Electrical Properties Of Tissues Research Articles

Wearable Blood Pressure Sensing Based on Transmission Coefficient Scattering for Microstrip Patch Antennas.

Painless, cuffless and continuous blood pressure monitoring sensors provide a more dynamic measure of blood pressure for critical diagnosis or continuous monitoring of hypertensive patients compared to current cuff-based options. To this end, a novel flexible, wearable and miniaturized microstrip patch antenna topology is proposed to measure dynamic blood pressure (BP). The methodology was implemented on a simulated five-layer human tissue arm model created and designed in High-Frequency Simulation Software “HFSS”. The electrical properties of the five-layer human tissue were set at the frequency range (2–3) GHz to comply with clinical/engineering standards. The fabricated patch incorporated on a 0.4 mm epoxy substrate achieved consistency between the simulated and measured reflection coefficient results at flat and bent conditions over the frequency range of 2.3–2.6 GHz. Simulations for a 10 g average specific absorption rate (SAR) based on IEEE-Standard for a human arm at different input powers were also carried out. The safest input power was 50 mW with an acceptable SAR value of 3.89 W/Kg < 4W/Kg. This study also explored a novel method to obtain the pulse transit time (PTT) as an option to measure BP. Pulse transmit time is based on obtaining the time difference between the transmission coefficient scattering waveforms measured between the two pairs of metallic sensors underlying the assumption that brachial arterial geometries are dynamic. Consequently, the proposed model is validated by comparing it to the standard nonlinear Moens and Korteweg model over different artery thickness-radius ratios, showing excellent correlation between 0.76 ± 0.03 and 0.81 ± 0.03 with the systolic and diastolic BP results. The absolute risk of arterial blood pressure increased with the increase in brachial artery thickness-radius ratio. The results of both methods successfully demonstrate how the radius estimates, PTT and pulse wave velocity (PWV), along with electromagnetic (EM) antenna transmission propagation characteristics, can be used to estimate continuous BP non-invasively.

The features of atrial fibrillation occurrence in patients who have undergone COVID-19

Funding AcknowledgementsType of funding sources: None.COVID-19 pandemic has a rather negative effect on patients with cardiovascular pathology, also in patients without cardiovascular disease because its pathogenesis is based on generalized vascuities of the microvasculature with the development of multiple thrombosis and thromboembolism. Atrial fibrillation (AF) is one of the major cardiac arrhythmias and accounts for almost one third of all arrhythmias. Changes in electrical, structural, and contractile properties of cardiac tissue that are thought to underlie AF maintenance and progression are reviewed. The aim of this study is to identify the features and predictors that contribute to the onset or development of AF in patients who have had COVID -19.MethodsThis was a three-center prospective study, conducted in the coronary care unit during the period of February 2020 to June 2021. This study included 196 patients with AF who underwent COVID-19 at different times of this period (I group). For comparison, the data of similar 203 AF patients without COVID (II group) were analyzed in the period from February 2018 to February 2019 from the same centers... Medical history, clinical, instrumental and laboratory data, including troponin-1, tissue factor (TF), and hsCRP were studied in all patients. The data obtained was analyzed for statistical significance including multivariable logistic regression using analyses by SPSS 16.ResultsThe compared results showed that the first-onset AF in patients from first group was observed in 18.7% compared with 8.1% in second group. In intensive care units, AF were registered in 44.2% of patients in I group vs. 7.1% of patients in II group. In first group among patients with ACS, AF occurred in 12.7% of cases vs. similar patients in II group- 8.4%. In first group hypokalemia was observed in 67.8% of cases vs. 28.6% in II group... Multivariable logistic regression was shown that among tested biomarkers, hsCRP, troponin‐I and TF were more higher in patients undergoing COVID in compared patients with AF without COVID (odds ratio, 3.48; p<0.001, 2.36 p<0.017 and 2.48 p<0.01 accordingly).ConclusionsSome features of the onset or development of AF were identified in patients undergoing COVID. So, In these patients compared with AF patients without COVID, AF more often occurs in clinically severe patients, with ACS, as well as in patients with severe hypokalemia, higher hsCRP, TF and troponin values.

