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Showing papers in "IEEE Transactions on Biomedical Engineering in 1985"


Journal ArticleDOI
TL;DR: A real-time algorithm that reliably recognizes QRS complexes based upon digital analyses of slope, amplitude, and width of ECG signals and automatically adjusts thresholds and parameters periodically to adapt to such ECG changes as QRS morphology and heart rate.
Abstract: We have developed a real-time algorithm for detection of the QRS complexes of ECG signals. It reliably recognizes QRS complexes based upon digital analyses of slope, amplitude, and width. A special digital bandpass filter reduces false detections caused by the various types of interference present in ECG signals. This filtering permits use of low thresholds, thereby increasing detection sensitivity. The algorithm automatically adjusts thresholds and parameters periodically to adapt to such ECG changes as QRS morphology and heart rate. For the standard 24 h MIT/BIH arrhythmia database, this algorithm correctly detects 99.3 percent of the QRS complexes.

5,782 citations


Journal ArticleDOI
TL;DR: The system illustrated in this paper has been designed and developed particularly for automatic and reliable analysis of body movement in various conditions and environments and is based on real-time processing of the TV images to recognize multiple passive markers and compute their coordinates.
Abstract: The system illustrated in this paper has been designed and developed particularly for automatic and reliable analysis of body movement in various conditions and environments. It is based on real-time processing of the TV images to recognize multiple passive markers and compute their coordinates. This performance is achieved by using a special algorithm allowing the recognition of markers only if their shape matches a predetermined "mask." The main feature of the system is a two-level processing architecture, the first of which includes a dedicated peripheral fast processor for shape recognition (FPSR), designed and implemented by using fast VLSI chips. The second level consists of a general purpose computer and provides the overall system with high flexibility. The main characteristics are: no restriction on the number of markers, resolution of one part in 2500, and a 50 Hz sampling rate independent of the number of markers detected. The prototype has been fully developed, and preliminary results obtained from the analysis of several movements are illustrated.

476 citations


Journal ArticleDOI
TL;DR: A nonlinear eighth-order agonist-antagonist muscle model is identified, based on engineering analysis and design criteria, as the desired structure for the broad-range study of a variety of fundamental human joint movements as mentioned in this paper.
Abstract: A nonlinear eighth-order agonist-antagonist muscle model is identified, based on engineering analysis and design criteria, as the desired structure for the broad-range study of a variety of fundamental human joint movements. To complement this structure, systematic protocols, that combine material and geometrical information for each muscle, are developed to obtain the model parameter values needed for the various muscle constitutive equations. The parameters describing the four basic nonlinear relations are easy to visualize, representing the peak curve values and "shape" parameters. Elbow, knee, wrist, and ankle fiexion-extension and eye, wrist, and head rotation are simulated by this same model structure.

410 citations


Journal ArticleDOI
TL;DR: Linear phase filtering is proposed for the removal of baseline wander and power-line frequency components in electrocardiograms with a considerably reduced number of impulse response coefficients.
Abstract: Linear phase filtering is proposed for the removal of baseline wander and power-line frequency components in electrocardiograms. In order to reduce the large number of computations involved in the digital filtering that are necessary, the desired filter spectrum was defined periodically. Making use of the property that the spectrum period is 50 Hz, the spectrum can be realized with a considerably reduced number of impulse response coefficients. This, in combination with the necessary impulse response symmetry, leads to a reduction in the number of multiplications per output sample by a factor of 10. A suitable impulse response is designed with a pass-band ripple of less than 0.5 dB and a high stop-band attenuation. The applicability is demonstrated by applying the filtering to exercise electrocardiograms.

339 citations


Journal ArticleDOI
TL;DR: It is shown that the conductivity distribution in the field can be estimated from the impedance data obtained for the body surface leads and the finite element model must be chosen properly to provide the unique solution.
Abstract: A simulation study of electrical impedance computed tomography is presented. This is an inverse problem. A field is discretized by the finite element method and an iterative approach derived from the sensitivity theorem is examined for leads taken on the field surface. It is shown that the conductivity distribution in the field can be estimated from the impedance data obtained for the body surface leads. Simulation suggests the availability and the limitation for impedance plethysmography application. The finite element model must be chosen properly to provide the unique solution.

