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S Abboud

Publications and source records attributed to S Abboud.

At least 37 records · Page 2Linked to original sources
PubMed1998

The forced expiratory volume-time curve estimation using the electrocardiogram.

The feasibility of estimating the forced expiratory volume-time curve from the amplitude modulation of the electrocardiogram was studied using a numerical torso model and ECG signal processing. A two dimensional numerical model of the torso was solved for the maximum expiration and inspiration to study the changes in the surface potential as a result of changes in the lung volume. The numerical model showed that significant changes in the surface potential amplitude occur between maximum inspiration and maximum expiration and that this amplitude change in the left-right axis of the torso might be three times as large as in the front-back axis. In the experimental setup, ECG waveforms from the surface of the chest and the mouth air flow were simultaneously recorded from four male subjects during several forced vital capacity (FVC) maneuvers. The amplitude of the QRS complex was measured for different expired lung volumes and an estimation of the forced expiratory volume-time curve was obtained. The FVC and the FEV1 (forced expiratory volume after 1 s) spirometry indices were calculated for the two volume-time curves obtained from the electrocardiogram and from the spirometry measurements. The results differ between 0.1 and 0.8 1. These preliminary results are encouraging and might indicate that a relationship between the volume-time curve during FVC test and the electrocardiogram signals does exist. Further validation in a larger number of subjects and patients is needed before the technique can be applicable for clinical use.

Adult↗
PubMed1997

Correlation between source asymmetry and scalp potential asymmetry in a prolate spheroid model of the head.

The correlation between electric source asymmetry in the brain and potential amplitude asymmetry developed on the scalp was investigated using a computerized analytical prolate spheroid model of the head. The source was modeled by a single current dipole located in the occipital region of the brain. The potential created by the dipole was calculated using Laplace's equation with boundary conditions while allowing a quasi-static formulation and linear media. The dipole was located in the inner part of a four-compartment medium representing the scalp, the skull (with non-isotropic conduction), the cerebrospinal fluid (CSF), and the cortex. The asymmetry was modeled by a dipole located with an angle to the major axis connecting the nasion and the inion. The present study shows that source asymmetry can cause non-negligible asymmetries in the potential amplitude measured on the scalp above homotopic points of the two hemispheres. A potential asymmetry of up to 15% in the O1-O2 pair of electrodes was found when the dipole is rotated from the symmetric major axis at an angle of 10 degrees. The source asymmetry in the occipital region can be related to falx deviation, which is an asymmetry present in the majority of the population. Since this asymmetry is not related to real physiologic and psychologic sources of potential amplitude asymmetries, it should be taken under consideration when potential distribution analysis is performed.

Brain↗
PubMed1997

Telespirometry: novel system for home monitoring of asthmatic patients.

OBJECTIVES: To describe a newly developed telespirometry system consisting of a portable spirometer that transmits the lung ventilatory values by telephone from the patient's home to a remote monitoring center and to assess the ability of the telespirometry system to detect early signs of asthmatic deterioration. METHODS: Thirty-nine patients with moderate to severe asthma were monitored with the telespirometry system. The lung function testing and transmission of the spirometric data by telephone from the patient's home to a remote monitoring center were performed according to the patient's judgment. All previous transmissions of the spirometric data were analyzed retrospectively to detect early signs of asthmatic deterioration, which resulted in dispatch of the mobile intensive care unit (MICU) to the patient's home. RESULTS: In 19 patients (49%), analysis of the spirometric data detected early signs of asthmatic deterioration. Analysis of the spirometric data correlated with decisions to dispatch the MICU in 22 of 39 (56%) patients. In patients with severe asthma, the decision was made during oral communication between the patient and the operator and was based on clinical impression rather than functional results. CONCLUSION: Home monitoring of asthmatic patients with the telespirometry system may improve the management of the disease and the quality of life and reduce costly hospitalizations.

Adolescent↗
PubMed1996

Relationship between late potentials and the predischarge electrocardiographic pattern in patients with acute anterior wall myocardial infarction.

