Electrical Bioimpedance Spectroscopy Measurements Research Articles

Evaluation of techniques used to assess skeletal muscle quantity in patients with cirrhosis.

Loss of skeletal muscle mass is a well-recognised complication of cirrhosis. Bedside methods to assess skeletal muscle mass including anthropometrics and bioelectrical impedance analysis (BIA) are negatively impacted by fluid overload in advanced cirrhosis and thus there is a need to identify alternatives. There is a paucity of data on the accuracy of commonly used radiological methods such as dual X-ray absorptiometry (DXA) to assess appendicular lean mass (ALM), and computed tomography (CT) skeletal muscle area in patients with cirrhosis. The aim of this study was to evaluate the relationships and agreement of several skeletal muscle mass estimation methods compared to a reference model in patients with cirrhosis. A cross-sectional, single centre study was performed by prospectively recruiting patients with cirrhosis referred to the Queensland Liver Transplant Service. Patients underwent assessment of skeletal muscle mass using bedside techniques (mid-upper arm muscle circumference (MUAMC), bioelectrical impedance spectroscopy (BIS), ultrasound muscle thickness (USMT)) and radiological methods (DXA ALM, CT skeletal muscle area). These were compared to a reference measurement of body cell mass derived from a multi-compartment model using isotope dilution tests and DXA. Forty-two patients (age 56 years, interquartile range 48-60, 86% male) were recruited. Bedside skeletal muscle mass estimation techniques were strongly correlated to the body cell mass reference, with BIS estimation having the strongest correlation coefficients (r=0.78-0.79; P<0.01). A novel technique measuring USMT offered no advantage over traditional bedside techniques. Of the radiological methods, DXA ALM had the strongest correlation coefficient (r=0.781; P<0.01). Weaker correlation coefficients were observed in patients with ascites, except when using the MUAMC. Bland-Altman analysis of BIS body composition estimates demonstrated significant systematic biases and large limits of agreement compared to reference values. These results confirm the difficulties in assessing skeletal muscle mass in patients with cirrhosis, particularly in those with ascites. DXA ALM and BIS measurements provided the best correlation to body cell mass. We suggest DXA ALM for estimation of skeletal muscle mass in patients with cirrhosis as there are established thresholds for skeletal muscle mass depletion, and an accurate assessment of bone mass and density can also be provided. The use of USMT over other bedside skeletal muscle mass estimates was not supported by our results. Further studies evaluating novel bedside skeletal muscle mass estimation techniques in cirrhosis patients are required.

Association analysis of body composition with survival among prevalent peritoneal dialysis patients.

Progressive decline in lean mass and gain of fat mass are common in patients treated with peritoneal dialysis (PD). It is unclear whether body composition or its longitudinal changes contribute to increased mortality among prevalent PD patients. This was a retrospective cohort study. Body composition was assessed using bioelectrical impedance spectroscopy (BIS). Lean and fat tissue indices were derived from lean and fat mass indexed to height-squared, respectively. The patient's baseline BIS results were used to explore its mortality risk prediction for the entire cohort. Among patients with subsequent BIS measurements, changes of lean and fat mass over time were also examined with survival outcomes. Among all participants (n = 555, PD vintage 38months), higher baseline lean tissue index was associated with lower mortality after adjusting for fat tissue index and confounders (HR 0.90; 95% CI 0.84-0.97, p = 0.01). However, this association was no longer significance after the final adjustment with serum albumin level (p = 0.06). A total of 136 patients had repeated BIS data. After the interval of 10.1months during two consecutive BIS measurements, there was a strong inverse correlation between the percentage changes of lean and fat tissue indices (r = - 0.73, p < 0.001). The longitudinal changes in lean mass, either high or low categories, were not significantly associated with all-cause mortality. In contrast, patients who were classified as having low values of fat tissue index (below median) from baseline to the next BIS measurements had a lower odds of death in the univariable (HR 0.32; 95% CI 0.12-0.84, p = 0.02) but not in the adjusted models. Among prevalent PD patients, higher baseline lean mass was independently associated with better survival. However, the longitudinal changes in lean mass were not significantly associated with mortality. In contrast, the maintenance of low fat status over time appeared to be associated with a lower likelihood of death among PD population.

