Showing papers in "IEEE Transactions on Biomedical Engineering in 1971"
TL;DR: The change in mutual impedance ?
Abstract: The change in mutual impedance ?Z resulting from a change ?g in the conductivity of a particular region of a volume conductor is shown to be given by ?Z = - ?g?Lt?·L? dv. L? and L? are the lead fields associated with the two ports used to measure ?Z. The integration is over the region where the conductivity has changed. The superscript t indicates that the lead field is to be evaluated following the change in conductivity. An example involving a spherical conductor is provided.
500 citations
TL;DR: A detailed theoretical analysis indicates the design considerations for achieving minimum losses in the vicinity of the implanted coil and predicts relevant internal losses of about one-half of 1 percent of the transported power.
Abstract: In systems in which inductive coupling between a pancake-shaped coil on the surface of the body and a similar coil within the body is utilized for the transport of electromagnetic energy, the minimization of temperature rise in the tissue is intimately related to the achievement of minimum losses in the region of the implanted coil. A detailed theoretical analysis indicates the design considerations for achieving minimum losses in the vicinity of the implanted coil and predicts relevant internal losses of about one-half of 1 percent of the transported power. Experimental verification of theoretical expectations has involved an operating frequency of 428 kHz for the transmission of 1 kW of power between a simple water-cooled coil on the surface of the chest and a coil implanted in the chest wall of a dog. A maximum tissue temperature of 103.5° F was observed. Since 1-h operation per day at the 1-kW level would supply the anticipated energy requirements for a patient with an artificial heart, the system may find application in the charging of internal energy storage units of artificial heart systems.
196 citations
TL;DR: This paper considers how many and which locations on the body surface must be measured (by taking ECGs at these positions) to be able to determine consistently the total-body QRS surface-potential distribution as it varies in time.
Abstract: This paper considers how many and which locations on the body surface must be measured (by taking ECGs at these positions) to be able to determine consistently the total-body QRS surface-potential distribution as it varies in time. The answers to these questions have implications about the complexity of models of heart electrical activity in addition to their experimental value. An advantage of using the ability to compute the total-body potential distribution as a criterion of quality is that untestable assumptions about the nature of heart electrical activity are avoided. The accuracy of computed potential distributions with respect to corresponding experimental ones is specified by the mean-square difference between them. Acceptable maps had an average relative mean square error of less than 4 percent in the presence of about 1 percent noise, since inspection of the surface maps showed this to be the maximum error allowable for the same clinical or physiological interpretation of the surface maps analyzed.
195 citations
TL;DR: In this article, the effectiveness of 88 types of untruncated and truncated exponential waveforms in reversing ventricular fibrillation was evaluated in large anesthetized dogs.
Abstract: From 10 560 transthoracic fibrillation-defibrillation episodes in large anesthetized dogs, the effectiveness of 88 types of untruncated and truncated exponential waveforms in reversing ventricular fibrillation was evaluated. The study involved waveforms which could be generated with stored energy levels (in the simple capacitor-switch sense) of 60, 90, 120, and 180 J and initial current levels of 10, 20, 30, 40, 60, 80, and 100 A. The 10-A waveforms were untruncated or truncated at final current values of 5, 7.5, and 9 A. The 20-, 30-, and 40-A waveforms were untruncated or truncated at 5, 10, and 15 A. The 60-, 80-, and l00-A waveforms were untruncated or truncated at the 15-A level.
190 citations
TL;DR: A preprocessor that detects in real time an electrocardiogram QRS complex and computes the R-R interval is described, which is encouraging as an ultrareliable means for locating the QRS.
Abstract: Digital preprocessors can ease the increasing data collection demands placed on real-time computers in patient monitoring. This paper describes a preprocessor that detects in real time an electrocardiogram QRS complex and computes the R-R interval. Detection is performed using multiple digital differentiation, which is encouraging as an ultrareliable means for locating the QRS. Inherent in the technique is a dependable control that can automatically compensate for signal-level variations. Clinical data demonstrate that detection is insensitive to low- and high-frequency noise, from baseline drift to muscle artifact and cautery bursts. The device can be connected directly to a patient, whose safety is guaranteed by optoelectronic isolation and interelectrode current limiting. Preprocessor operation has been human-engineered to a simple on/off procedure.
