Wang L, Patterson R
Medtronic, Inc., Minneapolis, MN 55432.
IEEE Trans Biomed Eng. 1995 Feb;42(2):141-8. doi: 10.1109/10.341826.
Two 3-D electrical models of the human thorax, each consisting of 216,000 control volumes, were constructed based upon MR images taken at end diastole and end systole. Using the finite difference method, the contributions of various sources to the impedance cardiogram were studied for the traditional band electrode configuration. The contributions were categorized into three areas: 1) the structural changes between end diastole and end systole, 2) the flow-induced blood resistivity changes in major arteries and veins, and 3) the lung resistivity variation due to the lung blood volume change. Based on the models, Zo and delta Z between end diastole and end systole were 24.4 omega and -0.132 omega, as compared with the measurements of 21.8 omega and -0.123 omega made on the same subject from whom the images were taken. Arterial and venous blood resistivity changes caused approximately 57% of the total impedance change. The lung resistivity change and the structural changes contributed 39% and 4%, respectively. The structural changes inside the thorax included the dimensional changes of blood vessels, the blood volume changes of the heart chambers, and heart movement. Although the net impedance change due to the structural changes was relatively small, the individual variation of various factors was large, with significant cancellation occurring. The results suggest that the thoracic impedance cardiographic signal is a mixed representation of many inseparable factors and may not be reliable for the stroke volume calculation. Also, the O-wave, which is clinically observed in various cardiac conditions, may be linked to the diastolic blood flow in the central veins.
基于在舒张末期和收缩末期拍摄的磁共振图像，构建了两个人体胸部的三维电模型，每个模型由216,000个控制体积组成。使用有限差分法，针对传统带状电极配置研究了各种来源对阻抗心动图的贡献。这些贡献被分为三个方面：1）舒张末期和收缩末期之间的结构变化；2）主要动脉和静脉中血流引起的血液电阻率变化；3）由于肺血容量变化导致的肺电阻率变化。基于这些模型，舒张末期和收缩末期之间的Zo和ΔZ分别为24.4Ω和 -0.132Ω，而从拍摄图像的同一受试者身上测量得到的结果为21.8Ω和 -0.123Ω。动脉和静脉血液电阻率变化约占总阻抗变化的57%。肺电阻率变化和结构变化分别占39%和4%。胸部内部的结构变化包括血管尺寸变化、心腔血容量变化和心脏运动。尽管结构变化引起的净阻抗变化相对较小，但各种因素的个体差异较大，存在显著的抵消现象。结果表明，胸部阻抗心动图信号是许多不可分割因素的混合表现，对于心输出量计算可能不可靠。此外，在各种心脏疾病中临床观察到的O波可能与中心静脉的舒张期血流有关。
