Showing papers in "Medical & Biological Engineering & Computing in 1977"
TL;DR: A new method for the measurement of the water exchange through the human skin, based on the estimation of the vapour-pressure gradient immediately adjacent to the surface of the skin, permits the surface investigated to be exposed to normal ambient air during the entire period of measurement.
Abstract: A new method for the measurement of the water exchange through the human skin has been developed. The method, based on the estimation of the vapour-pressure gradient immediately adjacent to the surface of the skin, permits the surface investigated to be exposed to normal ambient air during the entire period of measurement. A minimal influence on the humidity and the temperature of the microclimate surrounding the skin is thereby achieved. On the basis of the new method an instrument for measuring small amounts of water evaporated from or absorbed by a surface per unit time and area is described and its accuracy discussed. The instrument, which is intended for use in the temperature range 15–40°C and the atmospheric pressure range 98–104 kPa, has proved to offer a high accuracy and an improved sensitivity in comparison with devices previously employed. It has been used primarily for investigations of the rate of evaporation from the skin surface of newborn infants as well as of thyrotoxic and burned patients. The construction of the instrument, however, makes it well suited for the measurement of evaporation rates in many other fields of application.
415 citations
TL;DR: Radio frequency has been investigated as a means of externally powering miniature and long term implant telemetry systems and results were within the desired total system efficiency ranges of 18% and 23%, respectively.
Abstract: Radio frequency (r.f.) has been investigated as a means of externally powering miniature and long term implant telemetry systems. Optimum power transfer from the transmitter to the receiving coil is desired for total system efficiency. A seven step design procedure for the transmitting and receiving coils is described based on r.f., coil diameter, coil spacing, load and the number of turns of the coil. An inductance tapping circuit and a voltage doubler circuit have been built in accordance with the design procedure. Experimental results were within the desired total system efficiency ranges of 18% and 23%, respectively.
388 citations
TL;DR: The use of h.r.v.c. measurement in both clinical applications and the neural cardiovascular research is discussed and it is shown that these signals are based on modifications of one model, namely the integral pulse frequency modulator.
Abstract: A definition of heart-rate variability (h.r.v.) is given. The use of h.r.v. measurement in both clinical applications and the neural cardiovascular research is discussed. For the latter applications, four different signals describing h.r.v. are reviewed. It is shown that these signals are based on modifications of one model, namely the integral pulse frequency modulator. In Part 2, a hardware device for measuring h.r.v. based on one of these modifications is described.
152 citations
TL;DR: The equivalent circuit of the skin impedance, the theoretical relationships among the variable parameters in this circuit, and the impedance space are proposed as powerful concepts for the analysis of impedance changes.
Abstract: Skin impedance, for various reasons, changes in a very complex fashion. The range of change of skin impedance is determined experimentally and analysed theoretically. The equivalent circuit of the skin impedance, the theoretical relationships among the variable parameters in this circuit, and the impedance space are proposed as powerful concepts for the analysis of impedance changes. The experimental examples are practically analysed and can well be understood. A theoretical foundation taking into consideration the mechanism of the change has been established in this paper.
119 citations
TL;DR: It is shown that not only are the shapes of the N action potential images as viewed by the electrodes an important factor in defining the spectrum, but so is the interspike interval distribution of the impulse trains.
Abstract: The generation of an e.m.g. can be modelled by linear filtering of N impulse trains, regarded as the neural inputs to N motor units, where the e.m.g. is the sum of the outputs of the N filters. Starting from this model, it is shown that not only are the shapes of the N action potential images as viewed by the electrodes an important factor in defining the spectrum, but so is the interspike interval distribution of the impulse trains. Changes in the statistics of the pulse trains are shown to affect the low-frequency end of the power spectrum even if the motor-unit action potentials do not change shape. The effect is illustrated by use of data already published on deltoid muscle and brachii biceps. A means of including motor-unit synchronisation is introduced and it is shown that its effect can be contrary to that due to the firing statistics.
