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Showing papers in "Medical & Biological Engineering & Computing in 1983"


Journal ArticleDOI
TL;DR: A theory of coupled resonant coils has been developed which makes possible the design of radio frequency transcutaneous links of simultaneously high overall efficiency and good displacement tolerance while keeping circuitry simple while keep circuitry simple (particularly in the implanted receiver).
Abstract: A theory of coupled resonant coils has been developed which makes possible the design of radio frequency transcutaneous links of simultaneously high overall efficiency and good displacement tolerance while keeping circuitry simple (particularly in the implanted receiver). Series-tuned transmitter coils were used, obtaining high efficiency. In the first example a stimulator which has excellent displacement tolerance because it works at critical coupling is designed. The second example shows how the theory was used when the voltage in the implant was regulated. The design process involvesad hoc compromises between disparate quantities (e.g. efficiency against voltage transfer ratio), rendering a standard design procedure unsuitable. Fortunately, the derived theoretical formulae are simple enough for every design to be considered from fundamentals, based on coil parameters. Extensive coil loss data are presented here for the frequency band 0·2 to 20 MHz.

224 citations


Journal ArticleDOI
TL;DR: Over the entire frequency range of the study, the dielectric properties of the muscle were found to be significantly anisotropic, and these results are related to some of the very early work on the subject.
Abstract: The dielectric permittivity and conductivity of freshly excised dog skeletal muscle were measured at frequencies between 20 Hz and 1 MHz, with the tissue samples oriented either parallel or perpendicular to the applied electric field. At frequencies below 100 kHz a four-electrode technique was employed; at frequencies above 100 kHz a conventional two-electrode technique was used in conjunction with a commercial admittance bridge. All measurements were performed with the tissue sample at body temperature. Over the entire frequency range of the study, the dielectric properties of the muscle were found to be significantly anisotropic. At audio frequencies, the conductivity of the muscle measured in a direction parallel to the fibre orientation was typically found to be ten times higher than that measured perpendicular to the fibre axis; at frequencies approaching 1 MHz the conductivities measured in both directions approached a common value, near 8 ms cm−1. The dielectric permittivity in both orientations is strongly dependent on frequency. These data are analysed using the suspension equation, and comments are made on the mechanisms that are responsible for the observed properties. In an Appendix these results are related to some of the very early work on the subject.

206 citations


Journal ArticleDOI
TL;DR: The relationship between the conduction velocity and amplitude is analysed and it is concluded that, for a given fibre, the amplitude is inversely proportional to theConduction velocity, which agrees with the experimental data reported in the literature and with computationally fast and precise expressions developed.
Abstract: Using the volume conductor model, a single muscle fibre action potential can be expressed as a convolution of the transmembrane current and a weighting function. By simplifying the weighting function, the line source model is derived. We have developed similar expressions to compute the single muscle fibre action potential using simple models and physical considerations without any mathematical complexity. The relationship between the conduction velocity and amplitude is analysed and it is concluded that, for a given fibre, the amplitude is inversely proportional to the conduction velocity. This agrees with the experimental data reported in the literature.

183 citations


Journal ArticleDOI
TL;DR: Results are presented from the study of bilateral g.s.r. waves, the site dependence of the skin impedance, the differences between 10Hz and 1000 Hz data, and tissue segment impedance.
Abstract: The methods for the individual determination of skin surface electrode impedances are briefly discussed. A measurement technique is described with which it is possible to measure two skin surface electrodes simultaneously, but individually, at the same frequency. The design of a small, portable, battery-operated meter using this principle is described with block diagrams. Results are presented from the study of bilateral g.s.r. waves, the site dependence of the skin impedance, the differences between 10Hz and 1000 Hz data, and tissue segment impedance.