HYPOTHESIS: The presence of late potentials on the signal-averaged electrocardiogram (SAECG) identifies patients at high risk for development of ventricular tachyarrhythmias after myocardial infarction (MI). METHODS: The electrocardiogram and left ventricular function in 65 patients recovering from a first acute anterior wall MI were analyzed. We compared the pattern of the ST segment (isoelectric or elevated) and of the T wave (positive or negative) with the SAECG using an orthogonal bipolar lead configuration (X, Y, Z) with bidirectional Butterworth filtering (Simson's method). RESULTS: Abnormal SAECG was found in 17 (26%) patients; 11 of 18 patients with ST elevation had abnormal SAECG, and only 6 of 47 patients with isoelectric ST segment developed abnormal SAECG (p < 0.0001, odds ratio = 10.74). Of 19 patients with positive T waves, 10 had abnormal SAECG, and abnormal SAECG was found in 7 of 46 patients with negative T waves (p < 0.003, odds ratio = 5.27). When both parameters were considered together, 9 of 12 patients with ST elevation and positive T wave developed abnormal SAECG, and 35 of 40 patients with isoelectric ST and negative T wave had normal SAECG (p < 0.0002). Left ventricular ejection fraction was similar in patients with abnormal SAECG (43 +/- 14%) and normal SAECG (46 +/- 11%). CONCLUSION: These findings suggest that patients with anterior wall MI and a predischarge pattern of ST elevation and positive T wave have a higher incidence of abnormal SAECG and therefore may have a worse prognosis, especially related to the subsequent development of ventricular arrhythmias.

Action Potentials↗
PubMed1996

New model-based indices for maximum expiratory flow-volume curve in patients with chronic obstructive pulmonary disease.

New lung function indices based on a lumped parameter model of the maximal expiratory flow-volume (MEFV) curve are presented. The waveforms obtained by the model were compared to the flow-volume curves recorded from normal subjects and from patients with small airways disease, asthma and emphysema. We were able to reproduce the flow-volume curves using the model and calculate new parameters that indicate the degree of lung function impairment and may be applicable to identify mild chronic obstructive pulmonary diseases. Further studies in larger groups of patients are required to better define the true predictive value of the new indices described for the diagnosis of COPD.

Airway Resistance↗
PubMed1996

Simulation of cardiac activity and the ECG using a heart model with a reaction-diffusion action potential.

A computerized model of the heart for the simulation of the electrical cardiac activity is described. The cardiac cells are arranged in a three-dimensional cubic lattice and their action potential is governed by modified FitzHugh-Nagumo reaction-diffusion state equations system which exhibits properties such as oscillations, variable excitability and refractoriness. The modifications of the FitzHugh-Nagumo equations system account for asymmetric action potential regarding the fast depolarization and slow repolarization rate and for rotational anisotropic propagation. An isolated cell is tested for reproduction of the strength-duration curves and restitution. The structure basic unit cell is assigned with an individual set of control parameters that creates inhomogeneity and anisotropy to simulate the various cardiac components such as pacers, muscle cells and conduction fibers. The spatial resolution of the structure is 1 mm. The collective activity of the cells generates a realistic ECG waveform that scales the simulated temporal step unit to 0.2 msec. The effective diffusion coefficient ranges between 0.055 mm2/msec to 1 mm2/msec. The propagation velocity of the myocardial activation is calculated at normal direction to the wavefront surface and values obtained are 1.17 mm/msec at the muscle cells and 2.5 mm/msec at the main conduction fibers. An ischemia is induced to verify the capability of the model to account for abnormalities. The developed model can give an insight into the local and global complex dynamics of the heart's electrical activity in the transition from normal to abnormal myocardial activity and may help to estimate the effects of myocardial properties on the ECG rhythm.

Action Potentials↗
PubMed1996

Numerical solution of the potential due to dipole sources in volume conductors with arbitrary geometry and conductivity.

The integral conservation equation for biological volume conductors with general geometry and arbitrary distribution of electrical conductivity is solved using a finite volume method. An effective conductivity was defined for the boundaries between regions with abrupt change of the conductivity to allow the simultaneous solution of the entire domain although the derivatives are not continuous. The geometrical singularities arising from the spherical topology of the coordinate system are removed using the conservation law. The resulting finite volume solution method is efficient both in central processing unit (CPU) time and memory requirements, allowing the solution of the volume conductor equation using a large number of mesh points (of the order of 10(5)) even on small workstations (like SGI Indigo). It results in very accurate solutions, as several comparisons with analytical solutions of head models reveal. The proposed finite volume method is an attractive alternative to the finite element and boundary element methods that are more common in bioelectric applications.

