Estimation of the aortic flow and clinical application of thoracic bio-electrical impedance method.

当恒定的高频交流电流通过胸腔时，从胸腔检测到的电压变化指的是胸腔电学特性。生物电阻抗是电压与交变电流的比值。Kubicek从胸阻抗变化中引入了阻抗心动图来无创地估计脑卒中容量。本研究旨在扩大胸廓生物电阻抗法的临床应用，以获得更多的循环信息。得到以下结果：1)为了消除呼吸引起的阻抗变化，在不保持呼吸的情况下，将胸廓阻抗变化（DELTA Z）记录在数据记录仪上，然后用a - d转换器对DELTA Z数据进行数字化处理，通过三次样条插值得到DELTA Z的呼吸波动。用原始DELTA Z减去呼吸DELTA Z变化，得到新的无呼吸变化的DELTA Z波。2)为了更好地通过生物电阻抗变化选择性地检测主动脉血流，电极定位于心电图V_8点和后正中线上第二胸椎。通过该导联系统，阻抗变化一阶导数（dZ/dt）波的高度与导管尖端速度传感器获得的主动脉流速相关（r= 0.84）。这表明该系统的阻抗变化反映了主动脉流量的变化。通过阻抗变化幅度（DELTA Z）除以脉压计算主动脉顺应性指数。该指标(Y)与RI血管造影获得的体积弹性(X)相关，公式为Y = 124.52 X100/X + 4.52 （r = 0.78， P<0.001）。3)生物电阻抗法测定主动脉流量与下肢比值对动脉硬化闭塞症（ASO）的诊断有价值。4)应用频率可变阻抗分析仪研究妊娠期腿部组织液的变化。较低频率的施加电流可以通过细胞外流体，而高频率的施加电流可以通过细胞外和细胞内流体。我们使用了从2 kHz到300 kHz的12阶频率进行研究，并从导纳轨迹估计了细胞外液（Re）和细胞内液（Ri）的电阻。在妊娠中期观察到Re明显增加。5)通过测定胸腔含水量来估计肺充血（充血性心力衰竭）的程度。将胸腔视为截断锥模型，根据库比切克阻抗心电图的基础胸阻抗（Zo）计算平均胸阻抗（rho chest），频率从2 kHz到200 kHz不等。在10 KHz频率处获得最高的rho胸值。肺水肿患者的rho胸值明显低于健康对照组。虽然考虑到施加的电流在肺部的分布并不均匀，但我们采用了一个电极位于中央静脉而另一个电极位于胸腔表面的实验模型。采用70%右旋糖酐溶液诱导家兔充血性心力衰竭实验模型，测定中心静脉电极与颈胸下段联合电极之间的生物电阻抗。实验结束时，采用Pearce和Yamashita法测定肺血管外水容量。10 kHz电流下阻抗与PEWV （r= 0.87）和中心静脉压（r=0.93）显著相关，正在考虑进行人体研究。少

When a constant high frequency alternative electric current is passed through the thorax, voltage change detected from the chest refers to the thoracic electrical property. Bioelectrical impedance is obtained as the ratio of voltage to alternative electrical current. From the thoracic impedance change, Kubicek has introduced impedance cardiography to estimate stroke volume non-invasively. Present studies are intended to expand clinical application of the thoracic bio-electrical impedance method to obtain more informations on the circulation. Following results were obtained.1) To eliminate impedance change by respiration, we have recorded the thoracic impedance change (DELTA Z) without holding respiration to a data recorder, then DELTA Z data was digitalized by A-D converter, and respiratory fluctuation of DELTA Z was obtained by cubic spline interpolation. By subtraction of respiratory DELTA Z change from original DELTA Z, new DELTA Z wave without respiration change was obtained.2) To … More detect aortic flow selectively by bio-electrical impedance changes, the electrodes were positioned at the point of V_8 of ECG and of second thoracic vertebra on the posterior median line. By this lead system, height of the first derivative of impedance change (dZ/dt) wave was correlated with the aortic flow velocity obtained by the catheter tip velocity transducer (r= 0.84). This result indicates that the impedance change of this system reflects aortic flow. An index of the aortic compliance was calculated from division of amplitude of the impedance change (DELTA Z) by pulse pressure. This index(Y) was correated with volume elasticity(X) obtained, from RI angiography by equation of Y = 124.52 X100/X + 4.52 (r = 0.78, P<0.001).3) Ratio of aortic flow and lower leg determined with bioelectric impedance method was valuable for diagnosis of arteriosclerosis obliterance (ASO).4) Using frequency variable impedance analyzer, tissue fluid changes in the leg during pregnancy were studied. Lower frequency of applied current may pass through extra-cellular fluid, and high frequency of the current may pass both extra- and intra- cellular fluid. We used 12 steps of frequency from 2 kHz to 300 kHz for the study and estimated resistance of extracellular fluid (Re) and of intra cellular fluid (Ri) from a locus of admittance. An apparent increase in Re during the mid term of pregnancy was observed.5) Determination of water content in the thorax to estimate degree of lung congestion (congestive heart failure) was intended. The thorax was considered as truncated cone model and mean thoracic impedance (rho chest) was calculated from basal thoracic impedance (Zo) of Kubicek's impedance cardiography with variable frequency from 2 kHz to 200 kHz. The highest rho chest value was obtained at the frequency of 10 KHz. and significantly low rho chest value in the patients with pulmonary edema as compared with the healthy control subjects.Although, it is considered that the applied electric current does not distribute equally through the lung, we used an experimental model with one of the electrode in the central vein and the other on the surface of the thorax. Experimental model of congestive heart failure was induced in rabbits by infusion of 70% dextran solution and bio-electrical impedance was determined between an electrode in the central vein and combined electrode at the neck and lower thoracic. Pulmonary extravascular water volume was determined by the method of Pearce and Yamashita on desiccated lung at the end of the experiment. Impedance at 10 kHz of applied electric current was significantly correlated with PEWV (r= 0.87) and central venous pressure (r=0.93) Application for human study is under consideration. Less