265 citations


Journal ArticleDOI
TL;DR: A new, automatic signal-processing method (ADEMG) for extracting motor-unit action potentials (MUAP's) from the electromyographic interference pattern for clinical diagnostic purposes and measures their amplitudes, durations, rise rates, numbers of phases, and firing rates.
Abstract: We describe a new, automatic signal-processing method (ADEMG) for extracting motor-unit action potentials (MUAP's) from the electromyographic interference pattern for clinical diagnostic purposes. The method employs digital filtering to select the spike components of the MUAP's from the background activity, identifies the spikes by template matching, averages the MUAP waveforms from the raw signal using the identified spikes as triggers, and measures their amplitudes, durations, rise rates, numbers of phases, and firing rates. Efficient new algorithms are used to align and compare spikes and to eliminate interference from the MUAP averages. In a typical 10-s signal recorded from the biceps brachii muscle using a needle electrode during a 20 percent-maximal isometric contraction, the method identifies 8-15 simultaneously active MUAP's and detects 30-70 percent of their occurrences. The analysis time is 90 s on a PDP-11/34A.

206 citations


Journal ArticleDOI
TL;DR: The model predicts lower thresholds for cathodal than for anodal stimulation: the predicted degree of polarity selectivity is confirmed by direct stimulation of axons in animal experiments, but is at variance with the selectivity found in human transcutaneous stimulation.
Abstract: A model of myelinated nerve axon was used to study the initiation and propagation of action potentials for a variety of extracellular electrical stimuli. Frankenhaeuser-Huxley nonlinearities were incorporated at each of several nodes in a longitudinal array, and the extracellular current pulse was modeled as a spatial distribution of voltage disturbance along the membrane. Results from the model were compared to data from human sensory experiments and from animal electrophysiological experiments. Effects of polarity, electrode position, pulse duration, and biphasic oscillation frequency were examined. Biphasic pulses have higher excitation thresholds than monophasic pulses, provided the duration of a single phase is short relative to the time constant of the membrane depolarization process. The shapes of strength/duration curves from sensory experiments conform well to model predictions for monophasic stimuli. Strength/frequency curves derived from the model are similar to those from sensory stimulation with sinusoidal currents. The shapes of strength/frequency curves can be explained by membrane integration effects at high frequencies and membrane leakage effects at low frequencies. The model predicts lower thresholds for cathodal than for anodal stimulation: the predicted degree of polarity selectivity is confirmed by direct stimulation of axons in animal experiments, but is at variance with the selectivity found in human transcutaneous stimulation.

182 citations


Journal ArticleDOI
TL;DR: A computer program was developed, which automatically determined the potential source by applying a correlation calculation and a linear regression to the recorded signals and clarified the distribution of the innervation zones in the biceps brachii.
Abstract: A linear surface electrode array placed along the muscle fibers detects motor unit action potentials propagating bilaterally to the tendons. The location of the propagation source is presumed to mark an innervation zone. We developed a computer program, which automatically determined the potential source by applying a correlation calculation and a linear regression to the recorded signals. The spacing between the contacts in the electrode array was 5.0 mm, whereas for some recordings the histogram indicating the position of estimated source had a sharp peak concentrated in a 1.0 mm area. In the biceps brachii some subjects were found to have two innervation zones separated by 10-20 mm. The peaks corresponding to the innervation zones differentially changed their histogram scores according to the contraction force. We also constructed an electrode assembly, which had four columns of the linear electrode arrays, and clarified the distribution of the innervation zones in the biceps brachii.

173 citations


Journal ArticleDOI
TL;DR: A set of real-time digital filters each implemented as a subroutine that can be implemented on a diversity of available microprocessors to implement a desired filtering task on a single microprocessor.
Abstract: Traditionally, analog circuits have been used for signal conditioning of electrocardiograms. As an alternative, algorithms implemented as programs on microprocessors can do similar filtering tasks. Also, digital filter algorithms can perform processes that are difficult or impossible using analog techniques. Presented here are a set of real-time digital filters each implemented as a subroutine. By calling these subroutines in an appropriate sequence, a user can cascade filters together to implement a desired filtering task on a single microprocessor. Included are an adaptive 60-Hz interference filter, two low-pass filters, a high-pass filter for eliminating dc offset in an ECG, an ECG data reduction algorithm, band-pass filters for use in QRS detection, and a derivative-based QRS detection algorithm. These filters achieve real-time speeds by requiring only integer arithmetic. They can be implemented on a diversity of available microprocessors.

