Scharfetter H, Hartinger P, Hinghofer-Szalkay H, Hutten H
Institute of Biomedical Engineering, Technical University Graz, Austria.
Physiol Meas. 1998 May;19(2):247-61. doi: 10.1088/0967-3334/19/2/012.
We have developed a novel model for the simulation of artefacts which are produced by stray capacitance during bioimpedance spectroscopy. We focused on whole body and segmental measurements in the frequency range 5-1000 kHz. The current source was assumed to by asymmetric with respect to ground as is the case for many commercial devices. We considered the following stray pathways: 1, cable capacitance; 2, capacitance between neighbouring electrode leads; 3. capacitance between different body segments and earth; 4, capacitance between signal ground of the device and earth. According to our results the pathways 3 and 4 cause a significant spurious dispersion in the measured impedance spectra at frequencies > 500 kHz. During segmental measurements the spectra have been found to be sensitive to an interchange of the electrode cable pairs. The sensitivity was also observed in vivo and is due to asymmetry of the potential distribution along the segment with respect to earth. In contrast to previously published approaches, our model renders possible the simulation of this effect. However, it is unable to fully explain the deviations of in vivo measured impedance spectra from a single Cole circle. We postulate that the remaining deviations are due to a physiologically caused superposition of two dispersions from two different tissues.
我们开发了一种新型模型，用于模拟生物阻抗光谱期间由杂散电容产生的伪迹。我们专注于在5 - 1000 kHz频率范围内的全身和分段测量。假设电流源相对于地是不对称的，许多商业设备就是这种情况。我们考虑了以下杂散路径：1，电缆电容；2，相邻电极引线之间的电容；3，不同身体部位与地之间的电容；4，设备信号地与地之间的电容。根据我们的结果，路径3和4在频率> 500 kHz时会在测量的阻抗谱中引起显著的杂散色散。在分段测量期间，发现光谱对电极电缆对的互换敏感。这种敏感性在体内也被观察到，并且是由于沿身体部位相对于地的电位分布不对称所致。与先前发表的方法不同，我们的模型使得模拟这种效应成为可能。然而，它无法完全解释体内测量的阻抗谱与单个科尔圆的偏差。我们推测，剩余的偏差是由于来自两种不同组织的两种色散在生理上的叠加。
