Showing papers in "Medical & Biological Engineering & Computing in 1969"
TL;DR: It is indicated that for the longest life of a socket the optimum size of femoral head will be half that of the external diameter of the socket, which can be applied to other plastics more resistant to wearing than P.T.F.E.
Abstract: A study has been made of the wear of hip sockets of P.T.F.E. against various sizes of stainless steel femoral head in the course of total prosthetic replacement of the hip in the human subject. The most serious aspect of the failure of P.T.F.E. was the production of a tissue reaction by wear debris. Artificial hip joints using plastic sockets should, therefore, be designed to produce the minimum volume of wear debris over a given period. The smaller the diameter of the metal head the smaller the volume of wear debris, but below a certain optimal size the rate of penetration of the socket by the small head would be too rapid. Conclusions based on the observed behaviour of P.T.F.E. in the human body indicate that for the longest life of a socket the optimum size of femoral head will be half that of the external diameter of the socket. It is considered that these observations can be applied to other plastics more resistant to wearing than P.T.F.E. An unexpected observation from clinical practice was that the wear of a P.T.F.E. socket seemed to be more dependent on the activity of the patient than the weight of the patient.
198 citations
TL;DR: The low frequency impedance of bare silver electrodes in contact with physiological saline was found to exhibit capacitive reactance and by the deposition of chloride the impedance became resistive in nature and was found that a chloride deposit of 100–500 mA provided the lowest electrode-electrolyte impedance.
Abstract: The low frequency impedance of bare silver electrodes in contact with physiological saline was found to exhibit capacitive reactance and by the deposition of chloride the impedance became resistive in nature. It was found that a chloride deposit of 100–500 mA.sec/cm2 of electrode area provided the lowest electrode-electrolyte impedance. Prolongation of chloriding beyond this range increased the electrode-electrolyte impedance at all frequencies but did not alter the resistive nature of the impedance. To achieve a chloride deposit which is proportional to the product of mA and sec it was found that a minimum chloriding current density of 5 mA/cm2 of electrode area should be used.
88 citations
TL;DR: The applications in medical diagnosis of continuous wave Doppler techniques are reviewed, and some clinical applications of the method are considered.
Abstract: The applications in medical diagnosis of continuous wave Doppler techniques are reviewed. The principles of pulsed range-measuring systems with A-scope displays and gated receivers are discussed. The design of a 2 MHz range-gated instrument is described, details being given of the transmitter, the receiver, the demodulator, the store, and the filter. Recordings showing the use of the equipment in separating the Doppler signals from the anterior cusp of the mitral valve and the posterior heart wall are presented. Limitations of the present equipment and its possible improvement are discussed, and some clinical applications of the method are considered.
85 citations
TL;DR: No statistical correlation was found between the tendency of a particular blood to lyse osmotically and the tendency to lyses mechanically and the rate of mechanical energy dissipation under typical extracorporeal circulation systems.
Abstract: Typical extracorporeal circulation systems subject blood to abnormal and severe physical conditions. The local rate of mechanical hemolysis under such conditions is postulated to be a function of the local rate of mechanical energy dissipation. This hypothesis was tested by examining the rates of hemolysis in four types of flow. The average rate of hemolysis is expressed as a power function of the average dissipation rate. In the absence of cavitation, the lysis rate in all four cases depends on the average dissipation rate raised to the 1·2 power. The constant of proportionality in each case, however, depends on the spatial distribution of dissipation. The more non-uniform the dissipation, the greater the hemolysis rate for the same average dissipation rate. No statistical correlation was found between the tendency of a particular blood to lyse osmotically and the tendency to lyse mechanically.
74 citations
TL;DR: A positional servo-mechanism was designed to facilitate multi-layer electronic control of complex orthotic and prosthetic devices using lightweight, flexible and inexpensive components.
Abstract: A positional servo-mechanism was designed to facilitate multi-layer electronic control of complex orthotic and prosthetic devices. The design aim was to obtain adequate performance of the system using lightweight, flexible and inexpensive components. The mechanism is actuated by an antagonistic pair of McKibben pneumatic muscles. The muscles are controlled by a pair of twin electro-pneumatic valves operating in an on/off regime. System elements are described in the paper and some relevant design factors pointed out.
72 citations
TL;DR: The mathematical solution is surprisingly insensitive to shifts of the oxyhemoglobin dissociation curve and the assumptions utilized in the model and the analytic solution were verified by a series of experiments using cattle blood.