Anisotropy↗
PubMed1996

Effect of source location on the scalp potential asymmetry in a numerical model of the head.

The correlation between source asymmetry in the brain and the potential amplitude asymmetry on the scalp was studied by a two-dimensional (2-D) numerical model of the head. The model employed computerized tomography (CT) images to define the different compartments of the head. The source was modeled by a dipole layer in the occiput for an occipital source (visual evoked potential generators) or a dipole layer around the cortex representing spontaneous activity generators. The volume conductor equation for the potential distribution was solved numerically using a finite volume method for two CT images; one had relatively symmetric left-right anatomy while the other had a falx deviation of 6 degrees between the occiput and the nasion-inion line. By examining several arrangements of sources, it has been demonstrated that source asymmetry can cause nonnegligible asymmetry in the potential amplitude at the homotopic points on the scalp. This asymmetry, that is not related to real physiologic or psychological origin, should be taken into consideration in any EEG potential distribution analysis.

Body Fluid Compartments↗
PubMed1996

Analysis of high frequency QRS potential during exercise testing in patients with coronary artery disease and in healthy subjects.

High resolution ECG waveforms from leads V3, V4, V5, and V6 were analyzed in two groups of male subjects before, during, and following treadmill exercise testing. Group A included 32 coronary artery disease (CAD) patients, with arteriographically proven > 75% obstruction of at least two main coronary arteries, and group B included 30 healthy subjects, without history or symptoms of CAD. Signal averaging and filtering techniques were used in order to enhance the signal-to-noise ratio of the recorded ECG. The averaged QRS waveforms were filtered between 150 and 250 Hz. QRS complexes of the four leads were combined to form a "precordial average complex" (PAC). The PAC signals were examined for each subject at different stages of the exercise test and two parameters were computed: the root mean square (RMS) voltage; and the peak amplitude. The values of RMS and peak amplitudes measured at each stage of the exercise test were normalized to the values at rest. Normalized RMS (NRMS) values at peak exercise, immediately after peak exercise, and during the recovery phase were found to be higher for the healthy subjects than for the CAD group (1.17 +/- 0.31 vs 0.94 +/- 0.26, P < 0.008 at peak exercise, 1.13 +/- 0.24 vs 0.84 +/- 0.19, P < 0.001 after peak exercise, 1.08 +/- 0.22 vs 0.94 +/- 0.17, P < 0.007 during recovery). Cut-off NRMS value of one had a sensitivity of 81.3% and a specificity of 70.0% in differentiating CAD patients from healthy subjects in the examined groups. Normalized peak amplitude (NAMP) values exhibited similar behavior, with higher values for the healthy subjects than for the CAD group (1.23 +/- 0.48 vs 0.94 +/- 0.36, P < 0.03 at peak exercise, 1.20 +/- 0.34 vs 0.83 +/- 0.28, P < 0.001 after peak exercise, 1.10 +/- 0.29 vs 0.94 +/- 0.23, P < 0.02 during recovery). Specificity of 73.3% and sensitivity of 71.8% were found using a postpeak NAMP cut-off value of 1. In conclusion, the present study shows that using high frequency ECG may contribute to identifying patients with CAD. Further studies in larger groups of patients are required to better define the true predictive value of the method described for the diagnosis of CAD.

Adult↗
PubMed1996

Assessment of a new transtelephonic portable spirometer.

BACKGROUND: A new portable spirometer, the Spirophone, has been developed that records a subject's blow and can then transmit all the data by telephone to a receiving centre for analysis and comment. Tests of this device were undertaken to determine its accuracy and reliability. METHODS: The performance of the Spirophone was tested using computer generated wave forms, by delivering blows from calibrated syringes at different flows, and by comparing subjects' blows with those recorded with a commercial spirometer. RESULTS: Using computer generated wave forms all lung function indices were accurate to within 1% and blows delivered from calibrating syringes were accurate to within 5%. When subjects performed repeated forced vital capacity (FVC) manoeuvres there were no significant differences between lung function indices recorded with the Spirophone and with a commercial spirometer. With the Spirophone and commercial spirometer in series the FVC and forced expiratory volume in one second (FEV1) were within 5% of each other in nine out of 10 healthy subjects. CONCLUSION: The Spirophone recorded maximal forced expiratory manoeuvres with acceptable accuracy, reliability, and reproducibility, and this system offers the ability to monitor a patient's lung function at a centre remote from the patient.