114 citations
TL;DR: The possibilities for extending the class of lowpass recursive digital filters to include high pass, bandpass, and bandstop filters are described, and experience with a PDP 11 computer has shown that these filters may be programmed simply using machine code, and that online operation at sampling rates up to about 8 kHz is possible.
Abstract: After reviewing the design of a class of lowpass recursive digital filters having integer multiplier and linear phase characteristics, the possibilities for extending the class to include high pass, bandpass, and bandstop (‘notch’) filters are described. Experience with a PDP 11 computer has shown that these filters may be programmed simply using machine code, and that online operation at sampling rates up to about 8 kHz is possible. The practical application of such filters is illustrated by using a notch desgin to remove mains-frequency interference from an e.c.g. waveform.
104 citations
TL;DR: In this article, the two components of pure resistance, derivable from the model, were tested with square-wave electrical pulses of 1 to 10 mA, and it was concluded that the current intensity of transcutaneous electrical stimulation can only be controlled satisfactorily when current-regulated stimuli are used.
Abstract: Several problems concerning an electrical model equivalent to the skin are discussed. The two components of pure resistance, derivable from the model, were tested with square-wave electrical pulses of 1 to 10 mA. The larger resistance component, shown to be localised in the stratum corneum, varied markedly with the current intensity, the intensity of a previous pulse and the interval between the pulses. This component decreased with time and the decrease was dependent on the amount of electrical change transferred through the skin. When constant-voltage pulses were used, the decrease could be equated to a process that reinforces itself. The smaller resistance component showed only relatively small variations with the different stimulus properties previously mentioned. It was concluded that the current intensity of transcutaneous electrical stimulation can only be controlled satisfactorily when current-regulated stimuli are used.
88 citations
TL;DR: Afferent electrical nerve stimulation is an approach showing many promises with regard to sensory feedback for powered prostheses that is well tolerated, can transmit fairly high amounts of information, and has several characteristics making it superior to electrocutaneous and vibrotactile devices when applied to prostheses.
Abstract: Afferent electrical nerve stimulation is an approach showing many promises with regard to sensory feedback for powered prostheses. It is well tolerated, can transmit fairly high amounts of information, and has several characteristics making it superior to electrocutaneous and vibrotactile devices when applied to prostheses. The feedback information is transferred in modulated form either by means of the current pulse amplitude (a.m.) or by the current pulse frequency (f.m.) A.M. stimulation should be applied in such a way that it gives rise to characteristic changes in the distribution of paresthesias with changing current. Used in this way it is not dependent upon minor changes in electrode position, it is easy to learn and gives high rates of information, even in untrained subjects. The number of channels that can be used in each nerve is, however, limited because of the large amount of axons necessary to achieve the spatial spread. F.M. stimulation is more difficult to learn than a.m. but gives the same rate of information transfer when used in trained individuals. Like a.m. it is not dependent upon minor changes in electrode position, but a smaller number of axons is needed to achieve discrimination. Thus several channels can be used in each nerve. Both with a.m. and f.m. stimulation a trained subject can discriminate five or six discrete levels with a rate of correct recognition of more than 75%, the amount of transmitted information being about 1·8 bits per symbol.
76 citations
TL;DR: It is shown that a wide cuff does effectively accomplish this under its central region and the claim that ‘if the cuff is too wide, the reading will be erroneously low’ is not indicated in the analytical solution and has not been observed in the authors' experiments.
Abstract: For a sphygmomanometric method of indirect blood-pressure measurement to be accurate, the cuff must operate so that the intrabladder pressure is always the same as the pressure applied by the tissues of the arm to the artery wall. To determine under what conditions this occurs, analyses are presented assuming the arm to be a rotationally symmetric, incompressible solid cylinder acted upon by various cuff pressure fields. The results indicate that the pressure applied to the artery wall is markedly influenced by longitudinal motion of the arm tissue, which must be constrained to have an accurate pressure transmission. It is shown that a wide cuff does effectively accomplish this under its central region. The analyses agree with experiments in which indirect and direct blood-pressure measurements were made and most of the clinical observations of others. However, the claim that ‘if the cuff is too wide, the reading will be erroneously low’ is not indicated in the analytical solution and has not been observed in the authors' experiments. These analytical and experimental results were used to establish criteria for the design of appropriate occluding cuffs. Based upon these criteria, cuffs for clinical use have been produced from a plastic film in a variety of lengths and widths.