The influence of body position on bioelectrical impedance spectroscopy measurements in young children

Bioelectrical impedance techniques are easy to use and portable tools for assessing body composition. While measurements vary according to standing vs supine position in adults, and fasting and bladder voiding have been proposed as additional important influences, these have not been assessed in young children. Therefore, the influence of position, fasting, and voiding on bioimpedance measurements was examined in children. Bioimpedance measurements (ImpediMed SFB7) were made in 50 children (3.38 years). Measurements were made when supine and twice when standing (immediately on standing and after four minutes). Impedance and body composition were compared between positions, and the effect of fasting and voiding was assessed. Impedance varied between positions, but body composition parameters other than fat mass (total body water, intra- and extra-cellular water, fat-free mass) differed by less than 5%. There were no differences according to time of last meal or void. Equations were developed to allow standing measurements of fat mass to be combined with supine measurements. In early childhood, it can be difficult to meet requirements for fasting, voiding, and lying supine prior to measurement. This study provides evidence to enable standing and supine bioimpedance measurements to be combined in cohorts of young children.

Routine abdominal magnetic resonance imaging can determine psoas muscle area in paediatric Crohn's disease and correlates with bioelectrical impedance spectroscopy measures of lean mass.

Paediatric Crohn's disease (CD) has been associated with undernutrition. Accurate and accessible measures of body composition would provide data to personalise nutritional therapy. We assessed feasibility of MRI-derived measures of psoas cross-sectional area (PCSA) in paediatric CD and correlated with anthropometric and bioelectrical impedance spectroscopy (BIS) measures. MRI small bowel/pelvis images of patients with CD, aged <18 years, were retrieved. Patients with concurrent anthropometric and BIS measurements were eligible for inclusion. The PCSA at L3 was calculated by two assessors and combined. To assess reproducibility of measures we calculated the coefficient of variation (CoV). Age, height-Z-scores, weight-Z-scores and BIS measures were correlated with PCSA. Using normal paediatric data from CT-scans we derived psoas area Z-scores for our cohort. 10 patients were included. Mean age at MRI scan was 14.6 years (11.7-16.3). PCSA was calculated for all MRI scans. There was high reproducibility between measurers, mean CoV 0.099. There was a significant positive correlation between PCSA and BIA-derived fat free mass, Pearson correlation coefficient (PCC) 0.831, p=0.003. Correlation coefficients for PCSA and Height-for-age Z-score, weight-for-age -Z-score and age were PCC 0.343- p=0.33, PCC=0.222- p=0.54, and PCC 0.6034- p=0.065, respectively. The mean PCSA Z-score was-1.81, with 70% of the patients having a Z-score<-2.0. These data demonstrate the feasibility of deriving measures of body composition from routine MRI imagine. There was significant positive correlation between PCSA and BIS-derived lean mass. Further studies are required to confirm applicability of normal ranges prior to routine clinical implementation.

Fluid overload in patients undergoing TAVR: what we can learn from the nephrologists

AimsFluid overload (FO) puts aortic stenosis (AS) patients at risk for heart failure (HF) and death. However, conventional FO assessment, including rapid weight gain, peripheral oedema, or chest radiography, is inaccurate. Bioelectrical impedance spectroscopy (BIS) allows objective and reproducible FO quantification, particularly if clinically unapparent. It is used in dialysis patients to establish dry weight goals. BIS has not been tested for prognostication in AS. This study aimed to evaluate whether BIS adds prognostic information in stable patients undergoing transcatheter aortic valve replacement (TAVR).Methods and resultsConsecutive patients scheduled for TAVR underwent BIS in addition to echocardiographic, clinical, and laboratory assessment. On BIS, mild FO was defined as >1.0 L and severe as >3.0 L. Combined HF hospitalization and/or all‐cause death was defined as primary endpoint. Three hundred forty‐four patients (81.5 ± 7.2 years old, 47.4% female) were prospectively included. FO by BIS was associated with clinical congestion signs, higher serum markers of cardiac injury, poorer left ventricular function, higher pulmonary pressures, and more severe tricuspid regurgitation (all P < 0.05). Yet, clinical examination was unremarkable in >30% in mild FO, only detected by BIS. During 12.1 ± 5.5 months, 67 (19.5%) events were recorded (40 deaths, 15 HF hospitalizations, and 12 both). Quantitatively, every 1 L increase in FO was associated with a 24% (HR 1.24, 95% CI 1.13–1.35, P < 0.001) increase in event hazard. This association persisted after adjustment for STS/EuroSCORE‐II, NT‐proBNP, left ventricular ejection fraction, and renal function.ConclusionsIn patients undergoing TAVR, FO by BIS is strongly associated with adverse outcomes. BIS measurement conveys prognostic information not represented in any currently used AS/TAVR risk assessments.

