI) and resistance index (UtaRI/UARI) ratios. Design. Prospective longitudinal observational study. Setting. University hospital in Norway. Population. Fifty‐three low‐risk pregnant women. Methods. Uterine artery and umbilical vein blood flow was measured using Doppler ultrasonography at 4‐weekly intervals from 22+0 to 39+6 weeks of gestation. Main outcome measures. Ratios between utero‐placental and feto‐placental volume blood flows and between indices of uterine and umbilical artery impedance. Results. The TQuta/Quv ratio had a significant association with the gestational age (p < 0.00001) and decreased with advancing gestation during the second half of pregnancy. The mean UtaPI/UAPI (p = 0.094) and mean UtaRI/UARI (p = 0.323) ratios were not significantly associated with gestational age and remained relatively constant. There was no significant association between TQuta and Quv (p = 0.72), mean UtaPI and UAPI (p = 0.56), or mean UtaRI and UARI (p = 0.57). Conclusion. The gestational‐age‐related changes in the utero‐placental and feto‐placental circulations do not appear to be affected by each other under physiological conditions. We have established longitudinal reference ranges for the utero‐placental and feto‐placental blood flow and impedance ratios during the second half of pregnancy.

A new non-invasive method for measuring uterine vascular resistance and its relationship to uterine artery Doppler indices: a longitudinal study

To describe a new method for measuring uterine vascular resistance (Ruta), establish longitudinal reference ranges and explore the relationship between uterine artery (UtA) Doppler indices and Ruta.

Hemodynamic aspects of normal human feto-placental (umbilical) circulation.

Understanding the changes in normal circulatory dynamics that occur during the course of pregnancy is essential for improving our knowledge of pathophysiological mechanisms associated with feto‐placental diseases. The umbilical circulation is the lifeline of the fetus, and it is accessible for noninvasive assessment. However, not all hemodynamic parameters can be reliably measured in utero using currently available technology. Experimental animal studies have been crucial in validating major concepts related to feto‐placental circulatory physiology, but caution is required in directly translating the findings of such studies into humans due to species differences. Furthermore, it is important to establish normal reference ranges and take into account gestational age associated changes while interpreting the results of clinical investigation. Therefore, it is necessary to critically evaluate, synthesize and summarize the knowledge available from the studies performed on human pregnancies to be able to appropriately apply them in clinical practice. This narrative review is an attempt to present contemporary concepts on hemodynamics of feto‐placental circulation based on human studies.

Maternal functional hemodynamics in the second half of pregnancy: A longitudinal study

Objective Cardiovascular response to passive leg raising (PLR) is useful in assessing preload reserve, but it has not been studied longitudinally during pregnancy. We aimed to investigate gestational age associated serial changes in maternal functional hemodynamics and establish longitudinal reference ranges for the second half of pregnancy. Materials and Methods This was a prospective longitudinal study on 98 healthy pregnant women who were examined 3–5 times during 20–40 weeks of gestation (a total of 441 observations). Maternal cardiac function and systemic hemodynamics were assessed at baseline and 90 seconds after PLR using impedance cardiography (ICG). The main outcome measures were gestational age specific changes in ICG-derived variables of maternal cardiovascular function and functional hemodynamic response to PLR. Results Hemodynamic response to PLR varied during pregnancy. PLR led to an insignificant increase in stroke volume during 20+0 to 31+6 weeks, but later in gestation the stroke volume was slightly lower at PLR compared to baseline. PLR caused no significant change in cardiac output between 20+0 and 23+6 weeks and a significant decrease after 24+0 weeks. A decrease in heart rate, mean arterial pressure, and cardiac contractility was observed during PLR throughout the second half of pregnancy. Systemic vascular resistance was reduced by PLR up to 32+0 weeks, but increased slightly thereafter. Conclusion Healthy pregnant women appear to have limited preload reserve and reduced cardiac contractility, especially in the third trimester, which makes them vulnerable to fluid overload and cardiac failure.

Blood flow to the scarred gravid uterus at 22–24 weeks of gestation

To compare uterine artery volume blood flow (Quta), vascular resistance (Ruta), pulsatility index (Uta PI), and the fraction of maternal cardiac output (CO) distributed to the uteroplacental circulation in pregnant women with and without a previous caesarean section.

Agreement between umbilical vein volume blood flow measurements obtained at the intra-abdominal portion and free loop of the umbilical cord.

The umbilical vein (UV) is a single vessel and theoretically the volume of blood flowing through it should be equal whether it is measured at the intra‐abdominal portion (IA) or a free loop of the umbilical cord (FL). However, the reported values vary considerably depending on the technique and site of measurement. Our objective was to investigate the correlation and agreement between UV volume blood flows (Quv) measured at the IA and FL.