Objective: The aortic isthmus (AoI) blood flow has a characteristic shape with a small end-systolic notch observed during the third trimester of pregnancy. However, what causes the appearance of this notch is not fully understood. We used a lumped model of the fetal circulation to study the possible factors causing the end-systolic notch and the changes of AoI flow through gestation. Methods: A validation of the model was performed by fitting patient-specific data from two normal fetuses. Then, different parametric analyses were performed to evaluate the major determinants of the appearance of the end-systolic notch. The changes in the AoI flow profile through gestation were assessed. Results: Our model allows to simulate the AoI waveform. The delay in the onset of ejection together with the longer ejection duration of the right ventricle are the most relevant factors in the origin of the notch. It appears around 25 weeks of gestation and becomes more pronounced with advancing gestation. Discussion: We demonstrated that the end-systolic notch on the AoI flow occurs mainly as a result of a delayed and longer ejection of the right ventricle. Our findings improve the understanding of hemodynamic changes in the fetal circulation and the interpretation of clinical imaging.

Fouron JCC: The unrecognized physiological and clinical significance of the fetal aortic isthmus. Ultrasound Obstet Gynecol 2003;22:441-447.
Ruskamp J, Fouron JCC, Gosselin J, Raboisson MJJ, Infante-Rivard C, Proulx F: Reference values for an index of fetal aortic isthmus blood flow during the second half of pregnancy. Ultrasound Obstet Gynecol 2003;21:441-444.
Del Río M, Martínez JM, Figueras F, López M, Palacio M, Gómez O, Coll O, Puerto B: Reference ranges for Doppler parameters of the fetal aortic isthmus during the second half of pregnancy. Ultrasound Obstet Gynecol 2006;28:71-76.
Schmidt KG, Silverman NH, Rudolph AM: Phasic flow events at the aortic isthmus-ductus arteriosus junction and branch pulmonary artery evaluated by multimodal ultrasonography in fetal lambs. Am J Obstet Gynecol 1998;179:1338-1347.
Acharya G, Tronnes A, Rasanen J: Aortic isthmus and cardiac monitoring of the growth-restricted fetus. Clin Perinatol 2011;38:113-125, vi-vii.
De Muylder X, Fouron JC, Bard H, Riopel L, Urfer F: The difference between the systolic time intervals of the left and right ventricles during fetal life. Am J Obstet Gynecol 1984;149:737-740.
Chabaneix J, Fouron JC, Sosa-Olavarria A, Gendron R, Dahdah N, Berger A, Brisebois S: Profiling left and right ventricular proportional output during fetal life with a novel systolic index in the aortic isthmus. Ultrasound Obstet Gynecol 2014;44:176-181.
Kiserud T, Ebbing C, Kessler J, Rasmussen S: Fetal cardiac output, distribution to the placenta and impact of placental compromise. Ultrasound Obstet Gynecol 2006;28:126-136.
Molina FS, Faro C, Sotiriadis A, Dagklis T, Nicolaides KH: Heart stroke volume and cardiac output by four-dimensional ultrasound in normal fetuses. Ultrasound Obstet Gynecol 2008;32:181-187.
Acharya G: Technical aspects of aortic isthmus Doppler velocimetry in human fetuses. Ultrasound Obstet Gynecol 2009;33:628-633.
Fouron JC, Zarelli M, Drblik P, Lessard M: Flow velocity profile of the fetal aortic isthmus through normal gestation. Am J Cardiol 1994;74:483-486.
Machado MV, Chita SC, Allan LD: Acceleration time in the aorta and pulmonary artery measured by Doppler echocardiography in the midtrimester normal human fetus. Br Heart J 1987;58:15-18.
Sutton MS, Gill T, Plappert T, Saltzman DH, Doubilet P: Assessment of right and left ventricular function in terms of force development with gestational age in the normal human fetus. Br Heart J 1991;66:285-289.
Garcia-Canadilla P, Rudenick PA, Crispi F, Cruz-Lemini M, Palau G, Camara O, Gratacos E, Bijnens BH: A computational model of the fetal circulation to quantify blood redistribution in intrauterine growth restriction. PLoS Comput Biol 2014;10:e1003667.
Guettouche A, Challier JC, Ito Y, Papapanayotou C, Cherruault Y, Azancot-Benisty A: Mathematical modeling of the human fetal arterial blood circulation. Int J Biomed Comput 1992;31:127-139.
Luria O, Bar J, Kovo M, Malinger G, Golan A, Barnea O: The role of blood flow distribution in the regulation of cerebral oxygen availability in fetal growth restriction. Med Eng Phys 2012;34:364-369.
van den Wijngaard JPHM, Westerhof BE, Faber DJ, Ramsay MM, Westerhof N, van Gemert MJC: Abnormal arterial flows by a distributed model of the fetal circulation. Am J Physiol Regul Integr Comp Physiol 2006;291:R1222-R1233.
Pennati G, Bellotti M, Fumero R: Mathematical modelling of the human foetal cardiovascular system based on Doppler ultrasound data. Med Eng Phys 1997;19:327-335.
Luria O, Bar J, Shalev J, Kovo M, Golan A, Barnea O: Inverse solution of the fetal-circulation model based on ultrasound Doppler measurements. Cardiovasc Eng Technol 2014;5:202-216.
van Gemert MJC, Sterenborg HJ: Haemodynamic model of twin-twin transfusion syndrome in monochorionic twin pregnancies. Placenta 1998;19:195-208.
Arduini D, Rizzo G: Normal values of pulsatility index from fetal vessels: a cross-sectional study on 1556 healthy fetuses. J Perinat Med 1990;18:165-172.
Baschat AA, Gembruch U: The cerebroplacental Doppler ratio revisited. Ultrasound Obstet Gynecol 2003;21:124-127.
Schneider C, McCrindle BW, Carvalho JS, Hornberger LK, McCarthy KP, Daubeney PEF: Development of Z-scores for fetal cardiac dimensions from echocardiography. Ultrasound Obstet Gynecol 2005;26:599-605.
Ponzini R, Vergara C, Rizzo G, Veneziani A, Roghi A, Vanzulli A, Parodi O, Redaelli A: Womersley number-based estimates of blood flow rate in Doppler analysis: in vivo validation by means of phase-contrast MRI. IEEE Trans Biomed Eng 2010;57:1807-1815.
DeVore GR: Assessing fetal cardiac ventricular function. Semin Fetal Neonatal Med 2005;10:515-541.
Gallivan S, Robson SC, Chang TC, Vaughan J, Spencer JA: An investigation of fetal growth using serial ultrasound data. Ultrasound Obstet Gynecol 1993;3:109-114.
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