Sánchez, B.; Li, J.; Geisbush, T.; Bragos, R.; Rutkove, S. IEEE transactions on biomedical engineering Vol. 63, num. 8, p. 1602-1612 DOI: 10.1109/TBME.2014.2320132 Data de publicació: 2016-08-01 Article en revista
Alterations in the health of muscles can be evaluated through the use of electrical impedance myography (EIM). To date, however, nearly all work in this field has relied upon the measurement of muscle at rest. To provide an insight into the contractile mechanisms of healthy and disease muscle, we evaluated the alterations in the spectroscopic impedance behavior of muscle during the active process of muscle contraction. The gastrocnemii from a total of 13 mice were studied (five wild type, four muscular dystrophy animals, and four amyotrophic lateral sclerosis animals). Muscle contraction was induced via monophasic current pulse stimulation of the sciatic nerve. Simultaneously, multisine EIM (1 kHz to 1 MHz) and force measurements of the muscle were performed. Stimulation was applied at three different rates to produce mild, moderate, and strong contractions. We identified changes in both single and multifrequency data, as assessed by the Cole impedance model parameters. The processes of contraction and relaxation were clearly identified in the impedance spectra and quantified via derivative plots. Reductions in the center frequency f(c) were observed during the contraction consistent with the increasing muscle fiber diameter. Different EIM stimulation rate-dependencies were also detected across the three groups of animals.
Monte, E.; Anyo, M.; Torres, M.; Juarez, P.; Núñez, P.; Aragón, C.; Pedrosa, M.; Álvarez-Rodríguez, M.; González-Burguillos, M. IEEE transactions on biomedical engineering DOI: 10.1109/TBME.2016.2554661 Data de publicació: 2016-04-20 Article en revista
In this paper, we propose a method for screening for
the presence of type 2 diabetes by means of the signal obtained
from a pulse oximeter. The screening system consists of two parts;
the first analyses the signal obtained from the pulse oximeter, and
the second consists of a machine-learning module.
The system consists of a front end that extracts a set of features
form the pulse oximeter signal. These features are based on
physiological considerations. The set of features were the input
of a machine-learning algorithm that determined the class of
the input sample, i.e. whether the subject had diabetes or not.
The machine-learning algorithms were random forests, gradient
boosting, and linear discriminant analysis as benchmark. The
system was tested on a database of 1, 157 subjects (two samples
per subject) collected from five community health centres.
The mean receiver operating characteristic (ROC) area found
was 69.4% (median value 71.9% and range [75.4%-61.1%]), with
a specificity=64% for a threshold that gave a sensitivity=65%.
We present a screening method for detecting diabetes that
has a performance comparable to the glycated haemoglobin
(haemoglobin A1c HbA1c) test, does not require blood extraction,
and yields results in less than five minutes.
Sánchez, B.; Schoukens, J.; Bragos, R.; Vandersteen, G. IEEE transactions on biomedical engineering Vol. 58, num. 12, p. 3376-3385 DOI: 10.1109/TBME.2011.2166116 Data de publicació: 2011-11-18 Article en revista
Classicalmeasurements ofmyocardium tissue electrical impedance for characterizing the morphology of myocardium cells, as well as cell membranes integrity and intra/extra cellular spaces, are based on the frequency-sweep electrical impedance
spectroscopy (EIS) technique. In contrast to the frequency-sweep EIS approach, measuring with broadband signals, i.e., multisine
excitations, enables to collect, simultaneously, multiple myocardium
tissue impedance data in a short measuring time. However, reducing the measuring time makes the measurements to be prone to the influence of the transients introduced by noise and the dynamic time-varying properties of tissue. This paper
presents a novel approach for the impedance-frequency-response estimation based on the local polynomial method (LPM). The
fast LPM version presented rejects the leakage error’s influence on the impedance frequency response when measuring electrical
bioimpedance in a short time. The theory is supported by a set of validation measurements. Novel preliminary experimental results obtained from real-time in vivo healthy myocardium tissue impedance characterization within the cardiac cycle using multisine excitation are reported.
A correntropy-based technique is proposed for the characterization and classification of respiratory flow signals in chronic heart failure (CHF) patients with periodic or nonperiodic breathing (PB or nPB, respectively) and healthy subjects. The correntropy is a recently introduced, generalized correlation measure whose properties lend themselves to the definition of a correntropybased spectral density (CSD). Using this technique, both respiratory
and modulation frequencies can be reliably detected at their original positions in the spectrum without prior demodulation of
the flow signal. Single-parameter classification of respiratory patterns
is investigated for three different parameters extracted from the respiratory and modulation frequency bands of the CSD, and one parameter defined by the correntropy mean. The results show that the ratio between the powers in the modulation and respiratory frequency bands provides the best result when classifying CHF patients with either PBor nPB, yielding an accuracy of 88.9%.
