Mart Min

The monitoring of peripheral electrical bioimpedance (EBI) variations is a promising method that has the potential to replace invasive or burdensome techniques for cardiovascular measurements. Segmental or continuous recording of peripheral pulse waves can serve as a basis for calculating prognostic markers like pulse wave velocity (PWV) or include parameters such as pulse transit time (PTT) or pulse arrival time (PAT) for noninvasive blood pressure (BP) estimation, as well as potentially novel cardiovascular risk indicators. However, several technical, analytical, and interpretative aspects need to be resolved before the EBI method can be adopted in clinical practice. Our goal was to investigate and improve the application of EBI, executing its comparison with other cardiovascular assessment methods in patients hospitalized for coronary catheterization procedures. Methods: We analyzed data from 44 non-acute patients aged 45–74 years who were hospitalized for coronary catheterization at East Tallinn Central Hospital between 2020 and 2021. The radial EBI and electrocardiogram (ECG) were measured simultaneously with central and contralateral pressure curves. The Savitzky–Golay filter was used for signal smoothing. The Hankel matrix decomposer was applied for the extraction of cardiac waveforms from multi-component signals. After extracting the cardiac component, a period detection algorithm was applied to EBI and blood pressure curves. Results: Seven points of interest were detected on the pressure and EBI curves, and four with good representativeness were selected for further analysis. The Spearman correlation coefficient was low for all but the central and distal pressure curve systolic upstroke time points. A high positive correlation was found between PWV measured both invasively and with EBI. The median value of complimentary pulse wave velocity (CPWV), a parameter proposed in the paper, was significantly lower in patients with normal coronaries compared to patients with any stage of coronary disease. Conclusions: With regard to wearable devices, the EBI-derived PAT can serve as a substrate for PWV calculations and cardiovascular risk assessment, although these data require further confirmation.

Monitoring of peripheral electrical bioimpedance (EBI) variations is a promising method that has potential to replace invasive or burdensome techniques for cardiovascular measurements. Segmental or continuous peripheral pulse recording can be substrate for calculating prognostic markers as pulse wave velocity (PWV) or can contain substrates as pulse transit time (PTT) or pulse arrival time (PAT) for undisturbing BP calculation or even new cardiovascular risk markers. Still several technical, analytical, and interpretative aspects need to be resolved before the EBI method can be adopted in clinical practice. Our goal was to investigate and improve application of the EBI, executing its comparison with other cardiovascular assessment methods in patients hospitalized for coronary catheterization procedure; Methods: We analyzed data from 44 non-acute patients aged 45-74 years hospitalized for coronary catheterization in East-Tallinn Central Hospital in 2020-2021. The radial EBI and ECG were measured simultaneously with contralateral radial and central pressure curves. The Savitzky–Golay filter was used for signal smoothing. The Hankel matrix decomposer for extraction of cardiac waveforms from the multi-component signals was applied. After extracting the cardiac component, a period detection algorithm was applied to EBI and blood pressure curves; Results: We were able to detect seven points on the pressure and EBI curves, five with good representativeness were selected for further analysis. Spearman correlation coefficient was low for all but the central and distal pressure curve systolic upstroke time points. High positive correlation was found between PWV measured both invasively and with EBI. High positive correlation was found between invasive and noninvasive PWV calculations. Median CPWV was significantly lower in patients with normal coronaries compared to patients with any stage of coronary disease; Conclusions: With regard to wearable devices, the EBI derived PAT can serve as a substrate to PWV calculations and cardiovascular risk assessment, although these data require further confirmation.

A test and evaluation platform has been developed to research and develop solutions and algorithms for joint acquisition, processing, and reasoning from the electrical bioimpedance, electro-cardiography, and photoplethysmography (EBI, ECG, and PPG) signals. The solution is based on the low-cost Launchpad of the Texas Instrument TMS320F28379D dual core 16/32-bit DSP with 16-bit multichannel ADC and several other peripherals (PWM, ADC, timers, I2C, SPI, a lot of SRAM and flash memory). In the simplest mode, the platform is used to simultaneously acquire the EBI, ECG, and PPG signals at 1 kHz and send them to the PC by virtual COMport, for further analysis and presentation. The EBI, ECG, and PPG signals are sampled with a 16-bit ADC and have a resolution of more than four decimal digits, with an EBI error of less than 0.002%. In the next stage, various embedded and ”at the edge” measurement algorithms will be developed, tested, demonstrated, and evaluated on this platform.

Background: Pelotherapy is the traditional procedure of applying curative muds on the skin’s surface—shown to have a positive effect on the human body and cure illnesses. The effect of pelotherapy is complex, functioning through several mechanisms, and depends on the skin’s functional condition. The current research objective was to develop a methodology and electrodes to assess the passage of the chemical and biologically active compounds of curative mud through human skin by performing electrical bioimpedance (EBI) analysis. Methods: The methodology included local area mud pack and simultaneous tap water compress application on the forearms with the comparison to the measurements of the dry skin. A custom-designed small-area gold-plated electrode on a rigid printed circuit board, in a tetrapolar configuration, was designed. A pilot study experiment with ten volunteers was performed. Results: Our results indicated the presence of an effect of pelotherapy, manifested by the varying electrical properties of the skin. Distinguishable difference in the measured real part of impedance (R) emerged, showing a very strong correlation between the dry and tap-water-treated skin (r = 0.941), while a poor correlation between the dry and mud-pack-treated skin (r = 0.166) appeared. The findings emerged exclusively in the frequency interval of 10 kHz …1 MHz and only for R. Conclusions: EBI provides a promising tool for monitoring the variations in the electrical properties of the skin, including the skin barrier. We foresee developing smart devices for promoting the exploitation of spa therapies.