71 citations
70 citations
TL;DR: In this paper, the authors provide a brief review of the literature and present working definitions governing the theory for evaluation of the stationarity of the e.g. human electroencephalogram.
Abstract: The time and frequency domain characteristics of the human electroencephalogram continue to be parameters of significant interest to both research workers and clinicians alike. In nearly every analysis of the e.e.g., the question of stationarity is raised. This paper provides a brief review of the literature and presents working definitions governing the theory for evaluation of the stationarity of the e.e.g. An easily implemented stationarity-analysis method is detailed and the technique is applied to 104 clinically normal e.e.g.s. The results verify that epoch lengths used intuitively by many electroencephalographers are also appropriate from a theoretical consideration of the signal's characteristics. The method presented provides a simple and useful assessment of whether a given sample is sufficiently stationary for meaningful analysis.
TL;DR: Reflection photoplethysmography allows noninvasive recording of arterial-blood-volume pulses and the prospects of minimising these artefacts, by using improved transducer designs, are promising.
Abstract: Reflection photoplethysmography allows noninvasive recording of arterial-blood-volume pulses The method is based on monitoring backscattered infrared light and has promising diagnostic value: volume pulse shapes depend on cardiac performance and arterial elasticity The poor repooducibility of photoplethysmograms at repeated trials on the same subject impairs their usefulness, however The actual formation of photoplethysmograms was invastigated using agar blocks with blood-filled vessels embedded in them Two optical processes were observed: (a) Attenuation by the vessel of backscattered and back-reflected light, here vessel extension leads to ‘less’ light at the sensor;(b) Light reflection by the vessel wall proximal to the sensor, and vessel extension gives rise to ‘more’ light at the sensor, this counteracts the attenuation The combined effects of (a) and (b) make the recorded pulse shape dependent on the transducer/artery position relationship Volume-pulse transducers that monitor the displacement of arterial walls mechanically (eg piezoelectric crystals) are liable to produce similar artefacts The prospects of minimising these artefacts, by using improved transducer designs, are promising
TL;DR: This method is being used to investigate the variation of mechanical properties with such factors as age, sex, hormonal change, ultraviolet radiation and various disease states.
Abstract: An experimental method for obtaining the 2-dimensional skin tension/extension-ratio characteristics of living human skin is described. This method incorporates a strain-gauged pretension device used to determine the naturally existing tension and deformation fields in a specific skin area and a suction-cup system that applies a homogeneous, plane strain field to the skin at controlled straining rates. A series of experiments conducted to validate the use of the method for obtaining quantitative measures of the mechanical behaviour of skinin vivo is also presented. This method is being used to investigate the variation of mechanical properties with such factors as age, sex, hormonal change, ultraviolet radiation and various disease states.
TL;DR: It is concluded that apparently nondeterministic and unobservable aspects of animal behaviour can be accounted for within the general theory, provided the control space is carefully and properly defined.
Abstract: The paper is concerned with the development of behavioural models by computer simulation, revealing new features of the system, and examining problems emerging from the application of various techniques of systems analysis. We start with a description of a particular aspect of animal behaviour: the courtship of the smooth newt. From a basis of a deterministic general theory of animal behaviour, which has been developed in the literature, a series of four models of newt courtship is described. It is argued that a general feature of behavioural models is their apparent unobservability. Concepts from automata theory and from catastrophe theory are employed in the discussion of ways of circumventing the observability problem. It is concluded that apparently nondeterministic and unobservable aspects of animal behaviour can be accounted for within the general theory, provided the control space is carefully and properly defined.
TL;DR: The paper discusses proposals for recording multiple single-unit potentials from nerve fibres that become captured in an array of tube electrodes that may be through regeneration of cut fibres or by placement of dissected filaments into grooves which are then covered.
