Blood flow in obstetrics using Doppler ultrasound

Fetal Aortic and Umbilical Doppler Flow Velocity Waveforms in Pregnancy: The Concept of Aortoumbilical Column

Low impedance within the uteroplacental circulation is crucial for fetal development. Flow velocity waveforms (FVW) have been established for the aortic and umbilical arteries in low-risk pregnancies during the second half of pregnancy, but data regarding early gestation is limited. Both vascular territories exhibit higher impedance patterns in pregnancies complicated by fetal growth restriction (FGR), hypertensive disorders, fetal anemia, and chromosomal abnormalities. Early identification of these complications is critical in obstetric practice, to reduce perinatal morbidity and mortality through prevention and close antenatal surveillance. Available data suggest that aortic and umbilical impedances follow the same variation pattern as pregnancy progresses. This observation implies that both vessels may be considered as a single artery, referred to as the "aortoumbilical column". Our hypothesis posits that changes in the hemodynamic pattern of this column could identify high-risk pregnancies, particularly those complicated by preeclampsia, FGR, intrauterine fetal demise, fetal aneuploidies, and fetal anemia. Understanding vascular embryogenesis and the FVWs of the aortic and umbilical arteries enables comprehension of impedance changes throughout normal pregnancies. The continuous variation in impedance along a single vessel supports our concept of the aortoumbilical column. Deviations from the regular pattern could assist in identifying compromised fetuses during early pregnancy. Further research on normal aortoumbilical column FVW and the development of reference charts is necessary to consider this arterial column as a screening tool in clinical practice.

Morphological Analysis of in Vivo Velocity Field in the Alteration of the Vasomotor Tone

Vessel wall remodeling is involved in atherogenesis and in several important vascular diseases affecting mainly aged and prosthetic implanted patients. This adaptive response to pathological states in arterial hemodynamics strongly suggests that flow-derived stresses act as mechanical stimuli to the release of endothelium-derived vasoactive factors, leading to vascular alterations. As the correlation of intimal hyperplasia (IH) with blood flow alterations in arteries has been shown to be significant, and as it is well-known that clinical procedures carry a substantial risk of development of vascular disease, the relevance of local hemodynamics must be investigated to describe changes in compliance matching in prosthetic applications. The aim of our research is to investigate the use of principal components analysis, together with varimax rotation, in the individuation process of morphological characteristics of real time ultrasound in in vivo recordings of blood flow velocities, as provided by two different carotid perivascular manipulations. This would be of use in the clinical assessment of atherogenesis, hypertension, prosthetic replacement or more in general in all applications in which vascular tone may be impaired. Data recordings refer to previous animal experiments where the Moncada model was investigated by means of an ultrasound profilometer. The present study confirms the feasibility of the proposed analysis to follow vascular pathology evolution, distiguishing between an in progress and a static situation.

Hemodynamic model for analysis of Doppler ultrasound indexes of umbilical blood flow

A hemodynamic model for pulsatile fluid flow in a pressurized thin-walled elastic tube was applied for the computation of volumetric blood flow and velocity profiles for a given set of system parameters at any selected location along the umbilical artery. The velocity profiles over one heart cycle provide the fetal blood flow velocity waveforms (FVW) from which the usual Doppler indexes (DI) can be derived. The model was used for a comprehensive investigation of the correlation between DI and system parameters that reflect the anatomy and physiology of umbilical blood flow. The simulations showed that the radial location of the Doppler measurement is insignificant for the calculated DI, whereas the axial site is important. The analysis showed that decreasing the diameter or increasing the length of the umbilical artery reduces fetal mean blood flow rate and increases the DI. Increasing blood viscosity tends to induce similar patterns, whereas decreasing arterial compliance or increasing blood density decreases the DI with little effect on blood flow rate. Fetal heart rate has a minor effect on both DI and fetal blood flow rate. This study provides insight into the dependence of DI on the anatomic and physiological characteristics of umbilical blood flow.

Surgical hepatosplenic schistosomiasis mansoni in children: a Doppler duplex study of the portal vein and the hepatic artery

From January 1990 to September 1993, 25 children with hepatosplenic schistosomiasis mansoni and oesophageal varices underwent splenectomy, ligature of the left gastric vein and autoimplantation of 100 g of spleen into the great omentum at the University Hospital, Recife, Brazil. The diameters and the blood flow velocities of the portal vein and the hepatic artery were measured before and after surgery. A Doppler Duplex (Aloka 680) with a convex transductor of 3.5 MHz was used. Post-operative follow-up revealed (i) a significant decrease in the mean diameter of the portal vein from 12.6 +/- 2.1 mm to 9.6 +/- 1.9 mm, (ii) a significant increase in the mean diameter of the hepatic artery from 5.0 +/- 1.4 mm to 5.3 +/- 1.2 mm, (iii) a significant decrease in the mean blood flow velocity in the portal vein from 31.1 +/- 8.0 cm/s to 22.4 +/- 7.1 cm/s, and (iv) no significant change in blood flow velocity in the hepatic artery. The study supports the concept that surgical treatment for portal hypertension in patients with hepatosplenic schistosomiasis mansoni, which includes splenectomy, results in a decrease of venous portal blood flow to the liver associated with an increase in the arterial hepatic blood flow. The physiological implications of these haemodynamic changes in the long term remain to be investigated.