Comparison between bioelectrical impedance spectroscopy measurements and water volume displacement of ankle oedema variations during the course of a day

Objective: The purpose of this study was to find relationships between variations in bioelectrical impedance spectroscopy (BIS) measurements and those obtained by water displacement (WD) and calf (C) and ankle (A) perimetry on legs of patients with venous insufficiency and lower limb oedema, some with positive pitting test (PPT), others with negative pitting test (NPT). Approach: Twenty-nine (29) female subjects were clinically examined prior to inclusion in the trial. Measurements were taken once in the morning and then 6 h later, using perimetry, WD, and then BIS; subjects were standing. Leg volume was assessed using two WD volumeters, one ‘Tall’ (TWD) and one ‘Short’ (SWD). BIS was performed using a SFB7 impedance meter device (Impedimed®). Main results: Forty-three (43) legs with oedema were included. The results showed that 61% of the TWD variations variance was explained by SWD variations; less than 30% of the TWD variations variance was explained using BIS or perimetry alone, and 45% at best when used in combination. R0, related to extracellular water, was the key BIS parameter. For NPT subpopulation (32 legs), the composite parameter (C2 − A2)/R0 explained more than 60% of the TWD variations variance. For PPT subpopulation (11 legs), small or statistically non-significant variance explanations were found. Significance: Combination of anthropometric and BIS parameters gave a better forecast of WD results than using only one or other. A novel composite parameter, (C2 − A2)/R0, better predicted TWD changes than other parameters hitherto used in literature, with improved estimates for the NPT subpopulation. Study n°ANSM 2017-A01063-50.

Gene-sensor on the Basis of Magnetic Immobilization and Bioimpedance Measurements: a proof of concept

Detection of molecular markers or specific DNA sequences (genes) represents the future in genomic medicine. Gene detection requires expensive equipment and specialized technicians, thus biosensors development that allows such detection quickly, economically and simply is fundamental in the first level of health care. In this study the development and evaluation of a genosensor based on magnetic anchoring of DNA sequences and electrical bioimpedance spectroscopy measurements is presented. As a first proof of concept, bioimpedance measurements were developed in PCR product anchored by magnetic nanoparticles and two conditions were compared; PCR product and absence of amplicons. The experimental evaluation indicates technical feasibility of developing a biosensor of molecular markers or specific genes trough electric bioimpedance measurements assisted with magnetic nanoparticles. The observations show that the DNA biosensor proposal offers the possibility of detecting a PCR product and differentiating it from the absence of amplicons.

Rectal electrical bio-impedance spectroscopy in the detection of colorectal anomalies associated with cancer

Colorectal cancer is the third most common cancer worldwide. Tests available for screening this cancer have low sensitivity or are challenging and costly to implement. Based on the concept of field cancerization, or carcinogenic field effect, the possibility of early detection of cancer by electrical bioimpedance spectroscopy measurements on the rectum was studied. For this research, seventy-seven subjects who attended the clinic for total colonoscopy were examined, and readings were taken at eight frequencies with an electrical bioimpedance spectroscopy probe. Four measurements were taken from the rectum of each subject, with the electrical probe being introduced into the rectum through an anoscope, before a total colonoscopy. An inverse model was used to obtain Cole-Cole parameters for each electrical bioimpedance spectra. Two results were the more prominent in this research; firstly, the field cancerization effect was observed and secondly, a significative correlation between rectal electrical bioimpedance and abnormalities associated with cancer was found (p-value = 0.002).

