Showing papers in "Medical & Biological Engineering & Computing in 1980"
TL;DR: Use of the model is illustrated in investigating wave propagation in the arterial system and in simulation of arterial dynamics in such pathological conditions as arteriosclerosis and presence of a stenosis in the femoral artery.
Abstract: A model of the human arterial system was constructed based on the anatomical branching structure of the arterial tree. Arteries were divided into segments represented by uniform thin-walled elastic tubes with realistic arterial dimensions and wall properties. The configuration contains 128 segments accounting for all the central vessels and major peripheral arteries supplying the extremities including vessels of the order of 2·0 mm diameter. Vascular impedance and pressure and flow waveforms were determined at various locations in the system and good agreement was found with experimental measurements. Use of the model is illustrated in investigating wave propagation in the arterial system and in simulation of arterial dynamics in such pathological conditions as arteriosclerosis and presence of a stenosis in the femoral artery.
503 citations
TL;DR: The instrument has been useful in monitoring arterial oxygenation in patients with respiratory failure in the authors' intensive-care unit and the reproducibility was assessed in a healthy subject by measuring the oxygen saturation repeatedly 60 times.
Abstract: A noninvasive oximeter that analyses the oxygen saturation of arterial blood in the fingertip is described. The light, after attenuating the infrared portion to avoid thermal injury, is applied to the fingertip through an optical transmitter made of glass fibres. The transmitted light is transferred to an optical reception system where a spectrophotometric determination of oxygen saturation is performed. The determination is performed by considering only the change in the attenuation of light caused by the inflow of arterial blood into the fingertip. The correlation between the oxygen saturation measured with the present instrument (y) and that with the blood-gas method (x), was y=0·907x+8·592 with a standard deviation and a correlation coefficient of 0·135% and 0·983, respectively. The reproducibility was assessed in a healthy subject by measuring the oxygen saturation repeatedly 60 times. The mean saturation was 95·82±0·675% (mean±standard deviation). The instrument has been useful in monitoring arterial oxygenation in patients with respiratory failure in our intensive-care unit. One of the disadvantages of the instrument is that the measurement is interrupted when the fingertip changes its position against the light beam.
270 citations
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TL;DR: A QRS complex detector based on optimum predetection with a matched filter is described, which shows that differentiation reduces Gaussian error by √6 and errors caused by variable QRS amplitudes are close to zero.
Abstract: A QRS complex detector based on optimum predetection with a matched filter is described. In order to improve the accuracy of the QRS complex recognition under conditions of Gaussian noise and variable QRS amplitude, the first derivative of the e.c.g. was used with zero threshold detection. In addition, two nonlinear circuits cut off low amplitude noise and all spikes which appear for a fixed time after QRS detection. Calculation of errors shows that differentiation reduces Gaussian error by √6 and errors caused by variable QRS amplitudes are close to zero. This detector is especially useful with biotelemetry systems since it reduces many interferences due to patient movement and communication channel distortion.
136 citations
TL;DR: The present magnetic threshold curves show a close resemblance to corresponding curves obtained by electric stimulation at various frequencies provided the electric thresholds are divided by the a.c. frequency.
Abstract: Low-frequency and transient magnetic fields of moderate flux densities are known to generate visual phenomena, so-called magnetophosphenes. In the present study, time-variable very low frequency (10–50 Hz) electromagnetic fields of moderate flux density (0–40 mT) were used to induce magnetophosphenes. The threshold values for these phosphenes were determined as a function of the frequency of the magnetic field both in normal subjects and colour defective ones. Maximum sensitivity occurred at a frequency of approximately 20–30 Hz, and with broad-spectrum light the threshold flux density was 10–12 mT. The threshola values were found to be dependent upon the intensity and the spectral distribution of the background light. Sensitivity decreased during dark adaptation. In certain respects deutans differed from subjects with normal colour vision. Possible mechanisms for generation of magnetophosphenes are discussed. The present magnetic threshold curves show a close resemblance to corresponding curves obtained by electric stimulation at various frequencies provided the electric thresholds are divided by the a.c. frequency. These problems are under current investigation in our laboratory. This is in full agreement with the assumption that the fluctuating magnetic field affects retinal neurons by inducing currents which polarise synaptic terminals.