152 citations


Journal ArticleDOI
TL;DR: A new algorithm for QRS delineation has been developed and the stability of the method is demonstrated for transitions between different waveform morphologies.
Abstract: A new algorithm for QRS delineation has been developed. Based on the envelope of the e.c.g. signal a delineation function is defined, which yields a single positive pulse for each complex. From this function the onset and end of the QRS or, alternatively, a fiducial point is determined. To remove low-frequency component such as S-T abnormalities without distortion of the QRS complex, a filter with time-varying characteristics is used. The accuracy of the method has been evaluated in a test set of different QRS complexes obtained from coronary care patients. For QRS onset, the standard deviation of the difference between automated and manual determination was 7 ms in normal beats and 14 ms in ectopic beats. With simulated noise added to each waveform an average dispersion of 7 ms was observed in the recognition of the QRS onset at a signal-to-noise ratio of 15 dB. The corresponding dispersion in the location of a fiducial point was 2 ms. Using simulated e.c.g. data, the stability of the method is demonstrated for transitions between different waveform morphologies.

152 citations


Journal ArticleDOI
TL;DR: The problem of detecting the QRS complex in the presence of noise was analysed and an optimised threshold criterion based on FP/FN was developed.
Abstract: The problem of detecting the QRS complex in the presence of noise was analysed. Most QRS detectors contain a filter to improve the signal-to-noise ratio and compare the signal with a threshold. In an earlier paper we identified an optimal filter. Various techniques to generate threshold and detector designs were studied. Automatic gain-control circuits with a fixed threshold have a very slow response to different rhythms. Automatic threshold circuits based on simple peak-detection schemes have a fast response, but are very sensitive to sudden variations in QRS amplitudes and noise transients. None of the methods described to date present any optimisation criteria for detecting the signal (QRS complex) in the presence of noise. The probabilities of FPs (false positives) and FNs (false negatives) were investigated and an optimised threshold criterion based on FP/FN was developed. Presently, data are being collected to compare various techniques from their ROC (receiver operating characteristics).

151 citations


Journal ArticleDOI
TL;DR: A novel approach based on a ‘partition and input/output inversion’ technique which allows the full use of this new data set for validating a submodel of the previous model, instead of having to do an extra modelling effort, is presented.
Abstract: The validation process is an essential component of the modelling ofin vivo endocrine and metabolic systems. In the paper a validation study of a comprehensive model of the glucose regulation system, previously developed for intravenous testing, is performed on a new data set based on oral glucose tolerance studies. A novel approach based on a ‘partition and input/output inversion’ technique which allows the full use of this new data set for validating a submodel of the previous model, instead of having to do an extra modelling effort, is presented. The necessity of a new description for a number of glucose unit processes emerges from this study. The new submodel has been successfully tested and incorporated into the comprehensive model. Although the approach presented has been developed and illustrated with reference to a specific case study, it may have wider applicability in developing appropriate validation strategies for complex physiological control systems.

140 citations


Journal ArticleDOI
TL;DR: Major improvements over previous systems include controlled introduction of anisotropic flexing properties in the electrode array to facilitate insertion and optimal contact orientation, enlarged and stabilised contact surface area and the development of a new connector technology which combines high density, high reliability, biocompatibility and ease of operation during surgery.
Abstract: The technical and safety requirements for intracochlear electrical stimulation to restore hearing in the profoundly deaf are reviewed. A system has been implanted in human subjects which comprises a 16-contact flexible electrode array, radio receiver/stimulator and surgical disconnect which permits changing from percutaneous cable to transcutaneous telemetry. The design, fabrication, and mechanical and electrical testing of each of the components are discussed in detail. Major improvements over previous systems include controlled introduction of anisotropic flexing properties in the electrode array to facilitate insertion and optimal contact orientation, enlarged and stabilised contact surface area and the development of a new connector technology which combines high density, high reliability, biocompatibility and ease of operation during surgery.

87 citations


Journal ArticleDOI
TL;DR: It is argued that there are a number of situations in life science where it is desirable to attempt a two-sided linear filter identification and a simple method is presented for the determination of a nonparametric, two- sided linear filter from system input and output data.
Abstract: It is argued that there are a number of situations in life science where it is desirable to attempt a two-sided linear filter identification. A simple method is presented for the determination of a nonparametric, two-sided linear filter from system input and output data. The time-domain filter is determined from a matrix equation involving the input autocorrelation function and the two-sided cross-correlation function. The resulting filter minimises the sum of squared differences between the actual and predicted outputs.

