Volume 7 (2016): Issue 1 (January 2016)

Purpose: To assess body composition and obesity in individuals with spinal cord injury (SCI) who practice and do not practice physical activity using body mass index (BMI) and bioelectrical impedance analysis (BIA). Methods: 39 patients with SCI went through BIA evaluation and BMI was assessed. Patients were divided into four groups according to injury level (paraplegia or tetraplegia) and physical activity achievement (active or inactive). Results: 22 individuals with paraplegia (7 active and 15 inactive) and 17 with tetraplegia (5 active and 12 inactive) were evaluated. BMI, fat percentage, fat mass, lean tissue mass, total body water (TBW), and TBW percentage were assessed in groups. Tetraplegic inactive groups showed higher fat percentage featuring obesity. For paraplegic active group mean fat percentage was 19.61% (±9.27) and mean fat mass was 16.66 kg (±9.71) and for paraplegic inactive group fat percentage was 23.27% (±5.94) and fat mass 18.59 kg (±7.58). For tetraplegic groups in active group the fat percentage was 17.14% (±6.32) and fat mass was 11.22 kg (±5.16) and for inactive group mean fat percentage was 33.68% (±4.74) and fat mass was 25.59 kg (±2.91). When paraplegic and tetraplegic inactive groups were compared differences were observed in fat percentage (p = 0.0003) and fat mass (p = 0.0084). Also, when tetraplegic groups (activeXinactive) were compared differences in percentage (p = 0.0019) and fat mass (p = 0.034) were observed. Only for the paraplegic inactive group BMI result was higher than 25 kg/m². Conclusion: BMI does not discriminate between obesity levels in individuals with SCI and physical activity can improve body composition and prevent obesity in SCI patients.

A finite difference model of a four-electrode tissue conductivity measurement system was developed and shown to be within 10% of theory. The model is useful for explaining the behavior of conductivity measurement electrodes in tissue.

In recent years several electrical wound management systems, so called electroceuticals, have been introduced claiming an induced electrical response in the wounded tissue. Some have external current and voltage sources while others have internal constructions aiming at creating necessary therapeutic currents. We investigate two representative electroceuticals by mapping out their electrical field landscapes using a previously developed skin model within a numerical simulation scheme. We find very strong fields from the electroceuticals of the order of 1 kV/m amenable for electrotaxic influence on pertinent cell types for wound healing. Current densities can locally be as high as 1 A/cm².

This work presents a simulation analysis of the bioimpedance measurements at the human forearm. The Ansys® High Frequency Structure Simulator (HFSS) has been used to analyze the electrical response of a section of human forearm with three domains of dielectric behavior – fat, muscle and artery (blood). The impedance values were calculated as the ratio of the output voltage at the electrodes to the applied known current (1 mA). A model was developed and was simulated for impedance values obtained within a frequency range of 1 kHz to 2 MHz. The measurements were done at three instances of radial artery diameter. The maximum resistance and reactance values were calculated as 445 Ω and 178.5 Ω, 356 Ω and 138 Ω, and 368 Ω and 144.3 Ω for diameters 2.3 mm, 2.35 mm, and 2.4 mm respectively. The set of impedance values obtained followed the Cole-plot trend. The results obtained were found to be in excellent agreement with the Cole modelling. The set of values obtained at three different diameters reflected the effect of blood flow on impedance values.

Impedance cardiography (ICG) is a non-invasive tool for assessing the hemodynamic parameters. It has been used for diagnosing several cardiovascular diseases, such as heart failure, cardio-myopathy, and valvular diseases. Particularly, the valvular heart disease is characterized by the damage in one of the four heart valves: the mitral, aortic, tricuspid or pulmonary valves. The mitral valve insufficiency and the aortic valve stenos are the most frequent valve diseases in the world. In this paper, we propose to diagnosis the mitral valve insufficiency using the impedance cardiography technique. The study group consisted of 40 subjects (20 control subjects and 20 patients with mitral insufficiency). A parameter “I” is calculated from the impedance cardiogram waveform and it is used to differentiate control subjects from patients with mitral insufficiency. The parameter “I” was related significantly to the abnormalities of the impedance cardiogram waveform. For patients with mitral insufficiency, “I” was higher than for the healthy subjects with a difference ratio of 89% (p<0.001). To improve the diagnosis, we determined the stroke volume, cardiac output, and other hemodynamic parameters for the two groups of subjects. Finally, we concluded that we could identify, easily, patients with mitral insufficiency based on the abnormalities of the impedance cardiogram tracings and a characteristic parameter “I”.

Measuring brain electrical impedance (rheoencephalography) is a potential technique for noninvasive, continuous neuro-monitoring of cerebral blood flow autoregulation in humans. In the present rat study, we compared changes in cerebral blood flow autoregulation during CO₂ inhalation measured by rheoencephalography to changes measured by laser Doppler flowmetry, an invasive continuous monitoring modality. Our hypothesis was that both modalities would reflect cerebral blood flow autoregulation.

Male Sprague-Dawley rats (n=28; 28 control and 82 CO₂ challenges) were measured under anesthesia. The surgical preparation involved implantation of intracerebral REG electrodes and an LDF probe into the brain. Analog waveforms were stored in a computer.