Electrical Bioimpedance Spectroscopy as Biosensor Technique to Identify Pluripotent Stem Cells and Fibroblasts

Pluripotent stem cells have the capacity to differentiate into specialized cells, and it has relevance in the engineering of tissue regeneration. The identification and characterization of diverse cells types requires complex techniques as flow cytometry, immunocytochemistry and the exploration of molecular markers; such techniques require infrastructure and qualified personnel. The objective of this study was to analyse the use of Electrical Bioimpedance Spectroscopy (EBIS) measurements as non-complex alternative technique to identify populations of undifferentiated pluripotent mouse Embryonic Stem Cells (mESCs) and Mouse Embryonic Fibroblasts (MEFs). EBIS measurements were compared in populations of pluripotent stem cells and fibroblasts which were characterized previously using Fourier Transform Infrared (FTIR) spectroscopy and fluorescence microscopy. The results indicate that EBIS technique has potential sensitivity at certain frequency range to discriminate between both evaluated cell populations. Additional studies with different concentrations in order to evaluate quantitatively the sensitivity and specificity of the proposed technique are recommended.

Electrical bioimpedance spectroscopy as biosensor technique to identify cells lineages and cell differentiation process.

The identification and characterization of diverse cells types and cell differentiation process requires complex techniques as flow cytometry, immunocytochemistry and the exploration of molecular markers; such techniques require infrastructure and qualified personnel. The objective of this study was to analyze the use of Electrical Bioimpedance Spectroscopy (EBIS) measurements as a non-complex alternative technique to identify populations of undifferentiated mouse Pluripotent Stem Cells (mPSCs), Mouse Embryonic Fibroblasts (MEFs) and the differentiation process from preadipocytes (3T3-L1) to mature adipocytes. EBIS measurements were compared in populations of cells which were characterized previously using microscopy. The results indicate that EBIS technique has a potential sensitivity at certain frequency range to discriminate between both evaluated cell populations and some differentiation process. Additional studies with different concentrations to evaluate quantitatively the sensitivity and specificity of the proposed technique are recommended.

Bioimpedance spectroscopy measurements of phase angle and height for age are predictive of outcome in children following surgery for congenital heart disease

Children with congenital heart disease (CHD) are often growth restricted (low weight- and/or height-for-age) which may increase risk of poor post operative resilience. Bioelectrical impedance spectroscopy (BIS) has been used to determine body composition in different clinical settings and has been shown to mark differences in nutritional state and clinical outcome. In disease conditions were fluid is not normally distributed it is proposed that raw impedance values and BIS derived phase-angle may serve as prognostic indicators of clinical outcome. We sought to describe the relationship between nutritional status, phase-angle and post-operative outcomes in children with congenital heart disease. Single centre prospective cohort study. Paediatric Intensive Care Unit (PICU), Southampton Children's Hospital. 122 children with CHD following cardiac surgery (March 2015-April 2016). Outcome variables included growth, mechanical-ventilation, PICU length of stay (PICU-LOS) and phase-angle at 50Hz. BIS measurements were taken before and on the day of surgery (day 0), day 2 post-operatively and on discharge from hospital. Pre-operative moderate malnutrition defined as height-for-age-z-score (HAZ) ≤-2 was observed in 28.5% of infants and 20.6% of children. Regression analysis was used to investigate the relationship between phase-angle, HAZ and clinical outcomes. Moderate-malnutrition (HAZ ≤-2) was associated with an increased PICU-LOS (odds ratios (OR) with 95% confidence interval: 1.8; 1.1-2.7, p=0.008) whilst a low phase-angle (≤2.7° on day 2 was associated with longer PICU-LOS (OR 7.8; 2.7-22.45, p<0.001)); When the model was adjusted for age, known risk factors and length of surgery, HAZ ≤-2 and phase-angle ≤2.7° on day 2 were associated with longer PICU-LOS (p=0.001 and p=0.04 respectively) and together explained 81.7% of the variability in PICU-LOS. Moderate malnutrition (HAZ ≤-2) in infants and children undergoing cardiac surgery is associated with longer PICU-LOS. Post-operative measures of BIS phase angle may further improve our ability to identifying hose children with an increased risk of prolonged PICU-LOS compared to using pre-operative anthropometry alone.