Abstract: Gas transfer in membrane oxygenators can be limited by the liquid dispersion or the membrane diffusion. If limited by liquid dispersion, the increase in average oxygen saturation of blood flowing in straight gas-permeable tubes is dependent upon the flow rate, the tube length, and the diffusion coefficient and independent of the tube diameter. The mathematical solution is surprisingly insensitive to shifts of the oxyhemoglobin dissociation curve. The assumptions utilized in the model and the analytic solution were verified by a series of experiments using cattle blood. Tube staging, turbulence, and tube coiling bring about mixing and significantly improve the oxygenation rate. For coiled tubes, the oxygenation efficiency depends on the Reynolds number, the Schmidt number, and the tightness of the coil. The limit on the rate of oxygen addition and carbon dioxide removal might be imposed, for thick-walled tubes, by the diffusion through the tube wall. The wall-limited case is governed by CO2 removal.
42 citations
TL;DR: The theory of the flow of an incompressible, inviscid fluid through an elastic tube is developed and applied to a simple model of the female urethra during micturition, and it is shown that an elastic constriction near the mid-point of the Urethra leads directly to an asymmetrical profile.
Abstract: The theory of the flow of an incompressible, inviscid fluid through an elastic tube is developed and applied to a simple model of the female urethra during micturition. The importance of the fact that the flow velocity is comparable with the velocity of longitudinal elastic waves on the urethra is stressed. Flow rates and urethral profiles at different bladder pressures are calculated and found to agree qualitatively with experimental observations. In particular, it is shown that an elastic constriction near the mid-point of the urethra leads directly to an asymmetrical profile, funnelling down from the bladder neck to the constriction, and remaining narrow between the constriction and the external meatus, even in a urethra elastically symmetrical about the constriction. It is shown that the flow rate is governed by the elastic properties of the constriction, and that the effect of viscosity on the flow is relatively small, justifying the idealization that the fluid is inviscid.
41 citations
TL;DR: The results indicate that the magnitudes of the current thresholds to produce these phenomena increase with an increase in frequency.
Abstract: Experiments were conducted in man and the dog to determine the safe levels of sinusoidal alternating current which can be passed through the thorax. The sensation current threshold was determined over a frequency range of 20 Hz to 20 kHz in 8 normal adult males for two different electrode arrangements. The thresholds for vagal stimulation and ventricular fibrillation in the frequency range of 20 Hz to 3 kHz were determined in the dog for the same electrode arrangements, and the data obtained for fibrillation was extrapolated to estimate the comparable levels for man. The results indicate that the magnitudes of the current thresholds to produce these phenomena increase with an increase in frequency. Currents higher than 5 kHz in frequency are recommended for the measurement of physiological events by electrical impedance techniques.
38 citations
TL;DR: It is not justifiable to identify the source of echoes with interfaces lying in the transducer axis on the assumption that adequate insonation for echo formation will only be received by interfaces in and near the trans ducer axis.
Abstract: Evidence is given to show that an ultrasonic transmitter has its beam widely and irregularly scattered by the living skull and brain and that the pattern of this irregular scattering varies greatly with small movements of the transducer relative to the skull.
33 citations
TL;DR: A mechanical classification of fractures of the humerus is advanced which, it is suggested, may be generally applicable to long bones.
Abstract: It is possible to reproduce the common fractures occurring in the adult humerus by simple mechanical methods. This has allowed a detailed examination of the morbid anatomy of the fractures and the measurement of the forces involved. A mechanical classification of fractures of the humerus is advanced which, it is suggested, may be generally applicable to long bones. Fractures of the shaft of the humerus, or any long bone, vary according to the nature of the violence applied, whereas fractures at the proximal and distal ends are dependent on the anatomy of the bone which, in turn, is related to the embryological development of the epiphyses.
26 citations
TL;DR: The characteristics of the ideal data filter and the digital approximation to such a filter are discussed and the use of this filter with biological data is shown.
Abstract: Low pass digital filters are very suitable for use on stored biological data. This paper discusses the characteristics of the ideal data filter and the digital approximation to such a filter. The use of this filter with biological data is shown.
TL;DR: A miniaturized transducer for intravascular measurements of pressure variations has been developed that consists of a sensor in the form of a pneumatic chamber coupled by light fiber optics to a gallium arsenide diode light source and a silicon diode detector or a phototransistor.
Abstract: A miniaturized transducer for intravascular measurements of pressure variations has been developed. The probe has an outer diameter of 1·0–1·5 mm. Its frequency response is 0 to more than 200 Hz.* It consists of a sensor in the form of a pneumatic chamber with a mirror wall coupled by light fiber optics to a gallium arsenide diode light source and a silicon diode detector or a phototransistor. Experimental tests on dogs and humans have been made.
TL;DR: An improved flowmeter is described and its performance is compared, on the basis of sensitivity, power and bulk, with other designs of cuff flowmeter.