Abstract: The paper discusses proposals for recording multiple single-unit potentials from nerve fibres that become captured in an array of tube electrodes. Capturing may be through regeneration of cut fibres or by placement of dissected filaments into grooves which are then covered. The factors contributing to signal-to-noise ratios obtainable with this type of electrode are discussed. The design, construction and bench-test results are given for an electrode array in which thin-film microelectronic techniques are used to build a densely packed, flexible, 3-dimensional electrode array consisting of a bundle of plastic tubes with flat metal contacts at midtube.
TL;DR: An electrode-amplifier module is designed for use in limband trunkmovement studies on normal subjects and stroke patients and its characteristics are such that the effect of electrical interference is substantially reduced, and microphonics are virtually eliminated.
Abstract: MEASUaEMENT of the surface electromyogram (e.m.g.) in normal subjects, or patients with motor disorders, demands ideally a recording system with the following properties : amplification and recording of the signals should be achieved without contamination by electrical interference or noise; the electrodes should be firmly a t tached to the skin and be imperceptible to the subject. In many recording situations the electrodes are connected to amplifying and recording equipment by wires which may be up to several metres in length. The small amplitude and high source impedance of the signals make such a system inherently vulnerable to pick up of mains hum and other electrical interference. Furthermore, microphonic artefacts can be generated in the wires during movements made by the subject. An alternative approach, which has been described by BASMAJIAN and HUDSON (1974), with reference to e.m.g, recordings using needle electrodes, is to amplify the e.m.g, signals at the electrode site before transmitting them along wires at relatively high-amplitude and low impedance levels. By this means the effect of electrical interference is substantially reduced, and microphonics are virtually eliminated. When surface e.m.g.s are to be measured it is convenient to combine the electrode pair and a differential ampiifier within a single module. A multichannel e.m.g, measurement system of this type has been designed for use in limband trunkmovement studies on normal subjects and stroke patients (Fig. 1). Each electrode-amplifier module is connected to the battery pack by four flexible wires~two for power supply, one for earth and one for signal output. The characteristics of the module are such that its operation and the transmisssion of the amplified e.m.g, signals are essentially independent of the type or length or wires used. One of the preamplifier modules is shown in Fig. 2. It measures 4 0 • 2 1 5 and comprises a miniature
TL;DR: The efficiency of the spectral features for phonocardiogram classification has been confirmed experimentally and the characteristics for each class are well extracted and the results of the classifications are good.
Abstract: The paper reports some results with phonocardiogram pattern classification. Linear prediction analysis was applied to extract the spectral pattern from phonocardiogram signals, a relatively new technique. In this examination, 29 design samples are classified correctly, except for three samples; and 19 test samples correctly, except for five samples. The characteristics for each class are well extracted and the results of the classifications are good. The efficiency of the spectral features for phonocardiogram classification has been confirmed experimentally.
TL;DR: A technique that allows in vivo measurements of the specific impedance of brain structures is analysed and implemented and uses the 4-electrode method, which includes an optically isolated current source and an interchangeable electrode module.
Abstract: A technique that allowsin vivo measurements of the specific impedance of brain structures is analysed and implemented. This technique uses the 4-electrode method. The system includes an optically isolated current source and an interchangeable electrode module. Tests on the measuring system, including the electrodes and calibration procedures, are presented. Experiments in media of known resistivity and in cat brains define the present limits of the spatial resolution.
TL;DR: A simple expression is given for the estimation of transthoracic electrical impedance directly from externally measured dimensions of the thorax of a human subject, which can be used for assessing the pulmonary oedema fluid quantitatively.
Abstract: A simple expression is given for the estimation of transthoracic electrical impedance directly from externally measured dimensions of the thorax of a human subject. Clinically, the abnormalities due to an intrathoracic accumulation of fluid can be detected by comparing the estimated and the measured values of the impedances. A curve relating transthoracic electrical impedance and intrathoracic fluid volume is obtained by means of a computer program. The curve can be used for assessing the pulmonary oedema fluid quantitatively. The validity of the expression has been experimentally confirmed in 103 normal human subjects of various age groups, builds and of both sexes.
