Background: Wearable technologies for monitoring cardiovascular parameters, including electrocardiography (ECG) and impedance cardiography (ICG), propose a challenging research subject. The expectancy for wearable devices to be unobtrusive and miniaturized sets a goal to develop smarter devices and better methods for signal acquisition, processing, and decision-making. Methods: In this work, non-standard electrode placement configurations (EPC) on the thoracic area and single arm were experimented for ECG signal acquisition. The locations were selected for joint acquisition of ECG and ICG, targeted to suitability for integrating into wearable devices. The methodology for comparing the detected signals of ECG was developed, presented, and applied to determine the R, S, and T waves and RR interval. An algorithm was proposed to distinguish the R waves in the case of large T waves. Results: Results show the feasibility of using non-standard EPCs, manifesting in recognizable signal waveforms with reasonable quality for post-processing. A considerably lower median sensitivity of R wave was verified (27.3%) compared with T wave (49%) and S wave (44.9%) throughout the used data. The proposed algorithm for distinguishing R wave from large T wave shows satisfactory results. Conclusions: The most suitable non-standard locations for ECG monitoring in conjunction with ICG were determined and proposed.
ICG (impedance cardiography) is in parallel to ECG (electrocardiography) an important indicator of the functioning of the heart and of the overall cardiovascular system. Adding the ICG to ECG measurement functionality into the wearable devices improves the quality of health monitoring, as the ICG reflects relevant hemodynamic parameters (informative time intervals, but also the stroke volume and cardiac output and their variability). The most challenging task of the ICG signal processing is to extract the key points B, C, X of the cardiac periodstart, peak-location, and value at this point and the end of the LVET (left ventricular ejection time) sub-period in the cardiac cycle. A novel block diagram and analog implementation of it has been proposed, analyzed, and discussed, with discussion of the benefits of the proposed solution. The proposed solution enables developing of relatively simple very power-efficient solutions, monitoring the ICG values of the person with smart and efficient data acquisition and processing.
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