116 citations
TL;DR: The integrated electrode-buffer amplifiers described comply with specifications of the American Heart Association and should prove useful as a direct replacement for conventional paste-type electrodes in existing clinical EKG equipment as well as for long-term applications such as space missions and intensive-care-unit patient monitoring, where frequent attention to the electrodes is inconvenient.
Abstract: Experimentation regarding various aspects of a technique for recording electrocardiographic potentials from unprepared skin, without the use of conventional paste, is described. Because of the relatively high skin-to-electrode impedances encountered without electrolytic paste, high input impedance amplifiers must be utilized for acquisition of the signal. In order to minimize susceptibility to external electrostatic and electromagnetic interference, an inherent problem with high input impedance amplifiers, buffer amplifiers were incorporated directly within the electrode housing. Of the different metals tested, stainless steel proved to be the most stable skin contact material for pasteless operation. The integrated electrode-buffer amplifiers described comply with specifications of the American Heart Association and should prove useful as a direct replacement for conventional paste-type electrodes in existing clinical EKG equipment as well as for long-term applications such as space missions and intensive-care-unit patient monitoring, where frequent attention to the electrodes is inconvenient.
107 citations
TL;DR: Quantitative relationships among various hemodynamic parameters are obtained, and these appear to be in good agreement with the physiological characteristics of the left ventricle.
Abstract: A left-ventricular pumping model based on a left-ventricular systolic time-varying pressure/volume ratio e(t) has been proposed on the basis of the physiological studies indicating that the parameter e(t) is a function of time in systole, almost independent from left-ventricular volume and the arterial-loading conditions, and is a good index of myocardial inotropism. The model has been formulated by the following two equations: \begin{equation} p(t) = e(t) \bigg\{ v(0)-\int_0^t i(t) dt\bigg\} \end{equation} \begin{equation}p(t) = f\{i(t)\} \end{equation} where p(t) is the systolic left-ventricular pressure, v(o) is the left-ventricular end-diastolic volume (at the onset of systole), i(t) is the blood-flow rate ejected from the left ventricle, t is the time from the onset of systole, and ? is a function of the hydraulic impedance of the load against the ventricular ejection (including the aortic valve). Some theoretical analyses of this model are attempted, first analytically with simplifications of the time course of e(t) and the hydraulic impedance of the load, and then by an analog computer with e(t) approximated to the physiological data. Quantitative relationships among various hemodynamic parameters are obtained, and these appear to be in good agreement with the physiological characteristics of the left ventricle.
103 citations
TL;DR: The ultrasonic threshold doses to produce functional and structural irreversible effects in the mouse, rat, cat, monkey, and human central nervous systems are presented and it is concluded that ultrasound does not present a hazard, as currently employed for medical diagnostic purposes.
Abstract: The ultrasonic threshold doses (acoustic intensity and time duration of a single pulse) to produce functional and structural irreversible effects in the mouse, rat, cat, monkey, and human central nervous systems are presented for a wide range of the pertinent parameters. There does not appear to be an important dependence upon frequency in the range from 1 to 6 MHz. Embryonic tissue is found to be appreciably more sensitive than adult tissue. From considerations of the measured outputs of commercially available ultrasonic diagnostic instruments, the experimentally determined threshold dosages necessary to produce these irreversible effects, and reports of clinical experience, it is concluded that ultrasound does not present a hazard, as currently employed for medical diagnostic purposes.
101 citations
TL;DR: This investigation was divided into the development of a mathematical model relating respiration to those variations that it causes in heart rate and the use of digital filtering techniques to attenuate fluctuations inheart rate which are due to respiration.
Abstract: Respiratory sinus arrhythmia is the phenomenon by which respiration modulates heart rate in normal humans and in many animals. This investigation was divided into the following three categories: 1) the development of a mathematical model relating respiration to those variations that it causes in heart rate; 2) the use of digital filtering techniques to attenuate fluctuations in heart rate which are due to respiration; and 3) the development of methods that use only heart rate to get information about respiration.
82 citations
TL;DR: The simple chemistry of the cell precludes hydrogen gas generation and thus, for the first time, permits hermetic sealing of a battery and/or pacemaker in a welded stainless-steel enclosure which may be used as the indifferent anode electrode in a monopolar system.
Abstract: A new solid-state battery, designed for implantable prosthetics is described. Single cell voltage is 2.8 V. The anode is metallic lithium. The cathode is a proprietary iodide. The electrolyte is a crystal, lithium iodide. Cell impedance at 37°C for a typical pacemaker battery is under 1000? at beginning of life (BOL) and 16 000 ? at end of life (EOL). The simple chemistry of the cell precludes hydrogen gas generation and thus, for the first time, permits hermetic sealing of a battery and/or pacemaker in a welded stainless-steel enclosure which may be used as the indifferent anode electrode in a monopolar system.
