Safety Evaluation of Thoracic Bio-Electrical Impedance Technique
Jia Jing1,2, Ke Li1, Du Qiang1, Ren Ziyan1
1. School of Electrical Engineering Shenyang University of Technology Shenyang 110870 China; 2. College of Electrical Engineering Yingkou Institute of Technology Yingkou 115100 China
Abstract：Due to the increasingly serious aging society and environmental factors, the incidence of cardiovascular diseases is increasing year by year. According to data from the 25th National Forum on Interventional Cardiology, the number of pacemaker implants in China reached 99 000 units, a year-over-year increase of 15.1% in 2021. Cardiac implantable electronic devices contain multiple microcircuits, easily affected by medical devices such as magnetic resonance imaging, electrosurgery, and bio-electrical impedance. With the development and application of bio-electrical impedance technology, attention should be paid to electromagnetic interference. The alternating high-frequency signal is the core part of the bioelectrical impedance excitation system. When an alternating current is applied to the electrode, an alternating electric field is generated between the two electrodes, filling the entire space. Current is constrained by external excitation and space of electromagnetic field. Firstly, a 3D simulation model based on a simplified pacemaker electrode model and real thoracic. Secondly, the dielectric properties of biological tissue are set according to the website of dielectric properties of human tissues and organs. Thirdly, inject 5 mA current excitation at 4, 6, 10, 25, 40, 63, and 100 kHz. The excitation electrode is arranged near the 5th frame. To obtain the induced voltage that has the greatest influence on the pacemaker electrode, the excitation electrode and the pacemaker electrode are set at the same level, and the configuration form is adjacent, opposite, and cross, respectively. In this way, the induced voltage values of the pacemaker electrode under different excitations are obtained. Simulation results show that the level of electrical interference varies with frequency between 4 kHz and 100 kHz. The induced voltage of the expiratory state is lower than that of the inspiratory state. The tissue characteristics in the model are taken from the same database, and the interference degree is different due to the location of the excitation electrode. The interference of cross-excitation configuration is the highest, and the interference of adjacent excitation is the least. When the excitation frequency is 100 kHz, the interference is significantly reduced, and the data does not exceed the maximum voltage amplitude threshold. Overall, the interference in the inhaling state of the lung is higher than that in the exhaling state of the lung. The higher the excitation frequency, the smaller the induced voltage interference. A plastic circular cavity with salt water is used to simulate the chest cavity and tissue, and the titanium rod is in the salt water. The interference of input excitation to the resistance rod can be observed on the oscilloscope. It is found that the induced voltage on the resistance rod decreases gradually with the increase of frequency by changing the injected electrode. The changing trend is consistent with the human chest cavity model. The following conclusions can be drawn from the simulation analysis: (1) The level of electrical interference varies with frequency. The lower the excitation frequency, the stronger the interference. (2) The interference level of electrodes is different in different positions. The interference is strongest in cross-electrode configuration and weakest in adjacent. (3) Some induced voltages exceed the maximum threshold voltage specified in ISO 14117. Potential electromagnetic interference exists in patients with cardiac pacemakers. Since interference may affect the pacemaker's normal operation and cause serious events, the thoracic bio-impedance method is not recommended for testing on pacemaker wearers.
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2024, Vol. 39 
