Dodde Robert E, Kruger Grant H, Shih Albert J
Stryker Corporation , 4100 E. Milham Avenue, Kalamazoo, MI 49001 e-mail:
Mechanical Engineering, University of Michigan , 1031 H.H. Dow Building, 2350 Hayward Street, Ann Arbor, MI 48109 e-mail:
J Med Device. 2015 Jun;9(2):0210011-210018. doi: 10.1115/1.4029706.
Bioimpedance spectroscopy (BIS) has shown significant potential in many areas of medicine to provide new physiologic markers. Several acute and chronic diseases are accompanied by changes in intra- and extracellular fluid within various areas of the human body. The estimation of fluid in various body compartments is therefore a simple and convenient method to monitor certain disease states. In this work, the design and evaluation of a BIS instrument are presented and three key areas of the development process investigated facilitating the BIS measurement of tissue hydration state. First, the benefit of incorporating DC-stabilizing circuitry to the standard modified Howland current pump (MHCP) is investigated to minimize the effect of DC offsets limiting the dynamic range of the system. Second, the influence of the distance between the bioimpedance probe and a high impedance material is investigated using finite element analysis (FEA). Third, an analytic compensation technique is presented to minimize the influence of parasitic capacitance. Finally, the overall experimental setup is evaluated through ex vivo BIS measurements of porcine spleen tissue and compared to published results. The DC-stabilizing circuit demonstrated its ability to maintain DC offsets at less than 650 μV through 100 kHz while maintaining an output impedance of 1 MΩ from 100 Hz to 100 kHz. The proximity of a bioimpedance probe to a high impedance material such as acrylic was shown to increase measured impedance readings by a factor of 4x as the ratio of the distance between the sensing electrodes to the distance between the bioimpedance probe and acrylic reached 1:3. The average parasitic capacitance for the circuit presented was found to be 712 ± 128 pF, and the analytic compensation method was shown to be able to minimize this effect on the BIS measurements. Measurements of porcine spleen tissue showed close correlation with experimental results reported in published articles. This research presents the successful design and evaluation of a BIS instrument. Specifically, robust measurements were obtained by implementing a DC-stabilized current source, investigating probe-material proximity issues and compensating for parasitic capacitance. These strategies were shown to provide tissue measurements comparable with published literature.
生物电阻抗光谱法（BIS）在医学的许多领域已显示出巨大潜力，可提供新的生理标志物。几种急性和慢性疾病都伴随着人体各个区域细胞内液和细胞外液的变化。因此，估计人体各腔室中的液体是监测某些疾病状态的一种简单便捷的方法。在这项工作中，介绍了一种BIS仪器的设计与评估，并研究了开发过程中的三个关键领域，以促进对组织水合状态的BIS测量。首先，研究了将直流稳定电路并入标准改进型霍兰德电流泵（MHCP）的益处，以最小化限制系统动态范围的直流偏移的影响。其次，使用有限元分析（FEA）研究了生物阻抗探头与高阻抗材料之间距离的影响。第三，提出了一种解析补偿技术，以最小化寄生电容的影响。最后，通过对猪脾脏组织进行离体BIS测量对整个实验装置进行评估，并与已发表的结果进行比较。直流稳定电路显示出其在100 kHz频率下将直流偏移维持在650 μV以下的能力，同时在100 Hz至100 kHz频率范围内保持1 MΩ的输出阻抗。当传感电极之间的距离与生物阻抗探头和丙烯酸之间的距离之比达到1:3时，生物阻抗探头靠近丙烯酸等高阻抗材料会使测得的阻抗读数增加4倍。所呈现电路的平均寄生电容为712±128 pF，解析补偿方法能够最小化这种对BIS测量的影响。猪脾脏组织的测量结果与已发表文章中报道的实验结果密切相关。本研究成功设计并评估了一种BIS仪器。具体而言，通过实施直流稳定电流源、研究探头与材料的接近问题以及补偿寄生电容获得了可靠的测量结果。这些策略显示出能够提供与已发表文献相当的组织测量结果。