118 citations
TL;DR: It is shown that a bidirectional change in ventilation, involving hyper- and hypoventilation patterns, most adequately corresponds to the formula derived and has been validated by comparison with cardiac output data obtained by thermodilution.
Abstract: A method is presented for determining the pulmonary blood flow from measurements of the time-averaged end-tidal pCO2 and the CO2 output.
116 citations
TL;DR: Progress in the development of a system to provide sensory feedback of the pinch force of an artificial hand is described and details of a practical system, presently in use by two amputees prior to full-scale clinical evaluation, are presented.
Abstract: Progress in the development of a system to provide sensory feedback of the pinch force of an artificial hand is described. Design criteria relating to electrocutaneous stimulation and compatibility with myoelectric control are discussed. Details of a practical system, presently in use by two amputees prior to full-scale clinical evaluation, are presented.
99 citations
TL;DR: Automatic analysis systems are outlined which enable the quantitation of the static and dynamic distribution of pressures and loads under the foot.
Abstract: Automatic analysis systems are outlined which enable the quantitation of the static and dynamic distribution of pressures and loads under the foot The clinical usefulness of these systems is illustrated by several patient studies
88 citations
TL;DR: Angiographic data from the literature are used to calculate left ventricular wall force for normal and diseased hearts using a thin-walling spherical model, a thick-walled spherical model and six ellipsoidal models, and the results are compared.
Abstract: Myocardial wall force per area (=stress) is a major determinant of muscle function and oxygen consumption. It cannot be measured accurately but has to be derived from a mathematical model. Many models have been presented in the literature but a comparison between models has not been available. In this study angiographic data from the literature are used to calculate left ventricular wall force for normal and diseased hearts using a thin-walled spherical model, a thick-walled spherical model and six ellipsoidal models, and the results are compared. There appeared to be large differences between the stresses yielded by the models for the same cardiac geometry. The thick-walled sphere yields circumferential stresses that are approximately 25% lower than the stresses yielded by most of the ellipsoidal models. Of the ellipsoidal models the one suggested by Streeter el al. gives circumferential stresses that are 25% higher than those of the other ellipsoids. Similar differences are found for left ventricular wall stress in the longitudinal direction. However, all models correspond closely in the prediction of the deviation from normal stress in the various pathological states studied.
78 citations
TL;DR: A continuousin vivo pH measurement was successfully achieved in nonheparinised arterial blood of a japanese monkey, and the observed pH values were in accordance with those confirmed by a blood pH analyser.
Abstract: A catheter-tip pH sensor was developed for possible clinical and biomedical application, using an ion-sensitive field-effect transistor (i.s.f.e.t.). Its signal drift in buffer solutions during continuous measurement was less than 3 mV in 24 h (equivalent to about 0·05 pH in 24 h). The electric insulation was perfect when soaked in buffer solutions for more than 3 months. A continuousin vivo pH measurement was successfully achieved in nonheparinised arterial blood of a japanese monkey. There was no significant sign of clot formation for 8 hours. It revealed quick responses to respiratory acidosis and alkalosis, and the observed pH values were in accordance with those confirmed by a blood pH analyser. Also, a catheter-tip pCO2 sensor was prepared, using the catheter-tip pH i.s.f.e.t. The response time was 2 min for a 90% change in CO2 tension. The muscle pCO2 monitoring tested with it indicated a similar result to those with medical mass spectrometer.
77 citations
TL;DR: A detection algorithm for the first and the second heart sounds, which is one of the most important problems in an automatic diagnostic system for phonocardiograms, has been developed and is based on the frequency-domain characteristics of heart sounds analysed by a linear-prediction method.
Abstract: A detection algorithm for the first and the second heart sounds, which is one of the most important problems in an automatic diagnostic system for phonocardiograms, has been developed. It is based on the frequency-domain characteristics of heart sounds analysed by a linear-prediction method. The performance of the algorithm has been evaluated in 187 samples that contain 881 cardiac cycles including normal and abnormal subjects. The algorithm uses low frequency spectral tracking for the time series of the phonocardiogram. It can track spectral level smoothly so that it is fairly effective for the detection of heart sounds. This tracking procedure can be used in other applications such as electroencephalogram processing.
