Showing papers in "IEEE Transactions on Biomedical Engineering in 1977"
TL;DR: Three conceptually safe methods of injecting charge from a noble metal into tissue: modification of the electrical double layer at the interface and coupling via either of two symmetrical surface-layer oxidation-reduction processes.
Abstract: Electrical stimulation of the nervous system is of increasing importance for a variety of prospective neural prostheses. Electrochemical reactions which may occur at Pt or other noble metal-tissue interfaces are reviewed. Use of stimulus waveforms with a net direct current component increases the probability of tissue damage. There are three conceptually safe methods of injecting charge from a noble metal into tissue: modification of the electrical double layer at the interface and coupling via either of two symmetrical surface-layer oxidation-reduction processes. These reactions may be addressed with stimulus waveforms without a direct current component and with controlled charge densities.
329 citations
TL;DR: A method for finding transfer coefficients that relate the epicardial and body surface potential distributions to each other is provided, based on knowing the geometric location of each electrode, and on having enough electrodes to establish the geometric shape and the potential distribution of closed epicardials and body surfaces.
Abstract: Although it has been known throughout this century that a complex sequence of electrical events is produced on the body surface by the electrophysiological properties of the heart, the question of how well these body surface events can be explained mathematically on the basis of experimental measurements of cardiac geometry and electrical activity remains unanswered. Recent advances in experimental capabilities have made possible the near simultaneous measurement of both cardiac epicardial and corresponding body surface potential distributions from in vivo animal preparations using chronically implanted electrodes to keep the volume conductor intact. This report provides a method for finding transfer coefficients that relate the epicardial and body surface potential distributions to each other. The method is based on knowing the geometric location of each electrode, and on having enough electrodes to establish the geometric shape and the potential distribution of closed epicardial and body surfaces. However, the method does not require that either the heart or body surfaces have any special shape, such as that of a sphere, or that any electrical quantities, such as voltage gradients, be known in addition to the potentials. The use of potential distributions to represent heart electrical activity is advantageous since such distributions can be directly measured experimentally, without a transformation to any other form, such as multiple current-generating dipoles, being required. This report includes a statement of the underlying integral equations, the procedure. for finding the equations' coefficients from geometry measurements, some considerations for computer algorithms, and an example.
310 citations
TL;DR: The electric arc process used to expose Parylene-covered iridium and tungsten microelectrodes is found to give cleaner recording surfaces with impedances lower than those obtainable with previously described methods.
Abstract: One of the major problems in the design of neurophysiologiv extracellular microelectrodes is the application and selective removal of the insulation. In addition to the usual problems of achieving pin-hole-free coatings and reproducible tip exposures and impedances, chronic electrode designshave the additional requirement of maintaining megohm levels of electrical isolation for months in vivo. A method of insulating finely tapered microelectrodes with complicated shapes by vapor condensation of Parylene-C is presented, along with a method for exposing controlled, reproducible lengths of their tips. In vivo and in vitro impedance tests and unit records obtained over 100 days in monkey motor cortex are presented. The electric arc process used to expose Parylene-covered iridium and tungsten microelectrodes is found to give cleaner recording surfaces with impedances lower than those obtainable with previously described methods. Chronic iridium microelectrodes so fabricated have recorded unit potentials and maintained constant impedances for over 4 months in vivo.
270 citations
TL;DR: The maximum, biphasically applied charge which can be injected without electrolyzing water has been determined for Pt electrodes in simulated cerebral spinal fluid at 37°C, and microscopic observations of bubble formation indicate that these limits are conservative.
Abstract: The maximum, biphasically applied charge which can be injected without electrolyzing water has been determined for Pt electrodes in simulated cerebral spinal fluid at 37°C. Electrolysis of water would lead to gas bubble formation, which is thought to be harmful. The experimental method involved the use of electrical transients. With lead (anodic faist) electrodes, the theoretical non-gassing limit is 300 ±20 μC/real cm2, independent of current density in the range of ±50 to ±450 mA/cm2. For lag (cathodic first) electrodes, the theoretical non-gassing limit is 350 ±50 μC/real cm2 over the same current density range. In both cases, only part of the additional charge beyond these limits results in water electrolysis. Microscopic observations of bubble formation indicate that these limits are conservative. These limits are sufficiently large for most purposes; they do not restrict the use of Pt electrodes in stimulation.
240 citations
TL;DR: The results show that for these shapes the component of the total field normal to the surface of the volume conductor is produced completely or in large part by the dipole alone.