Do Bioimpedance Measurements of Over-Hydration Accurately Reflect Post-Haemodialysis Weight Changes?

Introduction: Bioelectrical impedance spectroscopy (BIS) devices are being used to determine ultrafiltration requirements to achieve target weight for haemodialysis (HD) patients. Pre-dialysis measurements are more convenient for both patients and staff. We wished to compare the changes in pre- and post-dialysis hydration measured by BIS with actual weight loss. Methods: We compared paired BIS measurements made pre and post HD using a BIS device based on a 3-compartmental model, designed to provide information on extracellular water (ECW) excess. Results: BIS was measured in 49 HD patients, 35 male (71.4%) with mean age 67.6 ± 14.2. Weight fell significantly from 69.2 ± 17.8 to 67.6 ± 17.4 kg, and BIS over hydration (OH) from 4.5 ± 3.3.4 to 3.4 ± 2.9 litres, and ECW from 16.8 ± 4.8 to 15.5 ± 4.4 litres, but there was no change in the amount of intracellular water. Weight loss correlated positively with the change in ECW, but exceeded the fall in OH; mean bias -0.58 (95% confidence limits -3.6 to 4.8 kg). Summary: We measured OH pre and post HD, but did not find that the change in OH correlated with changes in body weight. Although there was a correlation between changes in OH and ECW, there was none for weight. Our findings do not support total reliance on pre-dialysis BIS alone for assessing volume status in HD patients, but rather BIS should be considered an aid to clinical assessment of volume status.

Body composition by dual-energy X-ray spectrometry and bioelectrical impedance spectroscopy in a healthy population at age 75 and 80

Bioelectrical impedance spectroscopy (BIS) is a versatile field tool to obtain information about body composition (BC), if prediction equations are available that are valid for the group under consideration. We aimed to validate prediction equations for total body skeletal muscle mass (TBSMM) developed in healthy 75-year olds from the Gothenburg area (Sweden) in a similar sample examined at age 80. We give new prediction equations for fat mass (FM), fat-free mass (FFM), and TBSMM that are based on the entire group of elderly subjects, using values from Dual-energy X-ray spectrometry (DXA) as reference standard. Finally, we describe the longitudinal change in BC in the subset of subjects, who participated at both age 75 and 80. Body composition was measured by DXA and multiple-frequency BIS at age 75 (n=111) and 80 (n=91) years. Ordinary and mixed linear regression was used to examine previous and new prediction equations. Longitudinal change was assessed by paired sample t-test. The prediction equations for TBSMM developed in 75-year old subjects showed good validity when applied to the sample of 80 year olds. The results were independent of the presence of a metal prosthesis in hip or knee. New, sex-specific prediction equations for FM, FFM, and TBSMM were derived for 75 - 80 year-old subjects that further improved the accuracy of prediction. Using DXA-derived BC at ages 75 and 80, we observed a decline in TBSMM in both sexes, which was mainly due to muscle loss in the legs. In men, the decrease in trunk FFM was accompanied by an increase in FM, leaving no overall weight change in the trunk. When the 5-year change in TBSMM was based on longitudinal BIS measurements, the results from DXA were reproduced only when the prediction was based on BIS-values at 50kHz. Good cross-sectional validity of BIS equations for TBSMM was found in a population sample of 80-year olds. The presence of a metal prosthesis did not influence the quality of prediction. New prediction equations for FM, FFM, and TBSMM need to be evaluated in an independent sample.

Robustness study of the different immittance spectra and frequency ranges in bioimpedance spectroscopy analysis for assessment of total body composition