TL;DR: The displacement relationships describing the deformation of an elastic vessel under excess internal pressure which are derived from different theories of elasticity are compared and it is shown that there is little difference between the results of the more exact theories and those for a thin membrane corrected by means of a simple thickness factor.
Abstract: The displacement relationships describing the deformation of an elastic vessel under excess internal pressure which are derived from different theories of elasticity are compared. The main result of the comparison is that theories which take account of the thickness of the wall of the vessel produce a significantly better representation than those theories which treat the wall as a membrane. The classical and statistical theories of thick-walled tubes result in complicated pressure-radius relationships. It is shown that there is little difference between the results of the more exact theories and those for a thin membrane corrected by means of a simple thickness factor. A review of the different theories is necessary to decide which pressure-displacement relationship to apply as an approximation for the elastic properties of arteries. An indication is given of the manner in which the relationship is used in numerical computations. In Part 2 the experimental determination of the pressure-radius relationship for a rubber tube is described. The results are in agreement with the conclusions of the comparison of theoretical treatments in Part 1.
TL;DR: An ultrasonic transit-time micrometer has been developed to measure pulsatile changes in arterial diameter with sufficient accuracy to verify haemodynamic theories and yields results within the range of predicted values from pulsatile flow theory.
Abstract: An ultrasonic transit-time micrometer has been developed to measure pulsatile changes in arterial diameter with sufficient accuracy to verify haemodynamic theories. The instrument samples up to four distances at repetition frequencies above 1 kHz and is calibrated by a separate determination of the velocity of ultrasound in blood. New methods of transmitter pulse triggering and received pulse amplification and detection, and construction and testing of small arterial transducers, are described. The system will resolve distance changes smaller than 1 μm and will run continuously for long periods without temperature drift. Trials by measurement of the dynamic distension of a long water-filled rubber tube and comparison with the manometrically measured phase velocity showed that the technique yields results within the range of predicted values from pulsatile flow theory.
TL;DR: The spectral properties of the integral pulse frequency modulator (i.p.f.m.) are shown and the choice of a hardware device for lowpass filtering the cardiac event series by means of a stepwise convolution is discussed.
Abstract: Part 1 of the paper was dedicated to some general aspects of h.r.v. measurements. In Part 2, the spectral properties of the integral pulse frequency modulator (i.p.f.m.) are shown. The choice of a hardware device for lowpass filtering the cardiac event series by means of a stepwise convolution is discussed. A method to overcome the problems of distortion due to spurious spectral components in the filter passband is shown. The hardware realisation of the filter is described and results are given.
TL;DR: Compared with the conventional method of adding discrete capacitors to perform these functions, this design results in a lower total capacitance at the input, which reduces the high-frequency noise generated by the amplifier and facilitates the achievement of a low effective capacitance.
Abstract: A circuit is described which allows the input capacitance of an f.e.t. input integrated circuit to be used both as the feedback capacitance to neutralise the total input capacitance and to inject current pulses into the input. Compared with the conventional method of adding discrete capacitors to perform these functions, this design results in a lower total capacitance at the input, which reduces the high-frequency noise generated by the amplifier and facilitates the achievement of a low effective capacitance. A modified version having an ultralow (0·1pA) input current, for use with ion-sensitive microelectrodes, is also described.
TL;DR: The paper deals with an e.m.g.-operated prosthesis controller for locking and unlocking of the knee joint in an artificial leg for an above-knee amputee that is highly reliable in operation, uses less man-prosthesis interface and has a low power consumption.
Abstract: The paper deals with an e.m.g.-operated prosthesis controller for locking and unlocking of the knee joint in an artificial leg for an above-knee amputee. The controller is highly reliable in operation, uses less man-prosthesis interface and has a low power consumption.
TL;DR: The knee analyser should assist in the diagnosis of knee problems, follow-up of patients with rheumatoid arthritis, evaluation of operative procedures on the knee and should also provide fundamental information on the properties necessary for future knee replacements.