PO-618-03 REDUCTION IN DEFIBRILLATION THRESHOLD BY MODIFICATIONS TO THE SUBCUTANEOUS ICD COIL

Subcutaneous Implantable Cardioverter Defibrillators (S-ICDs) generally have higher defibrillation thresholds (DFTs) than transvenous ICDs, necessitating larger S-ICD generators and with S-ICD VF conversion testing recommended at implantation. We sought to determine whether modifications to the S-ICD coil configuration or characteristics would reduce DFTs compared to the standard S-ICD coil based on a computer model of defibrillation. We utilized a computer model built from MRI images of a normal thorax and simulation of electrical fields generated by defibrillation. The specific electrical properties of tissues and organs were assigned, as well as other characteristics of the shock circuit, with DFT defined as energy required to achieve an electrical field of 4V/cm in > 95% of ventricular myocardium. Coil configurations examined included a standard parasternal S-ICD coil, dual parallel para-sternal coils, dual coils in series (parasternal and along the left ribcage), and a larger flattened parasternal coil. The standard parasternal S-ICD coil configuration (with < 1mm intervening fat under the coil and generator) resulted in an estimated DFT of 33J. The other coil configurations resulted in marked reductions in DFT by as much as 37% (to 21J) (figure), predominantly related to lower shock impedance and improved electrical field distribution. Our modeling work suggests that modifications to the S-ICD coil design could lead to marked reductions in DFT. This could allow for the creation of S-ICDs with lower energy requirements and correspondingly smaller generators compared to current devices and might obviate the need for VF conversion testing with S-ICDs.

Exosomes‐Loaded Electroconductive Hydrogel Synergistically Promotes Tissue Repair after Spinal Cord Injury via Immunoregulation and Enhancement of Myelinated Axon Growth

Electroconductive hydrogels are very attractive candidates for accelerated spinal cord injury (SCI) repair because they match the electrical and mechanical properties of neural tissue. However, electroconductive hydrogel implantation can potentially aggravate inflammation, and hinder its repair efficacy. Bone marrow stem cell‐derived exosomes (BMSC‐exosomes) have shown immunomodulatory and tissue regeneration effects, therefore, neural tissue‐like electroconductive hydrogels loaded with BMSC‐exosomes are developed for the synergistic treatment of SCI. These exosomes‐loaded electroconductive hydrogels modulate microglial M2 polarization via the NF‐κB pathway, and synergistically enhance neuronal and oligodendrocyte differentiation of neural stem cells (NSCs) while inhibiting astrocyte differentiation, and also increase axon outgrowth via the PTEN/PI3K/AKT/mTOR pathway. Furthermore, exosomes combined electroconductive hydrogels significantly decrease the number of CD68‐positive microglia, enhance local NSCs recruitment, and promote neuronal and axonal regeneration, resulting in significant functional recovery at the early stage in an SCI mouse model. Hence, the findings of this study demonstrate that the combination of electroconductive hydrogels and BMSC‐exosomes is a promising therapeutic strategy for SCI repair.

Electrical Phenotyping of Human Brain Tissues: An Automated System for Tumor Delineation

Precise surgical excision of brain tumors depends on the surgeon&#x2019;s ability to accurately differentiate tumors from healthy brain tissues. We have developed an automated system integrated with biochips, an actuation unit, and electronics to measure the electrical resistivity of ex vivo human brain tissues for differentiating normal and tumor. The electrical resistivity of fresh (n &#x003D; 48), formalin-fixed for one week (n &#x003D; 48), and long-term (six months) formalin-fixed (n &#x003D; 27) healthy human brain samples from different anatomical regions and tumor samples (glioma n &#x003D; 6; fresh, formalin-fixed for one week, and formalin-fixed for six months) were measured using the automated system. The resistivity of glioma (22.4 &#x00B1; <inline-formula> <tex-math notation="LaTeX">$1.6~\Omega$ </tex-math></inline-formula>.cm) was significantly lesser than the normal region (98.6 &#x00B1; <inline-formula> <tex-math notation="LaTeX">$1.4~\Omega$ </tex-math></inline-formula>.cm) for fresh tissue samples (p &#x003D; 5e-8). The trend of lower resistivity of glioma compared to normal was preserved after one week and six months of formalin fixation. We also report the effects of heterogeneity of normal brain tissue and formalin-fixation on the electrical properties of tissues. White matter regions were found to have higher resistivity compared to grey matter regions. The heterogeneity associated with grey matter regions was lower than the white matter regions. Formalin-fixation was observed to increase the magnitude of resistivity measured while retaining the observed trend across the different regions of the brain and tumors. The study shows that the electrical resistivity could potentially be used as an additional biomarker for delineating normal from the tumor.