The estimation of body fluids is a useful and common practice for assessment of disease status and therapy outcomes. Electrical bioimpedance spectroscopy (EBIS) methods are noninvasive, inexpensive and efficient alternatives for determination of body fluids. One of the main source of errors in EBIS measurements in the estimation of body fluids is capacitive coupling. In this paper an analysis of capacitive coupling in EBIS measurements was performed and the robustness of the different immittance spectra against it tested. On simulations the conductance (G) spectrum presented the smallest overall error, among all immittance spectra, in the estimation of the impedance parameters used to estimate body fluids. Afterwards the frequency range of 10–500 kHz showed to be the most robust band of the G spectrum. The accuracy of body fluid estimations from the resulting parameters that utilized G spectrum and parameters provided by the measuring device were tested on EBIS clinical measurements from growth hormone replacement therapy patients against estimations performed with dilution methods. Regarding extracellular fluid, the correlation between each EBIS method and dilution was 0.93 with limits of agreement of 1.06 ± 2.95 l for the device, 1.10 ± 2.94 l for G [10–500 kHz] and 1.04 ± 2.94 l for G [5–1000 kHz]. Regarding intracellular fluid, the correlation between dilution and the device was 0.91, same as for G [10–500 kHz] and 0.92 for G [5–1000 kHz]. Limits of agreement were 0.12 ± 4.46 l for the device, 0.09 ± 4.45 for G [10–500 kHz] and 0.04 ± 4.58 for G [5–1000 kHz]. Such close results between the EBIS methods validate the proposed approach of using G spectrum for initial Cole characterization and posterior clinical estimation of body fluids status.

Electrical bioimpedance spectroscopy in time-variant systems: Is undersampling always a problem?

Abstract During the last decades, Electrical Bioimpedance Spectroscopy (EBIS) has been applied mainly by using the frequency-sweep technique, across a range of many different applications. Traditionally, the tissue under study is considered to be time-invariant and dynamic changes of tissue activity are ignored by treating the changes as a noise source. A new trend in EBIS is simultaneous electrical stimulation with several frequencies, through the application of a multi-sine, rectangular or other waveform. This method can provide measurements fast enough to sample dynamic changes of different tissues, such as myocard. This high sampling rate comes at a price of reduction in SNR and the increase in complexity of devices. Although the frequency-sweep technique is often inadequate for monitoring the dynamic changes in a variant system, it can be used successfully in applications focused on the time-invariant or slowly-variant part of a system. However, in order to successfully use frequency-sweep EBIS for monitoring time-variant systems, it is paramount to consider the effects of aliasing and especially the folding of higher frequencies, on the desired frequency e.g. DC level. This paper discusses sub-Nyquist sampling of thoracic EBIS measurements and its application in the case of monitoring pulmonary oedema. It is concluded that by considering aliasing, and with proper implementation of smoothing filters, as well as by using random sampling, frequency-sweep EBIS can be used for assessing time-invariant or slowly-variant properties of time-variant biological systems, even in the presence of aliasing. In general, undersampling is not always a problem, but does always require proper consideration.

Body composition of breastfed infants ő a comparison of bioelectrical impedance spectroscopy and ultrasound assessment (1017.3)

An accurate non‐invasive methodology to measure infant body composition is required to identify infants at risk of obesity. This study compared bioelectrical impedance spectroscopy (BIS) and ultrasound (US) methods and assessed effect of milk intake on BIS. Percentage Fat Mass (%FM) of 5 and 9 month old healthy, term infants was determined with BIS pre and post a breastfeed using software default calculations. Milk intake was measured by the test‐weigh method. Skin and subcutaneous fat thickness was measured at the tricipital and subscapular sites with US and the measurements were used to predict %FM. Milk intake (mL) was (median [IQR] 64.5 [43.3, 87.0]). Post and pre feed BIS measurements were not significantly different (p=0.29), regardless of milk intake. US %FM predictions (median [IQR] 25.5 [21.8, 28.8]) were consistent with reference values for infant body composition. BIS %FM measurements (median [IQR] 16.7 [14.5,19.4]) were significantly lower than US %FM (p&lt;0.001). Milk intake did not significantly affect BIS readings. Preliminary results indicate that US is an acceptable non‐invasive method for predicting %FM and BIS consistently underestimates %FM.Grant Funding Source: Medela AG

Stroke damage detection using classification trees on electrical bioimpedance cerebral spectroscopy measurements.

