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Altres ajuts: acords transformatius de la UAB Some inborn errors of metabolism and other diseases can result in increasing blood ammonium (hyperammonemia episodes), which can cause serious neurological complications in patients or even death. Early diagnosis, follow up and treatment are essential to minimize irreversible damages in brain. Currently, adequate analytical instrumentation for the necessary ammonium bedside determination is not available in all health centers but only in clinical laboratories of reference hospitals. We therefore have developed a low cost and portable potentiometric Point-of-Care microanalyzer (POC) to address this problem. It consists of a cyclic olefin copolymer-based microanalyzer, the size of a credit card and working in continuous flow, which integrates microfluidics, a gas-diffusion module and a potentiometric detection system. The analytical features achieved are a linear range from 30 to 1000 μmol L NH , a detection limit of 18 μmol L NH and a required sample volume of 100 μL, which comply with the medical requirements. Plasma and blood samples are analyzed with no significant differences observed between ammonium concentrations obtained with both the proposed microanalyzer and the reference method. This demonstrates the value of the developed POC for bedside clinical applications.

The phase angle is a versatile measurement to assess body composition, frailty and prognosis in patients with chronic diseases. In cirrhosis, patients often present alterations in body composition that are related to adverse outcomes. The phase angle could be useful to evaluate prognosis in these patients, but data are scarce. The aim was to analyse the prognostic value of the phase angle to predict clinically relevant events such as hospitalisation, falls, and mortality in patients with cirrhosis. Outpatients with cirrhosis were consecutively included and the phase angle was determined by electrical bioimpedance. Patients were prospectively followed to determine the incidence of hospitalisations, falls, and mortality. One hundred patients were included. Patients with phase angle ≤ 4.6° (n = 31) showed a higher probability of hospitalisation (35% vs 11%, p = 0.003), falls (41% vs 11%, p = 0.001) and mortality (26% vs 3%, p = 0.001) at 2-year follow-up than patients with PA > 4.6° (n = 69). In the multivariable analysis, the phase angle and MELD-Na were independent predictive factors of hospitalisation and mortality. Phase angle was the only predictive factor for falls. In conclusion, the phase angle showed to be a predictive marker for hospitalisation, falls, and mortality in outpatients with cirrhosis.

BACKGROUND Measurement of myocardial electrical impedance can allow recognition of infarct scar and is theoretically not influenced by changes in cardiac activation sequence, but this is not known. OBJECTIVES The objectives of this study were to evaluate the ability of endocardial electrical impedance measurements to recognize areas of infarct scar and to assess the stability of the impedance data under changes in cardiac activation sequence. METHODS One-month-old myocardial infarction confirmed by cardiac magnetic resonance imaging was induced in 5 pigs submitted to coronary artery catheter balloon occlusion. Electroanatomic data and local electrical impedance (magnitude, phase angle, and amplitude of the systolic-diastolic impedance curve) were recorded at multiple endocardial sites in sinus rhythm and during right ventricular pacing. By merging the cardiac magnetic resonance and electroanatomic data, we classified each impedance measurement site either as healthy (bipolar amplitude >= 1.5 mV and maximum pixel intensity = 40%). RESULTS A total of 137 endocardial sites were studied. Compared to healthy tissue, areas of infarct scar showed 37.4% reduction in impedance magnitude (P

Sport-related muscle injury classifications are based basically on imaging criteria such as ultrasound (US) and magnetic resonance imaging (MRI) without consensus because of a lack of clinical prognostics for return-to-play (RTP), which is conditioned upon the severity of the injury, and this in turn with the muscle gap (muscular fibers retraction). Recently, Futbol Club Barcelona's medical department proposed a new muscle injury classification in which muscle gap plays an important role, with the drawback that it is not always possible to identify by MRI. Localized bioimpedance measurement (L-BIA) has emerged as a non-invasive technique for supporting US and MRI to quantify the disrupted soft tissue structure in injured muscles. Objective: To correlate the severity of the injury according to the gap with the RTP, through the percent of change in resistance (R), reactance (Xc) and phase-angle (PA) by L-BIA measurements in 22 muscle injuries. Main results: After grouping the data according to the muscle gap (by MRI exam), there were significant differences in R between grade 1 and grade 2f (myotendinous or myofascial muscle injury with feather-like appearance), as well as between grade 2f and grade 2g (myotendinous or myofascial muscle injury with feather and gap). The Xc and PA values decrease significantly between each grade (i.e. 1 versus 2f, 1 versus 2g and 2f versus 2g). In addition, the severity of the muscle gap adversely affected the RTP with significant differences observed between 1 and 2g as well as between 2f and 2g. Significance: These results show that L-BIA could aid MRI and US in identifying the severity of an injured muscle according to muscle gap and therefore to accurately predict the RTP.