Abstract: An improved flowmeter is described and its performance compared, on the basis of sensitivity, power and bulk, with other designs of cuff flowmeter.
TL;DR: Prediction of the brain current density can be made from the application of various types of currents used in this study, since no general trend in impedance was observed during application of the electroanesthesia currents and the pulmonary and cardiovascular systems were stable.
Abstract: Methods are presented for determining the specific cerebral impedance and current density during the application of diffuse electrical currents such as those used for electroanesthesia. In experiments with monkeys, the average cortical and thalamic specific impedances remained within 5 per cent of the control value for electroanesthesia currents equal to twice those needed for surgical intervention. The current density in these regions was linearly proportional to the applied current. Simulation experiments were conducted to obtain a suitable correction factor for the influence of subcortical matter on cortical impedance. Current densities within the cortex and thalamus were within 2 standard deviation of each other. The minimal changes in cortical specific impedance in the absence of flat electrocorticogram suggest a spreading depression is not present during electroanesthesia. Since no general trend in impedance was observed during application of the electroanesthesia currents and the pulmonary and cardiovascular systems were stable, substantial circulatory changes or anoxia do not appear to be present during electroanesthesia. Since the brain current density was linearly proportional to the applied currents, prediction of the brain current density can be made from the application of various types of currents used in this study.
TL;DR: The object of the work is to develop a method to improve the detection of aortic insufficiency in the presence of mitral stenosis; this is of importance when cardiac surgery with heart lung machines is contemplated.
Abstract: Frequency analysis of heart murmurs was performed on 30 patients. The object of the work is to develop a method to improve the detection of aortic insufficiency in the presence of mitral stenosis; this is of importance when cardiac surgery with heart lung machines is contemplated. The technical details of the method are described.
TL;DR: A comparison of the rheological properties of the normal and pathological samples revealed several interesting characteristics which suggest that the mechanism of boundary lubrication may predominate in a human knee joint.
Abstract: The componentsp
12 andp
11-p
22 of the general stress tensor were measured for various samples of human knee joint synovial fluid subjected to simple shear. The samples investigated consisted of four ‘normal’ post-mortem specimens and four pathological specimens obtained from patients with rheumatoid arthritis. For three samples measurements were made at 18° and 28°C and in one case at several dilutions. From the results it was possible to calculate the contribution to the load bearing characteristics of the joint of a non-zero value of first normal stress differencesp
11-p
22 and this was found to be negligible for the cases investigated. A comparison of the rheological properties of the normal and pathological samples revealed several interesting characteristics which suggest that the mechanism of boundary lubrication may predominate in a human knee joint.
TL;DR: The experimental device described uses flexible pressure sensors, based on the principle of the mercury strain gauge, and an RC beat-frequency oscillator emits an audible sound whose frequency is a function of this pressure.
Abstract: Anaesthesia of the hand can result from injury or disease. It severely impairs the normal use of the hand and brings with it the danger of accidental self-inflicted injury due to the absence of pain. A prosthetic device intended to overcome this non-correctable handicap will have to measure the pressure at the finger of the hand and produce a suitable stimulus that is a function of this pressure. The experimental device described uses flexible pressure sensors, based on the principle of the mercury strain gauge. An RC beat-frequency oscillator emits an audible sound whose frequency is a function of this pressure. The considerations for the design of the device are discussed and first results of the practical use are reported.
TL;DR: A derivation of the Stewart-Hamilton formula is presented which is applicable to all the most usual cardiac output measurement techniques and also to the determination of regional blood flow.
Abstract: A derivation of the Stewart-Hamilton formula is presented which is applicable to all the most usual cardiac output measurement techniques and also to the determination of regional blood flow.
TL;DR: The relation between induced electromotive force and flow rate for implantable electromagnetic flowmeters is presented, and the errors introduced by the factors mentioned above are discussed.
Abstract: The magnetic flux density of implantable electromagnetic blood flowmeter can not be made uniform, since the size of flowmeter probe must be very small for physiological reasons. The velocity distribution of blood flow is axially non-symmetrical everywhere in arteries.
TL;DR: A viscoelastic model, consisting of a neurally controlled spring-damper combination connected in parallel with each other and in series with a passive elastic element, is shown to represent a significant number of the properties of muscle.
Abstract: In order to find a satisfactory representation of the dynamic behaviour of muscle, some of the known mechanical properties of muscle are examined. A viscoelastic model, consisting of a neurally controlled spring-damper combination connected in parallel with each other and in series with a passive elastic element, is shown to represent a significant number of the properties of muscle. The validity of the model is further tested by comparing the model's response to pulses with experimentally determined contractions of the frog sartorious muscle. The model is shown to fit the isometric contractions produced both by single pulses and by trains of pulses.