Magnetic Resonance Electrical Impedance Tomography.

Magnetic Resonance Electrical Impedance Tomography (MREIT) is a high-resolution bioimpedance imaging technique that has developed over a period beginning in the early 1990s to measure low-frequency (<1 kHz) tissue electrical properties. Low-frequency electrical properties are particularly important because they provide valuable information on cell structures and ionic composition of tissues, which may be very useful for diagnostic purposes. MREIT uses one component of the magnetic flux density data induced due to an exogenous-current administration, measured using an MRI machine, to reconstruct isotropic or anisotropic electrical property distributions. The MREIT technique typically requires two linearly independent current administrations to reconstruct conductivity uniquely. Since its invention, researchers have explored its potential for measuring electrical conductivity in regions such as the brain and muscle tissue. It has also been investigated in disease models, for example, cerebral ischemia and early tumor detection. In this chapter, we aim to provide a solid foundation of the different MREIT image reconstruction algorithms, including both isotropic and anisotropic conductivity reconstruction approaches. We will also explore the newly developed diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method, a practical method for anisotropic tissue property imaging, at the end of the chapter.

Variability in Specific Absorption Rate From Variation in Tissue Properties

This study evaluates the variance of specific absorption rate (SAR) due to expected variance in the dielectric properties of tissues in a 3D anatomical human head model exposed to a half-wave dipole antenna at 835 and 1900 MHz. Stochastic finite difference time domain (S-FDTD) is applied to calculate variations in the local SAR, and the 1- and 10-gram averaged SAR values. These are also compared at 835 MHz to variations found from Monte Carlo FDTD. It is found that for both frequencies dielectric property variance results in a variance of peak 1- or 10-gram SAR of approximately 30% to 55% of the mean SAR, depending on the frequency. These results show that to reach 95% confidence with the calculated SAR values for evaluating exposure guidelines, statistical variations in tissue electrical properties must be taken into account.

THE RELATIONSHIP BETWEEN BODY MASS INDEX AND BODY FAT PERCENTAGE, ESTIMATED BY BIOELECTRICAL IMPEDANCE IN A GROUP OF ROMANIAN FEMALE STUDENTS

Bioelectrical impedance analysis (BIA) also called bioelectrical impedance (BEI) is a non-invasive method based on the electric conductibility properties of tissues and is a commonly used technique for estimating body composition.Percentage of body fat is strongly associated with the risk of several chronic diseases but its accurate measurement is difficult. Body Mass Index is a useful population-level measure of overweight and obesity. It is used for all categories of people, male or female.The main objective of this study was to determine if there is a relationship between BMI and body fat percentage (BF%) in a group of Romanian female students. This relationship has been studiedin various ethnic groups before. To conduct the study, we examined 29 young females (aged 20-36 years old) estimating BF% from bioelectrical impedance analysis using Tanita Body Fat Monitor Scale UM-076.In this research group, the BMI and BodyFat dependent variables have a moderate to strong correlation (r = .839; 0.75 &lt; r &lt; 1), the favorable score for the first measurement being a statistically relevant benchmark for the second (sig &lt; 0.05).

Assessing Ischemic Injury in Human Intestine Ex Vivo with Electrical Impedance Spectroscopy.

