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是指胸腔的电特性。生物电阻抗是通过电压与交流电流的比值来获得的。根据胸阻抗的变化，库比切克引入了阻抗心动图来无创性地估计每搏量。本研究旨在扩大胸腔生物电阻抗法的临床应用，以获得更多关于循环的信息。1)为了消除呼吸引起的阻抗变化，在不保持呼吸的情况下，将胸阻抗变化(Delta Z)记录到数据记录器中，然后用A-D转换器对Delta Z数据进行数字化，并用三次样条插值法得到Delta Z的呼吸波动。通过从原始的增量Z中减去呼吸增量Z的变化，得到没有呼吸变化的新的增量Z波。2)到…进一步通过生物电阻抗变化选择性检测主动脉血流，电极放置在心电V8点和第二胸椎后正中线。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测得的主动脉血流速度相关(r=0.84)。这一结果表明，该系统的阻抗变化反映了主动脉血流。主动脉顺应性指数由阻抗变化幅度(Delta Z)除以脉压计算。此指标(Y)与RI血管造影测得的体积弹性(X)呈正相关，相关方程为Y=124.52，X_(100)/X+4.52(r=0.78，P<0.001)。3)生物电阻抗法测得的主动脉血流量与小腿血流量的比值对动脉硬化闭塞症的诊断有价值。较低频率的外加电流可能通过细胞外液体，而高频电流可能同时通过细胞外和细胞内液体。我们使用从2 khz到300 khz的12个频率阶跃进行研究，并从导纳轨迹估计细胞外液(Re)和细胞内液(Ri)的阻力。妊娠中期Re明显升高。5)通过测定胸腔水分含量来评估肺充血(充血性心力衰竭)的程度。将胸部视为截锥体模型，根据2~200 kHz频率变化的Kubinek心阻抗图的基础胸阻抗(Zo)计算平均胸阻抗(Rho胸阻抗)。当频率为10 kHz时，Rho胸值最高。肺水肿患者的Rho胸值明显低于健康对照组。虽然考虑到外加电流在肺中的分布不均匀，但我们采用了一个电极在中心静脉，另一个电极在胸部表面的实验模型。用70%右旋糖酐溶液复制兔充血性心力衰竭模型，测定中心静脉电极与颈、下胸联合电极之间的生物电阻抗。实验结束后，用Pearce和Yamashita的方法测定干燥肺的肺血管外水量。外加电流在10 kHz处的阻抗与PEWV(r=0.87)和中心静脉压(r=0.93)显著相关。较少

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