[EN] Actigraphy devices have been successfully used as effective tools in the treatment of diseases such as sleep disorders or major depression. Although several efforts have been made in recent years to develop smaller and more portable devices, the features necessary for the continuous monitoring of outpatients require a less intrusive, obstructive and stigmatizing acquisition system. A useful strategy to overcome these limitations is based on adapting the monitoring system to the patient lifestyle and behavior by providing sets of different sensors that can be worn simultaneously or alternatively. This strategy offers to the patient the option of using one device or other according to his/her particular preferences. However this strategy requires a robust multi-sensor fusion methodology capable of taking maximum profit from all of the recorded information. With this aim, this study proposes two actigraphy fusion models including centralized and distributed architectures based on artificial neural networks. These novel fusion methods were tested both on synthetic datasets and real datasets, providing a parametric characterization of the models' behavior, and yielding results based on real case applications. The results obtained using both proposed fusion models exhibit good performance in terms of robustness to signal degradation, as well as a good behavior in terms of the dependence of signal quality on the number of signals fused. The distributed and centralized fusion methods reduce the mean averaged error of the original signals to 44% and 46% respectively when using simulated datasets. The proposed methods may therefore facilitate a less intrusive and more dependable way of acquiring valuable monitoring information from outpatients., This work was partially funded by the European Commission: Help4Mood (Contract No. FP7-ICT-2009-4: 248765). E. FusterGarcia acknowledges Programa Torres Quevedo from Ministerio de Educacion y Ciencia, co-founded by the European Social Fund (PTQ-12-05693).

The Help4Mood EU FP7 project (H4M) [1] proposes to significantly advance the state-ofthe-art in computerized support for people with Major Depression by monitoring mood, physical activity and voice characteristics while promoting activities in reaction to examined inputs. Employing actigraphy can provide supplementary data about patients with depression. Nonetheless, its use is not standardized and there is a lack of public analyses about treated patients with depression using this technique, which is the objective of the project. The purpose of the Personal Monitoring System (PMS) used in H4M is to compile objective data about the changes and trends of activity patterns during long periods of time. This would comprise daily activity, rest time and, if possible, sleep quality. The PMS uses inconspicuous methods but keeping the cost associated with sensor installation at the patient¿s home to a minimum. This work focuses on the Wireless Sensor Network (WSN) enhancements introduced after real testbeds and considering User Quality of Experience (QoE), mainly oriented to reduce energy consumption and required data transmission and consequently improving the autonomy and range of the sensors.

A major challenge of cardiac tissue engineering is directing cells to establish the physiological structure and function of the myocardium being replaced. Our aim was to examine the effect of electrical stimulation on the cardiodifferentiation potential of cardiac adipose tissue-derived progenitor cells (cardiac ATDPCs). Three different electrical stimulation protocols were tested; the selected protocol consisted of 2 ms monophasic square-wave pulses of 50 mV/cm at 1 Hz over 14 days. Cardiac and subcutaneous ATDPCs were grown on biocompatible patterned surfaces. Cardiomyogenic differentiation was examined by real-time PCR and immunocytofluorescence. In cardiac ATDPCs, MEF2A and GATA-4 were significantly upregulated at day 14 after stimulation, while subcutaneous ATDPCs only exhibited increased Cx43 expression. In response to electrical stimulation, cardiac ATDPCs elongated, and both cardiac and subcutaneous ATDPCs became aligned following the linear surface pattern of the construct. Cardiac ATDPC length increased by 11.3%, while subcutaneous ATDPC length diminished by 11.2% (p = 0.013 and p = 0.030 vs unstimulated controls, respectively). Compared to controls, electrostimulated cells became aligned better to the patterned surfaces when the pattern was perpendicular to the electric field (89.71 ± 28.47o for cardiac ATDPCs and 92.15 ± 15.21o for subcutaneous ATDPCs). Electrical stimulation of cardiac ATDPCs caused changes in cell phenotype and genetic machinery, making them more suitable for cardiac regeneration approaches. Thus, it seems advisable to use electrical cell training before delivery as a cell suspension or within engineered tissue.

Injuries to lower limb muscles are common among football players. Localized bioimpedance analysis (BIA) utilizes electrical measurements to assess soft tissue hydration and cell membrane integrity non-invasively. This study reports the effects of the severity of muscle injury and recovery on BIA variables. We made serial tetra-polar, phase-sensitive 50 kHz localized BIA measurements of quadriceps, hamstring and calf muscles of three male football players before and after injury and during recovery until return-to-play, to determine changes in BIA variables (resistance (R), reactance (Xc) and phase angle (PA)) in different degrees of muscle injury. Compared to non-injury values, R, Xc and PA decreased with increasing muscle injury severity: grade III (23.1%, 45.1% and 27.6%), grade II (20.6%, 31.6% and 13.3%) and grade I (11.9%, 23.5% and 12.1%). These findings indicate that decreases in R reflect localized fluid accumulation, and reductions in Xc and PA highlight disruption of cellular membrane integrity and injury. Localized BIA measurements of muscle groups enable the practical detection of soft tissue injury and its severity.

In the present work, electrical impedance spectroscopy (EIS) measurements were performed during electroporation of C2C12 cells monolayers. The measuring strategy, based on multisine excitations, allows acquiring full impedance spectra at a rate of 1 spectrum/ms during the interval between pulses of a traditional electroporation treatment. The multifrequency information provided by the measuring system was then studied using models. In this study, the Cole model and an electrical equivalent circuit were used. The results show the ability of the system for monitoring the fast impedance dynamics of cells during electroporation. The differences in the information shown at different frequencies suggest the ability of the system to measure different phenomena at the same time, namely: membrane changes and medium conductivity variations. The use of the Cole model reveals the need of more complex models to correctly separate and interpret the results. The use of the proposed circuital model enables studying the dynamics of pore formation independently of the conductivity variations. This work confirms the advantages of performing EIS measurements in order to have a more complete snapshot of the system behavior.