78 citations
TL;DR: Telethermocoagulation is a neurosurgical technique that is now entering the phase of practical clinical application and in this system brain lesions are produced by heating implanted metallics by an external RF electromagnetic field.
Abstract: Telethermocoagulation is a neurosurgical technique that is now entering the phase of practical clinical application. In this system brain lesions are produced by heating implanted metallics by an external RF electromagnetic field.
TL;DR: The SNR depends, at least, upon the contraction level, type of smoothing filter, and the amount of smoothness for the particular filter, which is important in signal communication problems of both a design and theoretical nature.
Abstract: A common method of initially processing surface-detected electromographic (EMG) activity is to differentially amplify, rectify, and then smooth (using a low-pass filter) the rectified activity. The output of the filter exhibits a mean value slightly obscured by ripple. Both the mean value and ripple increase with increasing muscle contraction. The mean value can be called the signal while the ripple, undesirable when only the signal is desired, can be called noise. The SNR depends, at least, upon the contraction level, type of smoothing filter, and the amount of smoothing for the particular filter. This defined SNR is important in signal communication problems of both a design and a theoretical nature.
TL;DR: An optimally controlled respirator was developed that controlled ventilation by the patient's metabolic rate from continuously measured C0 2 output and respiratory rate is computed to minimize ventilatory work.
Abstract: An optimally controlled respirator was developed. It has three main features: 1) ventilation is controlled by the patient's metabolic rate from continuously measured C0 2 output, 2) physiologic dead space approximated as a linear function of tidal volume is used to estimate alveolar ventilation, and 3) respiratory rate is computed to minimize ventilatory work.
TL;DR: The literature on mathematical models of the human thermal system is reviewed and classified in this article, where the authors present a review of the literature on models of human thermal systems and their applications.
Abstract: The literature on mathematical models of the human thermal system is reviewed and classified.
TL;DR: These films have better chemical and electrical properties than the previously reported aluminum oxide films and can be used as insulators for insulated electrocardiograph electrodes.
Abstract: The use of anodic tantalum oxide films as insulators for insulated electrocardiograph electrodes is described. These films have better chemical and electrical properties than the previously reported aluminum oxide films. The electrodes performed satisfactorily.
TL;DR: Results indicate that electrocutaneous stimulation is not practical as a replacement for tactile stimulation, which is presently being used in the Optacon, a new reading aid for the blind.
Abstract: Electrocutaneous stimulation has been investigated for use in the Optacon, a new reading aid for the blind. Results indicate that electrocutaneous stimulation is not practical as a replacement for tactile stimulation, which is presently being used.
TL;DR: The feasibility of using an oscillator, the frequency of which is controlled by the bladder interelectrode resistance, to provide an electrical signal proportional to bladder volume for use in connection with an electronic bladder stimulator is presented.
Abstract: The resistance of the urinary bladder, as measured between two electrodes attached to the external bladder wall at frequencies above 100 kHz, is proportional to the bladder volume for properly placed electrodes. The feasibility of using an oscillator, the frequency of which is controlled by the bladder interelectrode resistance, to provide an electrical signal proportional to bladder volume for use in connection with an electronic bladder stimulator is presented. The implications of this result are discussed.
TL;DR: The results of the analysis indicate that the intracellular volume changes that would be expected during dialysis as a result of osmotic gradients are very small.
Abstract: A mathematical analysis is made of the changes in body fluid volume and solute composition that occur during hemodialysis. The analysis considers the movement of water and solutes across the dialyzer membrane and between the intracellular and extracellular compartments. Dialyzer operating variables such as dialysate addition rate, solute dialysances, and ultrafiltration rate are included. The output of the mathematical model agrees well with data obtained during clinical dialysis. The results of the analysis indicate that the intracellular volume changes that would be expected during dialysis as a result of osmotic gradients are very small. The effects on solute removal of varying dialysate addition rate, ultrafiltration rate, and dialysance are analyzed.
TL;DR: This work has measured the ratio of scattered light intensity to incident light intensity in the stroma for 12 rabbit corneas as a function of the wavelength in the range 3900 to 7250 A, in very good agreement with the theoretical prediction.