172 citations


Journal ArticleDOI
TL;DR: The results show that the shape of the transmembrane potential and the kinetics of the sodium current and conductance are highly determined by boundary effects at sites where impulse conduction begins and where it ends at a collision or an anatomical end.
Abstract: The purpose of this paper is to describe how the transmembrane and extracellular potential waveforms, and their derivatives, are related to each other and to the sodium current and conductance in propagating cardiac action potentials. The results show that the shape of the transmembrane potential and the kinetics of the sodium current and conductance are highly determined by boundary effects at sites where impulse conduction begins and where it ends at a collision or an anatomical end. These propagation nonuniformities produced a relationship between Vmax and the internal membrane variables gNa and INa that is just the opposite of the classical relation between Vmax and the magnitude of the sodium current. For example, in these cases, both peak INa and the area under the gNa curve decreased when Vmax increased. In addition, Vmax, was shown to coincide in time with the maximum rate of increase of gNa and INa. The maximum negative slope of the extracellular waveform coincided in time with Vmax of the transmembrane potential for all shapes of the waveforms. Therefore, either the maximum negative slope of the extracellular waveform or Vmax of the action potential provides a time marker for the same underlying depolarizing event, i.e., the maximum rate of increase of the depolarizing current and its conductance.

144 citations


Journal ArticleDOI
TL;DR: It is shown that the multiple cross spectrum of functionally related sequences exhibits significant peak frequencies, and it is conjecture that the peak frequencies in the multipleCross spectrum of sequences with the same boilogical function are related to this biological function.
Abstract: Informational content of linear macromolecules (DNA, RNA, and proteins) is analyzed by the method of digital signal processing. Each element (amino acid or nucleotide) of macromolecules is represented by the corresponding value of electron-ion interaction potential. This numerical representation of the primary structure of macromolecules is subjected to digital signal processing in order to extract the information corresponding to biological function. It is shown that the multiple cross spectrum of functionally related sequences exhibits significant peak frequencies. In the case of functionally unrelated sequences such peaks were not found. Peak frequencies are different for different biological functions. Based on this, we conjecture that the peak frequencies in the multiple cross spectrum of sequences with the same boilogical function are related to this biological function.

Journal ArticleDOI
TL;DR: Average muscle action potential conduction velocity values were obtained during isometric constant-force contractions by a cross-correlation technique to minimize the bias introduced by nondelayed activity appearing on the two myoelectric derivations.
Abstract: Average muscle action potential conduction velocity values were obtained during isometric constant-force contractions by a cross-correlation technique. To minimize the bias introduced by nondelayed activity appearing on the two myoelectric derivations, the signals were doubly differentiated. This arrangement effectively reduced the nondelayed activity and increased the accuracy of the estimate.

Journal ArticleDOI
TL;DR: The algorithm can be shown to give rigorously accurate values for instantaneous frequency and outperform the Fourier transform approach in poor signal-to-noise environments.
Abstract: A new technique for determining the Doppler frequency shift in a phase-coherent pulsed Doppler system is presented. In the new approach, the Doppler frequency shift is given directly in the time domain in terms of the measured I and Q components of the measured Doppler signal. The algorithm is based on an expression for the instantaneous rate of change of phase which separates rapidly varying from slowly varying terms. It permits noise smoothing in each term separately. Since the technique relies solely on signal processing in the time domain, it is significantly simpler to implement than the classic Fourier transform approach. In addition, the algorithm can be shown to give rigorously accurate values for instantaneous frequency and outperform the Fourier transform approach in poor signal-to-noise environments. Experimental results are presented which confirm the superiority of the new domain technique.