The correntropy mean offers excellent performance when classifying CHF patients versus healthy subjects, yielding an accuracy of 95.2% and discriminating nPB patients fromhealthy subjects with an accuracy of 94.4%.
Morgenstern, C.R.; Schwaibold, M.; Randerath, W.J.; Bolz, A.; Jane, R. IEEE transactions on biomedical engineering Vol. 57, num. 8, p. 1927-1936 DOI: 10.1109/TBME.2010.2047505 Data de publicació: 2010-04-15 Article en revista
The automatic differentiation of obstructive and central
respiratory events is a major challenge in the diagnosis of
sleep-disordered breathing. Esophageal pressure (Pes) measurement
is the gold-standard method to identify these events. This
study presents a new classifier that automatically differentiates
obstructive and central hypopneas with the Pes signal and a new
approach for an automatic noninvasive classifierwith nasal airflow.
An overall of 28 patients underwent night polysomnography with
Pes recording, and a total of 769 hypopneas were manually scored
by human experts to create a gold-standard annotation set. Features
were automatically extracted fromthe Pes signal to train and
test the classifiers (discriminant analysis, support vector machines,
and adaboost). After a significantly (p < 0.01) higher incidence of
inspiratory flow limitation episodes in obstructive hypopneas was
objectively, invasively assessed compared to central hypopneas, the
feasibility of an automatic noninvasive classifier with features extracted
from the airflow signal was demonstrated. The automatic
invasive classifier achieved a mean sensitivity, specificity, and accuracy
of 0.90 after a 100-fold cross validation. The automatic noninvasive
feasibility study obtained similar hypopnea differentiation
results as a manual noninvasive classification algorithm. Hence,
both systems seem promising for the automatic differentiation of
obstructive and central hypopneas.
Valencia, J.; Porta, A.; Vallverdu, M.; Clarià, F; Baranowski, R.; Orlowska-Baranowska, E.; Caminal, P. IEEE transactions on biomedical engineering Vol. 56, num. 9, p. 2202-2213 DOI: 10.1109/TBME.2009.2021986 Data de publicació: 2009-09 Article en revista
Morgenstern, C.R.; Schwaibold, M.; Randerath, W.J.; Bolz, A.; Jane, R. IEEE transactions on biomedical engineering Vol. 56, num. 8, p. 2006-2015 DOI: 10.1109/TBME.2009.2023079 Data de publicació: 2009-05-19 Article en revista
Jospin, M.; Caminal, P.; Jensen, E.; Litvan, H.; Vallverdu, M.; Struys, M.; Vereecke, H.; Kaplan, D. IEEE transactions on biomedical engineering Vol. 54, num. 5, p. 840-846 Data de publicació: 2007-05 Article en revista
The purpose of this paper is to analyze the influence of the metallic structures of a realistic car body frame on the specific
absorption rate (SAR) produced by a cell phone when a complete human body model is placed at different locations inside the vehicle, and to identify the relevant parameters responsible for these
changes. The modeling and analysis of the whole system was conducted by means of computer simulations based on the full wave
finite-difference time-domain (FDTD) numerical method. The excitation
considered was an 835 MHz 2 dipole located as a handsfree communication device or as a hand-held portable system. We compared the SAR at different planes on the human model, placed inside the vehicle with respect to the free space situation. The presence
of the car body frame significantly changes the SAR distributions, especially when the dipole is far from the body. Although
the results are not conclusive on this point, this change in SAR distribution
is not likely to produce an increase above the limits in current guidelines for partial body exposure, but may be signifi-
cant for whole-body exposure. The most relevant change found was the change in the impedance of the dipole, affecting the radiated power. A complementary result from the electromagnetic computations
performed is the change in the electromagnetic field distribution
inside a vehicle when human bodies are present. The whole vehicle model has been optimized to provide accurate results for
sources placed inside the vehicle, while keeping low requirements for computer storage and simulation time.