Electrical impedance spectroscopy is a well-established tool for monitoring changes in the electrical properties of tissue. Most tissue and organ types have been investigated in various studies. As for the small intestine, there are several published studies conducted on pig and rat models. This study investigates the changes in passive electrical properties of the complete wall of the human intestine non-invasively during ischemia. We aim to use the passive electrical properties to assess intestinal viability. The bioimpedance measurements were performed using a two-electrode set-up with a Solartron 1260 Impedance/gain-phase analyser. The small intestinal samples were resected from patients who underwent pancreaticoduodenectomy. Impedance measurements were conducted following resection by placing the electrodes on the surface of the intestine. A voltage was applied across the intestinal sample and the measured electrical impedance was obtained in the ZPlot software. Impedance data were further fitted into a Cole model to obtain the Cole parameters. The Py value was calculated from the extracted Cole parameters and used to assess the cell membrane integrity, thus evaluate the intestinal viability. Eight small intestinal segments from different patients were used in this study and impedance measurements were performed once an hour for a ten-hour period. One hour after resection, the impedance decreased, then increased the next two hours, before decreasing until the end of the experiment. For all the intestinal segments, the Py values first increased and reached a plateau which lasted for 1 - 2 hours, before it decreased irreversibly. The time interval where Py value reached the maximum is consistent with reported viable/non-viable limits from histological analysis.

Experimental tissue mimicking human head phantom for estimation of stroke using IC-CF-DMAS algorithm in microwave based imaging system

This paper presents the preparation and measurement of tissue-mimicking head phantom and its validation with the iteratively corrected coherence factor delay-multiply-and-sum (IC-CF-DMAS) algorithm for brain stroke detection. The phantom elements are fabricated by using different chemical mixtures that imitate the electrical properties of real head tissues (CSF, dura, gray matter, white matter, and blood/stroke) over the frequency band of 1–4 GHz. The electrical properties are measured using the open-ended dielectric coaxial probe connected to a vector network analyzer. Individual phantom elements are placed step by step in a three-dimensional skull. The IC-CF-DMAS image reconstruction algorithm is later applied to the phantom to evaluate the effectiveness of detecting stroke. The phantom elements are preserved and measured multiple times in a week to validate the overall performance over time. The electrical properties of the developed phantom emulate the similar properties of real head tissue. Moreover, the system can also effectively detect the stroke from the developed phantom. The experimental results demonstrate that the developed tissue-mimicking head phantom is time-stable, and it shows a good agreement with the theoretical results in detecting and reconstructing the stroke images that could be used in investigating as a supplement to the real head tissue.

Bidomain modeling of electrical and mechanical properties of cardiac tissue.

Throughout the history of cardiac research, there has been a clear need to establish mathematical models to complement experimental studies. In an effort to create a more complete picture of cardiac phenomena, the bidomain model was established in the late 1970s to better understand pacing and defibrillation in the heart. This mathematical model has seen ongoing use in cardiac research, offering mechanistic insight that could not be obtained from experimental pursuits. Introduced from a historical perspective, the origins of the bidomain model are reviewed to provide a foundation for researchers new to the field and those conducting interdisciplinary research. The interplay of theory and experiment with the bidomain model is explored, and the contributions of this model to cardiac biophysics are critically evaluated. Also discussed is the mechanical bidomain model, which is employed to describe mechanotransduction. Current challenges and outstanding questions in the use of the bidomain model are addressed to give a forward-facing perspective of the model in future studies.

Numerical simulation of changes in the electric properties of biological tissues under local heating by laser radiation

The mathematical model that describes the local heating of biological tissues by optical radiation is introduced. Changes of the electric properties of biological tissues in such process can be used as a reliable tool for analyzing heating and damage degrees of tissues.

Nonhomogeneous volume conduction effects affecting needle electromyography: an analytical and simulation study

Objective. Needle electromyography (EMG) is used to study the electrical behavior of myofiber properties in patients with neuromuscular disorders. However, due to the complexity of electrical potential spatial propagation in nonhomogeneous diseased muscle, a comprehensive understanding of volume conduction effects remains elusive. Here, we develop a framework to study the conduction effect of extracellular abnormalities and electrode positioning on extracellular local field potential (LFP) recordings. Methods. The framework describes the macroscopic conduction of electrical potential in an isotropic, nonhomogeneous (i.e. two tissue) model. Numerical and finite element model simulations are provided to study the conduction effect in prototypical monopolar EMG measurements. Results. LFPs recorded are influenced in amplitude, phase and duration by the electrode position in regards to the vicinity of tissue with different electrical properties. Conclusion. The framework reveals the influence of multiple mechanisms affecting LFPs including changes in the distance between the source–electrode and tissue electrical properties. Clinical significance. Our modeled predictions may lead to new ways for interpreting volume conduction effects on recorded EMG activity, for example in neuromuscular diseases that cause structural and compositional changes in muscle tissue. These change will manifest itself by changing the electric properties of the conductor media and will impact recorded potentials in the area of affected tissue.