Myocardial electrical impedance is influenced by the mechanical activity of the heart. Therefore, the ischemia-induced mechanical dysfunction may cause specific changes in the systolic-diastolic pattern of myocardial impedance, but this is not known. This study aimed to analyze the phasic changes of myocardial resistivity in normal and ischemic conditions. Myocardial resistivity was measured continuously during the cardiac cycle using 26 different simultaneous excitation frequencies (1 kHz–1 MHz) in 7 anesthetized open-chest pigs. Animals were submitted to 30 min regional ischemia by acute left anterior descending coronary artery occlusion. The electrocardiogram, left ventricular (LV) pressure, LV dP/d t, and aortic blood flow were recorded simultaneously. Baseline myocardial resistivity depicted a phasic pattern during the cardiac cycle with higher values at the preejection period (4.19 ± 1.09% increase above the mean, P < 0.001) and lower values during relaxation phase (5.01 ± 0.85% below the mean, P < 0.001). Acute coronary occlusion induced two effects on the phasic resistivity curve: 1) a prompt (5 min ischemia) holosystolic resistivity rise leading to a bell-shaped waveform and to a reduction of the area under the LV pressure-impedance curve (1,427 ± 335 vs. 757 ± 266 Ω·cm·mmHg, P < 0.01, 41 kHz) and 2) a subsequent (5–10 min ischemia) progressive mean resistivity rise (325 ± 23 vs. 438 ± 37 Ω·cm at 30 min, P < 0.01, 1 kHz). The structural and mechanical myocardial dysfunction induced by acute coronary occlusion can be recognized by specific changes in the systolic-diastolic myocardial resistivity curve. Therefore these changes may become a new indicator (surrogate) of evolving acute myocardial ischemia.

This paper describes a multi-frequency single-channel electrical implantable bioimpedance monitor (35 mm × 35 mm × 10 mm, weight 52 g) powered by a NiMH battery. By using the tetrapolar method and injecting 10 µA(peak), the monitor is capable of measuring at 14 different frequencies, from 100 Hz to 200 kHz. It contains a ZigBee transceiver to monitor the measurements performed, and has an embedded memory for backing up the data. RC networks and in-situ heart excised tissues were used to test the system. When measuring a full spectrum every 5 min, 35 days of autonomy are possible due to the low power consumption of the monitor. Temperature drift was estimated by short-term and long-term measurements. Temperature cycling was used to measure modulus and phase angle stability. The result was a very low effect on a modulus decrease of 2.34 Ω, with respect to an impedance of 322 Ω, at 100 Hz and a phase angle increase of 1.1°, at 200 kHz. In addition, measurement errors were bigger at low frequencies because of the high impedance of the electrodes used, which was higher than 10 kΩ at frequencies below 1 kHz.

The relation between the right-side (RS) electrical impedance phase angle (PA) and segmental PA in five configurations at 50 kHz was analyzed in 23 peritoneal dialysis male patients before complete drainage of the abdominal cavity. The impedance vector (Z/H) components were standardized by the height H of the subjects (R/H and Xc/H). BIVA software was used to analyze the individual RS vector. The Pearson correlation was used to analyze the correlation between RS and segmental configurations. Student's t test and Hotelling's T2 test were used to analyze the separation of groups obtained by BIVA. The highest significant Pearson correlation was between RS and right leg total (RLEGT) in a longitudinal direction (r = 0.925, P < 0.001). We obtained a significant difference (P < 0.05) in R/H, Xc/H (for RS and RLEGT) using Hotelling's T2 test, and in PA using Student's t test. The transverse measurement in the leg (RTRLEG) showed the lowest correlation (r = 0.261). In conclusion, we can obtain similar information through the phase angle, whether RS is measured or if we measure on RLEGT. The phase angle of the transverse measurements provides different information from the phase angle of the longitudinal measurements.

In this study, electrical impedance spectroscopy measurements are performed during electroporation of monolayers of differentiated myotubes. The time resolution of the system (1 spectrum/ms) enable 860 full spectra (21 frequencies from 5 kHz to 13 MHz) to be acquired during the time gap between consecutive pulses (interpulse) of a classical electroporation treatment (8 pulses, 100 mu s, 1 Hz). Additionally, the characteristics of the custom microelectrode assembly used allow the experiments to be performed directly in situ in standard 24 multi-well plates. The impedance response dynamics are studied for three different electric field intensities (400, 800 and 1200 V/cm). The multifrequency information, analysed with the Cole model, reveals a short-term impedance recovery after each pulse in accordance with the fast resealing of the cell membrane, and a long-term impedance decay over the complete treatment in accordance with an accumulated effect pulse after pulse. The analysis shows differences between the lowest electric field condition and the other two, suggesting that different mechanisms that may be related with the reversibility of the process are activated. As a result of the multifrequency information, the system is able to measure simultaneously the conductivity variations due to ion diffusion during electroporation. Finally, in order to reinforce the physical interpretation of the results, a complementary electrical equivalent model is used.

