名取 道也¹, 大矢 晃久², 吉田 丈児¹, 境田 通泰¹, 田中 守¹, 河野 八朗¹, 石本 人士¹, 小林 俊文¹, 野沢 志朗¹

Michiya NATORI¹, Akihisa OHYA², Joji YOSHIDA¹, Michiyasu SAKAIDA¹, Mamoru TANAKA¹, Hachiro KONO¹, Hitoshi ISHIMOTO¹, Toshibumi KOBAYASHI¹, Shiro NOZAWA¹

¹慶応義塾大学医学部産婦人科学教室, ²慶応義塾大学理工学部電気工学科

¹Dept. of Obstetrics and Gynecology, School of Medicine, Keio University, ²Dept. of Electrical Engineering, Faculty of Science and Technology, Keio University

キーワード : Simulation, Mathematical model, Umbilical artery, Velocity waveform, Pulsatility index

Researchers have discussed the idea of increasing peripheral resistance and elevating values of the umbilical artery waveform indices. This study aimed to reveal the factors influencing these waveform indices. The electrical circuit model of umbilical artery to placenta circulation was converted into a mathematical one.
The computer simulations revealed that blood pressure elevation lowered these indices and that decreases in the umbilical arterial diameter elevated the indices. Increased placental resistance elevated the indices, but the relationship was not linear. In this non-linear relationship, a 2 SD increase in the pulsatility index (PI) , corresponding to a 30% increase in the mean value, resulted in a 50% obstruction of the placental unit. An increase in the index of greater than 100% is feasible, but placental obstruction of more than 70% is not feasible in live fetuses. This suggests that more factors, besides resistance, cause index elevation. In recent reports using animal models, resistance elevation induced by angiotensin II was shown to be irrelevant to the index. However, this simulation has suggested its relevance in terms of the blood pressure elevation.
Simultaneous simulation of pressure elevation and resistance increase showed small changes to the indices when unit obstruction is below 60%. This simulation also revealed that a single index value corresponded to multiple values for pressure and resistance. Simulation revealed that at least three factors may influence a waveform index and different circulatory conditions may indicate the same indices.