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The estimation of body fluids is a useful and common practice in the status assessment of diseasemechanisms and treatments. Electrical bioimpedance spectroscopy (EBIS) methods are non-invasive,inexpensive, and efficient alternatives for the estimation of body fluids. However, these methods areindirect, and their robustness and validity are unclear.Regarding the recording of measurements, a controversy developed regarding a spectrum deviationin the impedance plane, which is caused by capacitive leakage. This deviation is frequentlycompensated for by the extended Cole model, which lacks a theoretical basis; however, there is nomethod published to estimate the parameters. In this thesis, a simplified model to correct thedeviation was proposed and tested. The model consists of an equivalent capacitance in parallel withthe load.Subsequently, two other measurement artefacts were considered. Both artefacts were frequentlydisregarded with regard to total body and segmental EBIS measurements as their influence isinsignificant with suitable skin-electrode contact. However, this case is not always valid, particularlyfrom a textile-enabled measurement system perspective. In the estimation of body fluids, EBIS dataare fitted to a model to obtain resistances at low and high frequencies. These resistances can berelated to body fluid volumes. In order to minimise the influence of all three artefacts on theestimation of body fluids and improve the robustness and suitability of the model fitting the differentdomains of immittance were used and tested. The conductance in a reduced frequency spectrum wasproposed as the most robust domain against the artefacts considered.The robustness and accuracy of the method did not increase, even though resistances at low and highfrequencies can be robustly estimated against measurement artefacts. Thus, there is likely error in therelation between the resistances and volumes. Based on a theoretical analysis, state of the artmethods were reviewed and their limitations were identified. New methods were also proposed. Allmethods were tested using a clinical database of patients involved in growth hormone replacementtherapy. The results indicated EBIS are accurate methods to estimate body fluids, however they haverobustness limits. It is hypothesized that those limits in extra-cellular fluid are primarily due toanisotropy, in total body fluid they are primarily due to the uncertainty ρi, and errors in intra-cellularfluid are primarily due to the addition of errors in extracellular and total body fluid. Currently, theseerrors cannot be prevented or minimised. Thus, the limitations for robustness must be predicted priorto applying EBIS to estimate body fluids. QC 20130917

Applications based on measurements of Electrical Bioimpedance Spectrocopy (EBIS) analysis are proliferating. The most spread and known application of EBIS is the non-invasive assessment of body composition. Fitting to the Cole function to obtain the Cole parameters, R0 and R∞, is the core of the EBIS analysis to obtain the body fluid distribution. An accurate estimation of the Cole parameters is essential for the Body Composition Assessment (BCA) and the estimation process depends on several factors. One of them is the upper frequency limit used for the estimation and the other is the number of measured frequencies in the measurement frequency range. Both of them impose requirements on the measurement hardware, influencing largely in the complexity of the bioimpedance spectrometer. In this work an analysis of the error obtained when estimating the Cole parameters with several frequency ranges and different number of frequencies has been performed. The study has been done on synthetic EBIS data obtained from experimental Total Right Side (TRS) measurements. The results suggest that accurate estimations of R0 and R∞ for BCA measurements can be achieved using much narrower frequency ranges and quite fewer frequencies than electrical bioimpedance spectrometers commercially available nowadays do.

Very often in Electrical Bioimpedance (EBI) spectroscopy measurements the presence of stray capacitances creates a measurement artefact commonly known as Hook Effect . Such an artefact creates a hook-alike deviation of the EBI data noticeable when representing the measurement on the impedance plane. Such Hook Effect is noticeable at high frequencies but it also causes a data deviation at lower measurement frequencies. In order to perform any accurate analysis of the EBI spectroscopy data, the influence of the Hook Effect must be removed. An established method to compensate the hook effect is the well known Td compensation , which consists on multiplying the obtained spectrum, Z meas (ω) by a complex exponential in the form of exp[jωTd]. Such a method cannot correct entirely the Hook Effect since the hook-alike deviation occurs a broad frequency range in both magnitude and phase of the measured impedance, and by using a scalar value for Td . First a scalar only modifies the phase of the measured impedance and second, a single value can truly corrects the Hook Effect only at a single frequency. In addition, the process to select a value for the scalar Td by an iterative process with the aim to obtain the best Cole fitting lacks solid scientific grounds. In this work the Td compensation method is revisited and a modified approach for correcting the Hook Effect including a novel method for selecting the correcting values is proposed. The initial validation results confirm that the proposed method entirely corrects the Hook Effect at all frequencies. QC 20120206

Projecte realitzat mitjançant programa de mobilitat 2011. [ANGLÈS] The electrical Bioimpedance (EBI) has become very useful for many different clinical applications. EBI measurements may contain artifacts that can lead to errors which have to be analyzed. It has to be added to the already known capacitive leakage artifact caused by a parasitic capacitance, other effects, between them can be remarked the electrode polarization impedance effect, especially when there is electrode imbalance. In this work is developed a software tool in Wolfram Mathematica environment, this tool will help to the evaluation of EBIS measurements realized in non-ideal conditions through EBIS measurements modeling. As an example of application, the effects produced by the electrode polarization impedance together with the parasitic capacitance artifacts over the estimation of the Cole parameters were analyzed. The tool will make able to identify errors in real measurements. [CASTELLÀ] La bioimpedancia eléctrica (EBI) ha ido cogiendo mayor importancia para muchas aplicaciones clínicas. Las mediciones EBI pueden contener componentes que pueden llevar a errores que han de ser analizados. Tiene que ser añadido al error por componente capacitiva (capacitive leakage artifact) ya conocido causado por una capacidad parásita, otros efectos, entre ellos se puede notar el efecto del electrodo de polarización de la impedancia (electrode polarization impedance effect). En este trabajo se ha desarrollado una herramienta de software en el entorno de Wolfram Mathematica, esta herramienta ayudará a la evaluación de las mediciones realizadas en condiciones EBIS no ideales a través del modelado de mediciones EBIS. Como un ejemplo de aplicación se analizan los efectos producidos por la impedancia del electrodo de polarización junto con los errores producidos por la capacitadad parásita con de la estimación de los parámetros Cole. El objetivo de la aplicación es identificar los errores en mediciones reales. [CATALÀ] La bioimpedància elèctrica (EBI) ha anat agafant més importància per a moltes aplicacions clíniques. Les mesures EBI inclouen components que poden induir a errors que han de ser analitzats. Ha de ser afegit a l'error per la component capacitiva (capacitive leakage artifact) ja conegut causat per una capacitat paràsita, altres efectes, entre ells es pot notar l'efecte de l'elèctrode de polarització de la impedància (electrode Polarization impedance effect). En aquest treball s'ha desenvolupat una eina de software en l'entorn de Wolfram Mathematica. Aquesta eina ajudarà a l'avaluació de mesures realitzats en condicions EBIS no ideals a través del modelatge de mesures EBIS. Com un exemple d'aplicació s'analitzen els efectes produïts per la impedància de l'elèctrode de polarització juntament amb els errors produïts per la capacitadad paràsita amb de l'estimació dels paràmetres Cole. L'objectiu de l'aplicació és identificar els errors en mesures reals.