Localized bioimpedance (BIA) was measured with a single frequency phase-sensitive analyzer at 50 kHz in three post-traumatic types of injuries on four professional soccer players: (1) myositis ossificans, (2) intramuscular seroma and (3) trochanteric (hip) bursitis. Normal reference value (no injury) was obtained from the contra lateral not injured limb at a mirror-like location of the injury. The relative variations resistance (R) and reactance (Xc) at the time of injury was confronted with the not injured values. Relative variations between acute measurements and post medication ones on intramuscular seroma and bursitis have been computed. In intramuscular seroma and trochanteric bursitis we have obtained a percent of change between injury data and after medical intervention. On myositis ossificans, localized BIA showed a 7-8 % decrease in Xc whereas the percent of change of R was negligible (1 %). These percent of changes are in concordance with histological evidence. In the case of a presence of seroma or the lower thigh and trochanteric bursitis, the soft tissue cavity accumulates fluid. Post-injury localized BIA, relative with respect to non-injured side, confirmed sizeable soft tissue destruction evidenced by 50 % decrease of Xc and 24-31 % decrease of R due to interstitial fluid accumulation. Once the seroma and the blood in the bursitis was removed the localized the immediate post-injury BIA parameters increased as follows: a) intramuscular seroma + 10 % on R and + 74 % of Xc; b) trochanteric bursitis + 20 % of R and +24 % of Xc. Localized BIA other than classifying soft tissue injuries, can be useful to understand the pathophysiology and structural impairments of other kind of injuries and to understand their behavior. Language: en

The whole body bioimpedance technique is a highly promising non-invasive, reproducible, fast and inexpensive bed-side method for monitoring hydration status. Using segmental bioimpedance measurements, it is possible to obtain information about the fluid change in each body segment (Song, Lee, Kim and Kim 1999 Perit. Dial. Int. 19 386-90). In this pilot study we have measured 25 male patients (30-65 yr, BMI 20-32 kg m(-2)) undergoing continuous ambulatory peritoneal dialysis (CAPD). Tetrapolar impedance measurements were obtained using the right-side technique (whole body), and a segmental impedance method focused in the thorax region. Blood pressure (BP) measurements were taken manually with a sphygmomanometer. Patients were classified as either stable (group 0) or unstable (group 1) using clinical parameters of overall cardiovascular risk. The Mahalanobis distance (dM2) was calculated for the mean blood pressure (BP(mean)), and the impedance parameter R normalized by body height H for the right-side (R(RS)/H) and the thorax segment (R(TH)/H). Differences between groups were significant (p0.0001) for R(TH)/H and for BP(mean), and less significant (p = 0.016) for R(RS)/H. Group 1 patients showed a small dM2 as compared with a reference patient (a critical patient with acute lung edema) with high BP(mean) and low values of R(TH)/H and R(RS)/H. Moreover, Group 0 patients showed a larger dM2 with respect to the reference patient, with lower BP(mean) and higher values of R(TH)/H and R(RS)/H. All patients classified as unstable by clinical assessment were correctly classified using R(TH)/H in conjunction with BP(mean) using dM2. Segmental-monofrequency non-invasive bioimpedance of the thoracic region could provide a simple, objective non-invasive method of support for facilitating the clinical assessment of CAPD patients.

a ICREC Research Group, Health Research Institute Germans Trias i Pujol, Badalona, Spain b Department of Electronic Engineering, Technical University of Catalonia, Barcelona, Spain c Cardiology Service, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain d Cardiology Service, Hospital Universitari Germans Trias i Pujol, Badalona, Spain e Department of Medicine, Universitat Autonoma de Barcelona, Barcelona, Spain

In this study, a new microelectrode assembly based on spiral geometry applicable to in situ electroporation of adherent cell monolayers on standard multiwell plates is presented. Furthermore, the structure is specially conceived to perform electrical impedance spectroscopy (EIS) measurements during electroporation. Its performance for cell membrane permeabilization is tested with a fluorescent probe. Gene electrotransfer is also assayed using a plasmid DNA encoding GFP in four different cell lines (CHO, HEK293, 3T3-L1 and FTO2B). Additionally, siRNA alpha-GFP electrotransfection is tested in GFP gene-expressing CHO cells. Our data show considerable differences between permeabilization and gene transfer results and cell line dependence on gene expression rates. Successful siRNA electro-mediated delivery is also achieved. We demonstrate the applicability of our device for electroporation-mediated gene transfer of adherent cells in standard laboratory conditions. Finally, electrical impedance measurements during electroporation of CHO and 3T3-L1 cells are also given.

The optimal cell lineage for cardiac-regeneration approaches remains mysterious. Additionally, electrical stimulation promotes cardiomyogenic differentiation of stimulated cells. Therefore, we hypothesized that electrical conditioning of cardiomyocyte progenitor cells (CMPCs) might enrich their cardiovascular potential. CMPCs were isolated from human adult atrial appendages, characterized, and electrically stimulated for 7 and 14 days. Electrical stimulation modulated CMPCs gene and protein expression, increasing all cardiac markers. GATA-binding protein 4 (GATA4) early transcription factor was significantly overexpressed (P = 0.008), but also its coactivator myocyte enhancer factor 2A (MEF2A) was upregulated (P = 0.073) under electrical stimulation. Moreover, important structural proteins and calcium handling-related genes were enhanced. The cardioregeneration capability of CMPCs is improved by electrical field stimulation. Consequently, short-term electrical stimulation should be a valid biophysical approach to modify cardiac progenitor cells toward a cardiogenic phenotype, and can be incorporated into transdifferentiation protocols. Electrostimulated CMPCs may be best-equipped cells for myocardial integration after implantation. Electronic supplementary material The online version of this article (doi:10.1186/scrt482) contains supplementary material, which is available to authorized users.