A method for estimating the uncertainty in time-domain indices of RR time series is described. The method relies on the central limit theorem that states that the distribution of a sample average of independent samples has an uncertainty that asymptotically approaches to the sample
standard deviation divided by the square root of the number of samples. Because RR time series cannot be characterized by a set of independent samples, we propose to estimate the uncertainty of indices by computing them in blocks that satisfy that the obtained partial indices are independent.
We propose a methodology to search sets of independent partial indices and apply this methodology to the estimation of the uncertainty in the mean RR, SDRR, and r-msDD indices. The results show that the uncertainty can be higher than the 10% of the index for the SDRR and even higher for the r-msDD. Moreover, a statistical test for the difference of two indices is proposed.
Towards establishing electrical interfaces with patterned in vitro neurons, we have previously described the fabrication of hybrid elastomer-glass devices polymer-on-multielectrode array technology and obtained single-electrode recordings of extracellular potentials from confined neurons (Claverol-Tinturé et al., 2005). Here, we demonstrate the feasibility of spatially localized multisite recordings from individual microchannel-guided neurites extending from microwell-confined somas with good signal-to-noise ratios (20 dB) and spike magnitudes of up to 300 μV.
Single-cell current source density (scCSD) analysis of the spatio-temporal
patterns of membrane currents along individual processes is illustrated.
Unbalance between electrode-skin impedances is a major problem in biopotential recordings, leading to increased power-line interference. This paper proposes a simple, direct method to measure that unbalance at power-line frequency (50-60 Hz), thus allowing the determination of actual recording conditions for biopotential amplifiers. The method is useful in research, amplifier testing, electrode design and teaching purposes. It has been experimentally validated by using both phantom impedances and real electrode-skin impedances.
We analyze the radiated emissions from a low power electrosurgical unit (ESU). Measurements at a 3-meter distance are performed in order to find a suitable measurement setup intended to reproduce realistically the real working ESU behavior in a test lab. The broad-band and narrow-band characteristics of the perturbation are studied in order to address the other equipment immunity.
Electrical properties of myocardial tissue are anisotropic due to the complex structure of the myocardial fiber orientation and the distribution of gap junctions. For this reason, measured myocardial impedance may differ depending on the current distribution and direction with respect to myocardial fiber orientation and, consequently, according to the measurement method. The objective of this study is to compare the specific impedance spectra of the myocardium measured using two different methods. One method consisted of transmural measurements using an intracavitary catheter and the other method consisted of nontransmural measurements using a four-needle probe inserted into the epicardium. Using both methods, we provide the in situ specific impedance spectrum (magnitude and phase angle) of normal, ischemic, and infarcted pig myocardium tissue from 1 kHz to 1 MHz. Magnitude spectra showed no significant differences between the measurement techniques. However, the phase angle spectra showed significant differences for normal and ischemic tissues according to the measurement technique.
The main difference is encountered after 60 min of acute ischemia in the phase angle spectrum. Healed myocardial tissue showed a small and flat phase angle spectrum in both methods due to the low content of cells in the transmural infarct scar. In conclusion, both transmural and nontransmural measurements of phase angle
spectrum allow the differentiation among normal, ischemic, and infarcted tissue.
Fully differential amplifiers yield large differential gains and also high common mode rejection ratio (CMRR), provided they do not include any unmatched grounded component. In biopotential measurements, however, the admissible gain of amplification stages located before dc suppression is usually limited by electrode offset voltage, which can saturate amplifier outputs. The standard solution is to first convert the differential input voltage to a single-ended voltage and then implement any other required functions, such as dc suppression and dc level restoring. This approach, however, yields a limited CMRR and may result in a relatively large equivalent input noise. This paper describes a novel fully differential biopotential amplifier based on a fully differential dc-suppression circuit that does not rely on any matched passive components, yet provides large CMRR and fast recovery from dc level transients. The proposed solution is particularly convenient for low supply voltage systems. An example implementation, based on standard low-power op amps and a single 5-V power supply, accepts input offset voltages up to /spl plusmn/500 mV, yields a CMRR of 102dB at 50 Hz, and provides, in accordance with the AAMI EC38 standard, a reset behavior for recovering from overloads or artifacts
AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz
A new index is proposed to estimate the variance of the differentiated heart rate (RR) time series from its truncated
histogram. The index is more robust to artifacts than the standard deviation of the differentiated RR time series (rMSDD) and, unlike the pNN50, does not saturate for very high or very low heart rate variability.