Abstract: A machine is described which is capable of accurately determining the mechanical behaviour of the knee as it undergoes mediolateral bending under controlled conditions. This knee analyser applies a constant valgus and varus angular deflection rate to the knee up to a preset moment limit. The applied moment is sensed by a strain-gauged pillar and the angular deflection by a precision potentiometer. The resulting voltages are fed to an xy recorder yielding a plot of moment against angle. By monitoring distraction of the joint concurrently, the deformation characteristics of ligament and cartilage components can be evaluated. The machine should assist in the diagnosis of knee problems, follow-up of patients with rheumatoid arthritis, evaluation of operative procedures on the knee and should also provide fundamental information on the properties necessary for future knee replacements.
TL;DR: The capabilities and limitations of both guarded and unguarded measurements are discussed and it is shown that the application of guarding does not, normally, fulfil the capabilities being ascribed to it.
Abstract: The application of the guard ring has been advanced as a method for focusing the applied current in performing electrical-impedance measurements of volume conductors. The objective is to obtain impedance and/or its variation at localised regions of heterogeneous tissue. The paper discusses the capabilities and limitations of both guarded and unguarded measurements and shows that the application of guarding does not, normally, fulfil the capabilities being ascribed to it. A comparison is made of the guarded system under constant-current and constant-voltage constraints with an unguarded electrode system, and it is shown that the guarded system does not have any significant advantages.
TL;DR: The method is used to determine the stress-distribution pattern of the human left ventricular chamber modelled as an axisymmetric shell for an isotropic medium and also for a layered wall.
Abstract: A finite-element stress-analysis method for the left ventricular chamber is presented. The formulation uses an axisymmetric thick-shell element of the isoparametic type with three nodes to accommodate the meridional curved surface. The analysis also takes into account different fibre orientations across the myocardial wall. The method is used to determine the stress-distribution pattern of the human left ventricular chamber modelled as an axisymmetric shell for an isotropic medium and also for a layered wall.
TL;DR: A tracking task of the type widely used to measure the performance of skilled operators in a manual control taks is used here to encourage controlled movement in the semiparalysed arm.
Abstract: The present assessment of partially-paralysed victims of stroke is complicated by a lack of objective measurement. A tracking task of the type widely used to measure the performance of skilled operators in a manual control taks is used here to encourage controlled movement in the semiparalysed arm. Quantitative measures derived from such tests provide sensitive indication of trends in performance during rehabilitation, which cannot be detected by routine clinical examination.
TL;DR: A feasibility study to show that movement plasticity can be improved using a gradually modulated stimulation sequence and suggests that a more important correction of hemiplegic gait using multichannel continuously modulated sequences can be achieved.
Abstract: The paper presents a feasibility study to show that movement plasticity can be improved using a gradually modulated stimulation sequence. The stimulation amplitude can be adjusted to eight above-threshold levels for 16 equal intervals within the walking cycle. The efficiency of such stimulation was demonstrated on the drop-foot correction with two hemiparetic patients. The pretibial muscle group was stimulated and a significant improvement of the ankle-joint goniograms was shown. This fact suggests that a more important correction of hemiplegic gait using multichannel continuously modulated sequences can be achieved.
TL;DR: The results of 24 hearing-level thresholds determined by the detection instrument show better agreement with conventional pure-tone audiometry than results from subjective assessment of the averaged a.c.p.s obtained by averaging alternative responses in a stimulus run at constant intensity and frequency.
Abstract: A simple analogue electronic instrument is described which produces an objective yes/no indication of the presence of an auditory evoked cortical potential (aecp) It correlates two aecps obtained by averaging alternative responses in a stimulus run at constant intensity and frequency The 5 and 1% significance levels of the correlation coefficient are derived and used as the criterion for whether or not a response is present A modified correlation coefficient is used which permits considerable simplification of the circuitry involved The results of 24 hearing-level thresholds determined by the detection instrument show better agreement with conventional pure-tone audiometry than results from subjective assessment of the averaged aecps