A computational model provides knowledge of haemodynamic changes in the foetus during the last trimester of pregnancy

In maternal-foetal medicine, the Doppler ultrasound is an essential tool for the diagnosis and monitoring of various problems that can affect the foetus, such as intrauterine growth restriction, foetal anaemia or twin-to-twin transfusion syndrome, a severe complication that affects pregnancies with identical twins sharing the placenta.

A study has shown for the first time by using a computational model of foetal circulation that the peak reverse flow observed in the ultrasound images at the end of the systole in the aortic isthmus during the last trimester of pregnancy, that some clinical studies had attributed to an artefact, actually corresponds to delayed right ventricular ejection compared to the left.

This same study also demonstrates the effectiveness of the computational model that enables estimating specific parameters of the patient that could not be evaluated clinically, which helps improve the understanding of the haemodynamic changes that take place in the circulation of the foetus during gestation.

These are the findings of a study published on 24 February in the journal Fetal Diagnosis and Therapy, by Patricia García-Cañadilla as first author, a researcher of the Physense Research Group coordinated by Bart Bijnens, ICREA researcher of the Department of Information and Communication Technologies (DTIC) at UPF, together with researchers from research centres linked to Hospital Clínic and Hospital of St. Joan de Déu, as well as the CIBER-ER.

We needed a better understanding of Doppler ultrasound patterns

The study assumes that, the correct application and interpretation of the data obtained by Doppler ultrasound requires a good understanding of the patterns of Doppler speeds applied to foetal haemodynamics which, in some cases, was lacking. For example in the patterns of Doppler speeds of the foetal aortic isthmus (Aol), an anatomical structure that has a strategic haemodynamic role in the foetus, the patterns of which were not fully established.

This anatomical structure is characterized by the sole arterial connection between the right ventricle (venous blood) and the left (arterial blood) and it behaves in such a way that it may increase or reduce the amount of blood flowing to vital organs like the heart or the brain of the foetus, depending on the level of oxygen supply to the placenta.

For the study of the foetal cardiovascular system and haemodynamic changes that occur in foetal circulation, computational models are an indispensable tool. As Patricia García-Cañadilla, first author of the study explains, “we have developed and validated a model of foetal circulation grouped with the main arteries and vascular beds and used it to better understand the meaning of certain ultrasound images such as peak reverse flow in the flow profile of the foetal aortic isthmus”.

via GIPHY

The computer model was able to explain a phenomenon that was believed to be an artefact

In addition to providing detailed information on changes in blood flow in the aortic isthmus of the foetus during gestation, the study has also provided a surprising fact, according to the authors: “this in silico study reveals that the temporary differences between pulmonary and aortic blood flow are the main determining factor of the development of inverse flow at the end of systole in the foetal aortic isthmus”.

That is to say, as García-Cañadilla explains: “our computational model has shown that the peak reverse flow characteristic of the foetal aortic isthmus at the end of systole and at the end of gestation occurs primarily as a result of delayed right ventricular ejection compared to the left and is therefore not an artefact as had been previously suggested in some clinical studies”.

Reference work:

Garcia-Canadilla P., Crispi F., Cruz-Lemini M., Valenzuela-Alcaraz B., Rudenick P.A., Gratacos E., Bijnens B.H, (2016), “Understanding the Aortic Isthmus Doppler Profile and its Changes with Gestational Age Using a Lumped Model of the Fetal Circulation”, Fetal Diagn Ther, DOI:10.1159/000444142.