Background. Today, central aortic pressure (CAP) is measured through the invasive procedure of angiography. The only feasible alternative is applanation tonometry, requiring experienced staff to perform reliable measurements. The method of measuring the electrical bioimpedance (EBI) from the wrist gives promising results in estimating the CAP. However, the origin of the EBI data, its quality, and approaches to acquiring the signal are still vague. This study is aimed at determining the dependency of EBI of blood on the diameter, branching, and hindering the blood flow by squeezing the vessel. Methods. An on‐desk hydraulic and mechanical pipe system that imitates the arterial tree in the forearm with the modulated flow of saline solution to imitate the pulsating blood was constructed. The setup was verified in the simulation model. The flexible and rigid pipes were squeezed at selected locations of radial and ulnar arteries, and the superficial palmar arc and the pressure with impedance were measured. Results. The multifaceted effect of squeezing the selected locations of arteries in the forearm on the measured EBI and pressure was verified. The effect of arterial stiffening was verified, revealing a very strong inverse correlation of the time‐varying impedance (ΔZ(t)) of rigid pipe compared to the measured data of the wrist. Conclusion. To gain the highest magnitude of ΔZ(t), our research suggests applying pressure on the radial artery and measuring the EBI of the ulnar artery. Our results propose physiology‐based suggestions to increase the sensitivity of measured EBI of the pulse wave, constituting a base for designing novel wearable monitoring devices and algorithms for CAP estimation.

The paper investigates the impacts of the selected electrical equivalent circuit model, measurement setup, and surrounding environment on the trustworthiness of electrical bioimpedance measurement and obtained model data in the human body. The influence of these constitutive components of the system on finding the model parameters is analyzed and illustrated with examples. The results based on experimental measurements on a forearm near the wrist are provided by employing the model, measurement setup, and novel 16-bit compact wireless impedance analyzer (CIA) according to the outcome of the analysis. The area near the wrist is of interest because of attempts to get cardiac-activity-related impedance changes. It is concluded that a two-electrode system with voltage excitation suits better for determining bioimpedance model parameters in the β dispersion area. The results obtained with the CIA and two capacitive bracelet electrodes on a left forearm were used for the fitting model parameters. Despite the small dimensions of 60 × 60 × 25 mm of the CIA reducing stray capacitance to 8 pF, it provides relative impedance magnitude measurement error below 0.3% and phase error below 0.2 ° in the 10 MHz range. Analysis of the model parameters allowed separation of the electrodes, skin, and internal tissue spectra and revealed the relative significance of model components at different frequencies.

Continuous cardiac output is a significant matter that must be considered in monitoring the functioning of cardiovascular system. A non-invasive sensing system that is based on measuring electrical bioimpedance variations of radial artery is proposed to evaluate the physical condition of patient. To optimize the signal acquisition, different electrode placement strategies are compared with the goal of finding the most suitable ones. The finite element method (FEM) simulation of sensitivity distribution and experimental measurements on radial artery are performed for experimenting circular and distal electrode placements. Importantly, also the modified electrode placement strategies, guided by the idea of focused impedance method (FIM), are investigated. To reduce the number of electrodes in measurement setup, its novel version is proposed: a five-electrode FIM strategy. The efficiency of the proposed strategy can be seen in the reduced amount of required number of electrodes: the smaller area of electrode-skin contact interface results in smaller influence of uncertainties. Moreover, the reduced number of electrodes contributes to benefit through developing simpler instrumentation having lower energy consumption and cheaper manufacturing costs. The results show the advances of the proposed novel five-electrode FIM strategy for measuring the pulsating volume of blood in radial artery with the goal of determining the central aortic pressure (CAP) of blood.

Changes in a certain parameter are often a few magnitudes smaller than the base value of the parameter, specifying significant requirements for the dynamic range and noise levels of the measurement system. In case of electrical bioimpedance acquisition, the variations can be 1000 times smaller than the entire measured value. Synchronous or lock-in measurement of these variations is discussed in the current paper, and novel measurement solutions are presented. Proposed methods are simple and robust when compared to other applicable solutions. A common feature shared by all members of the group of the proposed solutions is differentiation. It is achieved by calculating the differences between synchronously acquired consecutive samples, with lock-in integration and analog differentiation. All these methods enable inherent separation of variations from the static component of the signal. The variable component of the bioimpedance can, thus, be acquired using the full available dynamic range of the apparatus for its detection. Additive disturbing signals and omnipresent wideband noise are considered and the method for their reduction is proposed.

The pipeline stress internal detection technology is an international frontier subject in the field of pipeline internal detection, in which the micro-magnetic method has a great application potential. However, the pipeline micro-magnetic stress internal detection technology lacks an effective theoretical model as a scientific guide due to the complex stress distribution inside the pipe wall during the operation of the pipeline. In this paper, based on the complex stress magneto-mechanical coupling model, we have studied the corresponding relationship between the stress and the micro-magnetic signal and analyzed the influence of the external magnetic field on magneto-mechanical relationship under the non-magnetic saturation condition. And the correctness of the theoretical model is proved by a systematic experimental research. The results indicate that: The stress have a one-to-one linear relationship with the micro-magnetic signal in the stress concentration region. The error rate between the theoretical calculation result of the uniaxial stress magneto-mechanical coupling model and the experimental result is 89.4%, and the error rate between the theoretical calculation result of the complex stress magneto-mechanical coupling model and the experimental result is 0.5%, which proves that the complex stress magneto-mechanical coupling model established in this paper is more suitable for the data analysis of the pipeline stress detection. Further, the force magnetic change rate and the micro-magnetic signal in the stress concentration region increase with the increase of the external magnetic field intensity in non-magnetic saturation state.