Javier Rosell-Ferrer

A multifrequency magnetic induction tomography system using planar gradiometers: data collection and calibration

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 amplifiers 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).

Localized bioimpedance to assess muscle injury.

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.

Measurement errors in multifrequency bioelectrical impedance analyzers with and without impedance electrode mismatch.

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 is more 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.

Electrical stimulation of cardiac adipose tissue-derived progenitor cells modulates cell phenotype and genetic machinery

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. Copyright

Bioelectrical impedance vector analysis (BIVA) in stable and non-stable heart failure patients: A pilot study

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

Assessment and follow-up of muscle injuries in athletes by bioimpedance: Preliminary results

Mono-frequency (50 kHz) whole-body and segmental bioimpedance is measured before sport training in 14 high performance athletes. The athletes are classified in two groups according to the team sport: football and basketball. Bioelectrical impedance vector analysis (BIVA) method is used to obtain the individual whole-body impedance and 6 segmental impedance vectors in the main muscular groups in the lower-limbs. The whole-body vector is analyzed in the tolerance ellipses of the reference population. Individual impedance vector components are standardized by the height H of the subject, (R/H and Xc/H) to obtain the impedance vector (Z/H) of each segment. The hypotheses of the study are: 1) Not all the sports have the same pattern of bioimpedance vector by muscle group. 2) In elite well trained athletes their muscle groups are symmetrical (right and left sides), thus each athlete is its own reference for future comparisons. 3) We expect a change in the two components of bioimpedance vector (R/H and Xc/H) in front of a muscle injury. In order to compare the differences between the complex Z/H vector (R/H, Xc/H) we use Hotellings T2 test. Preliminary results show a significant difference (P < 0.05) in bioimpedance vectors between groups according to the team sport, and also between normal muscle condition and after muscle injury producing hyper-hydration.

Changes in myocardial electrical impedance in human heart graft rejection

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.

Thoracic versus whole body bioimpedance measurements: the relation to hydration status and hypertension in peritoneal dialysis patients.

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 (p < 0.0001) 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.

Interpulse multifrequency electrical impedance measurements during electroporation of adherent differentiated myotubes

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 1.3 MHz) to be acquired during the time gap between consecutive pulses (interpulse) of a classical electroporation treatment (8 pulses, 100 μs, 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.

Physiological conditioning by electric field stimulation promotes cardiomyogenic gene expression in human cardiomyocyte progenitor cells

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.