Abstract: Expressions are presented for the magnetic fields produced by current dipoles in four basic volume conductor shapes. These shapes are the semi-infinite volume, the sphere, the prolate spheroid (egg-shape), and the oblate spheroid (discus-shape). The latter three shapes approximate the shape of the human head and can serve as a basis for understanding the measurements of the brain's magnetic fields. The semi-infinite volume is included in order to investigate the effect of the simplest boundary between a conductor and nonconductor. The expressions for the fields are presented in a form which separates the total field into two parts. One part is due to the dipole alone (the dipole field); the other is due to the current generated in the volume conductor by the dipole (the volume current field). Representative plots of the total field and the volume current field are presented for each shape. The results show that for these shapes the component of the total field normal to the surface of the volume conductor is produced completely or in large part by the dipole alone. Therefore, measurement and use of this component will greatly reduce the complexity of determining the sources of electrical activity inside a body from measurements outside the body by removing the necessity of dealing with the volume current field.
228 citations
TL;DR: Motion artifacts frequently cause erroneous results in biopotential measurement when surface electrodes and conducting paste are used, and light abrasion of the sidn with fine sandpaper is then required to avoid skin irritation.
Abstract: Motion artifacts frequently cause erroneous results in biopotential measurement. When surface electrodes and conducting paste are used, a major cause of motion artifact is change in skin potential. The most effective means of minimizing this artifact is light abrasion of the sidn with fine sandpaper. A very mild paste is then required to avoid skin irritation.
212 citations
TL;DR: A theoretical model of the electromyographic (EMG) signal showed that the EMG can be represented as an amplitude modulation process of the form EMG = [Kn(t)1/2 w( t) with the stochastic process, w(t), having the spectral and probability characteristics of the EMg during a constant contraction.
Abstract: A theoretical model of the electromyographic (EMG) signal has been developed In the model, the neural pulse train inputs were considered to be point processes which passed through linear, time-invariant systems that represented the respective motor unit action potential The outputs were then summed to produce the EMG It was assumed, that in the production of muscle force, the controlled parameter was the number of active motor units, n(t) The model then showed that the EMG can be represented as an amplitude modulation process of the form EMG = [Kn(t)1/2 w(t) with the stochastic process, w(t), having the spectral and probability characteristics of the EMG during a constant contraction Various assumptions made in the model development have been verified by experiments
164 citations
TL;DR: A heuristic feedback system model for the human disparity-vergence eye movements is described and simulation studies of the model responses for both step and sinusoidal responses fit the experimentally obtained results.
Abstract: A heuristic feedback system model for the human disparity-vergence eye movements is described. The system has been modeled as a continuous negative feedback system with a modified integral-derivative controller, a time-delay element, and a third-order plant. Simulation studies of the model responses for both step and sinusoidal responses fit the experimentally obtained results.
117 citations
TL;DR: A two step procedure is described for measuring the characteristics of visual evoked brain potentials by aligning the corresponding components in different waveforms and averaging over the waveform segment in the immediate vicinity of the peak to obtain a latency corrected average.
Abstract: A two step procedure is described for measuring the characteristics of visual evoked brain potentials. First, the recorded waveforms are processed by a filter designed to minimize the mean square error produced by the ongoing EEG. This filter is different for each subject and is based on certain statistical properties of the measured data. Second, the filtered potentials are searched automatically by a computer to determine the existence and location of the individual components in the responses. By aligning the corresponding components in different waveforms and averaging over the waveform segment in the immediate vicinity of the peak, a latency corrected average is obtained that provides a new representation of the response waveform.
112 citations
TL;DR: An electrical method is described which is suitable for determining exposed areas of Pt-stimulation electrodes prior to implantation.
Abstract: An electrical method is describqd which is suitable for determining exposed areas of Pt-stimulation electrodes prior to implantation.
108 citations
TL;DR: It is shown that the resonant frequency observed in these spectra will vary as the cardiac pressure changes, so the variations of the resonance can be calibrated to give the pressure excursions in a cardiac chamber.
Abstract: We suggest and analyze a new technique for making non-invasive cardiac measurements. The technique involves measurement of the spectrum of ultrasound scattered from small bubbles injected into the circulatory system as they pass through the heart. We show that the resonant frequency observed in these spectra will vary as the cardiac pressure changes. Thus the variations of the resonance can be calibrated to give the pressure excursions in a cardiac chamber. Preliminary bench tests of the method are described which show the predicted shift with pressure of the resonance frequency of bubbles in water.