Asthma↗
PubMed1995

Maximum expiratory flow-volume curve: mathematical model and experimental results.

A mathematical simulation of the maximum expiratory flow-volume (MEFV) curve was developed using a lumped parameter model. The model uses a theoretical approximation of an activation function representing the lung's pressure-volume relationship during maximally forced expiration. The waveforms obtained by the model were compared to the flow-volume curves recorded from normal subjects and for patients with small airways disease, asthma, and emphysema. We were able to reproduce the flow-volume curves using the model and calculate new parameters that reflect the dependency of airways resistance on expired volume during FVS manoeuvre. These new parameters are based on the entire information presented in the flow-volume curve and on the reduction in flow at all lung volumes. We also calculated the mean slope of the resistance-expired volume curves obtained from the model by fitting a straight line to the curve. Using representative data for normal and COPD patients different mean slopes of 0.095, 0.13, 0.49 and 1.44 litre-1 were obtained for normal subject, small airways disease, asthma and emphysema patients, respectively. The model-based parameters may be applicable to human studies. However, further studies in large groups of patients are required to better define the true predictive value of the new indices described for the diagnosis of COPD.

Asthma↗
PubMed1995

Correlation between skull thickness asymmetry and scalp potential estimated by a numerical model of the head.

The contribution of asymmetric skull thickness to the scalp potential amplitude was investigated numerically. The model consisted of four conductive layers representing the scalp, the skull, the cerebrospinal fluid, and the cortex with a current dipole in the occipital region. The potential created by the dipole was calculated assuming quasistatic formulation and linear media. The governing equation was discretized by the finite volume method to ensure the conservation of fluxes even in regions with abrupt changes of the conductivity. The large set of the algebraic equations for the electric potential was solved iteratively by the successive overrelaxation method. The model confirmed previous experimental studies suggesting that the potential amplitude is 60% smaller on the side with the thicker bone if the asymmetry of the skull thickness exceeds 40%. The model developed suggests that skull thickness asymmetry can create nonnegligible asymmetries in the potential measured on the scalp above homotopic points of the two hemispheres.

Adult↗
PubMed1994

Numerical calculation of the potential distribution due to dipole sources in a spherical model of the head.

A three-dimensional spherical model of the head was investigated numerically. The model consists of four conductive layers representing the scalp, the skull, the cerebrospinal fluid, and the cortex with a dipole current source. The potential created by the dipole was calculated using quasistatic formulation and a linear medium. The volume conduction equation was discretized by the finite volume method to ensure the conservation of fluxes and efficient solution method. The large set of algebraic equations for the electric potential was solved iteratively by the successive over relaxation method. The new formulation of the volume conduction problem was validated by comparing the numerical results with two analytical solutions. The first test-case considers a homogeneous spherical model with a dipole in the center. The potential on the outer surface, as well as within the volume conductor, was calculated and very good agreement was obtained with the analytical solution. In the second test-case, the scalp potential due to a radially oriented eccentric dipole in a four concentric spheres model was compared with an analytic solution. It was found that a grid of 90 x 90 x 90 volume elements yielded accurate results on the scalp surface with errors on the order of 1%. The present numerical model can be extended to general cases with any volume conductor shape or with any distribution or orientation of the current dipoles. Compared to other numerical methods, this approach offers enhanced accuracy for given computational resources (both in CPU time and memory). The gain might be more than one order of magnitude, allowing simulation with considerably larger meshes.

Body Surface Area↗
PubMed1994

Real-time multichannel abdominal fetal ECG monitor using digital signal coprocessor.

A real-time multichannel fetal ECG monitor based on a personal computer (PC) and a MOTOROLA DSP56001 Digital Signal CoProcessor (DSP) is introduced. The DSP board is plugged into the PC, which functions as a HOST computer. An analog 8 Leads Interface and Analog to Digital circuits module is connected to the DSP through a synchronous, optical-isolated communication channel. The fetal ECG detection is based on a cross-correlation technique. An averaged maternal ECG waveform is generated using a cross-correlation alignment procedure and a user-defined template. The fetal ECG signals present in the maternal waveform is suppressed during the averaging procedure, since both are uncorrelated. The average maternal ECG waveform is then subtracted from the abdominal real time signals, and maternal-free fetal ECGs signals are obtained, including fetal QRS complexes that coincide with maternal ones. Using the abdominal ECGs signals after subtraction, an averaged fetal waveform is generated. The maternal and the fetal heart rate are calculated during the process. The algorithm described above can be performed in real time on up to eight abdominal ECG traces by the DSP, and the desired results are passed to the HOST PC, to be stored and displayed. Electrodes positioning procedures for detecting the fetal QRS complexes with the best signal to noise ratio are not needed. Using the multichannel system, the user can select the best channel for fetal QRS detection, and accurate results for the heart rate signal are obtained. Averaged fetal waveforms are obtained from all the leads.

