A Feasibility Study of the Suitability of an AD5933-based Spectrometer for EBI Applications

Projecte final de carrera realitzat en col.laboració amb University of BoräsElectrical Bioimpedance (EBI) measurements have proven their validity in several medical applications like body composition analysis and detection of melanoma among others. The successful application of EBI technology on the field of medicine has lead the way for applications in the field of personal healthcare and body performance in the field of sports. Due to the widespread use of the EBI technology and rising of new EBI applications requiring system portability or even suitable to wear, the manufacturer Analog devices has introduced in the market the first integrated system dedicated to measure EBI, the impedance network analyzer AD5933. The availability of this EBI spectrometer device opens up new horizons for the integration of the measurement systems to meet the demands of new EBI applications and allowing the development of portable and even wearable measurement systems. This project is focused on the AD5933 impedance network analyzer, and it aims to identify the EBI applications in which, the use of an AD5933 device is suitable. To adapt the AD5933 device for biomedical measurements an Analog Front-End (AFE) has been used to enable the system for 4-electrodes measurements. In order to evaluate the performance of AD5933 with the AFE, experimental measurements on electrical equivalent models have been taken with the AD5933+4E-AFE system and the EBI spectrometer Impedimed SFB7. The obtained impedance spectral data have been used to estimate the values of the equivalent circuit under measurement and the estimated values have been mutually compared in terms of estimation accuracy

Does performing moderate-to-vigorous physical activity in 12 to 24 hours prior Bioelectrical Impedance Analysis affects the validity of body water compartments assessment?

Purpose: One of the bioelectrical impedance spectroscopy (BIS) requirement is to avoid performing physical activity in the 12-24h prior measurement, which can be difficult in highly active populations. This investigation aimed: to examine if moderate to vigorous physical activity (MVPA) performed in 12-24h prior BIS testing, affects the validity of determining total body water (TBW), extracellular water (ECW) and intracellular water (ICW) using dilution techniques as the reference method. Methods: Twenty-seven healthy highly active males, aged 20 to 39 years (72.4 ± 8.7 Kg;1.77 ± 0.07 m) were evaluated. BIS and dilution techniques were used to assess TBW, ECW, and ICW. Pearson coefficient of correlation was used to analyze if MVPA was associated with the difference between methods for TBW, ECW, and ICW. Results: No significant differences between BIS and the dilution technique for TBW, ECW, and ICW volumes were observed (p>0.05). For all water compartments, no association was found between MVPA in the previous 12-24h with the differences between methods (p>0.05). Conclusion: This study showed that performing MVPA 12-24h prior measuring water compartments may not compromise a valid estimation of TBW, ECW, and ICW from BIS compared to dilution techniques. Indeed, the magnitude of the differences between methods in body water assessment was not related with the amount of MVPA performed by highly active adults.Objetivo: Um dos requisitos de bioimpedância elétrica por espectroscopia prende-se com evitar a prática de atividade física nas 12-24h antes da medição, o que pode ser difícil em populações altamente ativas. Esta investigação teve como objetivo: examinar se a atividade física moderada a vigorosa (AFMV) realizada entre 12-24h antes do teste de bioimpedância elétrica por espectroscopia afeta a validade da determinação da água corporal total (ACT), água extracelular (AEC), e água intracelular (AIC) usando técnicas de diluição como o método de referência. Métodos: Foram avaliados vinte e sete homens saudáveis, altamente ativos, com idades entre os 20 e os 39 anos (72,4 ± 8,7Kg; 1,77 ± 0.07m). A bioimpedância elétrica por espectroscopia e as técnicas de diluição foram usadas para avaliar TBW, ECW e ICW. O coeficiente de correlação de Pearson foi usado para analisar se a AFMV estava associada à diferença entre os métodos para ACT, AEC e AIC. Resultados: Não foram observadas diferenças significativas entre a bioimpedância elétrica por espectroscopia e a técnica de diluição para os volumes ACT, AEC e AIC (p> 0,05). Para todos os compartimentos de água, não foi encontrada associação entre AFMV com as diferenças entre os métodos (p> 0,05). Conclusões: O presente estudo mostrou que a realização de AFMV 12-24h antes da medição dos compartimentos de água poderá não comprometer uma estimativa válida de ACT, AEC e AIC do BIS em comparação com as técnicas de diluição. De fato, a magnitude das diferenças entre os métodos na avaliação da água corporal não demonstrou associação com a quantidade de AFMV realizada por adultos altamente ativos

A Feasibility Study of the Suitability of an AD5933-based Spectrometer for EBI Applications