83 citations


Journal ArticleDOI
TL;DR: The feasibility of using a fast Walsh transform algorithm to implement a real-time microprocessor-based e.
Abstract: The feasibility of using a fast Walsh transform algorithm to implement a real-time microprocessor-based e.c.g. data-compression system was studied. Using the mean square error between the original and reconstructed e.c.g. signals as a measure of the utility of the reconstructed signals, the limit to which an e.c.g. signal could be compressed and still yield an acceptable reconstruction was determined. The possibility of enhancing the quality of the reconstructed signals using linear filtering techniques was also investigated.

72 citations


Journal ArticleDOI
TL;DR: Electro-osmosis may be a source of error in skin ionic permeability studies with electrical parameters because it implies current rectification, a powerful skin breakdown mechanism with potentials larger than 50V, and that negative d.c. potentials are more dangerous than positive on dry skin.
Abstract: It is well known that skin conductance is dependent on current flow through skin. It is shown that this may be due to an electro-osmotic effect. This can explain why in some cases negative and in other cases positive potentials increase skin conductance. Electro-osmosis implies current rectification, a powerful skin breakdown mechanism with potentials larger than 50V, and that negative d.c. potentials are more dangerous than positive on dry skin. Electro-osmosis may be a source of error in skin ionic permeability studies with electrical parameters.

Journal ArticleDOI
TL;DR: An automatic system (CoSTEL) which permits the reconstruction of the instantaneous 3-dimensional position of target points (infra-red light emitting body markers) in a laboratory frame was designed and is able to track eight landmarks per subject side simultaneously.
Abstract: An automatic system (CoSTEL) which permits the reconstruction of the instantaneous 3-dimensional position of target points (infra-red light emitting body markers) in a laboratory frame was designed. The 3-dimensional CoSTEL transducer is based on a suitable spatial arrangement of three one-dimensional transducers. Each transducer is made of a charge-coupled device linear array image sensor lying on the focal plane of a toroidal lens and appropriately aligned with it. The system was conceived for 3-dimensional whole body movement analysis and is able to track eight landmarks per subject side simultaneously. Its basic features are resolution of 1/4000, maximum sampling frequency 1·1 kHz (100 Hz is actually used), large insensitivity to background light and transducer output in digital form. These features provide a high level of accuracy, reliability and working stability.

Journal ArticleDOI
TL;DR: The lead field is computed for several values of the radii involved and is shown to posses a pronounced directional sensitivity and possible applications are discussed.
Abstract: The computation of the lead field of a plane bipolar electrode with axial symmetry is discussed. The numerical technique used is based on an analogy of the ‘charge density method’. An explicit analytical formula describing the potential arising from a plane annulus having uniform (current) density is presented. A verification of the technique is given by comparing the results with both a known analytical expression describing the field of a disc electrode and measurements inside a tank. The lead field is computed for several values of the radii involved and is shown to posses a pronounced directional sensitivity. Possible applications are discussed.

Journal ArticleDOI
TL;DR: In the analysis of the electrical signals recorded from 13 healthy subjects whose antrum position had been determined by X-rays, the gastric signal amplitude was wider in the configuration corresponding with the antral axis than on other ones.
Abstract: The study aims at determining a characterising configuration useful in obtaining the gastric signal of man from cutaneous electrodes. To do this, a daisy-chain electrode was placed on the abdominal surface making sure that a configuration was on the direction of the antral axis previously defined. The study is based on the analysis of the electrical signals recorded from 13 healthy subjects whose antrum position had been determined by X-rays. In the analysis the gastric signal amplitude was wider in the configuration corresponding with the antral axis than on other ones.

