Topic : Biomechanics of the Placenta and Placental Circulation during Intrauterine Growth Restriction

Speaker :  
Dr. Yap Choon Hwai
Assistant Professor, Biomedical Engineering, National University of Singapore
Date & Location : 2019/12/12 (Thu) 3:30 pm - 5:20 pm
Engineering 5 Building B1 International Conference Hall (工程五館 B1 國際會議廳)
Abstract : 
Intrauterine Growth Restriction (IUGR) is a pregnancy complication where flow resistance in the placenta is high, leading to insufficient nutrient and oxygen transport to the fetal baby. This causes a 5-10x higher mortality rate, and long-term morbidities such as heart diseases, diabetes, hypertension, and neural maldevelopment. The prevalence is high, at 3% in the developed world and 10-15% in the developing world, but to date, we have no proven strategy to prevent or treat the disease. Early detection is important, as it can management strategies to improve outcomes, but detection rate is low. There is thus a need for improved understanding of the disease, to lead to better detection and management strategies. To this end, we performed a series of biomechanics investigations in the umbilical-placenta system, given that there has been few previous biomechanics studies here, to understand physiology and tissue properties, and to seek new means of better detecting IUGR.
     In our studies of umbilical-placenta blood vessels, we first discovered, through clinical measurements and human samples, that IUGR vascular hemodynamic environments were similar to normal ones, despite IUGR vessels being smaller. This suggest that even in IUGR, vascular mechanosensing were not dynsfunction and is unlikely to be the cause of the disease. Our vascular mechanical testing of chorionic arteries demonstrated that arteries in severely IUGR placentas had increased vascular distensibility or compliance compared to those in normal placentas, and modelling work demonstrated that this could be the reason that IUGR pregnancies are associated with elevated umbilical arterial pulsatility indices. We believe this can demonstrate the importance of studying placenta vascular biomechanics.
     A second effort we embarked on was to measure whole placenta mechanical properties, and to test if ultrasound strain elastography can be a good method to detect IUGR, via non-invasive measurement of the mechanical properties of the placenta. We found that placenta tissues were substantially viscoelasticity, and measurements can change with different compression rates, and thus recommended motorized palpation during elastography to standardize motion speed, which we showed significantly increased measurement precision. We further found placenta tissues to be surprisingly isotropic, and consequently, simpler strain energy functions were sufficient to describe its properties. We found high mechanical property spatial variability in each placenta, suggesting that elastography must be conducted at several locations and averaged. Finally, we found that IUGR placenta had increased stiffness over normal ones (likely due to altered collagen-to-elastin ratio), but the difference was only significant at specific palpation settings: at lower compression rates and depths. This provided guidance for elastography settings during disease detection. Our investigations show that elastography has promise as a detection tool for IUGR, but caution and deeper consideration for the biomechanical conditions are necessary.
     Overall, our investigations demonstrated that using biomechanics to analyze IUGR disease can yield much novel understanding, and can lead to clinical advances with regards to IUGR.

Speaker Profile :
     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.  
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