TL;DR: The results compare favorably with a thermal model for prediction of thresholds which considers the activation energy for thermal destruction of the tissues, their thermal diffusivity, absorption coefficients, time and intensity of exposure, and baseline temperature.
Abstract: Thresholds are reported for production of focal ultrasonic lesions in rabbit liver, kidney, and testicle for 2 and 6 MHz, singe pulse exposures ranging in length from 1 to 60 s. Intensity-exposure time thresholds are found to be nearly independent of frequency as shown in earlier work for brain tissue. The results compare favorably with a thermal model for prediction of thresholds which considers the activation energy for thermal destruction of the tissues, their thermal diffusivity, absorption coefficients, time and intensity of exposure, and baseline temperature. All thresholds are of the same magnitude as those previously reported for brain. Those differences which are observed can be explained by the thermal model for the action of ultrasound on tissue.
TL;DR: Solutions of the inverse problem for the terms in the EME model indicate that when a limited number of measurements are used, the best results can be obtained by uniform distribution of the measurements over the torso.
Abstract: Several aspects of the forward and inverse problems of electrocardiography are investigated through the use of digital computer models. Two forms of a fixed location, variable moment, 20-dipole cardiac model of QRS are developed from actual cardiac excitation data. One form uses time-varying orientation dipoles; the other uses fixed orientation dipoles. An electric multipole expansion (EME) cardiac model employing the dipole, quadrupole, and octupole terms is also developed and used as an equivalent forward and inverse cardiac model. Two realistically shaped torso models are used. The homogeneous torso has uniform conductivity; the inhomogeneous torso contains realistically shaped lung regions with reduced conductivity. It is found that when the EME model is used as an equivalent forward cardiac model, it can accurately represent the actual 20-dipole cardiac model in the homogeneous torso. Limb leads are accurately represented by the dipole terms alone while the precordial leads require the quadrupole and octupole terms. It is also found that while the lung regions have little effect on the ECG's produced by the models, these regions can have a significant effect on the inverse solutions for certain dipoles in the 20-dipole cardiac model. These lung regions appear to have a much smaller effect on the dipole terms in the EME model. Solutions of the inverse problem for the terms in the EME model indicate that when a limited number of measurements are used, the best results can be obtained by uniform distribution of the measurements over the torso.
TL;DR: It is shown that scatterers moving in the near field of the sound beam generated by a single transducers ultrasound Doppler system produce a spectrum whose breadth is primarily determined by the range of angles over which backscattered ultrasound is received by the transducer.
Abstract: The bandwidth of the output spectrum of blood flow meters may prove of value in estimating flow parameters such as the degree of turbulence. It is therefore important to determine the various factors which affect this bandwidth. It is shown that scatterers moving in the near field of the sound beam generated by a single transducer ultrasound Doppler system produce a spectrum whose breadth is primarily determined by the range of angles over which backscattered ultrasound is received by the transducer. An empirical method of calculating the bandwidth of the output spectrum is described, and the results are compared with direct Doppler measurements. Since the spectrum broadening depends on the angle between the target path and the ultrasound beam, it is suggested that the phenomenon may be usable to provide an independent measure of this angle.
TL;DR: A new simple procedure for analyzing and evaluating human gait that can be easily performed in clinical practice is presented.
Abstract: A new simple procedure for analyzing and evaluating human gait that can be easily performed in clinical practice is presented. Signals proportional to forces produced by a subject walking along a walkway are registered by a common force plate and processed by a specially made hybrid computer.
TL;DR: The objective is to present major mathematical models of human thermoregulatory systems which can be used in simulation and design for practicing engineers.
Abstract: The literature on engineering models of the human Thermoregulatory system is reviewed and classified. The present review is a sequel to "A Review on Mathematical Models of the Human Thermal System." Emphasis in this review is the incorporation of physiological thermoregulation into engineering models. The objective is to present major mathematical models of human thermoregulatory systems which can be used in simulation and design for practicing engineers.
TL;DR: A window discriminator for the separation of multi-unit neuronal spike trains which will display simultaneously the recorded spike information and the time-amplitude window levels.
Abstract: Usually extracellular microelectrodes record the activity from several neurons. In order to quantify the activity of an individual neuron in the record some form of spike discrimination is required. This paper describes a window discriminator for the separation of multi-unit neuronal spike trains which will display simultaneously the recorded spike information and the time-amplitude window levels. The window levels are displayed and can be delayed to include any portion of the spike waveform either above or below the initial threshold level. Several instruments can be cascaded for multiple time-amplitude interrogations of the same spike class from a single electrode recording. The instrument utilizes inexpensive commercially available integrated circuits.
