Visser K R, Lamberts R, Zijlstra W G
Department of Physiology, University of Groningen, The Netherlands.
Cardiovasc Res. 1990 Jan;24(1):24-32. doi: 10.1093/cvr/24.1.24.
PURPOSE OF INVESTIGATION - To determine the contribution of variations in orientation of erythrocytes (orientation effect) to the heart synchronous variations in thoracic impedance in impedance cardiography. DESIGN - The blood of four dogs was gradually replaced by stroma free haemoglobin solution, causing a decrease in resistivity and orientation effect. The decrease in orientation effect was used to determine the contribution of the orientation effect using an extended form of the "parallel conductor" model of the thorax (parallel connection of a tissue admittance Yt and a blood conductance Gb). SUBJECTS - Four adult splenectomised mongrel dogs. MEASUREMENTS and RESULTS - Packed cell volume and resistivity at body temperature of every volume of circulating fluid removed was measured. Real and imaginary parts of the transthoracic impedance and the modulus of the heart synchronous impedance variations were measured just before each exchange. The parallel conductor model was extended to account for the influence on Gb of packed cell volume and orientation of erythrocytes. Applying this extended model, the average variations in Gb at a packed cell volume of 40% were estimated to be 7.46%:3.03% due to volume variations, 4.43% due to orientation effect. After further extending the model to account for the influence of small changes in blood pressure and heart rate, the average volume variations were estimated to range from 2.8% to 3.3% and the average orientation effect from 4.1% to 4.7% at a packed cell volume of 40%. CONCLUSION - Resistivity of the blood is far from constant and the contributions of variations in blood conductivity and volume to the heart synchronous thoracic impedance are of comparable magnitude. The contribution of the volume variations is the sum of the volume variations in the contributing intrathoracic vessels. The effects of variations in orientation are added up in proportion to the relative volumes of the contributing vessels. The extensions of the parallel conductor model brought out all physiological factors determining the heart synchronous thoracic impedance variations: pulse pressures and flows, mean pressures and flows, compliances of all contributing blood vessels, packed cell volume and heart rate, as well as the relevant properties of blood: the relations between volume, flow and orientation effect and the change in orientation effect during decelerating flow.
研究目的——确定红细胞取向变化（取向效应）对阻抗心动图中胸段阻抗的心脏同步变化的贡献。设计——用无基质血红蛋白溶液逐渐替代四只狗的血液，导致电阻率和取向效应降低。利用胸廓“平行导体”模型（组织导纳Yt和血液电导Gb的并联连接）的扩展形式，通过取向效应的降低来确定取向效应的贡献。研究对象——四只成年脾切除杂种狗。测量与结果——测量每次去除循环液体积时的血细胞比容和体温下的电阻率。在每次交换前测量经胸阻抗的实部和虚部以及心脏同步阻抗变化的模量。扩展平行导体模型以考虑血细胞比容和红细胞取向对Gb的影响。应用此扩展模型，估计血细胞比容为40%时Gb的平均变化为：由于体积变化为7.46%:3.03%，由于取向效应为4.43%。在进一步扩展模型以考虑血压和心率微小变化的影响后，估计血细胞比容为40%时平均体积变化范围为2.8%至3.3%，平均取向效应为4.1%至4.7%。结论——血液的电阻率远非常数，血液电导率和体积变化对心脏同步胸段阻抗的贡献大小相当。体积变化的贡献是胸内相关血管体积变化的总和。取向变化的影响按相关血管的相对体积成比例相加。平行导体模型的扩展揭示了所有决定心脏同步胸段阻抗变化的生理因素：脉压和流量、平均压力和流量、所有相关血管的顺应性、血细胞比容和心率，以及血液的相关特性：体积、流量和取向效应之间的关系以及减速流动期间取向效应的变化。