Abdomen↗
PubMed1993

Prediction of arrhythmic events after acute myocardial infarction using two methods for late potentials recording.

One hundred consecutive patients recovering from an acute myocardial infarction underwent, prior to home discharge, signal-averaged electrocardiography (ECG), left ventriculography, and 24-hour Holter ECG recording. The signal-averaged ECG was recorded and analyzed using two procedures: the orthogonal bipolar XYZ lead configuration with a bidirectional filter; and a precordial unipolar lead configuration with a nonrecursive digital filter. An abnormal signal-averaged ECG was seen in 40% of patients with the XYZ system and in 30% of patients in the precordial method, abnormal ejection fraction (< 40%) in 24% of patients and high grade ectopy activity in 22%. During the 24-month follow-up period, 12 patients (12%) had an arrhythmic event defined as either sudden death (11 patients) or sustained ventricular tachycardia (1 patient). Neither the signal-averaged ECG with the XYZ configuration, the abnormal ejection fraction, nor the high grade ectopy were able to statistically predict a higher arrhythmic event rate. The signal-averaged ECG with the precordial configuration was able to statistically predict a higher arrhythmic event rate, P < 0.03; odds ratio = 3.96. The combination of the orthogonal XYZ configuration signal-averaged ECG with the ejection fraction (P < 0.01, odds ratio = 7.33), or with ejection fraction and Holter monitoring (P < 0.06, odds ratio = 6.17) was able to predict a higher arrhythmic event rate. The combination of the precordial configuration signal-averaged ECG with the ejection fraction (P < 0.002, odds ratio = 14.4), or with ejection fraction and Holter monitoring (P < 0.06, odds ratio = 10) was able to better predict a higher arrhythmic event rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Real-time abdominal fetal ECG recording using a hardware correlator.

A real-time fetal ECG monitoring system using abdominal recording is presented. The system is based on an IBM AT compatible personal computer. The computer lacks the performance required for real-time analysis. Therefore, a new design of a fast hardware correlator board was developed to enhance the computer throughput. The technique is based on a cross-correlation procedure. An averaged maternal ECG waveform is derived using the cross-correlation function for the waveform's alignment. With this procedure a template signal corresponding to one complete maternal ECG is obtained. The averaged maternal ECG is then subtracted from the abdominal signals. Thus, it is possible to detect all the fetal ORS complexes in spite of their coincidence with the maternal ECG. An average fetal ECG is then extracted to improve the signal-to-noise ratio, making it possible to recognize fetal P and T waves.

Algorithms↗
PubMed1991

Fourier transform versus bidirectional digital filters for late potentials recording in the electrocardiogram.

Late potentials occur after the QRS complex and can be detected by using signal averaging and filtering techniques. In this study the filtered averaged electrocardiograms (ECGs) obtained using two types of filters were compared: the bidirectional digital recursive filter with a 40 Hz high-pass cut-off frequency, and the Fourier transform non-recursive digital filter with a 60 Hz high-pass cut-off. Strong correlation was found between the numerical values obtained when using these two filtering procedures. In addition, close diagnostic concordance was found between the late potential parameters in patients with normal and abnormal signal averaged ECGs. Visual comparison between the bidirectional and the Fourier plots revealed a close morphological similarity between the vector magnitudes. There was no significant difference in the mean root mean square voltage of the terminal 40 ms and the late potential duration, less than 40 mV, between the bidirectional and the Fourier filters in patients with a normal or an abnormal signal averaged ECG. The QRS duration was found to be significantly longer using Fourier filtering. This can be explained by the contributions of two factors: using the bidirectional procedure with a phase delay from each end of the data window, a shortening of the filtered QRS duration may occur and, alternatively, when using the Fourier filter, minimal stretching of the QRS complex may occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