New Approach to Designing Reliable Circuit for Acquiring Impedance Cardiography Signal (ICG)
Nguyen Minh Duc1, Nguyen Tuan Linh2, Nguyen Duc Thuan3
1Nguyen Minh Duc, M.Sc. Department of Electronics technology and Biomedical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam.
2Mr. Nguyen Tuan Linh, Department of Electronics technology and Biomedical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam.
3Prof. Nguyen Duc Thuan, Department of Electronics technology and Biomedical Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam.
Manuscript received on March 07, 2015. | Revised Manuscript received on March 13, 2015. | Manuscript published on March 15, 2015. | PP: 36-42 | Volume-3 Issue-4, March 2015. | Retrieval Number: D0824033415/2015©BEIESP
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© The Authors. Published By: Blue Eyes Intelligence Engineering and Sciences Publication (BEIESP). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Abstract: Impedance Cardiography (ICG) is a non-invasive method which can continuously monitoring cardiac activities. By measuring the changes of thoracic impedance (∆Z) during a cardiac cycle, many Hemodynamic parameters can be calculated such as Stroke Volume (SV), Cardiac Output (CO), Total Fluid Content (TFC) and so on, that are impossibly derived using solely ECG. However, the accuracy of this method is still a problem. One of the major causes comes from the analog system that acquires and processes the input signals, in which ∆Z is too small compared to noises. Some common drawbacks were found in some ICG measurement devices, including non-optimal demodulation method, cut-off frequency being to low, DC noises and analog differentiation. Therefore, ICG signals often lose its higher frequency components, that are maybe related to a certain cardiac symptom. On this paper, we propose a new design that can ensure acquiring completely thoracic impedance signals (including the impedance change – ∆Z and the base impedance – 𝒁𝟎), that has a bandwidth of being up to 50Hz, without distorting the signal. This new design was experimented with simulated signals to evaluate the system’s accuracy and efficiency. Specifically, amplitude-modulated sine, containing both AC and DC components with various amplitudes corresponding with ∆Z and 𝒁𝟎, were used in the first experiment. Then, simulated Electrocardiography (ECG) and Electromyography (EMG) were used for evaluating the capability of this new system when dealing with a small physiological signal. The frequency spectrums of the input and output signals were measured consecutively 20 times and compared to each other after each measurement. The positive results, which were expressed by average value and the corresponding standard deviation (SD) of Pearson correlation and a predefined parameter called Spectrum Amplitude Error (SAD), exhibited the high accuracy and reliability of this new system.
Keywords: Impedance Cardiography (ICG), Impedances changes (∆Z), Base impedance (𝒁𝟎), simulated signals, demodulation, Biomedical toolkit.