Journal ArticleDOI
TL;DR: Simple models that manifest input impedances of arterial systems are compared and an improvement upon documented two-, three-, and five-element models is presented.
Abstract: Simple models that manifest input impedances of arterial systems are compared. An improvement upon documented two-, three-, and five-element models is presented. The classical two-element model (the windkessel) accounts for the lowest frequency components, and the three-element model (the modified windkessel) accounts for both low-and high-frequency components of the spectrum of interest. Five-element models, however, by allowing for reflection, can account for principal features over the entire frequency range of interest.

Journal ArticleDOI
TL;DR: Two main problems to be solved in designing truly effective mobility aids for the blind are to determine what kinds and how many pieces of information are necessary and/or sufficient to mobilize humans, and to establish the optimal coding and display method of the acquired information.
Abstract: Two main problems to be solved in designing truly effective mobility aids for the blind are: 1) to determine what kinds and how many pieces of information are necessary and/or sufficient to mobilize humans, and 2) to establish the optimal coding and display method of the acquired information.

Journal ArticleDOI
TL;DR: For simulating glucose-insulin control systems with respect to application in an optimized therapy of insulin-dependent diabetes, a global transfer model was generated and supplemented with a structural model of the opened control circuit to determine those control constants of glucose-controlled insulin provision that are optimally adapted to a given set of state variables.
Abstract: For simulating glucose-insulin control systems with respect to application in an optimized therapy of insulin-dependent diabetes, a global transfer model was generated and supplemented with a structural model of the opened control circuit. The transfer characteristics within the established linear range of the intact system, which is identical with the range of euglycaemia, can be described by a 4th-order differential equation. A test strategy was developed to identify the state variables of the opened, i. e., of the diabetic, system and to determine by pole assignment those control constants of glucose-controlled insulin provision that are optimally adapted to a given set of state variables. The model system was verified by the prediction of plasma insulin and blood glucose reponses to various loads of glucose and/or insulin, by isotopic studies (U-14C-glucose) of glucose turnover, and by predicting the rates of absorption (i. e., of appearance within the distribution space) of orally administered glucose. The latter situations provide fields of application for this model strategy in addition to the main goal, namely, the individual optimization of control parameters for open-loop or closed-loop insulin therapy.

Journal ArticleDOI
TL;DR: It will be the objective of this communication to show how the essential constants can be obtained.
Abstract: The strength-duration curve is a plot of the lowest (threshold) current (I) required for stimulation versus pulse duration (d); it forms the basis for describing the excitability of a given tissue. It is extremely useful in all manner of studies in which excitable tissues are stimulated because it describes the manner in which the current required is changed when the pulse duration is changed. Moreover, it can be used to determine the charge and energy-duration relationships. It will be the objective of this communication to show how the essential constants can be obtained.

Journal ArticleDOI
TL;DR: Close form expressions for dielectric permittivity and conductivity are suggested for use as estimators over the 10 Hz-100 GHz range.
Abstract: A computer program was developed to fit multiple-term Debye-type expressions to published data of permittivity for muscle. The number of terms in this expression was varied and tested for significance. Based on these results, closed form expressions for dielectric permittivity and conductivity are suggested for use as estimators over the 10 Hz-100 GHz range.

Journal ArticleDOI
TL;DR: This first paper, of two, describes a three-dimensional finite element computer model representing nonhomogeneous electrical conductivity of the human thorax, taking account of various tissue types and other biological materials.
Abstract: This first paper, of two, describes a three-dimensional finite element computer model representing nonhomogeneous electrical conductivity of the human thorax. The spinal canal is treated in detail, taking account of various tissue types and other biological materials. Solutions are presented for the electrical fields generated within the spinal cord from bipolar epidural electrodes. Included in an Appendix is a validation study which compares experimental data in the literature, for subdural electrode arrays in a monkey, to theoretical solutions following the same method as the main work.

Journal ArticleDOI
TL;DR: Moving dipole inverse solutions provide a very useful method of estimating the location of an electrical source in the brain from EEG's or MEG's measured at the surface of the head.
Abstract: Moving dipole inverse solutions provide a very useful method of estimating the location of an electrical source in the brain from EEG's or MEG's measured at the surface of the head. In this method, a dipolar source model is moved about in a model of the head while its amplitude and orientation are also adjusted to obtain the least-squares error fit between the measured EEG's or MEG's and those produced by the dipolar source.