We report a numerical study of the induced electric fields and specific absorption rate (SAR) produced by microwave radiation from a half-wavelength dipole near tissue models, and the resulting transient and steady-state temperature rises. Several models were explored, including a uniform emi-infinite plane of tissue, uniform sphere, a phantom model of the head filled with tissue-equivalent material, a numerical model of the head with uniform dielectric properties (obtained from a digitized computed tomography image), and a numerical model of the head with different dielectric properties corresponding to various tissues. The electromagnetic calculations were performed for half-wave dipoles radiating at 900 and 1900 MHz at various distances from the model, using the finite-difference-time-domain (FDTD) method. The resulting temperature rises were estimated
by finite element solution of the bioheat equation. The calculated SAR values agree well with an empirical correlation due to
Kuster. If the limiting hazard of such exposures is associated with excessive temperature increase, present exposure limits are very conservative and guidelines that are easier to implement might
provide adequate protection.
We measured transthoracic impedance in nine presumed healthy adult subjects with a two-frequency plethysmograph at 57 kHz and 185 kHz. The measurement protocol included periods of normal breathing without motion and periods of motion without breathing. We
analyzed the cross-correlation and the ratio between the signals at both frequencies for all the different maneuvers. The correlation coefficient was between 0.97 and 1 for breathing, the minimal cross-correlation (0.81) was for simulated obstructive apnea. We found that the amplitude ratio between the two-frequency signals was different for normal breathing and for motion. Based on these results, we designed and tested an adaptive filter to increase the signal-to-artifact ratio (SAR). The increase in SAR(mean ± standard deviation) compared with the signal at 57 Miz was: 183% ± 117% for arm movement, 133% ± 93% for leg movement, and 34% ± 62% for simulated obstructive apnea.
We measured transthoracic impedance between 12.5 and 185 kHz in nine adults. We used a system with two impedance channels, both simultaneously detecting the real part of impedance at two different frequencies. We used only two electrodes in the midaxillary line, connecting both channels in parallel. The amplitude relation between the two channels was measured for different maneuvers and frequencies. Results show for normal breathing an increase of the signal of 20% and a decrease in motion artifacts from 12.5 to 185 kHz. We conclude that, for
the maneuvers studied, it is better to work at higher frequencies than the ones commonly used. Also, we suggest a method to further increase the signal-to-motion artifact ratio based on measurement at two frequencies.
Jofre, L.; Hawley, M.; Broquetas, A.; de los Reyes, E.; Ferrando, M.; Elias, A. IEEE transactions on biomedical engineering Vol. 37, num. 3, p. 303-312 DOI: 10.1109/10.52331 Data de publicació: 1990-03 Article en revista
A microwave tomographic scanner for biomedical applications is presented. The scanner consists of a 64 element circular array with a useful diameter of 20 cm. Electronically scanning the transmitting and receiving antennas allows multiview measurements with no mechanical movement. Imaging parameters are appropriate for medical use: a spatial resolution of 7 mm and a contrast resolution of 1% for a measurement time of 3 s. Measurements on tissue-simulating phantoms and volunteers, together with numerical simulations, are presented to assess the system for absolute imaging of tissue distribution and for differential imaging of physiological, pathological, and induced changes in tissues.
We present a model describing the rotation of the cardiac vector as a possible mechanism resulting in the presence of respiratory information in the ECG. The way in which this information is revealed
is analyzed and the predictions subjected to qualitative experimental assessment via spectral analysis. The results show that respiratory frequencies occur in the ECG
spectrum due to heart movement. By measuring on a patient wearing a pacemaker and ventilated to control respiratory rate we show that even in the absence of respiratory sinus arrhythmia (RSA) there is a baseband information in the ECG spectrum, attributable neither to electrode artifacts nor to emg, and sidebands from the respiratory cycle.
We propose an AC-coupled amplifier that offers a high in-put impedance, thus making it suitable for bioelectric signal amplifi-
cation. We also present the necessary formulas for calculating its input impedance and transfer function in order to facilitate its adaptation to different applications.
We measured the impedance of skin coated with gel, but otherwise unprepared from 1 Hz to 1 MHz at ten sites on the thorax, leg, and forehead of ten subjects. For a 1 cm2 area, the 1 Hz impedance varied from 10 kΩ to 1 MΩ, which suggests that biopotential amplifier
input impedance should be very high to avoid common mode to differential mode voltage conversion. 1 MHz impedance was tightly clustered about 120 Ω. 100 kHz impedance was about 220 Ω,which suggests that the variation in skin impedance may cause errors in two electrode electrical impedance tomographs.