TL;DR: A general technique for the real-time extraction of a physiological signal in the presence of well-characterized noise is described using a noninvasive fetal ECG detection system as an example application.
Abstract: A general technique for the real-time extraction of a physiological signal in the presence of well-characterized noise is described using a noninvasive fetal ECG detection system as an example application.
TL;DR: The results suggest that the estimated ê(t), like the actual pressure/volume ratio measured by Suga is related to the contractile state of the left ventricle.
Abstract: The goal of this study is to estimate the values of the parameters of a simple electrical model of the cardiovascular system and to evaluate whether some physical interpretation can be given to the left ventricular parameters. In this model, the left ventricle is represented by a time varying capacitance C(t) analogous to the instantaneous left ventricular pressure/volume ratio, and the systemic vascular bed by two capacitances (Cl, C2), one inductance (L) and one resistance (r). The parameter values are computed from only two measurements: the instantaneous pressurepao(t) and the mean flow Q?ao at the root of the aorta during one beat. First, r is calculated as the ratio between P?ao and Q?ao. Thereafter, Jazwinski's nonlinear filter is used to compute L, C1, C2 from the diastolic part of pao (t), and C(t) from the systolic part of pao(t). The shape of e(t), i.e., 1/?(t) during one beat, estimated from our experiments on dogs, varies strongly after isoproterenol injection (increase in myocardial contactility) but remains unchanged after neosynephrine and amyl nitrite administration (changes in peripheral vascular resistance). These results suggest that the estimated e(t), like the actual pressure/volume ratio measured by Suga is related to the contractile state of the left ventricle.
TL;DR: The Extended Boundary Condition Method is used to calculate resonance region power deposition in prolate spheroid models of animals and man, providing a theoretical basis for the interpretation of experimental results and in extrapolating experimentally derived animal results to man's body configuration.
Abstract: The Extended Boundary Condition Method is used to calculate resonance region power deposition in prolate spheroid models of animals and man. The mathematical models consist of homogeneous distributions of muscle tissue, although in the case of the man model calculations, a model consisting of homogenized muscle, fat, and bone is also considered. Calculations are made for bodies isolated in free space and irradiated by a plane wave. Resonant frequencies and power absorption characteristics are predicted for man and a number of commonly used experimental animals. The results given here will be useful in providing a theoretical basis for the interpretation of experimental results and in extrapolating experimentally derived animal results to man's body configuration.
TL;DR: A numerical method for predicting current and normal electric field distributions induced on humans situated in the near vicinity of the lines, based on the method of moments in which the human body is modeled as a collection of straight cylindrical segments with lengths and radii comparable to that section of the body being modeled.
Abstract: With the advent of EHV transmission lines and the almost certain possibility of UHV lines, it becomes increasingly important to describe accurately the transmission line electromagnetic field interaction with life forms. This paper develops a numerical method for predicting current and normal electric field distributions induced on humans situated in the near vicinity of the lines. The technique is based on the method of moments in which the human body is modeled as a collection of straight cylindrical segments with lengths and radii comparable to that section of the body being modeled. Various scenarios are considered, eg., a well-insulated person standing on the ground beneath the transmission line; an individual in good contact with the earth; or a lineman working in very close proximity to an energized conductor. The position of the arms is varied; for example, arms extended or down at the side. The question of biological hazards from exposure to fields of these systems is also discussed.
TL;DR: It is shown that through proper handling of these data, useful images can be obtained and the system offers the advantages of eliminating the need for a highly stabilized, linear translating mechanism, and also of requiring relatively low patient dosage.
Abstract: In this paper we investigate the possibility of constructing computerized tomograms using data collected from a fluoroscopic system. It is shown that through proper handling of these data, useful images can be obtained. The system offers the advantages of eliminating the need for a highly stabilized, linear translating mechanism, and also of requiring relatively low patient dosage. In addition, the data gathering can be done in essentially real time.
TL;DR: Experimental and theoretical results agree very well and a discussion on the use of angular scattering for determining the mechanical properties of the erythrocyte is presented.
Abstract: The angular scattering of 5-MHz ultrasonic waves by blood was measured in the range from 60 to 1500. Experimental and theoretical results agree very well. A discussion on the use of angular scattering for determining the mechanical properties of the erythrocyte is presented.
TL;DR: A device for measuring uniplanar force systems from orthodontic appliances that can be used to rapidly determine forces and moments from appliances which are statically indeterminate is described.