Journal ArticleDOI
TL;DR: The linear and nonlinear transient behaviour of a platinum electrode in physiological saline (0·9% NaCl) was investigated and it is concluded that the interface can be analysed and modelled in either domain in the linear range and at the onset of nonlinearity.
Abstract: The linear and nonlinear transient behaviour of a platinum electrode in physiological saline (0·9% NaCl) was investigated. The interface overpotential (current) in response to a step current (voltage) was monitored over six decades of pulse duration starting at 10 μs, both in the linear range, i.e. where the polarising current and the polarisation voltage are proportional, and in the nonlinear range, where this proportionality is lost. The time invariance of the Pt electrode/physiological saline interface parameters in the linear range and at the onset of nonlinearity over the studied band of frequencies and pulse durations is deduced from the equivalence of experimental results obtained in the frequency and time domains using the appropriate transformation when mapping the two domains. We conclude that the interface can be analysed and modelled in either domain in the linear range and at the onset of nonlinearity.

Journal ArticleDOI
TL;DR: A microprocessor-based system is described for data capture and analysis of dynamic foot pressure images and can be analysed to produce pressure against time curves or printed or plotted as isopressure contour plots.
Abstract: A microprocessor-based system is described for data capture and analysis of dynamic foot pressure images. A run-length encoding video digitiser captures up to 32 frames at a rate of 25 per second and stores the data in memory. These data are displayed on a colour monitor and can be analysed to produce pressure against time curves or printed or plotted as isopressure contour plots.

Journal ArticleDOI
TL;DR: An improved filtration method which enables reliable measurements of red cell deformability in whole blood to be performed is presented, and can avoid artefacts caused by artificial treatments added on blood samples and time changes after blood sampling.
Abstract: A method which enables reliable measurements of red cell deformability in whole blood to be performed is presented. It is based on the Nuclepore filtration method described byReid et al. (1976). Its reliability was much improved, obtaining an accuracy of within 5% by a technique to remove air bubbles trapped in the filter pores, which caused the poor reproducibility observed before. Simple analyses of the flow characteristics of whole blood and the haematocrit dependence of whole blood passage time were given to eliminate the effect of transient pore blockings of white cells and the contribution of different haematocrit in the whole blood passage time. A mean pore passage time of single red cells is obtainable as a quantitative index of red cell deformability. Furthermore, a good utilisation was achieved by making full use of electrically operated valves and aspiration pumps. It is possible to repeat measurements at intervals of 3 min. This improved filtration method will be useful for diagnostic purposes since it can avoid artefacts caused by artificial treatments added on blood samples and time changes after blood sampling.

Journal ArticleDOI
TL;DR: A technical description, constructional details and performance characteristics are presented for a whole-body calorimeter, which with the equipment metabolic heat production, sensible (radiative and convective) and insensible heat exchange of a subject during rest and exercise can be monitored continuously.
Abstract: A technical description, constructional details and performance characteristics are presented for a whole-body calorimeter. With the equipment metabolic heat production (oxygen consumption), sensible (radiative and convective) and insensible heat exchange (water vapour loss) of a subject during rest and exercise can be monitored continuously. The basic principle of the construction is to prevent any heat transfer across the wall of a well ventilated cylinder, so that all heat exchange by the subject can be measured by differential thermometry and hygrometry between inlet air and outlet air. The air flow through the calorimeter itself is more than 12·5 m3 min−1, which makes its response to changes in heat dissipation of the subject fast. The time constant for evaporative water loss is 1·5 min. There are two time constants for sensible heat exchange: 0·86 min and 7·4 min. The calorimeter inlet air temperature is controlled to within 0·03°C and dewpoint temperature to within 0·15°C. Changes in sensible heat exchange can be measured with an accuracy of 1 W. Changes in water vapour loss can be detected within 100 mg min−1; consequently, changes in insensible heat exchange can be assessed to about 4W. There is no heat loss through the wall of the calorimeter, even at a temperature difference between calorimeter temperature and laboratory temperature close to 30°C, and the calibrations are correct. This has been verified by measuring water vapour losses from a water tray at various calorimeter temperatures and the heat required for this evaporation. The latter can be measured as sensible heat exchange. The quotient of the two gives the heat of vaporisation of water, which can be compared favourably with the values from steam tables. Particular emphasis has been given to the subject's safety and comfort.