CO₂ inhalation caused transient, simultaneous increases in the signals of both laser Doppler flow (171.99 ± 46.68 %) and rheoencephalography (329.88 ± 175.50%). These results showed a correlation between the two measured modalities; the area under the receiver operating characteristic curve was 0.8394.

The similar results obtained by measurements made with laser Doppler flowmetry and rheoencephalography indicate that rheo-encephalography, like laser Doppler flowmetry, reflects cerebral blood flow autoregulation. Rheoencephalography therefore shows potential for use as a continuous neuro-monitoring technique.

In this study, we explore the potential of electrical impedance tomography (EIT) for miniaturised 3D samples to provide a non-invasive approach for future applications in tissue engineering and 3D cell culturing. We evaluated two different electrode configurations using an array of nine circular chambers (Ø 10 mm), each having eight gold plated needle electrodes vertically integrated along the chamber perimeter. As first method, the adjacent electrode configuration was tested solving the computationally simple back-projection algorithm using Comsol Multiphysics in time-difference EIT (t-EIT). Subsequently, a more elaborate method based on the “polar-offset” configuration (having an additional electrode at the centre of the chamber) was evaluated using linear t-EIT and linear weighted frequency-difference EIT (f-EIT). Image reconstruction was done using a customised algorithm that has been previously validated for EIT imaging of neural activity. All the finite element simulations and impedance measurements on test objects leading to image reconstruction utilised an electrolyte having an ionic strength close to physiological solutions. The chosen number of electrodes and consequently number of electrode configurations aimed at maximising the quality of image reconstruction while minimising the number of required measurements. This is significant when designing a technique suitable for tissue engineering applications where time-based monitoring of cellular behaviour in 3D scaffolds is of interest. The performed tests indicated that the method based on the adjacent configuration in combination with the back-projection algorithm was only able to provide image reconstruction when using a test object having a higher conductivity than the background electrolyte. Due to limitations in the mesh quality, the reconstructed image had significant irregularities and the position was slightly shifted toward the perimeter of the chamber. On the other hand, the method based on the polar-offset configuration combined with the customised algorithm proved to be suitable for image reconstruction when using non-conductive and cell-based test objects (down to 1% of the measurement chamber volume), indicating its suitability for future tissue engineering applications with polymeric scaffolds.

In recent years, the degree of spread of osteoporosis in men and women has increased considerably. According to the existing statistics 20 percent of women above the age 50 are suffering from osteoporosis and the degree of its growth has been more among men rather than women. In the following research, a three-dimensional electrical computer model of cancellous bone tissue has been presented which consists of a unit cell made of cortical bone where we adjust the amount of bone density as desired. Using a commercial electromagnetics simulation software, we put the intended piece under the effect of electric field and calculate the electric current and extract the impedance of the tissue. Considering the fact that the electrical properties of the components of the intended piece is different for each frequency, the obtained impedance would be variable with frequency. Changes of the impedance caused by alteration of the bone density, can thus be computationaly estimated and leads to a model-based estimation of impedance sensitivity to changes in bone density. Consequently, it would be advantageous to find a frequency range that causes the highest relative change in the amount of the impedance as bone density is varied. The obtained results in a wide frequency range of 1 kHz – 1 GHz indicated that by the alteration of the bone density from 10 to 30 percent, the highest sensitivity in the electrical properties of cancellous bone occurres at frequencies less than 100 kilohertz.

Under an alternating electrical signal, biological tissues produce a complex electrical bioimpedance that is a function of tissue composition and applied signal frequencies. By studying the bioimpedance spectra of biological tissues over a wide range of frequencies, we can noninvasively probe the physiological properties of these tissues to detect possible pathological conditions. Electrical impedance spectroscopy (EIS) can provide the spectra that are needed to calculate impedance parameters within a wide range of frequencies. Before impedance parameters can be calculated and tissue information extracted, impedance spectra should be processed and analyzed by a dedicated software program. National Instruments (NI) Inc. offers LabVIEW, a fast, portable, robust, user-friendly platform for designing data-analyzing software. We developed a LabVIEW-based electrical bioimpedance spectroscopic data interpreter (LEBISDI) to analyze the electrical impedance spectra for tissue characterization in medical, biomedical and biological applications. Here, we test, calibrate and evaluate the performance of LEBISDI on the impedance data obtained from simulation studies as well as the practical EIS experimentations conducted on electronic circuit element combinations and the biological tissue samples. We analyze the Nyquist plots obtained from the EIS measurements and compare the equivalent circuit parameters calculated by LEBISDI with the corresponding original circuit parameters to assess the accuracy of the program developed. Calibration studies show that LEBISDI not only interpreted the simulated and circuit-element data accurately, but also successfully interpreted tissues impedance data and estimated the capacitive and resistive components produced by the compositions biological cells. Finally, LEBISDI efficiently calculated and analyzed variation in bioimpedance parameters of different tissue compositions, health and temperatures. LEBISDI can also be used for human tissue impedance analysis for electrical impedance-based tissue characterization, health analysis and disease diagnosis.