76 citations
TL;DR: The r-L-C-R model contains one additional parameter (inductance L) that allows for a better representation of the input impedance of the complex model and of the systemic circulation in dog, resulting in meaningful values for the parameters r, C, R.
Abstract: The parameters of a simple model (r-L-C-R) of the systemic circulation are estimated from aortic root pressure and flow, which are either simulated by a complex model of the systemic circulation or measured in dogs. This model contains one additional parameter (inductance L) as compared with the r-C-R model proposed by Westerhof (1973); it allows for a better representation of the input impedance of the complex model and of the systemic circulation in dog, resulting in meaningful values for the parameters r, C, R. Because there is a good relation between C and the sum of the compliances of the complex model, and because C varies in the direction of the expected changes in compliance following angiotensin and sodium nitroprusside administration in dogs, C appears to ba a valid estimate of the total systemic arterial compliance.
TL;DR: Comparisons between the phosphene types would increase knowledge of the mechanism of the interaction between magnetic fields and electric current, respectively, and excitable tissue, and deviations between the curves may be due to the generation of different current paths in electrical and magnetic stimulation, respectively.
Abstract: The purpose of this study was to compare the threshold values for magnetophosphenes and electrophosphenes under identical experimental conditions. Such comparisons between the phosphene types would increase our knowledge of the mechanism of the interaction between magnetic fields and electric current, respectively, and excitable tissue.
TL;DR: Two-dimensional finite-element models representing non-homogeneous electrical conductivity of the human thorax in the mid-sagittal and tranverse planes suggest support is given to the view that stimulation from epidural electrodes place dorsolaterally will preferentially involve dorsal root axons.
Abstract: Two-dimensional finite-element models are described representing non-homogeneous electrical conductivity of the human thorax in the mid-sagittal and tranverse planes. The spinal canal is treated in detail and various tissue types and other biological material have been represented.
TL;DR: A distinction is made between ‘diagnostic’ and ‘monitoring’ purposes for gait analysis which substitutes step asymmetry for the temporal asymmetry index and measures stride time as an indicator of general walking ability.
Abstract: A distinction is made between ‘diagnostic’ and ‘monitoring’ purposes for gait analysis. Two systems which use the temporal components of the walking cycle for the latter purpose are described. One is a laboratory-based system which derives a temporal asymmetry index combining the asymmetries of the swing and double-stance phases. The other is a gait monitor unit designed for clinical use which substitutes step asymmetry for the temporal asymmetry index and measures stride time as an indicator of general walking ability. Examples of the results obtained with both systems are given.
TL;DR: By measuring and processing the responses of a subject, and computed the frequency-response functions of the posture-control system, pseudorandom acceleration disturbances were imposed upon a standing subject.
Abstract: By means of a servocontrolled force plate, pseudorandom acceleration disturbances were imposed upon a standing subject. By measuring and processing the responses of a subject, we computed the frequency-response functions of the posture-control system. The experimental results are discussed from a viewpoint of control engineering.
TL;DR: The performance of a skin evaporimeter is analysed in terms of three resistances to the diffusion of water vapour and the manufacturer's calibration is valid when the skin resistanee rs is much larger than rp and ra—a condition satisfied when evaporation is close to the basal rate.
Abstract: The performance of a skin evaporimeter is analysed in terms of three resistances to the diffusion of water vapour. The instrument underestimates evaporation when the resistance of the probe rp is greater than the boundary layer resistance it replaces ra. The underestimation is trivial and the manufacturer's calibration is valid when the skin resistanee rs is much larger than rp and ra—a condition satisfied when evaporation is close to the basal rate. Very rapid evaporation, e.g. from burns, is underestimated because the presence of the probe restricts the flux of vapour when rs is of the same order as rp. An empirical correction is given for arbitrary values of ra.
TL;DR: A preliminary study of the error probability for 5-state control of a myoelectric control system based on the utilisation of a single muscle site for the 3- state control of an myoeLECTric prosthesis.
Abstract: A myoelectric control system is one in which the operation of a device is controlled by the electric potential produced by voluntary contraction of a muscle. The utilisation of a single muscle site for the 3-state control of a myoelectric prosthesis has proven beneficial for certain amputees. It has been proposed that a single muscle site could be used for 5-state control, perhaps for an elbow and hand. This paper presents a preliminary study of the error probability for 5-state control.