Journal ArticleDOI
B. Tedner1
TL;DR: Estimates of fluid-volume changes obtained by the method were compared with concomitant changes in the body weight of ten patients undergoing haemodialysis, and a correlation coefficient of 0·89 was found.
Abstract: An instrument for continuous monitoring of fluid-volume changes has been developed. A tetrapolar whole-body impedance technique is employed with a constant current of 100 μA at 1·5 kHz and 150 kHz. A microprocessor automatically calculates changes in fluid volume from changes in whole-body impedance. Body-surface area is used as a normalising factor together with an empirically determined constant to obtain readings expressed in litres. Estimates of fluid-volume changes obtained by the method were compared with concomitant changes in the body weight of ten patients undergoing haemodialysis, and a correlation coefficient of 0·89 was found.

Journal ArticleDOI
TL;DR: This instrument was shown to permit the nonivasive and accurate tracking of instantaneous arterial pressure and to perform acceptably over a wide range of arterial Pressure.
Abstract: For the noninvasive monitoring of the beat-to-beat systolic and diastolic pressure and pressure waveform in the human finger, a new automated instrument was designed. This measurement is based on a principle called the vascular unloading technique. Using a hydraulic servocontrol system, the vascular volume change caused by intra-arterial pressure change can be compensated by applying counter pressure to maintain a constant vascular volume in the unloaded state. In this state the controlled counterpressure instantaneously follows the intra-arterial pressure. In this instrument all the necessary procedures, such as the setting of the reference value for the servocontrol, control of the servogain, processing and displaying of the data on a recorder, were carried out automatically. The simultaneous comparison of data with direct measurements and a few examples of the indirect pressure recordings by this instrument are shown and the principles, operation and evaluation of this method are described. This instrument was shown to permit the nonivasive and accurate tracking of instantaneous arterial pressure and to perform acceptably over a wide range of arterial pressure.

Journal ArticleDOI
TL;DR: A laboratory cadaveric model was used to evaluate rigidity improvements associated with a number of fixation design innovations and a new and very simple traingular framework was designed and constructed for which the fixation rigidity was found to rival that of much more complex and cumbersome double anterior frames.
Abstract: A laboratory cadaveric model, developed previously for the study of currently employed external fixation devices used for unstable pelvic fractures was used to evaluate rigidity improvements associated with a number of fixation design innovations. Based on quasistatic shearing displacements measured at the sacro-iliac joint and symphysis pubis disruption sites, otherwise identical anterior frameworks constructed on 5 mm fixation halfpins, rather than upon standard 4 mm halfpins, were able to sustain markedly (58% to 210%) greater loadings. A new and very simple traingular framework was designed and constructed for which the fixation rigidity was found to rival that of much more complex and cumbersome double anterior frames. When used as the posterior component of combined anterior/posterior fixation systems, a new double cobra-type (internal) plate allowed the injury model pelvises to sustain near-physiological load levels. A pair of dynamic compression plates attached across a disrupted symphysis pubis was found to be a biomechanically acceptable substitute for an anterior external fixator.


Journal ArticleDOI
TL;DR: A technique for calculating the ensemble averages of locomotor electromyographic patterns is decribed, which combines standard linear envelope detection with LaGrange interpolation.
Abstract: A technique for calculating the ensemble averages of locomotor electromyographic patterns is decribed. It combines standard linear envelope detection with LaGrange interpolation. The e.m.g. envelope in each stride is demarcated with times obtained from foot-contact patterns and the time base is altered to 256 points by interpolation. The time-normalised envelopes are then averaged together to form the ensemble average.

Journal ArticleDOI
TL;DR: A mathematical model for the steady flow of non-Newtonian fluid through a stenotic region indicates that the general shape and size of the stenosis together with rheological properties of blood are important in understanding the flow characteristics and the presence of flow separation.
Abstract: A mathematical model for the steady flow of non-Newtonian fluid through a stenotic region is presented. The results indicate that the general shape and size of the stenosis together with rheological properties of blood are important in understanding the flow characteristics and the presence of flow separation.

