Analysis of Phasic Coronary Arterial Flow and Wave Characteristics Using Hybrid Circulation Model

• Main Authors: Chun-Hao Hung, 洪俊豪
• Other Authors: Pong-Jeu Lu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/40866625710997668590

碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 97 === Counter-pulsation circulation support has been clinically proven to be a viable means for treating various acute heart dysfunctions. To date, why counter-pulsation therapeutics, namely, systolic unloading and diastolic augmentation, can help the diseased myocardium recover has not been completely understood. It was clinically found that epi- and endo-myocardial coronary perfusion characteristics show a relative phase difference during systole and diastole, for which intra-myocardial muscle action and the induced tissue pressurization and relaxation play a critical role. The present research hypothesizes that it is the wave propagation which enables a long-range energy transport that improves the perfusion in the microvessels of the myocardium. In order to study the wave effects on the coronary flow, the present research proposed a hybrid circulation model consisting of a continuous one-dimensional (1-D) flow model and a lumped Windkessel model. The coronary vascular bed was divided into two categories comprising arterial vessels with diameters greater than 1~2 mm and other arteriolar, capillary and venous networks. The larger arterial trunks were represented using 1-D flow model whereas the microcirculation simulated by Windkessel models. Linear tissue pressure distribution was adopted to represent the myocardial pressure occurring in the segmented ventricular wall. The dependence of resistance and capacitance on transmural pressure and vessel collapse was taken into account to characterize the coronary vasculature bed. The constructed numerical model was validated using data obtained from in-vivo porcine experiments supported by counter-pulsatile means including intra-aortic balloon pump (IABP) and para-aortic blood pump (PABP). Simulation results show that capillary perfusion volume has maximum value when pump inflation was initiated at the aortic valve closure instant. PABP and IABP can increase 8.3% and 4.2% perfusion volume in capillary, respectively. Coronary regurgitation was traditionally seen accompanied with IABP support during systolic unloading. However, this detrimental blood flow reversal can be avoided by the PABP deflation control. The present work found that PABP deflation period can be optimized into early heart systole acrossing the instant of aortic valve opening. This deflation control strategy not only decreases the coronary regurgitation but also maintains a high reduction of the left ventricular (LV) stroke work. It was observed that larger pumping volume yields stronger wave and better endo-myocardial perfusion at the expense of a slightly increased coronary reversed flow and a decreased end diastolic aortic pressure. In conclusion, the present simulation reveals that: 1) Larger counter-pulsatile pumping volume is more effective in perfusing the endomyocardium where infarction is prone to occur; 2) PABP generates stronger compression wave and perfusion volume than does IABP on coronary diastolic augmentation; and 3) Non-occlusive PABP can be optimized to provide superior LV unloading and end organ perfusion without incurring significant coronary regurgitation.