In this study, in situ electroporation is applied to adherent cell monolayers growing on standard multiwell plates. A new microelectrode assembly based on spiral geometry and fabricated using standard PCB tecnology with slight modifications is used. The system was tested in the electroporation of two different cell lines (CHO and HEK 293). A fluorescent probe was initially used to test the extent of permeabilization and adjust experimental conditions. Subsequently, plasmid DNA encoding green fluorescent protein (GFP) was transfered by electroporation. Together with these experiments, cell viability was studied. We show for permeabilization experiments up to 70 % of fluorescent cells detected in both cells lines. Successful gene electrotransfer was obtained with more than 9 % and 15 % for CHO and HEK 293 respectively. In this work we prove how our device can be used for electroporation of adherent cells under the same standard laboratory conditions as regular biochemical treatments.

Magnetic induction (MI) measurement technique could provide an unobtrusive contactless method for continuous monitoring of vital signs such as breathing and cardiac activity in bed. In this paper, we present a magnetic induction system to evaluate the feasibility of monitoring heart and lung activity and the preliminary measurement results. The excitation and detection coils are designed to be implemented in a single printed circuit board, allowing the use of the system in a bed with coils under the mattress. The electronic system is based on a 16 bit arbitrary waveform generator (PXI-5422, National instrument) operating at a sample rate of 200 MS/s for the excitation signal and the detected amplified signal is then, sampled at 100 MS/s by a 14 bit digitizer (PXI-5122, National Instruments). The preliminary results at 10 MHz show the ability of the system to detect solutions with different conductivities. However the capacitive effect is in the same order of magnitude as the inductive effect due to eddy currents. Safety of the system has been evaluated to be in accordance with the standards of human exposure to the magnetic fields.

Physical activity (PA) has been identified as a key health indicator and has been assessed in multiple studies as the study of cardiovascular diseases, diabetes mellitus, obesity and psychological conditions. For this reason the use of accelerometers to quantify PA is widely accepted in either clinical/laboratory settings as well as in freeliving environments. The use of accelerometers in the measurement of PA is a relatively new technique and, therefore, has been not standardized. The aim of this work is to study the influence of signal processing stages in the estimation of PA while measuring simultaneously in three different sites to provide robust indicators of activity in front of changes in site measurement. With our measurement we show that a proper choice of signal processing steps can improve the agreement among activity indices measured from different sites on the same individual. The results also show that the most suited index is the time above threshold. In this case, the best combination of axes is by applying the quadratic mean, the best filtering of axes is using a cut-off frequency of around 1.5 Hz and a threshold to compute the index of 0.04 g.

Monitoring people during sleep time is of particular interest to patients with sleep disorders and elderly people or infants. We have developed a battery powered electronic system to monitor people in the bed, store the data and send them through a wireless link to a PC. The resulting data will be subject to further analysis using pattern recognition to evaluate the feasibility of using the system as an indicator of sleep quality. The system is able to detect presence on the bed and movements and breathing of the patient. The changes in pressure distribution on the mattress cause changes in pressure in the layers of the sensor and a voltage will appear on the electrodes. The detection ability depends strongly on the shape of the mattress and the bedbase.

Measurements of myocardium tissue impedance during the cardiac cycle have information about the morphology of myocardium cells as well as cell membranes and intra/extra cellular spaces. Although the variation with time of the impedance cardiac signal has information about the myocardium tissue activity during the cardiac cycle, this information has been usually underestimated in the studies based on frequency-sweep Electrical Impedance Spectroscopy (EIS) technique. In these cases, the dynamic behavior was removed from the impedance by means of averaging. The originality of this research is to show the time evolution of in-vivo healthy myocardium tissue impedance during the cardiac cycle, being measured with a multisine excitation at 26 frequencies (1 kHz-1 MHz). The obtained parameters from fitting data to a Cole model are valid indicators to explain the time relation of the systolic and diastolic function with respect to the myocardium impedance time variation. This paper presents a successful application of broadband Impedance Spectroscopy for time-varying impedance monitoring. Furthermore, it can be extended to understand various unsolved problems in a wide range of biomedical and electrochemical applications, where the system dynamics are intended to be studied.