TL;DR: Because the requirements demanded from implant materials for artificial hip joints are extremely high, only a very few materials are suitable for this purpose, and the inadequate material strength of hip prostheses made of the latter material is compensated for by a larger cross-section of the prosthetic stem, this depending on the geometric conditions of the femur.
Abstract: Because the requirements demanded from implant materials for artificial hip joints are extremely high, only a very few materials are suitable for this purpose. The metallic materials standardised by the ISO still predominantly include cobalt-based alloys, in cast form for wear-resistant ball heads and in forged form for fracture-resistant anchorage stems. Forged titanium-based alloys have been also used for some years for highly stressed femoral component stems. Both alloy types exhibit a higher resistance to pitting, crevice and galvanic corrosion, stress-corrosion cracking and corrosion fatigue than wrought stainless steel of relatively low strength properties. For this reason, the inadequate material strength of hip prostheses made of the latter material is compensated for by a larger cross-section of the prosthetic stem, this depending on the geometric conditions of the femur. The decision for the selection of the implant material should be made by the orthopaedic surgeon on the basis of his clinical experience, and it should not be influeced by price considerations at the expense of the quality.
TL;DR: The result of this experimental activity has produced a relationship between fibrillation threshold and current density and this relationship is summarised in Fig. 1, which summarizes and defines the microshock hazard in terms of 60 Hz current.
Abstract: THERE has been an increase in activity over the past few years in determining fibrillation thresholds for 60 Hz currents applied directly to the heart. Thresholds have been determined for both animals and man. The result of this experimental activity has produced a relationship between fibrillation threshold and current density and this relationship is summarised in Fig. 1. Fig. 1 has been compiled from the material which has been published (see all References), and for which catheter surface-areas were given or could be deduced. The values shown in the Figure are for currents flowing for 3 s or longer and include results from human hearts (WATSON et al., 1973) small-bore dye-injection catheters as well as pacing catheters. Also shown in the Figure is the 10/zA current standard and consequently the safety factor. The curves shown in Fig. 1 were drawn from the results of Roy (1979) and these results are tabulated in Table 1. The data in Tables 1 and 2 are obtained from~dog experiments. It is felt that Fig. 1 summarises and defines the microshock hazard in terms of 60 Hz current. The situation in terms of 60 Hz voltage is not as clear.
TL;DR: An improvement of the blood compatibility of implantable material has been achieved on the basis of an identification of interfacial reactions between clotting plasma proteins and the solid surface.
Abstract: Alloplastic materials have found wide application in heart-valve prostheses, in spite of the need for permanent anticoagulant treatment. Though biological valves exhibit excellent thromboresistance, they fail in long-term application because of a disintegration of the tissue structure. An improvement of the blood compatibility of implantable material has been achieved on the basis of an identification of interfacial reactions between clotting plasma proteins and the solid surface. Rutile ceramics offer advantageous properties because: (i) surface induced activation processes are diminished and (ii) the chemical and mechanical resistance shows long-term stability. Rutile ceramics are utilised for a central-flow heart-valve prosthesis which is being subjected to accelerated fatigue studies.
TL;DR: This paper describes a technique using a mode-locked laser to generate the light pulse and to control an ultra high-speed optical Kerr cell, and the Duguay shutter enables one to use an ordinary camera to record the range-gated image.
Abstract: WE REPORT on a light-scattering technique based on picosecond optical range-gating. Picosecond pulses provided by a mode-locked. Nd:glass laser and second harmonic generation in k:d.p, have been compressed in time by stimulated Raman scattering. The Stokes pulses at 627 nm, which are only weakly absorbed by muscle, were used to illuminate objects such as isolated hearts. An optical CS2 Kerr shutter serves to range-gate the back-scattered pulses. This shutter transmits only the light scattered from the desired depth by range-gating with the 1060 nm light pulses which traverse an adjustable delay line. Submillimetre depth resolution has been achieved by use of an ordinary camera. Pictures of intracavity details of the heart have been realised. Quantitative 3-dimensional analysis of objects is often very useful in biology. Especially in organs with cavities such as the heart, it would be very interesting to investigate malformations or make spatiotemporal measurement of the volume of the cavity. Interferometric methods such as holography and Moire interferometry have been in use for several years, but their utilisation seems restricted for 3-dimensional records of large objects and they are unsuitable for 3-dimensional measurement with good resolution (CAULFIELD et ak, 1977). Recently, a stereometric imaging method, based on laser rangefinding utilising a mode-locked laser and a streak camera, has been reported (CAuLFXEL[~, 1969). The depth resolution was limited by the pulse duration and the streak camera. In fact, the streak camera seems to be the major problem: first, the profile to be analysed must have a time-bandwidth product much smaller than that of the streak camera. This limited the object depth which could be recorded and the problem becomes more difficult with moving objects. Furthermore, such a system using a high-frame-rate streak camera is very expensive. In this present paper, we describe a technique using a mode-locked laser to generate the light pulse and to control an ultra high-speed optical Kerr cell. The Duguay shutter enables one to use an ordinary camera to record the range-gated image.
