CE Seminar by Dr. Yap Choon Hwai

Author: Collage of Engineering
Time: 10:00
Location: ENG 120






Speaker: Dr. Yap Choon Hwai

Title: Does Abnormal Blood Flow Fluid Mechanics Play a Role in Embryonic and Fetal Heart malformations?

Date: 22 January 2018, Monday

Time: 10:00

Place: ENG 120

Host: Kerem Pekkan




Congenital Heart Malformations (CHM) affects 0.6-1.9% of pregnancies, and include very severe malformations such as the Tetralogy of Fallot (TOF) and Hypoplastic Left Heart Syndrome (HLHS). Studies have shown that genetics can only account for a small number of cases of these malformations, leading to the hypothesis that epigenetic factors are responsible for their pathogenesis. Several studies have suggested that abnormal mechanical forces of blood flow to be one such epigenetic factor. It is thus important to understand the mechanical force environments in the prenatal heart, and it consequential mechanobiology. In my talk, I will discuss our efforts in studying the mechanical force environments in the small animal embryonic hearts (using the chick model) and in human fetal hearts, both in health and during malformations, using image-based computational fluid dynamics (CFD).


In chick embryos, we developed a novel 4D high-frequency ultrasound scanning technique that could provide non-invasive 4D reconstructions of the heart with substantially greater imaging depth than OCT. The technique enabled imaging of fine anatomic structures such as the pharyngeal aortic arches, quantification of organ dynamics and heart function, and supported detailed dynamic mesh CFD. CFD results showed that the primitive ventricle has spatial variability of wall shear stresses (WSS), and a double helical flow in the outflow tract. The dividing line between the two helical flow structures spiralled down the outflow tract for about 180o, in a similar manner as how the septum would eventually develop in the outflow tract to divide it into the pulmonary artery and aorta.


In human fetal hearts, we utilized 4D clinical ultrasound images to support CFD simulations. We characterized the flow and energy dynamics in normal 22 and 31 weeks old human fetal hearts, as well as those with TOF malformations. In both normal and diseased hearts, there were interesting ventricular diastolic vortex rings that interacted with one another and with the walls of the ventricle to elevate shear stresses. We discovered that the normal right ventricle also exhibited an interesting peristaltic-like motion, which reduced work done needed for ejection. Further, TOF right ventricles experienced higher intraventricular pressure gradients (IVPG), higher wall shear stresses, and featured more dynamic and chaotic vorticity compared to normal hearts, due to increased inflow via the tricuspid inlet and reduced stroke volumes. In contrast, the TOF left ventricles experienced much less significant changes from normal ventricles.


Brief Introduction:


Dr. Yap Choon Hwai graduated with PhD from Georgia Institute of Technology, and worked as a postdoctoral scholar in University of Pittsburgh School of Medicine. He is currently an Assistant Professor in the Department of Biomedical Engineering in the National University of Singapore. Part of his research focus on the mechanics of prenatal cardiovascular system, and how abnormal blood flow mechanical force environment may be the cause of congenital heart malformations. His lab is the first to perform computational fluid dynamics (CFD) of human fetuses based on clinical ultrasound imaging, and pioneered a novel 4D imaging techniques with high-frequency ultrasound for image-based CFD of small animal embryonic hearts. Another part of his research is to fabricate low-thrombosis blood pumps using novel surface coating technologies.CE