TL;DR: A simplified analogue computer model of the human cardiovascular control system is developed and can be adjusted to reproduce the response of a subject to a submaximal work-load.
Abstract: A simplified analogue computer model of the human cardiovascular control system is developed in this paper. This model can be adjusted to reproduce the response of a subject to a submaximal work-load. The validity of the model is evaluated and suggestions for its further development are included.
TL;DR: It is now possible to deduce the elastic behaviour and the mechanical hysteresis loss of plastic materials as a function of frequency over the range 0–300 c/s and beyond, which means that the method may prove a useful tool for research into the physical properties of plastics.
Abstract: A transmission testing technique has recently been developed whereby some of the characteristics of a liquid-filled tube, as used in electromanometry, can be measured at sub-audio and audio frequencies, using apparatus readily available in teaching hospitals. Pressure ratios and phase readings are obtained from Lissajous figures displayed on an oscilloscope. The attenuation and phase constants of the tube are determined by simple calculations from these readings. The transfer loss and phase shift of the output transducer and its associated hardware can sometimes be measuredin situ as part of the same test. Using additional data derived from static measurements and formulae well-known in electrical theory, it is possible to deduce practically all the information required for engineering purposes, including an approximate analysis of the various losses of the tube and the determination of the characteristic impedance as a complex function of frequency.
TL;DR: Some physiological aspects of this type of plethysmography are discussed which illuminate the difficulty in discriminating between skin-flow and muscular flow and a detailed calculation of the elastic influences follows and shows that one cannot generally expect a cancellation of these influences when comparing measurements with the calibration.
Abstract: A short introductory treatment of the basic theory of the mercury strain-gauge plethysmograph is presented. Some physiological aspects of this type of plethysmography are then discussed which, among other things, illuminate the difficulty in discriminating between skin-flow and muscular flow. A detailed calculation of the elastic influences follows and shows that one cannot generally expect a cancellation of these influences when comparing measurements with the calibration. This part illuminates further the difficulties in discriminating between skin-flow and muscular flow. As a result, such discrimination should be regarded as dubious. Some other sources of error are also discussed briefly. Two proposals for a new design are given. Finally, the Appendix shows the values of the gauge stretch which will give cancellation of the elastic errors in a simple model. The actual values cannot be used in practice but they indicate that the amount of stretch is quite critical.
TL;DR: A 400 c/s transistorized squarewave electromagnetic flowmeter has been developed with adequate signal-to-noise ratio for use with coreless and low sensitivity iron-cored transducers such as those commonly used with sinewave flowmeters.
TL;DR: Results on electrical threshold levels, inter-electrode cardiac resistance and the pathology of the heart muscle at the stimulating site and adjacent tissue are given.
Abstract: This paper describes the effects of chronic pacing on the canine cardiac muscle. Results on electrical threshold levels, inter-electrode cardiac resistance and the pathology of the heart muscle at the stimulating site and adjacent tissue are given.
TL;DR: Three designs of low sensitivity electromagnetic cuff flow transducers have provided satisfactory baseline stability when used with the transistorized squarewave flowmeter.
Abstract: Three designs of low sensitivity electromagnetic cuff flow transducers have provided satisfactory baseline stability when used with the transistorized squarewave flowmeter. One coreless design, based on the single coil coreless type of Kolin and Wisshaupt, and two iron-cored designs, a C-cored and a split-pole type similar to that of Kolin and Vanyo, have been developed. Transducers for vessels greater than 2·5 mm dia, have electrodes recessed in the wall of the cuff sleeve. All transducers have high quality insulation and electrostatic screening between the magnet and electrode circuits; and electrodes are of platinized platinum. Transducer output is a linear function of axisymmetric flow rate. Sensitivity to blood of 40 per cent haematocrit is 70–80 per cent the sensitivity to saline.
TL;DR: The findings from the research reported in this paper may be summarized as follows: There is a preferred cardiac axis for effective defibrillation and there is a greater risk of electrolysis than with alternating current.
Abstract: The findings from the research reported in this paper may be summarized as follows: Cardiac defibrillation is an electric current oriented phenomenon. There is a preferred cardiac axis for effective defibrillation. The cardiac preferred axis cannot be related easily to body surface electrode placement. More effective methods of defibrillation involve the use of endoesophageal or endotracheal electrodes rather than two body surface electrodes. Impedance measurements of the thoracic region and the heart indicate that low frequency alternating current is probably the most effective defibrillating stimulus. While direct current is effective, there is a greater risk of electrolysis than with alternating current.