Previous studies demonstrate that it is possible to evaluate a heart graft rejection condition using a bioimpedance technique by means of an intracavitary catheter. We propose to use a less invasive technique consisting in the use of a transoesophageal catheter and two standard ECG electrodes on the thorax. The aim of this work is to evaluate, using the finite element method, several parameters affecting the transoesophageal impedance measurement, including sensitivity to electrical conductivity and permittivity of different organs in the thorax, changes in magnitude and phase due to a lesion producing a scar, a global ischaemia of the heart, pleural effusion in the lungs, fat thickness increase, displacement of the catheter inside the oesophagus and movement of one electrode on the thorax surface. From these results, we deduce the best estimator for cardiac rejection detection and obtain the tools to identify eventual cases of false positives due to other factors. To achieve these objectives we have created a thoracic model and we have simulated different situations at the frequencies of 13, 30, 100, 300 and 1000 kHz. Our simulation demonstrates that the phase, at 100 and 300 kHz, would be a better estimator than the magnitude to evaluate a heart rejection condition.

Heart Failure (HF) is a clinical syndrome characterised by signs of systemic and pulmonary fluid retention, shortness of breath and/or fatigue. There is a lack of reliable indicators of disease state. Benefits and applicability of non-invasive bioimpedance measurement in the hydration state of soft tissues have been validated, fundamentally, in dialysis patients. Four impedance configurations (2 longitudinal and 2 transversal) were analyzed in 48 HF patients (M=28, F=20) classified according to a clinical disease severity score (CDSS) derived from the Framingham criteria: CDSS􀂔2 (G1: M= 23, F= 14) and CDSS>2 (G2: M= 5, F= 6). The aim of this study is to analyze longitudinal and transversal bioimpedance measurement at 50 kHz, in addition to clinical diagnosis parameters of heart failure, including: clinical disease severity score (CDSS) and a biomarker concentrations (NTproBNP). The Kolmogorov-Smirnov test was used for the normality test of all variables. The CDSS, NTproBNP and impedance parameters between groups (G1 and G2) were compared by mean of Mann Withney U-test. The statistical significance was considered with P < 0.05. Whole-body impedance measured was analyzed using RXc graph.

More relevant information of the fluid changes in peritoneal dialysis (PD) might be obtained with segmental bioimpedance measurements rather than whole-body measurement, who hidden information of body composition. Whole-body and segmental bioimpedance measurements were obtained using 5 configurations (whole-body or right-side (RS), longitudinal-leg (L-LEG), longitudinal-abdomen (L-AB), transversal-abdomen (T-AB), and transversal-leg (T-LEG)) in 20 patients: 15 males (56.5 ± 9.4 yr, 24.2 ± 4.2 kg/m2) and 5 females (58.4 ± 7.1 yr, 28.2 ± 5.9 kg/m2) in peritoneal dialysis (PD). The aim of this study is to analyze the relationship between whole-body, longitudinal-segmental (L-LEG and L-AB) and transversal-segmental (TAB and TLEG) bioimpedance measurement at 50 kHz, with clinical parameters of cardiovascular risk, dyslipidemia, nutrition and hydration. The Kolmogorov- Smirnov test was used for the normality test of all variables. Longitudinal bioimpedance parameters were normalized by the height of the patients. The Spearman correlation was used to analyze the correlation between bioimpedance and clinical parameters. The statistical significance was considered with P < 0.05. Transversal bioimpedance measurements have higher correlation with clinical parameters than longitudinal measurements.

Previous studies have proved that posttransplant cardiac rejection is associated with changes in endomyocardial electrical impedance in humans. The aim of this study is to develop a safe transoesophageal system able to measure cardiac electrical impedance in transplanted patients and to evaluate the capability of this technique to detect heart graft rejection in humans in order to reduce the number of repetitive biopsies. The impedance measurement is performed using a four wire configuration. We measured the impedance spectrum from 13 kHz to 1 MHz. The oesophageal ECG signal is used to evaluate the position of the catheter in the oesophagus with regard to the patient’s heart. So far measurements have been carried out on a group composed of 11 healthy volunteers (5 men) and 9 cardiac transplanted patients (7 men) with no histological signs of cardiac rejection. Impedance spectrum measurements at different locations in the oesophagus showed a decrease of the impedance magnitude with the increase of the depth of the catheter in the oesophagus (about 1 ohm/cm). The phase value does not show significant changes when changing the catheter’s position in the oesophagus. There are gender differences in the magnitude but not in the phase angle of the transoesophageal cardiac electrical impedance. Transplanted patients with no graft rejection show impedance values similar to that of healthy volunteers, suggesting that the surgical intervention does not affect the impedance measures. The oesophageal approach is safe and was considered for transplanted patients less annoying than the biopsy method. In consequence, if further results show a significant change of impedance in patients with cardiac rejection, a new lessinvasive clinical method to detect graft rejection can be envisaged.

Previous studies have proved that a heart infarction produces an electrical impedance change in the ischemic area that could be measured with four electrodes inserted in the tissue. Our objective is to evaluate the feasibility of detecting the changes of the ischemic area with a less invasive technique based on a esophageal probe. A further objective is to demonstrate the capability of this technique to detect heart graft rejection in humans to avoid repetitive biopsies. Impedance measurement is performed using a four electrode method. Current is injected between the distal electrode of the esophageal probe and one pregeled electrode on the thorax. Voltage measurement is taken between the proximal electrode of the probe and another electrode on the thorax. We used a custom system based on an optically isolated patient interface that acquires two ECG channels (standard I derivation and a unipolar esophageal derivation) and electrical impedance. After isolation, the raw impedance signals are digitalized and processed to calculate impedance magnitude and phase angle. Impedance measurements are taken between 10 kHz and 1 MHz. The ischemia was produced in animals using a balloon inflated in the Left Anterior Descending artery. We compared different probes in animals and selected the one with the greatest stability, showing lower electrode impedance and fewer motion artifacts due to esophagus contractions. The resolution of the designed system is not enough to detect the changes produced by ischemia on the tissue impedance when the ischemic area is small, however the death of the animal produces a significant change in the measured impedance. Nevertheless, the detection of a global change of the myocardial tissue, like the one produced by a heart rejection in transplanted patients, could not be discarded