Bioimpedance Sensors: A Tutorial

Electrical bioimpedance entails the measurement of the electrical properties of tissues as a function of frequency. It is thus a spectroscopic technique. It has been applied in a plethora of biomedical applications for diagnostic and monitoring purposes. In this tutorial, the basics of electrical bioimpedance sensor design will be discussed. The electrode/electrolyte interface is thoroughly described, as well as methods for its modelling with equivalent circuits and computational tools. The design optimization and modelling of bipolar and tetrapolar bioimpedance sensors is presented in detail, based on the sensitivity theorem. Analytical and numerical modelling approaches for electric field simulations based on conformal mapping, point electrode approximations and the finite element method (FEM) are also elaborated. Finally, current trends on bioimpedance sensors are discussed followed by an overview of instrumentation methods for bioimpedance measurements, covering aspects of voltage signal excitations, current sources, voltage measurement front-end topologies and methods for computing the electrical impedance.

A Goertzel Filter-Based System for Fast Simultaneous Multi-Frequency EIS

Bioimpedance measurement is a non-invasive, radiation-free, and inexpensive method for measuring the electrical properties of biological tissues. In applications where transients occur, the commonly used swept sinewave is replaced with broadband signals such as multisine. This makes the signal generation and the extraction of the real and imaginary parts of the impedance challenging. In this brief, an alternative to traditional fast Fourier transform (FFT) or coherent demodulation is presented. Based on the Goertzel filter, this alternative is simpler and requires very few digital resources. Its robustness to the harmonic fold back phenomenon, enables simple ternary current pulses to be used for excitation. The developed digital architecture is capable of simultaneous demodulation of 16 frequencies with an accuracy of 97% and 96% on the magnitude and phase measurement respectively. Employing a ternary sequence allows the use of a low power H-bridge current driver. The analog front-end and demodulation algorithm were implemented in an ASIC using a 180-nm CMOS technology. The system was tested on an isolated pig heart distinguishing edema from non-edema tissue by impedance changes.

Non-invasive blood pressure as an application of electrical impedance: a short review

Electrical bioimpedance (EBI) has gained importance as a diagnostic technique in medicine to determine the electrical properties of tissues. For example, it has been used in tissue characterization, cancer detection, and electromyography. Some of the characteristics of EBI are its low cost, the absence of irradiation during the measurement process, and its non-invasive nature. In this sense, there is interest in developing medical equipment that performs non-invasive measurements of blood pressure (BP). Electrical Impedance Plethysmography (EIP) is a technique commonly used to extract the waveform associated with BP. In this short review, we will cover research articles published in peer-reviewed journals during the last decades, and show developments in the area of EIP, with a brief discussion of relevant results and current challenges.

Development and evaluation of a low cost 8-electrode Electrical Impedance Tomography system

Electrical impedance tomography (EIT) is a medical imaging modality that considers the electrical properties of tissues to obtain a conductivity distribution of a region of interest using the level of resistance it presents to the passage of a small electrical current. This work describes the design of an 8-electrode EIT prototype that offers the possibility of changing the excitation parameters and freedom of movement of the demodulation synchrony by means of conventional electronics. The image reconstruction obtained can locate disturbances in the study medium using the adjacent electrode method. A comparison of the voltage measurements acquired on a homogeneous test medium in two different collection cycles was implemented to determine the precision of the system. The data obtained indicate a maximum error percentage of 2.6% between measurements, which represents an acceptable first approach towards the design of a device with greater stability and precision.