Projecte final de carrera realitzat en col.laboració amb University of BoräsElectrical Bioimpedance (EBI) measurements have proven their validity in several medical applications like body composition analysis and detection of melanoma among others. The successful application of EBI technology on the field of medicine has lead the way for applications in the field of personal healthcare and body performance in the field of sports. Due to the widespread use of the EBI technology and rising of new EBI applications requiring system portability or even suitable to wear, the manufacturer Analog devices has introduced in the market the first integrated system dedicated to measure EBI, the impedance network analyzer AD5933. The availability of this EBI spectrometer device opens up new horizons for the integration of the measurement systems to meet the demands of new EBI applications and allowing the development of portable and even wearable measurement systems. This project is focused on the AD5933 impedance network analyzer, and it aims to identify the EBI applications in which, the use of an AD5933 device is suitable. To adapt the AD5933 device for biomedical measurements an Analog Front-End (AFE) has been used to enable the system for 4-electrodes measurements. In order to evaluate the performance of AD5933 with the AFE, experimental measurements on electrical equivalent models have been taken with the AD5933+4E-AFE system and the EBI spectrometer Impedimed SFB7. The obtained impedance spectral data have been used to estimate the values of the equivalent circuit under measurement and the estimated values have been mutually compared in terms of estimation accuracy

Development of a capacitive bioimpedance measurement system

Bioelectrical impedance spectroscopy (BIS) is a well-established and non-invasive method to determine and monitor body composition. Commercially available bioelectrical impedance systems use coated hydrogel-aluminium electrodes, where the hydrogel acts as an adhesive and as an electrolytic medium. The gel/adhesive is physiologically inert over short periods. However, when used over longer periods, hydrogel-aluminium electrodes present limitations, which capacitive electrodes may overcome. First measurements using capacitive electrodes have shown that commercial devices are not designed to work with these kind of electrodes. The presented high impedance, specially at low frequencies (e.g. 5kHz), presents a challenge for the current injection and therefore for the design of the current source. Within this project, a bioimpedance spectroscopy (BIS) system to perform measurements using capacitive electrodes has been developed. The system has been tested in the critical frequency range, namely in the lower frequency range (5 kHz - 43 kHz). Measurements have been performed using dummy electrical models, which simulate di erent values of skin and electrode impedance. The results obtained show the better performance of the device in comparison to a commercial device (Xitron Hydra 4200, Xitron Technologies) for that frequency range. An important item in this thesis has been the design of a multi-frequency current source able to perform measurements using capacitive electrodes

A system to monitor segmental intracellular, interstitial, and intravascular volume and circulatory changes during acute hemodialysis

This paper describes a new combined impedance plethysmographic (IPG) and electrical bioimpedance spectroscopic (BIS) instrument and software that allows noninvasive real-time measurement of segmental blood flow and changes in intracellular, interstitial, and intravascular volumes during various fluid management procedures. The impedance device can be operated either as a fixed frequency IPG for the quantification of segmental blood flow and hemodynamics or as a multi-frequency BIS for the recording of intracellular and extracellular resistances at 40 discrete input frequencies. The extracellular volume is then deconvoluted to obtain its intra-vascular and interstitial component volumes as functions of elapsed time. The purpose of this paper is to describe this instrumentation and to demonstrate the information that can be obtained by using it to monitor segmental compartment volumes and circulatory responses of end stage renal disease patients during acute hemodialysis. Such information may prove valuable in the diagnosis and management of rapid changes in the body fluid balance and various clinical treatments

Development of a capacitive bioimpedance measurement system

Bioelectrical impedance spectroscopy (BIS) is a well-established and non-invasive method to determine and monitor body composition. Commercially available bioelectrical impedance systems use coated hydrogel-aluminium electrodes, where the hydrogel acts as an adhesive and as an electrolytic medium. The gel/adhesive is physiologically inert over short periods. However, when used over longer periods, hydrogel-aluminium electrodes present limitations, which capacitive electrodes may overcome. First measurements using capacitive electrodes have shown that commercial devices are not designed to work with these kind of electrodes. The presented high impedance, specially at low frequencies (e.g. 5kHz), presents a challenge for the current injection and therefore for the design of the current source. Within this project, a bioimpedance spectroscopy (BIS) system to perform measurements using capacitive electrodes has been developed. The system has been tested in the critical frequency range, namely in the lower frequency range (5 kHz - 43 kHz). Measurements have been performed using dummy electrical models, which simulate di erent values of skin and electrode impedance. The results obtained show the better performance of the device in comparison to a commercial device (Xitron Hydra 4200, Xitron Technologies) for that frequency range. An important item in this thesis has been the design of a multi-frequency current source able to perform measurements using capacitive electrodes

Towards wearable spectroscopy bioimpedance applications: power management for a battery driven impedance meter