Journal ArticleDOI
TL;DR: The influence of the electrical shunting of the urethral mucosa is shown to permit this, provided that the impedance of the mucosa in the closed urethra is measured in each patient investigated.
Abstract: A system for the measurement of urethral urinary stream cross-sectional areas and pressures is described. The system consists of: (1) A 4 French gauge probe with electrodes for the electrical impedance measurement of cross-sectional areas and side-holes for pressure measurements (2) an electrical field generator and impedance detecting section and (3) a side-hole perfusion and pressure measuring part.

Journal ArticleDOI
TL;DR: The errors in electrical impedance plethysmography are not well known and in the paper errors due to inadequate instrumentation, improper electrode application, and physiological changes have been analysed.
Abstract: The errors in electrical impedance plethysmography are not well known In the paper errors due to inadequate instrumentation, improper electrode application, and physiological changes have been analysed Minimum electrical requirements for a general purpose four-electrode instrument are: (a) input impedance of voltage-sensing circuit+4 kΩ; (b) output impedance of constant-current source+20 kΩ; (c) cmrr+400; (d) common-mode input impedance+40 kΩ; and (e) apparent change of resistance due to noise×0·5 mΩ All electrodes should be separated by at least one limb diameter Changes of electrode impedance due to pressure produce negligible error in a four-electrode configuration The only way to eliminate the large subject-motion errors is to eliminate the motion Changes of blood resistivity with velocity produce an error estimated at 10 per cent A repeatability test on the upper arm gave a standard deviation of 6 per cent of the mean

Journal ArticleDOI
TL;DR: The midsagittal plane of the human thorax is represented by a two-dimensional finite-element model and Interpretations in terms of current density show that variations of bone conductivity have little influence on the fields.
Abstract: The midsagittal plane of the human thorax is represented by a two-dimensional finite-element model. Solutions of steady-state potential fields of bipolar epidural stimulation are computer generated. Effects of biological tissue conductivity and geometry on the fields are studied. Interpretations in terms of current density show that variations of bone conductivity have little influence on the fields. For constant current stimulation, the presence of the tough dura mater, irrespective of its thickness, does not seem to be significant. In contrast, the crucial factor affecting the field is the width of subarachnoid space which contains the highly conductive cerebrospinal fluid.

Journal ArticleDOI
TL;DR: Elastic mismatching is studied by an impulse technique and in all cases a good agreement is shown between the measured reflection coefficient and the value calculated theoretically.
Abstract: Elastic mismatching is studied by an impulse technique. Elastic mismatches are created by joining two latex rubber tubes of the same internal diameter but different wall thickness. A short duration pressure impulse is generated at the entrance of the water-filled tube system and the transmission characteristics of the impulse are determined from a series of measurements along the tube system using a catheter-tip pressure manometer. This technique enables the magnitude and phase change of the reflection at the elastic discontinuity to be obtained. A number of tube combinations are examined and in all cases a good agreement is shown between the measured reflection coefficient and the value calculated theoretically.

Journal ArticleDOI
TL;DR: It can be seen that tracheal sound detection can be a useful screening tool to indicate patients in need of more detailed sleep study, although it introduces some error into apnoea detection.
Abstract: Recent interest in the occurrence of sleep apnoea has brought about the development of several methods of detecting apnoeas. Complete polygraphic evaluation of sleep involves considerable equipment, expense, and personnel time for the collection and analysis of the data. Not infrequently these results will indicate that a patient has an insufficient number of apnoeic events to clinically impair health, thus yielding little information at great expense. This being the case, an automated method of reliably evaluating patients for sleep apnoea using a minimum of apnoea detection equipment and personnel time would be clinically useful. Such a method has been devised, using tracheal sound as the physiological indicator of apnoea. Treacheal sound is monitored by a microcomputer, which detects periods of low tracheal sound corresponding to a lack of airflow. Periods of low tracheal sound which last 10 s or longer are recorded overnight and stored for review by the user at any time. This tracheal sound method of apnoea detection has been compared with data obtained during polygraphic sleep studies utilising thermistors to detect airflow and an ear oximeter to monitor arterial oxygen saturation. The results compare favorably, and although tracheal sound detection introduces some error into apnoea detection, it can be seen that tracheal sound detection can be a useful screening tool to indicate patients in need of more detailed sleep study.