Abstract: It is well known that the almost lossless transmission of light through normal mammalian corneas, an obvious fact, requires a theoretical explanation. The reason for this is the pronounced scattering one would expect if the spatial arrangement of the large number of long transversely submicroscopic fibrils that exist in the stroma were purely random. In a recent theory it was shown that the high corneal transparency can be quantitatively well explained if the fibril arrangement can be described in terms of distorted lattices. One conclusion of this theory is that the ratio of scattered light intensity to incident light intensity in the stroma should be inversely proportional to the fifth power of the light wavelength. In the present work this ratio has been measured for 12 rabbit corneas as a function of the wavelength in the range 3900 to 7250 A. The results are in very good agreement with the theoretical prediction.
TL;DR: It is found that the 12 correlated visual evoked potential parameters can be transformed into a reduced set of four uncorrelated components accounting for approximately 76 percent of the total variance of the original set.
Abstract: The average visual evoked potential in man is found to be characterized by six major potential waves or deflections. A computer-aided visual inspection technique is used to extract and measure the 12 parameters corresponding to the amplitude and latency of the six peaks from the responses of 50 subjects. It is then demonstrated that each of these parameters is approximately individually Gaussian distributed and their means and variances are found. With this information, a simple statistical model for the normal visual evoked potential is constructed. It is next assumed that the same 12 parameters are jointly Gaussian distributed and the correlation matrix is computed. A principal components analysis is then applied to this matrix and it is found that the 12 correlated visual evoked potential parameters can be transformed into a reduced set of four uncorrelated components accounting for approximately 76 percent of the total variance of the original set. The four components are then rotated using a varimax technique and the correlation between these components and the original 12 parameters is found to reveal some interesting aspects of the visual evoked potential (VEP) pattern behavior.
TL;DR: A system for the measurement of velocity of particles suspended in liquids was developed, based on the on-line computation of the time to maximum cross correlation between the optical signatures made by particles, as their image traverses two adjacent photo-detectors aligned in the direction of flow.
Abstract: A system for the measurement of velocity of particles suspended in liquids was developed, based on the on-line computation of the time to maximum cross correlation between the optical signatures made by particles, as their image traverses two adjacent photo-detectors aligned in the direction of flow. Cross correlation computation is performed with a commercially available computer, and the time to maximum cross correlation is detected by digital pulse circuitry. The system is particularly suited for measurements of blood flow in vivo and in vitro. Frequency response is linear to 1 Hz where the phase lag is 30°.
TL;DR: An instrument for real-time separation of interleaved neuronal spike trains has been developed and Amplitude of the spike at two selectable time points provides the criteria for separating spikes into as many as nine different classes.
Abstract: An instrument for real-time separation of interleaved neuronal spike trains has been developed. Amplitude of the spike at two selectable time points provides the criteria for separating spikes into as many as nine different classes. The amplitude-time windows are displayed on an oscilloscope along with the spike for adjustment purposes. The system is mainly constructed with integrated circuits for low cost and ease of fabrication.
TL;DR: The spontaneous fluctuations of voltage across a glass microelectrode have been studied as a function of the average difference in voltage across the electrode and the concentration of internal and external salt solutions to serve as a model for studying noise generated when ions move through a micropore.
Abstract: The spontaneous fluctuations of voltage across a glass microelectrode have been studied as a function of the average difference in voltage (V) across the electrode and the concentration of internal (n 2 ) and external (n 1 ) salt solutions. A stationary fluctuation was observed, with a mean square value many times greater than that calculated from the Nyquist formula for noise due to the thermal agitation of charge, for all states of the electrode except n 2 =n 1 , V=0. Here the fluctuations equal the Johnson level. The spectral density of the fluctuation and its dependence on (n 1 , n 2 , V) are given in the range 3-0.003 MKCl and V = ±200 mV. The dependence on the species of cation (potassium and sodium) was also determined. The work has practical implications for users of microelectrodes who wish to minimize noise. It also serves as a model for studying noise generated when ions move through a micropore.
TL;DR: An experimental technique is described for measuring the equivalent multipole model for isolated beating hearts from weighted sums of 20 electrode potentials on the surface of a 6.35-cm diameter sphere.
Abstract: An experimental technique is described for measuring the equivalent multipole model for isolated beating hearts. The dipole, quadripole, and octapole moments are measured from weighted sums of 20 electrode potentials on the surface of a 6.35-cm diameter sphere. An iterative procedure is used to eliminate the effects of source eccentricity for dipolar data.