The purpose of this study is to compare measurement errors in two commercially available multi-frequency bioimpedance analyzers, a Xitron 4000B and an ImpediMed SFB7, including electrode impedance mismatch. The comparison was made using resistive electrical models and in ten human volunteers. We used three different electrical models simulating three different body segments: the right-side, leg and thorax. In the electrical models, we tested the effect of the capacitive coupling of the patient to ground and the skin–electrode impedance mismatch. Results showed that both sets of equipment are optimized for right-side measurements and for moderate skin–electrode impedance mismatch. In right-side measurements with mismatch electrode, 4000B is more accurate than SFB7. When an electrode impedance mismatch was simulated, errors increased in both bioimpedance analyzers and the effect of the mismatch in the voltage detection leads was greater than that in current injection leads. For segments with lower impedance as the leg and thorax, SFB7 ismore accurate than 4000B and also shows less dependence on electrode mismatch. In both devices, impedance measurements were not significantly affected (p > 0.05) by the capacitive coupling to ground.

Background Monitoring of post-transplant heart rejection is currently based on endomyocardial biopsy analysis. This study aimed to assess the effects of heart graft rejection on myocardial electrical impedance. Methods and results Twenty-nine cardiac transplant patients and 9 controls underwent measurement of myocardial electrical impedance using a specifically designed amplifying system. The module and phase angle of myocardial impedance were measured. Histopathological rejection grading was performed according to ISHLT classification. Fifty impedance tests were performed in transplanted patients. Myocardial impedance (Z) was higher in controls than in transplanted patients (p

Magnetic induction tomography (MIT) is a low-resolution imaging modality for reconstructing the changes of the complex conductivity in an object. MIT is based on determining the perturbation of an alternating magnetic field, which is coupled from several excitation coils to the object. The conductivity distribution is reconstructed from the corresponding voltage changes induced in several receiver coils. Potential medical applications comprise the continuous, non-invasive monitoring of tissue alterations which are reflected in the change of the conductivity, e.g. edema, ventilation disorders, wound healing and ischemic processes. MIT requires the solution of an ill-posed inverse eddy current problem. A linearized version of this problem was solved for 16 excitation coils and 32 receiver coils with a model of two spherical perturbations within a cylindrical phantom. The method was tested with simulated measurement data. Images were reconstructed with a regularized single-step Gauss–Newton approach. Theoretical limits for spatial resolution and contrast/noise ratio were calculated and compared with the empirical results from a Monte-Carlo study. The conductivity perturbations inside a homogeneous cylinder were localized for a SNR between 44 and 64 dB. The results prove the feasibility of difference imaging with MIT and give some quantitative data on the limitations of the method.

We developed a 14-channel multifrequency magnetic induction tomography system (MF-MIT) for biomedical applications. The excitation field is produced by a single coil and 14 planar gradiometers are used for signal detection. The object under measurement was rotated (16 steps per turn) to obtain a full data set for image reconstruction. We make measurements at frequencies from 50 kHz to 1 MHz using a single frequency excitation signal or a multifrequency signal containing several frequencies in this range. We used two acquisition boards giving a total of eight synchronous channels at a sample rate of 5 MS s(-1) per channel. The real and imaginary parts of DeltaB/B(0) were calculated using coherent demodulation at all injected frequencies. Calibration, averaging and drift cancellation techniques were used before image reconstruction. A plastic tank filled with saline (D = 19 cm) and with conductive and/or paramagnetic perturbations was measured for calibration and test purposes. We used a FEM model and an eddy current solver to evaluate the experimental results and to reconstruct the images. Measured equivalent input noise voltage for each channel was 2 nV Hz(-1/2). Using coherent demodulation, with an integration time of 20 ms, the measured STD for the magnitude was 7 nV(rms) (close to the theoretical value only taking into account the amplifier's thermal noise). For long acquisition times the drift in the signal produced a bigger effect than the input noise (typical STD was 10 nV with a maximum of 35 nV at one channel) but this effect was reduced using a drift cancellation technique based on averaging. We were able to image a 2 S m(-1) agar sphere (D = 4 cm) inside the tank filled with saline of 1 S m(-1).

Our objective is to evaluate whether it is possible to characterize the passive electrical properties of myocardial tissue in contact with the electrocatheters used in arrhythmia diagnosis or radio frequency ablation techniques. To characterize the tissue, we propose the use of electrical impedance spectroscopy to measure the impedance between the catheter tip and an external electrode, assuming a three-electrode method. We constructed a 3D finite-element model of the thorax to estimate the impedance as measured in different situations. We defined an area on the anterior wall of the left ventricle in which we simulated three tissue states: healthy, acute ischaemic and scar. We studied the effect of the following parameters on the measured impedance spectrum: the position of the external electrode, the position and orientation of the catheter tip and the overall effect of the subject's respiration. Results show that the highest frequency phase (around 300 kHz) yields the best differentiation of tissue states and that it is less sensitive to respiration than the impedance magnitude. The phase is also less influenced by the catheter tip position (either touching the wall or floating) and the orientation of the catheter inside the left ventricle. The best position for the external electrode is on the chest; this position is less affected by breathing and is more sensitive to tissue changes. One can still distinguish between tissue states if the external electrode is placed on the back, but the effect of respiration is higher.