TL;DR: A mathematical model for pulsatile flow in a partially occluded tube has applications in studying the effects of blood flow characteristics on atherosclerotic development and shows fairly good agreement with the available experimental results.
Abstract: A mathematical model for pulsatile flow in a partially occluded tube is presented. The problem has applications in studying the effects of blood flow characteristics on atherosclerotic development. The model brings out the importance of the pulsatility of blood flow on separation and the stress distribution. The results obtained show fairly good agreement with the available experimental results.
TL;DR: The use of 0·2 ms pulses of the amplitude meets the safety requirements established by other workers and results indicate that this pulse duration is optimal in terms of safety requirements, as well as energy requirements.
Abstract: Patients receiving chronic spinal-cord stimulation in the management of multiple sclerosis have been stimulated at a frequency of 33 Hz, with pulses whose duration has been varied between 0·05 ms and 2·0 ms. Measurements on the stimulating pulses show that the energy requirement was at a minimum when the pulse duration was 0·2 ms. The current and energy requirements of different patients using 0·2 ms pulses vary over a large range but measurement of the current requirement of a particular patient can be a useful observation in predicting his response to treatment: low current requirements are often associated with a good response and high currents with a poor response to treatment. The use of 0·2 ms pulses of the amplitude we have used meets the safety requirements established by other workers and our results indicate that this pulse duration is optimal in terms of safety requirements, as well as energy requirements.
TL;DR: The results indicate that the pins' contribution to load bearing is small in the unfractured case, for which the stresses on the neck can be predicted by cantilever-beam theory.
Abstract: Five pairs of matching hips were tested under conditions of low-speed mechanical loading in the unfractured and artificially fractured states, to gain an understanding of the mechanism of load transfer for various orientations of Muller cancellous screws used in the internal fixation of the femoral neck. The results indicate that the pins' contribution to load bearing is small in the unfractured case, for which the stresses on the neck can be predicted by cantilever-beam theory. In the fractured state, a triangular 3-pin orientation of two superior and one inferior pin was found to be optimal for osteoporotic bone, particularly with a small neck, under conditions of good pin placement. A 4-pin orientation was found better than a 3-pin orientation for non-osteoporotic bone with a large femoral neck.
TL;DR: The application of the technique of biplanar radiography for measurement of intervertebral movement in the lumbar spine is described and the accuracy has been defined, and it has been used to describe abnormality of interVertebral motion in a group of patients.
Abstract: Assessment of movements of joints is an important part of their clinical examination. However, movements of the spine are particularly difficult to measure because of its inaccessibility. Normally X-ray measurements are complicated by magnification and distortion, and are restricted to two dimensions. This paper describes the application of the technique of biplanar radiography for measurement of intervertebral movement in the lumbar spine. The positions of nine bony landmarks on each vertebra have been measured in three dimensions. Statistical techniques have been used to obtain a ‘best fit’ of these landmarks in successive radiographic views. Accuracy of measurement has been improved by using the constraint that each vertebra should be a rigid body. The accuracy of the technique has been defined, and it has been used to describe abnormality of intervertebral motion in a group of patients.
TL;DR: A model of 2-dimensional anisotropic cardiac tissue which permits the examination of the electrical sources arising from excitation at a point is developed and the effects of anisotropicity in cardiac tissue discussed.