Abstract: A device for measuring uniplanar force systems from orthodontic appliances is described. The device can be used to rapidly determine forces and moments from appliances which are statically indeterminate.
TL;DR: The concept of linked oscillators applied to the modeling of electrical rhythms in the mammalian digestive tract is extended to cover the use of Hodgkin-Huxley-type dynamics to find multiple solutions in contrast to coupled Van der Pol oscillators.
Abstract: The concept of linked oscillators applied to the modeling of electrical rhythms in the mammalian digestive tract is extended to cover the use of Hodgkin-Huxley-type dynamics. as the basic oscillating unit. The singe action potential of the normal Hodgkin-Huxley equations is converted into auto-rhythmic behavior either by the addition of a shunt conductance term or by increasing the power of the non-linear potassium conductance term to 6. Interconnection of units of this type using either resistive, capacitive, orinductive terms causes entrainment at a frequency not greater than the highest uncoupled frequency in the array. Multiple solutions have not been found in contrast to coupled Van der Pol oscillators.
TL;DR: The aim of this paper is to find those properties of the sensor unit which would enable the optimal integrated behavior of the whole system to be obtained.
Abstract: This paper deals with a system of planary distributed transducers called "Artificial skin." The material used for this purpose is soft, homogeneous and elastic. The Belgrade hand prosthesis is covered with it. The aim of this paper is to find those properties of the sensor unit which would enable the optimal integrated behavior of the whole system to be obtained. Two basic integral properties of artificial skin are implemented: tactile perception and perception proportional to pressure on the skin. From this it is possible to have slipping perception of the grasped objects.
TL;DR: Analysis of the time constants and Bode plots obtained from current injection leads to the development of an equivalent model circuit describing the functional relationships of the individual neuronal elements, which will act as a framework on which active properties such as burst form, timing, and termination can be tested.
Abstract: This paper deals with a quantitative analysis of a network of electrically coupled neurons (cyberchrons) in the snail Helisoma trivolvis. This network produces regular bursts of activity which drive the motoneurons controlling the feeding musculature. Analysis of the time constants and Bode plots obtained from current injection leads to the development of an equivalent model circuit describing the functional relationships of the individual neuronal elements. The equivalent model is used to demonstrate compensation of the frequency response of an individual neuron by the effective loading of the rest of the network. However, the current observed in a postsynaptic neuron is intergrated across the long cell time constant resulting in increased temporal and spatial summation. This frequency compensation and long duration of the postsynaptic response are both believed to be instrumental in the maintenance of a high frequency burst. This model will act as a framework on which active properties such as burst form, timing, and termination can be tested.
TL;DR: An electromagnetic device has been developed which can detect the magnetic fields associated with this charge and which is capable of monitoring stress waves in bone in vivo, independent of the mechanical properties of the soft tissue overlying the bone.
Abstract: A stress wave propagating in a long bone is accompanied by a traveling electrical charge generated as a result of the piezoelectric character of bone. An electromagnetic device has been developed which can detect the magnetic fields associated with this charge and which is capable of monitoring stress waves in bone in vivo. The field measurement is independent of the mechanical properties of the soft tissue overlying the bone, so that difficulties previously encountered with vibration and wave propagation tests to determine in vivo properties of bone are avoided. Applications to the diagnosis of bone disorders are discussed.
TL;DR: Physiological experiments performed in the vestibulo-cerebellum of the turtle appear to validate some of the conclusions of the model which predicts that the cerebellar cortex may act in part as a higher order lead-lag compensator.
Abstract: A model for the cerebellar cortex is developed which qualitatively describes its temporal behavior This neural network is treated as a lumped linear system with pure time delays between elements The model predicts that the cerebellar cortex may act in part as a higher order lead-lag compensator Physiological experiments performed in the vestibulo-cerebellum of the turtle appear to validate some of the conclusions of the model
TL;DR: AC impedance between two acupuncture points (Li-4 and Li-12) and two pairs of anatomically similar points with the same separation was studied via Laplace plane analysis of the time domain current response to a predetermined voltage perturbation.
Abstract: AC impedance between two acupuncture points (Li-4 and Li-12) and two pairs of anatomically similar points with the same separation was studied via Laplace plane analysis of the time domain current response to a predetermined voltage perturbation. The series resistance between the two acupuncture points was found to be significantly lower than between either pair of control points. The characteristic impedance of an equivalent transmission line was lower and the signal propagation velocity higher for the acupuncture point system as compared to both controls.