A system for detection of cardiac graft rejection based in the temperature, ECG and electrical impedance is described. The temperature is measured with two sensors to obtain the absolute temperature and the differential between two points inside the heart. A standard ECG lead and an intracavitary electrogram are also recorded. The electrical impedance of the tissue is measured with a three electrode configuration. In order to validate the system and the method several experiments are done with healthy anesthetized pigs.

We measured the myocardial electrical impedance with a custom system using an intracavitary catheter. We calculated the impedance differences between the measurement in the right ventricle with the tip of the catheter in contact with the myocardial wall, and the measurement in the right atrium with the catheter in a floating position. Our study includes two groups of patients. Group I was composed of 33 patients who underwent cardiac transplantation. Some patients in this group were measured more than once, so a total of 57 measurement sessions were done with different biopsies results: 0,1A and 3A. Group II included 9 control patients without clinical and echocardiographic evidence of structural heart disease, who underwent an electrophysiologic testing. Results show that estimated myocardial impedance difference between ventricle and atrium is higher in controls than in transplanted patients. Furthermore, moderate cardiac rejection causes a significant decrease in the myocardial impedance, differences are more significant (p

Muscle injuries in the lower limb are common among professional football players. Classification is made according to severity and is diagnosed with radiological assessment as: grade I (minor strain or minor injury), grade II (partial rupture, moderate injury) and grade III (complete rupture, severe injury). Tetrapolar localized bioimpedance analysis (BIA) at 50¿kHz made with a phase-sensitive analyzer was used to assess damage to the integrity of muscle structures and the fluid accumulation 24¿h after injury in 21 injuries in the quadriceps, hamstring and calf, and was diagnosed with magnetic resonance imaging (MRI). The aim of this study was to identify the pattern of change in BIA variables as indicators of fluid [resistance (R)] and cell structure integrity [reactance (Xc) and phase angle (PA)] according to the severity of the MRI-defined injury. The % difference compared to the non-injured contralateral muscle also measured 24-h after injury of R, Xc and PA were respectively: grade I (n = 11; -10.4, -17.5 and -9.0%), grade II (n = 8; -18.4, -32.9 and -16.6%) and grade III (n = 2; -14.1, -52.9 and -43.1%), showing a greater significant decrease in Xc (p < 0.001). The greatest relative changes were in grade III injuries. However, decreases in R, that indicate fluid distribution, were not proportional to the severity of the injury. Disruption of the muscle structure, demonstrated by the localized determination of Xc, increased with the severity of muscle injury. The most significant changes 24¿h after injury was the sizeable decrease in Xc that indicates a pattern of disrupted soft tissue structure, proportional to the severity of the injury.

In this study, the electrical impedance of myocardial tissue is measured dynamically during the cardial cycle. The multisine-based approach used to perform electrical impedance spectroscopy (EIS) measurements allows acquiring complete spectral impedance information of the tissue dynamics during contraction. Measurements are performed in situ in the left ventricule of swines during contractility stress tests induced by dobutamine infusion. Additionally, the ECG and the left ventricular (LV) pressure are also acquired synchronously to the impedance signals. The calculated impedance magnitude exhibits a periodic behavior during tissue contraction. The amplitude (peak-to-peak) of this signal is quantified and the compared to the maximum first derivative of the LV pressure (dP/dtmax) that is used as an indicator of contractility variations. The results show a linear correlation between impedance amplitude and dP/dtmax during dobutamine-increased contractility. The present work demonstrates how fast EIS measurements during heart contraction can represent a feasible method to assess changes in myocardial contractility.

Hyper-hydration, malnutrition, and arterial hy- pertension are the most common risk factors associated with mortality in peritoneal dialysis PD patients. Segmental bioim- pedance measured placing electrodes at the ends of the supe- rior and inferior limbs, and in the trunk can be used to moni- tor changes in regional fluid status. In this work three impedance based estimators were analyzed: impedance Z, impedance divided by the height of the patient Z/H, and im- pedance multiplied by the body mass index ZBMI. We meas- ured 6 configurations of segmental impedance measurements, at 50 kHz, in 23 male patients undergoing PD, classified as normo-hydrated or hyper- hydrated. Wilcoxon test was used to analyze the bioimpedance change produced by a PD session. Mann-Whitney U test was used to analyze the separation be- tween groups obtained by means of clinical parameters. Spearman correlation was used to study the correlation be- tween segmental impedance and clinical assessment. Statistical significance was set at P < 0.05. The ZBMI index gives infor- mation about the specific resistivity of tissues and not to fluid and fat mass changes. Longitudinal measurement in the thorax region are useful to corroborate the hydration with cardiovas- cular risk, and nutritional state in PD patients.