Projecte realitat en col.laboració amb el centre Hogskolan i Boras (Suècia)In recent years, due to the combination of technological advances in the fields of measurement instrumentation, communications, home-health care and textile-technology the development of medical devices has shifted towards applications of personal healthcare. There are well known the available solutions for heart rate monitoring successfully provided by Polar and Numetrex. Furthermore new monitoring applications are also investigated. Among these non-invasive monitoring applications, it is possible to find several ones enable by measurements of Electrical Bioimpedance. Analog Devices has developed the AD5933 Impedance Network Analyzer which facilitates to a large extent the design and implementation of Electrical Bioimpedance Spectrometers in a much reduced space. Such small size allows the development of a fully wearable bioimpedance measurement. With the development of a Electrical Bioimpedance-enable wearable medical device in focus for personal healthcare monitoring, in this project, the issue of power management has been targeted and a battery-driven Electrical Bioimpedance Spectrometer based in the AD5933 has been implemented. The resulting system has the possibility to operate with a Li-Po battery with a power autonomy over 17 hours

A portable bioimpedance spectroscopy system for congestive heart failure management

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 139-149).Congestive Heart Failure (CHF) is a chronic medical condition that causes reduced exercise tolerance, shortness of breath, and fluid buildup in the lungs, legs, and abdomen. While CHF-related mortality has reduced in recent years, this reduction has been accompanied by an increase in hospitalizations and readmissions. This thesis takes the first steps toward developing a compression sock based bioimpedance monitoring system for patients with CHF to help reduce readmission rates. The primary goals of the thesis were to better understand the calf bioimpedance measurement in a controlled environment (hemodialysis) and to develop portable hardware to perform measurements. Calf bioimpedance was measured on 17 patients undergoing hemodialysis using both a commercial measurement system and the experimental system developed in this thesis. Measured calf bioimpedance data showed that more fluid is recruited from the calf at higher ultrafiltration rates. Fluid shifts into or out of cells also depended on the ultrafiltration rate. It was also observed that patients with high calf fluid overload accumulate fluid in the calf, rather than lose it. Bioimpedance measurements were also compared between the side of the leg and back of the leg. Changes in calf bioimpedance were higher on the back in 4/7 patients measured, suggesting that ideal electrode placement depends on the individual patient. Finally, a portable bioimpedance system was developed and verified against a commercial system on the bench and during hemodialysis. The two systems measured bioimpedance changes within 2 in most cases, with outliers limited to patients with particularly low calf bioimpedance. While the relationship between calf fluid status and total fluid status is complex, there is likely utility in calf bioimpedance measurements for CHF remote monitoring. In the ideal use case, patients will start out at dry weight and gain comparable amounts of fluid compared with the fluid removed during hemodialysis. This should result in measurable calf bioimpedance changes on the same order of those measured here. Additionally, rates of both fluid accumulation and removal will be an order of magnitude slower than hemodialysis, so volume compartments should be in equilibrium, unlike immediately following hemodialysis as was measured in this thesis.by Maggie Delano.Ph. D

Characterising fluid status, distribution and dynamics in haemodialysis patients to improve fluid management strategies

Both the removal of too much and the failure to remove enough fluid during haemodialysis are associated with morbidity and mortality. It has been suggested that bioimpedance measurements using the Body Composition Monitor (BCM) and relative blood volume (RBV) monitoring can improve fluid management. However, both lack a robust evidence base characterising measurements in the clinical setting. BCM measurements were made in healthy controls to characterise the effect of measuring outside standard conditions and were made alongside RBV measurements in haemodialysis cohorts with well-defined clinical characteristics that were perceived to influence BCM results. The results suggested that BCM protocols can be flexible regarding measurement paths and timing of measurement to ensure as many patients as possible can benefit from the technology. The observed tendency for patients with high body mass index (BMI) to finish dialysis fluid-depleted does not appear to be related to systematic bias in the BCM models, but to a greater tolerance of fluid removal. The tendency for elderly subjects to have a degree of excess fluid, as measured by BCM, does appear to be associated with changes in tissue hydration linked to sarcopenia. Standard measurements in patients with localised lower-limb oedema can lead to attempts to remove unrealistic fluid volumes and alternative paths can help optimise targets. Feasibility for a trial of interventions to promote fluid mobilisation from oedematous tissue was not demonstrated. Simultaneous use of RBV with BCM suggested that assumptions underlying current RBV shape analysis use for fluid management can be violated and that there is a need for further studies. BCM can be used across the haemodialysis population, but an understanding of its application in individuals with particular characteristics is essential. RBV provides complementary information to BCM but there is a need for re-evaluation of RBV interpretation, standardisation of measurement categorisation and development of intravascular volume measurements