Journal ArticleDOI
TL;DR: A lumped network model of the myelinated nerve axon is used to predict stimulation thresholds for afferent fiber pathways in the dorsal columns and dorsal roots, and Comparisons are made to other possible targets of stimulation.
Abstract: This second paper, of two, draws upon earlier finite element solutions for electrical fields generated within the spinal cord by epidural electrodes. Given those fields, a lumped network model of the myelinated nerve axon is used to predict stimulation thresholds for afferent fiber pathways in the dorsal columns and dorsal roots. Threshold predictions for dorsal column fibers of 5 and 10 , im diameters correspond closely with sensory thresholds reported experimentally. Descending fibers in the lateral corticospinal tracts are also considered. Comparisons are made to other possible targets of stimulation, and the theoretical indications are discussed in the context of clinical findings.

Journal ArticleDOI
TL;DR: Wheezing was found to be strongly dependent upon air flow, and generally followed the changes in pulmonary function as indicated by the forced expiratory volume at 1 s (FEV1).
Abstract: Breath sounds were recorded in normal and asthmatic children over the chest and trachea. The power spectra of the sounds were analyzed for peaks of high amplitude and high frequency as indications of wheezing. The percent of inspiration and expiration spent wheezing was used as an indication of the severity of bronchial obstruction. Wheezing was found to be strongly dependent upon air flow, and generally followed the changes in pulmonary function as indicated by the forced expiratory volume at 1 s (FEV1). The trachea was found to be a better location for analyzing wheezes than the lung.

Journal ArticleDOI
TL;DR: The theory of the linear, insulated antenna embedded in an electrically dense medium is applied to microwave antennas used for hyperthermia cancer therapy and the pattern of power deposition is computed.
Abstract: The theory of the linear, insulated antenna embedded in an electrically dense medium is applied to microwave antennas used for hyperthermia cancer therapy. The pattern of power deposition is computed for a square array of four antennas with a side length of 3 cm under the assumption of no coupling among antennas. The driving frequency is set to seven values between 300 and 915 MHz, and the antenna halflength is set to three values: 3 cm, 6 cm, and the resonant value.

Journal ArticleDOI
TL;DR: The various methods of estimating the attenuation and velocity of ultrasound in biological media are described and the effect of velocity dispersion on the measurement of velocity in tissues is discussed as well.
Abstract: In this paper, the various methods of estimating the attenuation and velocity of ultrasound in biological media are described. Special attention is paid to the influence of the transducer used in the measurement, i.e., the diffraction effect. This influence is investigated in a systematic way using realistic three-dimensional computer simulation techniques. The results of the analysis are given as universal sets of curves. These curves can be used by the interested reader to estimate the influence of the diffraction effect on the measurements for his own experimental conditions. Methods of preventing the systematic errors caused by the diffraction effect are discussed. For the sake of completeness, the effect of velocity dispersion on the measurement of velocity in tissues is discussed as well.

Journal ArticleDOI
TL;DR: According to the theoretical and experimental results obtained, some general operating rules and optimal setups for each of the most common experimental situations are proposed, with the aim of standardizing saccade analysis for both researchers and clinicians.
Abstract: A set of quantitative data about signal processing effects on the evaluation of amplitude, duration, and peak-velocity of single saccadic eye movements, as well as on the evaluation of the coefficients of amplitude-peak velocity and amplitude-duration characteristics of a family of saccades, is given. The following aspects of signal processing are theoretically discussed, experimentally supported, and summarized by normative graphs: 1) the analog low-pass filtering applied to the recorded eye movement; 2) its sampling and digitization; 3) the low-pass filtering applied to the digitized signal; 4) the algorithm used to compute the eye velocity; 5) the criteria adopted to determine the beginning and the ending points of the saccades; and 6) the laws used to fit the saccadic characteristics. According to the theoretical and experimental results obtained, some general operating rules and optimal setups for each of the most common experimental situations are proposed, with the aim of standardizing saccade analysis for both researchers and clinicians.