Abstract: This paper develops a model of 2-dimensional anisotropic cardiac tissue which permits the examination of the electrical sources arising from excitation at a point. The specific results depend on the anisotropy parameters and two cases are considered in detail. For assumed equal anisotropicity ratios in the interstitial and intracellular space the isochrones are (asymptotically) confocal ellipses and the total double layer source is (asymptotically) uniform. Surface fields are calculated and plotted for this condition. (For nonequal anisotropy ratios the total double layer source is necessarily nonuniform). When the preparation is very thin so that all fibres are essentially in contact with the extracellular medium the isochrones are (asymptotically) confocal ellipses but the total double-layer sources are now nonuniform. The sources for this case are determined and the fields at the surface of the cardiac tissue evaluated and plotted. The aforementioned ‘thin’ and ‘thick’ tissue preparations are contrasted with each other and the effects of anisotropicity in cardiac tissue discussed.
TL;DR: The results of these experiments showed that the force-velocity relationship was a function of both the order of motor unit recruitment and the fibre composition of the muscles.
Abstract: Two of the lower leg muscles of the cat were examined to assess the influence of the order in which motor units are recruited (slowest to fastest or fastest to slowest) and the fibre composition on the force-velocity relationship and fatiguability of skeletal muscle. The muscles examined were the soleus, a slow twitch muscle, and the medial head of the gastrocnemius muscle, a predominantly fast twitch muscle of mixed composition. The results of these experiments showed that the force-velocity relationship was a function of both the order of motor unit recruitment and the fibre composition of the muscles. However, at either recruitment order, the ability of the computer to control the velocity of contraction and the resultant fatiguability of the muscle for these contractions was similar.
TL;DR: Anin vivo preparation is described in which the compressed artery under an occlusive blood pressure cuff is shown to possess a dynamic negative-resistance characteristic that permits self-excited and sustained oscillation of the intraluminal pressure and flow to occur.
Abstract: Anin vivo preparation is described in which the compressed artery under an occlusive blood pressure cuff is shown to possess a dynamic negative-resistance characteristic. In this situation the pressure drop along a segment of artery decreases despite an increase in flow. Such characteristics have been previously observed only inin vitro preparations. Under the appropriate conditions this characteristic permits self-excited and sustained oscillation (relaxations oscillations) of the intraluminal pressure and flow to occur. A plausible model in which the origin of Korotkoff sounds is linked to such self-excited oscillations is described.
TL;DR: Some ceramics have been shown to be biocompatible in a particular way and tribologically favourable, a surprising type of bonding between some glass-ceramics and bone tissue was discovered, and biodegradable types of calciumphosphate open the possibilities for temporary implants which need not be removed by a second operation.
Abstract: Historically ceramics are the oldest man-made non-animal-based materials. The use of metals began some thousand of years later and plastics have only become available during the last century. In contrast to this sequence of events, systematic and detailed evaluation of the applicability of ceramics for use in artificial organs or as bone and joint replacements did not start before the 1960s; while metals and plastics had already been in use for several decades. The research work on ceramics soon revealed surprising properties: some ceramics have been shown to be biocompatible in a particular way and tribologically favourable, a surprising type of bonding between some glass-ceramics and bone tissue was, discovered. Biodegradable types of calciumphosphate open the possibilities for temporary implants which need not be removed by a second operation, and there are ceramics which obviously can be used in the cardiovascular system.
TL;DR: It is concluded that electrical impedance plethysmography reflects changes in conductivity confined to the region between the electrodes; and that the ratio of deep to superficial impedance sensitivity is a function of the electrode spacing.
Abstract: Electrical impedance plethysmography of the lower leg is now a widely used test for detection of deep vein thrombosis. The origin of the impedance signal is difficult to evaluate in the living subject, and experimental animals have important anatomic differences. A controlled study on human cadavers was therefore undertaken. Conductive and nonconductive fluids were injected into the lower legs of cadavers, while electrical impedance changes were recorded utilising a 4-electrode technique. X-ray studies confirmed the localisation of the injections. Results from ten cadavers showed that significant impedance changes occurred only in response to injections of saline in the region between the electrodes. Injections of nonconductive silicone oil caused a small increase in the measured impedance. It is concluded that electrical impedance plethysmography reflects changes in conductivity confined to the region between the electrodes; and that the ratio of deep to superficial impedance sensitivity is a function of the electrode spacing.