Fabrication and Experimental Evaluation of Simple Tissue-Mimicking Phantoms with Realistic Electrical Properties for Impedance-Based Sensing

Venipuncture is one of the most often performed invasive clinical procedure. Nevertheless, complications still occur. One opportunity to counteract these complications is to indicate the insertion by electrical impedance measurement, which bases on the various electrical properties of different tissues. This paper presents the evaluation and reproducible fabrication of simple tissue-mimicking phantoms for investigation of impedance sensing techniques. Three different tissue-mimicking phantoms, representing blood, fat, and skin, were made on water-based recipes, including agar and gelatin as gelling agents. For evaluation of the electrical properties an electrode probe, made of hypodermic needles, was fabricated and characterized using six sodium chloride (NaCl) solutions of defined concentrations. For characterization of the phantoms, conductances were measured over a frequency range from 20 Hz up to 1 MHz using the self-fabricated electrodes. The calculated conductivities of the tissue-mimicking phantoms showed sufficient agreement with corresponding electrical literature data of native tissue. Tests with a layered tissue structure proved usability for impedance-based venous entry tests. However, the method proposed was not suitable for investigation of relative permittivity, which would be required for full electrical characterization.

Bone Piezoelectricity-Mimicking Nanocomposite Membranes Enhance Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells by Amplifying Cell Adhesion and Actin Cytoskeleton.

Ferroelectric biomaterials have been widely investigated and demonstrated to enhance osteogenesis by simulating the inherent electrical properties of bone tissues. Nevertheless, the underlying biological processes are still not wellunderstood. Hence, this study investigated the underlying biological processes by which bone piezoelectricity-mimicking barium titanate/poly(vinylidene fluoride-trifluoroethylene) nanocomposite membranes (BTO nanocomposite membranes) promote osteogenesis of Bone Marrow Mesenchymal Stem Cells (BMSCs). Ourresults revealed that the piezoelectric coefficient (d33) of nanocomposite membranes aftercontrolled corona poling was similar to that of native bone, and exhibited highly-stable piezoelectrical properties and concentrated surface electrical potential. These nanocomposite membranes significantly enhanced the adhesion and spreading of BMSCs, which was manifested as increased number and area of mature focal adhesions. Furthermore, the nanocomposite membranes significantly promoted the expression of integrin receptors genes (α1, α5 andβ3), which in turn enhanced osteogenesis of BMSCs, as manifested by upregulated Alkaline Phosphatase (ALP) and Bone Morphogenetic Protein 2 (BMP2) expression levels. Further investigations found that the Focal Adhesion Kinase (FAK)-Extracellular Signal-Regulated Kinase1/2 (ERK 1/2) signaling axis may be involved in the biological process of polarized nanocomposite membrane-induced osteogenesis. This study thus provides useful insights for betterunderstanding of the biological processes by which piezoelectric or ferroelectric biomaterials promote osteogenesis.

Electroactive Polymeric Composites to Mimic the Electromechanical Properties of Myocardium in Cardiac Tissue Repair.

Due to the limited regenerative capabilities of cardiomyocytes, incidents of myocardial infarction can cause permanent damage to native myocardium through the formation of acellular, non-conductive scar tissue during wound repair. The generation of scar tissue in the myocardium compromises the biomechanical and electrical properties of the heart which can lead to further cardiac problems including heart failure. Currently, patients suffering from cardiac failure due to scarring undergo transplantation but limited donor availability and complications (i.e., rejection or infectious pathogens) exclude many individuals from successful transplant. Polymeric tissue engineering scaffolds provide an alternative approach to restore normal myocardium structure and function after damage by acting as a provisional matrix to support cell attachment, infiltration and stem cell delivery. However, issues associated with mechanical property mismatch and the limited electrical conductivity of these constructs when compared to native myocardium reduces their clinical applicability. Therefore, composite polymeric scaffolds with conductive reinforcement components (i.e., metal, carbon, or conductive polymers) provide tunable mechanical and electroactive properties to mimic the structure and function of natural myocardium in force transmission and electrical stimulation. This review summarizes recent advancements in the design, synthesis, and implementation of electroactive polymeric composites to better match the biomechanical and electrical properties of myocardial tissue.