Journal ArticleDOI
TL;DR: An approach is explicitly formulated to blend a local with a global theory to investigate oscillatory neocortical firings to determine the source and the information-processing nature of the alpha rhythm.
Abstract: An approach is explicitly formulated to blend a local with a global theory to investigate oscillatory neocortical firings to determine the source and the information-processing nature of the alpha rhythm. The basis of this optimism is founded on a statistical mechanical theory of neocortical interactions which has had success in numerically detailing properties of short-term memory (STM) capacity at the mesoscopic scales of columnar interactions, and which is consistent with other theories deriving similar dispersion relations at the macroscopic scales of electroencephalographic (EEG) and magnetoencephalographic (MEG) activity.

Journal ArticleDOI
TL;DR: In vitro calibration indicates that there is a constant ratio between the frequency responses at both wavelengths used, and the decrease of this ratio encountered in in vivo measurements is attributed to different depths of investigated skin microcirculation according to the incoming wavelengths.
Abstract: A new experimental laser Doppler setup has been designed to discriminate between total and superficial skin blood flow. This selectivity is based on the use of two wavelengths with different penetration depths into the skin. An argon ion and helium-neon laser are mounted on the same optical bench and are stabilized by an optical feedback loop. A single optical fiber directs the beams to the skin and collects the reflected light back to a photodetector, the signal of which is sampled and Fourier transformed to give a frequency power spectrum. Several models of light scattering by the skin are examined, and a single Lorentzian function is found to be the best fit for our experimental power spectra. Flow parameters have been thus measured for several in vitro and in vivo situations. In vitro calibration indicates that there is a constant ratio between the frequency responses at both wavelengths used. The decrease of this ratio encountered in in vivo measurements is attributed to different depths of investigated skin microcirculation according to the incoming wavelengths.

Journal ArticleDOI
TL;DR: A comparison of the major methodologies utilized in computer simulations of electrocardiographic potential calculations suggests that the use of a basic finite element formulation improves the accuracy over that obtainable with integral equations, and the improvement in accuracy is particularly notable for inverse estimation.
Abstract: This paper is a comparison of the major methodologies utilized in computer simulations of electrocardiographic potential calculations. Two integral equation methods (Green's theorem and the equivalent single layer) and finite element methods are compared for forward and inverse solutions. The results suggest that the differences in accuracy between the two integral equation formulations are small. However, the use of a basic finite element formulation improves the accuracy over that obtainable with integral equations, and the improvement in accuracy is particularly notable for inverse estimation.

Journal ArticleDOI
TL;DR: A speech prosthesis has been developed based on the following idea: when a handicapped person such as a laryngectomee tries to speak in vain, the movements of the mouth, tongue, etc., are elicited and what he or she is trying to say can be determined.
Abstract: A speech prosthesis has been developed based on the following idea. When a handicapped person such as a laryngectomee tries to speak in vain, the movements of the mouth, tongue, etc., are elicited. By detecting the movements, what he or she is trying to say can be determined. Then a speech synthesizer is driven to produce a voice of good quality.

Journal ArticleDOI
TL;DR: Results indicate that SFEMG recordings from a normal MU contain mainly the AP's of the closest one to three muscle fibers of the MU, and the amplitude and area of simulated macro-EMG MUAP's increase with the number of muscle fibers in the MU.
Abstract: A motor unit action potential (MUAP) recorded in clinical electromyography (EMG) is the spatial and temporal summation of the action potentials (AP's) from all muscle fibers in a motor unit (MU) An important determinant of MUAP waveform characteristics is the size of the recording electrode In this paper, we have described the use of a modified line source model of single muscle fiber action potentials to simulate MUAP's as recorded by single fiber (SF) EMG, concentric needle (CN) EMG, and macro-EMG electrodes Results indicate that SFEMG recordings from a normal MU contain mainly the AP's of the closest one to three muscle fibers of the MU The amplitude, area, and duration of the simulated CNEMG MUAP's are determined mainly by the number and size of muscle fibers within a semicircular territory of 05, 15, and 25 mm, respectively, around the tip of the electrode The amplitude and area of simulated macro-EMG MUAP's increase with the number of muscle fibers in the MU