TL;DR: In this article, the authors describe several studies that contribute to an understanding of the ways in which inhomogeneities and anisotropies may contribute to the formation of multiple peaks of potential on the body surface.
Abstract: This paper describes several studies that contribute to an understanding of the ways in which inhomogeneities and anisotropies may contribute to the formation of multiple peaks of potential on the body surface.
TL;DR: Experiments indicate that a reading speed of over 30 words a minute including line change can be attained with 200 h of training (over a year) and a method of dichotic presentation has been proposed to increase the reading speed and preliminary experiments have produced encouraging results.
Abstract: The operation of the Lexiphone, a reading machine for the blind, is described. The Lexiphone produces a sound pattern for each of the alphabet symbols, and the blind reader has to learn to associate each of these patterns with the corresponding letter. With practice, whole words and short phrases are recognized as entities. As the Lexiphone machine reads each line of print by scanning it with a column containing a large number of photodiodes (54), the visual resolution is quite high and the equivalent quantizing noise is low The signals from the photocells are processed by digital circuits to. produce the modulating signals of a single square wave. The square wave is modulated both in frequency and amplitude, the frequency component being the chief one to identify the letter, and the code sounds generated by the machine reported to be quite pleasant. The physical construction of the Lexiphone is robust and a description of the machine is given. The reading speed of the Lexiphone is discussed. Experiments indicate that a reading speed of over 30 words a minute including line change can be attained with 200 h of training (over a year). A method of dichotic presentation has been proposed to increase the reading speed and preliminary experiments have produced encouraging results.
TL;DR: An electromechanical system that includes patient controllable mechanisms to provide for retention of intravesical content interrupted by intermittent expulsion is described.
Abstract: Techniques for reflex simulation as a treatment for the neurologically impaired bladder must restore volitional control of bladder function. This paper outlines the engineering commitments necessitated by biological considerations and the exclusive biological problems that must be dealt with in order to accomplish this. An electromechanical system that includes patient controllable mechanisms to provide for retention of intravesical content interrupted by intermittent expulsion is then described.
TL;DR: An optical Doppler velocimeter utilizing optical heterodyning techniques was used to measure radial velocity profiles of pulsatile flow in a cardiovascular circulation model, using a single-mode frequency-stabilized He-Ne CW laser and an acoustical frequency modulator as part of a directional flow measurement system.
Abstract: An optical Doppler velocimeter utilizing optical heterodyning techniques was used to measure radial velocity profiles of pulsatile flow in a cardiovascular circulation model. The light source was a single-mode frequency-stabilized He-Ne CW laser (6328 A, 0.1 mW). The laser beam was focused to a 30-?m in diameter spot in the flow stream. Polystyrene spheres 0.73 ?m in diameter, suspended in distilled water, were used as light scatterers. The optical signal beam contained Doppler-shifted scattered light. The reference beam was split from the source beam in one configuration; in a second configuration an acoustical frequency modulator was installed in the reference beam pathway as part of a directional flow measurement system. The circulation model consisted of an artificial heart, a Windkessel model, a peripheral resistance, a capillary model, a reservoir, and an optical glass window section. The flow test section was positioned by a three-dimensional finely adjustable holder. From 10 to 34 point measurements were obtained to plot one velocity profile, which covered 95 percent of the tube diameter.
TL;DR: A tuned transcutaneous transformer which utilizes ferrite pot cores with Litz windings with power levels of 150 W into a 16-?
Abstract: The development of a practical power transmission system for a rechargeable artificial heart requires not only a means of efficiently coupling the required electromagnetic energy across the skin, but also a charge regulator, a primary cooling loop, and a suspension system for aligning the cores. This paper describes a tuned transcutaneous transformer which utilizes ferrite pot cores with Litz windings. Typically, the transformer operates over a frequency range from 12 to 20 kHz. Power levels of 150 W into a 16-? load have been demonstrated in vivo.
TL;DR: A review of the major experimental and modeling advances that assisted in understanding the basic operation of the pupillary light reflex system can be found in this paper, where the authors present a detailed discussion of the most important advances in this area.
Abstract: During the past 15 years, many models have been developed for the pupillary light reflex system. Some of these models have been inadequately described while others have never been tested to determine their compliance or noncompliance with known experimental data. This paper reviews the major experimental and modeling advances that assisted in understanding the basic operation of the pupillary light reflex system.