After cancer and cardio-vascular disease, stroke is the third greatest cause of death worldwide. Given the limitations of the current imaging technologies used for stroke diagnosis, the need for portable non-invasive and less expensive diagnostic tools is crucial. Previous studies have suggested that electrical bioimpedance (EBI) measurements from the head might contain useful clinical information related to changes produced in the cerebral tissue after the onset of stroke. In this study, we recorded 720 EBI Spectroscopy (EBIS) measurements from two different head regions of 18 hemispheres of nine subjects. Three of these subjects had suffered a unilateral haemorrhagic stroke. A number of features based on structural and intrinsic frequency-dependent properties of the cerebral tissue were extracted. These features were then fed into a classification tree. The results show that a full classification of damaged and undamaged cerebral tissue was achieved after three hierarchical classification steps. Lastly, the performance of the classification tree was assessed using Leave-One-Out Cross Validation (LOO-CV). Despite the fact that the results of this study are limited to a small database, and the observations obtained must be verified further with a larger cohort of patients, these findings confirm that EBI measurements contain useful information for assessing on the health of brain tissue after stroke and supports the hypothesis that classification features based on Cole parameters, spectral information and the geometry of EBIS measurements are useful to differentiate between healthy and stroke damaged brain tissue.

Studying the Performance of Conductive Polymer Films as Textile Electrodes for Electrical Bioimpedance Measurements

With the goal of finding novel biocompatible materials suitable to replace silver in the manufacturing of textile electrodes for medical applications of electrical bioimpedance spectroscopy, three different polymeric materials have been investigated. Films have been prepared from different polymeric materials and custom bracelets have been confectioned with them. Tetrapolar total right side electrical bioimpedance spectroscopy (EBIS) measurements have been performed with polymer and with standard gel electrodes. The performance of the polymer films was compared against the performance of the gel electrodes. The results indicated that only the polypropylene 1380 could produce EBIS measurements but remarkably tainted with high frequency artefacts. The influence of the electrode mismatch, stray capacitances and large electrode polarization impedance are unclear and they need to be clarified with further studies. If sensorized garments could be made with such biocompatible polymeric materials the burden of considering textrodes class III devices could be avoided.

Prediction of body water compartments in preterm infants by bioelectrical impedance spectroscopy

To evaluate nutritional interventions in preterm infants, a simple, accurate assessment of the type of growth, that is, change in body composition through the relative contributions of lean body tissue and fat mass to weight gain, is needed. Bioelectrical impedance may provide such a method. The aim of this study was to develop resistivity coefficients appropriate for use in bioelectrical impedance spectroscopy (BIS) analysis of body water volumes in preterm infants. A total of 99 preterm infants were enrolled (mean gestational age 32 completed weeks). Total body water (TBW) and extracellular water (ECW) were determined using the reference methods of deuterium and bromide dilution. BIS measurements taken at the same time allowed calculation of resistivity coefficients. Predictions of TBW and ECW obtained using these coefficients were then validated against volumes determined using the reference methods in a separate cohort of infants. Data were available for 91 preterm infants. BIS-predicted TBW and ECW correlated well with the measured volumes (Pearson's r(p)=0.825 and 0.75, respectively). There was a small bias (TBW 10 ml and ECW 40 ml) but large limits of agreement (TBW ± 650 ml and ECW ± 360 ml). BIS appears to have limited clinical utility; however, the relatively small bias means that it may be useful for measurements within a population or for comparisons between groups in which population means rather than individual values are compared.

Software Tool for Analysis of Breathing-Related Errors in Transthoracic Electrical Bioimpedance Spectroscopy Measurements

During the last decades, Electrical Bioimpedance Spectroscopy (EBIS) has been applied in a range of different applications and mainly using the frequency sweep-technique. Traditionally the tissue under study is considered to be timeinvariant and dynamic changes of tissue activity are ignored and instead treated as a noise source. This assumption has not been adequately tested and could have a negative impact and limit the accuracy for impedance monitoring systems. In order to successfully use frequency-sweeping EBIS for monitoring time-variant systems, it is paramount to study the effect of frequency-sweep delay on Cole Model-based analysis. In this work, we present a software tool that can be used to simulate the influence of respiration activity in frequency-sweep EBIS measurements of the human thorax and analyse the effects of the different error sources. Preliminary results indicate that the deviation on the EBIS measurement might be significant at any frequency, and especially in the impedance plane. Therefore the impact on Cole-model analysis might be different depending on method applied for Cole parameter estimation.